I just finished rebuilding a Bally MPU. I thought I'd give it another test before I put it the parts drawer. I connected my power supply and got a solid on LED. I turned it off then on again and it booted fine. Tried it again a few times and it booted every time. Then I tried a Stern MPU and it booted first time. I went back to the Bally and it got solid on , on the first try then booted. It does this every time I let it set for a few minutes. I got 5.2 V and 13 V with solid on and when booted. I then tried my old power supply and got the same results. The only game I have available at this time is a working Meteor (MPU 200). So I connected only the J4 to test in the game. Same results - solid on the fist try. Turn it off the back on and it boots.

I've tried two power supplies and in a game. It just won't boot the first time.

This is going to be a tough one. Any suggestions where to look?

Thanks

Bob

IMG_3874 (resized).JPG

Thanks Quench,

I just checked VR1 - upper side reads same as TP2 , 12.9 V. Lower side reads 5.14 V.

Just to check I tested the Stern board. It reads 4.61 on the lower side. But it boots fine every time.

Tomorrow I'll check to see if I have a new VR1.

Thanks

Bob

Before coming upstairs I checked my parts drawer. I have "ONE" VR1 - 1N4738A Diode, Zener, 8.2V, 1W.

Didn't you say something about having problems with VR1's a while back? Didn't you say you usually replace them?

Thanks

Bob

With power on or off?

Sorry - I guess that was a dumb question (must be late).

Putting one lead on one side and another on the other side of the zener will tell me how much voltage is going through the zener. I didn't know that. I love learning stuff.

Now I know what a zener is for.

I'll get on it tomorrow.

Thanks

Bob

If you subtract the difference from one side to the other side and get 7.76 V going through it - wouldn't a "1N4738A Zener, 8.2V" depend on the input voltage? Let's say I have 12 volts on the input and get 8.2 V across - A 5 V or 25 V input wouldn't give me the same 8.2 V would it? Why is it called a 8.2 V zener?

Is there a formula to figure what voltage you get with a certain voltage going in? If I had a 14 V source and wanted a 5 volt output, What size zener would I need? If I had a certain size input and a certain size zener could I calculate what the output voltage would be?

This stuff is fascinating.

Bob

First thing I checked was across the zener = 7.86 V. I also checked above and below the zener. 13.03 and 5.16.

Just for grins I checked the Stern board. 8.25 across the zener. 12.87 above and 4.60 below.

Next I replaced the zener. I still get solid on , on the first try but now it takes several attempts to get it to boot. But at least the zener now reads 8.02 across the legs.

It looks like Q1 has been replaced (bad solder job). But why would it work after several tries?

I knew this would not be easy.

Thanks

Bob

IMG_3924 (resized).JPG

IMG_3925 (resized).JPG

IMG_3928 (resized).JPG

Same thing - solid on the first try then it boots on the second try. The socket at U8 has been changed. It's a AUGAT socket - looks like machined pin. I looked over the RAM and it looks pretty good - no corrosion.

When I get solid on I read 5.48 at U9 pin 40. When I short pin 40 - 39 it goes to boot. After booting I get 5.49 at Pin 40.

Thanks

Bob

Q1 looks right "F2N 4401 EBC"

Next I lifted one leg of C13. And it booted first try - I tried again and solid on.

I checked the voltages from the schematic. See photo - my results are in red. I tested while it was solid on.

I think C13 has also been replaced. Bad solder joints. The reason for the bad solder joints is because of missing solder pads on the top side. Looks like C80 and CR7 have the same problem. This board is not as good as I thought. And it looks like I'm not the only one to lose pads on this board. Do you think we can save it?

Thanks

Bob

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I just noticed I missed a voltage - Q1 collector to R138 and R140. Schematic shows 0.3 VDC. I got 9.6 mV. I got the same results with solid on and booted.

Then I checked the Stern and got 37.1 mV.

Thanks

Bob

Should I change it if I have a 10nF?

Didn't seem to make a difference - but it's still disconnected. Would that make a difference on reading 9.6 mV at Q1?

I'm pretty sure I have a replacement from GPE - either 2N3904 or 2N4401. I'll check tomorrow.

Can these be checked in circuit?

Shop is closed for tonight - wife went to bed.

I'll get on this tomorrow.

Thanks

Bob

Tomorrows "to do" list:

1 - change C13 - I should have one.

2 - replace Q1 - I should have one.

3 - check R11, R138, R140, CR5 and CR7.

4 - pull out the oscilloscope . That will take a while to set up - I've never used the second channel. My scope has a run/stop switch. If I hit that switch before I power up I think it should capture the moment it powers up and no more - is that what it's for?

Quench, you know you're lucky I'm not your neighbor - I'd be there all day asking questions. I can just see me with a schematic running along side of you while you're cutting grass. you'd never get anything done.

Thank you for teaching me so much.

Bob

I have no idea what I'm doing but I'm having fun learning. I didn't follow my to do list. I started with the oscilloscope first.

Blue probe is connected to CR5 - Yellow is VR1. First scan is Stern. Second is Bally.

I'm having problems with my scope. The vertical and horizontal controls don't seem to be doing anything. I'm sure I got something messed up in the menus somewhere. I'll mess with that later.

Thanks

Bob

stern 1 (resized).jpg

bally 1 (resized).jpg

I just checked the resistors and diodes. Both Bally and Stern:

R11 - Bally = 88.2 - Stern = 96.5
R138 - B = 48.1k - S = 45.9k
R140 - B = 19.71k - S = 20.45k
CR7 - B = 0.561 V - S = 0.563 V
CR5 - B = 0.593 V - S = 0.553 V

Next I'll check my parts drawer for Q1 and C13.

Thanks

Bob

I just discovered something real strange. I replaced C13 and was going to buzz my connections. The schematic shows one side to ground and the other to R12. I looked for R12 and it looks like a diode there. See first photo in post 12 above. I checked it with my ohm meter and I read like 5.2 m ohms and open in the other direction.

Can this be right????

Am I missing something?

I checked the Stern board and it's a resistor there.

WHAT???

Bob

I just got back on line after studying the schematic. I noticed R12 is going to the batteries. Someone put in a diode to block the batteries from being charged. That's pretty clever.

I change C13 and buzzed the connections. All good.

I then connected the power supply and tried to boot. It took 5 tries before it booted.

I haven't changed Q1 yet.

First I need to figure out how to get the scope to adjust. Too many buttons and menus. I guess I'll get out the manual.

I'll be back when I get this figured out.

Thanks

Bob

I think my oscilloscope is real sick. I can't get any knobs to function. No vertical (channel 1 or 2). No horizontal. No trigger level. I just can't figure it out.

Bob

It does have a default setting. But the strange thing is if you change your settings after a few seconds that becomes the new default setting. I wish it had an "original" default setting but I can't find it. The "auto set" works fine but I just can't change any settings. I don't know if it's some setting I screwed up or if it's just broke. I've read most of the manual and can't find anything to reset the settings.

Thanks

Bob

I just replaced Q1 and checked its continuity. Still don't boot first time.

Could U9 be causing this problem? Maybe I'll switch U9's tomorrow. I'm running out of ideas.

Thanks

Bob

Not that I have found yet. Don't know where to look - it has a zillion menus. And I can't find anything in the manual about factory defaults. I think I can download the latest software and put it in the scope. I don't know if that would help?

Thanks

Bob

I don't think I ever changed the firmware. I got the scope in 2018 so 25-Jan-2019 would be a later version.

I also think found how to get back to the default settings.

I'll give it a try tomorrow.

Thanks

Bob

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First I tried the oscilloscope. I went to default setup - I pressed cancel to go to the previous setup. I did that several times and it still didn't work. Then I downloaded the latest firmware and installed it. Still don't work. Looks like all the control knobs (potentiometers) are not working. Might be just a bad connector but I think it's still under warranty. I got it through Amazon so I'll contact them next.

Next I swapped the U9's. (Stern to Bally). I first put the Stern U9 in the Bally and it booted right up. Turned it off then on again and got solid on. Got solid on several times and it finally booted again. I put the Bally U9 in the Stern and it works every time.

The sockets on this board are AUGAT and the connections look really small. Should I change the U9 socket? I know I'll lose a bunch of solder pads. They just fall off this board.

Thanks

Bob

Thanks Quench,

I don't like to lever off of components. With my luck they'll break. I placed a toothpick on the ends of the socket and levered off that - worked pretty good. The pins looked OK but they are really small and some aren't closed completely. I decided to replace the socket. I'm very carefully heating each pin and removing them one at a time. This is going to take some time but I'm not doing anything anyway. I'll let you know how it works out.

The U8 socket has already been replaced - looks like machined pin socket.

This has been a crappy day. I didn't get the MPU fixed and I didn't fix the oscilloscope. I could have just stayed in bed. Hope your day was better.

Bob

Hi Mark,

It's DSO5072P.

Good catch - it was set on 10X.

But the problem is none of the knobs are working. Can't adjust volts/div , sec/div , trigger level , not even the VO menu. It has 8 knobs and not a one will work. If it was one knob out I would suspect a bad pot. But they're all out so it must be power to the pots or something like that. I'm trying to get a schematic.

I contacted the supplier but nothing yet.

Thanks

Bob

How many times have you burnt you fingers? I got some tweezers with Teflon tips. But that's still slow for me. But remember I'm old and slow.

Bob

The supplier contacted me today and asked the same thing. Yes all the buttons work as they should. The volts/div and seconds/div will change when I use the auto set button. So the scope is working fine but I just can't change anything with the knobs.

That's what it acts like.

It's 15 months old. The supplier said one year warranty. But Hantek says three year.

Those schematics are nothing like a pinball.

Hopefully the supplier will come up with something showing how the pots are connected.

How old is your scope?

I thought of that. I have a laptop next to the scope but I've never connected the two. Have you?

Thanks

Bob

I get burnt enough accidently - I don't need to stick my fingers in there.

I did get all the pins removed today - some didn't want to come off easily. Just a little clean up and a close inspection and I can install the new socket.

Thanks

Bob

Just before I purchased mine I found a scope on Craigslist for 200.00. I think it was a Tektronix - about 20 or 50 Mhz - 4 inch screen - no color. He wouldn't budge on the price. I almost bought it but I shopped around and found this one for just a few dollars more - brand new. Better deal!

I heard that Hantek found that the mod was so easy and everyone was doing it that they just sell the 200 Mhz in a 70 Mhz case. Seems they had to modify the 200 down to 70 so they just quit modifying them. I think mine is a 200 Mhz but I don't know. 70 Mhz or 200 Mhz - it works fine for me.

I wasn't interested in connecting my scope to USB either. If I didn't have this problem I doubt if I would try it but I wonder if it would allow me to adjust the controls. Might give some insight on where the problem lies. I'm going to give it a try when I have time.

I've seen several videos and photos of the inside of this scope but haven't seen anything with the front removed. I hate to dig into it if the supplier or Hantek can repair it. With my luck I'll just make things worse.

Thanks

Bob

I got the socket changed today. Installed another U9 and still got the same results. Solid on , on the first try - then it booted. I let it set for a few minutes and tried again. This time it took 4 tries before it booted.

Quench, did you ever have a MPU that you just couldn't fix? I hate to give up but I think it's got us beat.

Do you think the U7 or U11 sockets are bad?

Thanks

Bob

Well at least something seems to be going right. The oscilloscope - I been in contact with the supplier. They said one year warranty. I told the Hantek says 3 year warranty. Basically they said I should contact Hantek. BS - I didn't buy it from Hantek. So I contacted Amazon. I ended up on the phone with them. They also said I should send it back to Hantek. I told them I bought it from Amazon - not Hantek. After a bunch of bitching and talking to the supervisor he said they will replace it - it should be here Saturday. We'll see.

Bob

Mark, by the way I tried to connect the scope to my laptop. I downloaded TTScope but I don't think I got the right drivers for the scope. Hantek is pretty vague on their drivers. Me and computer drivers never did get along.

Thanks

Bob

Advice from two of the most respected and talented people I know. I listen to everything you say. You two guys have taught me a lot. It’s little surprise that your routine is basically the same.

I don’t mind putting the work and time into this board (even though it’s just a spare). I don’t have much else to do anyway. The board didn’t look to be too corroded when I got it (see photo below) but I cleaned and polished everywhere it looked questionable. I remember seeing a board Andrew did years ago where he removed about 75 percent of the components and rebuilt the entire board. That impressed me.

The problem I’m having (as did the previous owner) is the solder pads keep falling off when I remove anything. Especially when there’s no trace connected. That requires soldering on the top or stitching. It seems that the glue used to adhere the pads to the board has dried out. I've noticed several missing pads from the previous owner.

Since the board won’t boot on the first try maybe is has to do with the ROMs. Next I’ll try swapping the ROMs. If that don’t do it I’ll attack the IC sockets.

Thank you all for the help.

Bob

IMG_3801 (resized).JPG

Thanks Mark, I have seen that thread before. barakandl started that thread years ago.

I’d be very cautious about using a strong acid on anything. Years ago I remodeled apartments for a local village. A maintenance worker a couple of buildings down was cleaning a clogged sink. He poured in some really strong acid drain cleaner and it blew up out of the drain. Burned his hand and arm pretty bad. The stuff he was using was for commercial use only - I'm sure it wasn't what Andrew is using.

I’m always careful using any kind of acid.

Bob

I guess my description isn't clear. It's not just the solder is missing but the entire pad. Nothing left to solder to.

08 (resized).jpg

I know that was part of the problem. See photo. It's difficult to heat both sides at once. When i did the Stern board I heated the pins on the back and most of the headers just came out. Most of the Bally headers didn't come out so easy and some of the pads stuck to the headers. Same desoldering tool - same temperature - different results.

I assure you my de-soldering skills and tools are average at best. But I try to be careful and use heat sparingly. Just when I work on a board with no loss of pads then I get a board like this Bally and start losing many pads I get concerned. I lost 4 or 5 header pads but the previous owner lost even more removing components. When I worked on the U9 I only lost if two half pads. And that took me two days. Cutting the components out and removing the legs still leaves solder inside the through hole. The only way to get it out is to suck it out or drill it out.
I doubt I’ll ever get the skill most of you have obtained but it’s not for lack of trying. I'm thinking it takes a special skill like playing a piano.

Thanks for the lessons.

Bob

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When I remove components I always clean the pads with very fine sandpaper - Solder attached or bare copper pads I give them a good cleaning.

When I said suck it out I meant using the desoldering tool. Adding more solder just seems counterproductive but I'm learning it usually helps.

Today was a much better day. I received my new oscilloscope - Way to go Amazon!. I didn't get much time to mess with it but it seems to work great. I only used it to set the probe and all the controls worked.

Then I changed ROMs in the Bally board. I connected it and it booted first try. I let it set and tried again (several times) and it booted first time everytime. Looks like the ROMs were bad. Later I'll connect the scope to be sure I have activity on all the pins. I don't know what ROMs I'm using because I got them from my parts box. But it's just a spare board anyway.

The only bad news is I broke one of the legs off one of the Stern ROMs - it stuck in the IC socket. Looks like I need to replace the U2 socket on the Stern board.

Since I have a new scope I plan on taking the old one apart to see if I can fix it.

More stuff to do.

Bob

Quench, Going back to post 20 - now my scope is working. Yellow probe on VR1 and blue on CR5. Scan is from the Bally.

Is this what we're looking for?

Bob

bally 01 (resized).jpg

Only about half of the leg broke off in the socket. I got it out but the socket pin is bent and probably won't make good contact.

Someone suggested a long time ago to insert the chip into a machine pin socket and solder the broken leg to the socket. Since I had half the leg still in place, that worked pretty good.

Please don't say that. I hate the thought of working on that Bally board. Unlike the Stern where I just removed the socket and didn't lose any pads. I just have to clean it up and remove the solder from the holes.

Which reminds me, how do you remove the left over solder from the thru-holes? Desoldering gun?

I suspect the grounding issue. The ground wires on the probes are very short. So I connect a jumper wire to the TP4 - then connect both probes to the jumper wire. That's the best solution I could come up with.

It wouldn't be easy to connect the probe to pin 40 without just holding it there. It would be easier to connect the probe to something and have my hands free. Would connecting to R139 do the same thing?

I'll play with it tomorrow.

Thanks

Bob

Maybe I should try the Bally ROMs in the Stern board and see if I get the same problem. I'll try that after I get the Stern board back together.

Bob

By the way - Amazon didn't ask for the old oscilloscope to be returned. Maybe after I get these MPUs sorted out I may dig into the old scope. That should be interesting. I'll keep you posted.

Quench, did you ever think about becoming a brain surgeon?

Most of the day was spent cleaning up the Stern board to install the new socket at U2. Once that was done I installed the ROMs and tested - OK. Then I put the old Bally ROMs in and tested. Same results as I was getting on the Bally - solid on for the first few times then it booted. I'm sure now those ROMs were the problem.

Then time for the fun stuff. I connected the yellow probe to R139 and blue to TP5. The first scan is the Bally - 4.00 ms and 5V per division. Second scan is Stern. I couldn't get the top of the blue trace in at 5V so I changed it to 10V per division.

I think this is what we were looking for. Looks like the 5V is steady before the R139 kicks in. My question is why does the 5V look so high? Looks like the yellow trace is topped out at 5V but the blue trace looks like 15 volts on the Bally and over 30 volts on the Stern. I would have thought both the yellow and the blue would top out at 5V.

This stuff is so interesting.

Thanks

Bob

IMG_3932 (resized).JPG

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I remember reading this part of PinWiki years ago –

” The purpose of the reset circuit is to ensure the +5 vdc is stable before allowing the system to start. At startup, the reset signal is held low via pull-down resistor R139 until the +12 vdc line rises above the zener diode VR1's value (8.2 or 9.1 volts depending on your board). At this time, the input voltage threshold for the +5 regulator on the solenoid driver board has been met with some headroom. Q1 starts conducting, turning on Q5, which provides the actual reset signal. All of this happens in approximately 50 milliseconds.”

Today (especially with the oscilloscope demonstration above) That’s beginning to make sense.

PinWiki says it happens in approximately 50 milliseconds. Looking at my scope it happens in 8 milliseconds. Am I not seeing something?

You guys have taught me a lot.

Thanks

Bob

My hat’s off to you guys that put that PinWiki together. That had to be a heck of a lot of work and it’s very educational and well done. I often go back and re-read some of the information that didn’t make sense years ago.

I remember seeing an oscilloscope for the first time (must have been in the 60’s). Small round green tube. I didn’t have a clue what I was looking at but was amazed that I was seeing electricity.

As far as the 50 milliseconds is concerned – looking back at the Bally scan – if the timing starts at the beginning of the trace then the timing is closer to 32 milliseconds. It’s 8 milliseconds from the time the 12 volts starts and the 5 volts stabilize.

I noticed the glitch too. There’s also a small glitch at the top of the Stern scan. I thought that was just caused from the on/off switch on the power supply bouncing.

Quench, I think your right that the probes aren’t set correct. I did check the probes themselves and they are both set on 1X. But there is a menu on the scope that also must be set. I’m pretty sure the menu for the yellow probe (channel 1) is set to 1X but not sure about the blue channel. I’ll have to check. Too many menus and settings. I might do that test again – it was fun and interesting.

You’re right the Stern board said Nugent – The Bally board said Evel Knievel. I don’t know what’s in the Bally now but they work. Both boards are spares so if I use them in a game the ROMs will probably need to be changed anyway.

Thanks

Bob

Another experiment. First I checked the probe menu - you were correct. The scope menu probe for channel 2 was set at 10X. I gotta be more careful about that. This scan shows more reasonable levels.

Forget my theory about the time starting 32 milliseconds earlier. I think that's just when the scope starts getting the sample. This scan shows much longer. I think the 8 - 10 milliseconds is the correct time.

Also my theory about the switch bouncing is probably wrong. This scan don't show that glitch. Don't know what caused that on the other test.

You are making me a better oscilloscope user. The first scan tonight looked very fuzzy. I adjusted my grounds and the next scan was much better. Who knows, I may learn to use this thing after all.

Next I'll dig into the old scope.

Thanks

Bob

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I tore into the old scope tonight. It's definitely not like any MPU I've ever worked on. I may be way out of my league - especially without a schematic. I looked it over for any damaged or broken traces or wires. All looks OK. But this is what I've found so far.

Six of the eight pots have a push-in switch. (see photos below) They are controlled through A and B. It seems that all the A's are common to all switches. The C and D connections are just the pot housing - they are all common and grounded.

It looks like all the G terminals are all connected but not the E's or F's. I haven't traced them down yet. How does a three terminal potentiometer work? (I understand two terminals but not three). I'm thinking E - F - and G are going to the potentiometer. I'm thinking if none of the pots are working the problem may be with the G terminal.

I haven't applied any power yet. I'm a little leary of turning it on with all it's guts laying on the bench. But I guess the next step would be to see if the G's get any power.

Maybe tomorrow I'll get my confidence up.

Bob

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IMG_3959a (resized).jpg

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I may have found a schematic

https://www.mikrocontroller.net/articles/Datei:Hantek_Tekway_DSO_MSO_hw1007.pdf

See page 8.

Now if I just knew what I was looking at.

Still discovering more - what I been calling a potentiometer is actually an encoder. They are driven by the decoder chips. (I think I'm calling them by the right names). If this is true then the E terminals are also tied together. The E 's and G 's all go to common terminals on the chip. All the F 's go to separate terminals.

PLEASE don't be a bad chip. I've never worked on surface mounted components.

I'll get into it more tomorrow. Now I gotta get some rest before my brain explodes.

If you have any comments, suggestions or advice please let me know.

Thanks

Bob

I don't think this scope has a "factory" reset. You can reset the setup to the previous setup. I've done that several times and it didn't make a difference. Because all the controls are not working I'm thinking it's a power or connection problem.

That's what I'm working on.

I've looked at that ribbon cable but just didn't know how to disconnect it. It looks fragile.

If I get time tonight I'll dig into it more - I think that schematic might be a big help.

Bob

Thanks Mark, I didn't know that for sure. When I hit default setup the menu says "cancel". That doesn't seem to change anything - maybe because I already have factory settings setup?

I'm just learning to use the "help" button - nice feature.

Bob

I had a little shop time tonight. First I disconnected the ribbon cable - thanks Quench. I would have never figured it out on my own. Having the board not connected makes it much easier to work on.

I traced more connections tonight and made notes as I went. Page 8 of the schematic seems to be spot on - once you figure out what's what on the schematic. To me it's very hard to understand. Also those SMD's are difficult to probe.

Also I need to learn how these encoders / decoders work. Looks like the two outside connectors of the potentiometers are connected to U2 but the center connector connects to another chip (U3). Why? How does that work? Strange.

I also traced the hot lead (?) back to the ribbon connector. So far all the connections are good.

I'm a little reluctant to add power and check traces - those SMD's are so small - It would be easy to touch 2 pins with the probe. Maybe I need a smaller probe.

Thank you

Bob

schematic 1 (resized).JPG

Why didn't I see that - I know when it says "2A" there should be a "2B". I guess I just didn't look very well. One of the things I wanted to know was the voltage for U2 and where is comes from. Looks like 3.3 VDC at pin 16 - and pin 16 on U4 which is for the switches - and they all seem to work. If I have continuity from pins 16 on U2, U3, and U4 I would think the voltage is present on all 3 chips.

Also it looks like 3.3 comes in on pins 4 and 5 on the ribbon cable.

I'll do more testing tonight.

Thanks

Bob

I just checked and I have continuity on pin 16 on all 4 chips - plus continuity back to ribbon cable pins 4 and 5. If the switches work (U4) then I assume I have power on all chips.

More investigating to do.

It's looking like everything on the board is checking out fine. I'm thinking the weak point is the ribbon cable. I guess I should concentrate on that.

Bob

The switches connected to U2 worked. So U2 (or at least parts of it) is working.

I'm trying to make a road map of the connections. Hopefully this will help me understand what's going on.

I made a screen capture of the switches from page 8 of the schematics. I wanted to get everything on one page so it didn't come out very clear. I circled all the U2 connections and indicated what pin they are going to. The only pattern I see is U2 P4 , P5 and P6 are connected to the non-working pots and not connected to any switches.

The connections not circled are going to U3. But all seven pots center connections are going to seven different pins on U3. Next I'll map out U3.

I'm still studying the datasheet for 4051. So far it's over my head.

Thanks

Bob

front U2 (resized).jpg

Here's the map for U3. Since the center tap of all the pots are connected to seven different pins on U3 and the fact the the other switches (using the same pins) are working - we can assume U3 is OK. Right?

I sort of understand what's going on with U2 but what I don't understand is what's driving "Enable - C - B - A"? Pins 6 - 9 - 10 - 11. Looks like 9 - 10 - 11 are controlled from U1 (pins 5 - 4 - 3). If pin 9 is held low then the problem could be U1 pin 5?

I can see me using my logic probe in the near future. The problem is powering up that board with all the guts all over the bench.

One last question - if the Enable pin is pin 6 and the schematic shows pin 6 going to ground - how could pin 6 ever go high? Wouldn't that be a short?

You guys are amazing - teaching an old dog new tricks.

Thanks

Bob

front U3 (resized).jpg

Sense I'm going to be pulling out my logic probe soon, I have a couple of questions. When do you use CMOS and TTL? I know they're for different chips but the chips don't say they are CMOS or TTL. Is there an easy way to determine which setting I should be using?

The other question I always have is where to connect the red clip? When the probe shows HI does that indicate it's higher than where the red clip is connected. If I connect to 5 volts and the probe says HI - does that mean it's above 5 V? And LO means less than 5 V?

Thanks

Bob

One last question tonight - what are these - circled in red. They look like piano keys.

I haven't checked the board - it's after 3 AM and the shop is closed for the night.

I'm thinking some kind of test points.

Thanks

Bob

IMG_3959b (resized).jpg

I'm not absolutely sure but I don't think they were working. I seldom use them anyway. And if I can't change the settings, hitting the buttons don't center the settings anyway.

I realized that back in post 90 but I have a hard time remembering which is encoder and decoder so I just call them pots and chips. So, there's no resistance value in there at all - It just tracks if it's going up or down. That's neat.

I discovered that late last night. It looks like U1 and U3 might be OK. More and more U2 is looking suspect.

I know just enough about logic probes (and oscilloscopes) to be dangerous. Need more training. I haven't seen that Sparkfun tutorial but I have read several of their articles.

I may be in trouble with the red logic probe clip. I don't see anywhere on this board to attach it to get power. I was hoping those piano keys were test points (so I could get power) but it looks like Mark is right. They are all ground. I guess they are some kind of shied but they don't touch anything. No pads. The board is attached to the front cover and held off the back plate by a quarter inch or so. The LCD screen is held between the front cover and rubber pads.

I'm thinking about using the scope instead of the logic probe. The scope just needs ground.

Quench, I'll get back to you later about your last post - I need to read it a few more times.

Thanks

Bob

This is what I’m understanding – CLR is a signal from the motherboard – CLK is like a ratchet (next , next , next). U1 is like a traffic cop – he’s directing where to send the signal and where to receive the signal. He sends the signal out to U3 who send it to the proper switch (according to the directions from U1). The signal is read at U2 (again according to the directions from U1). Then the signal is send back to the motherboard. Once the signal is received the motherboard tells CLK to go to the next.

This is the logic probe I have:

https://www.amazon.com/Elenco-Electronics-LP-560-Logic-Probe/dp/B000Z9HAP4/ref=asc_df_B000Z9HAP4/

It says voltage range 4 to 18 volts. I don’t think it will work on 3.3 V either.

Once I get the board back in and connected I’ll check it with the scope. The ribbon cable connecting the board is just long enough to reach. Not much room to spread it out. I’ll have to work in close quarters.

I have thought about (and worried about) attempting replacing that chip. This will NOT be easy. I have never worked on surface mounted components – let alone a 16 pin IC chip. It’s like jumping into the deep end. Any suggestions, comments, or lessons will be greatly appreciated. From anyone.

I know the chip is cheap but the shipping cost is outrageous. Anyone have a suggestion on where to buy this chip?

As far as Amazon and I are concerned we’re even. They never asked for a return. If they ask now I’ll just dump everything into a box and send it back – at their expense. I don’t think they’ll ask.

Thanks

Bob

I found I have more room to work if I pull the ribbon cable out to the front and connect the board there.

I tested U2 - pins 1 - 2 - 3 show activity and the trace on the scope is moving around. Pins 4 - 5 shows a trace on the scope but it don't move like the first 3.

Photo 1 shows pin 4. Photo 2 is pin 5.

Bob

pic_8_1 (resized).jpg

pic_8_2 (resized).jpg

I tested the encoder - the voltage seems to change 5.12 to 4.81 when I turn the pot. It's kinda difficult to do when I have to turn the pot, hold the probe and control the scope. I'll try again later - Dinner time.

Bob

Wish you were here.

Glad you guys are on line - I just wish you were both here in my shop - I'd learn something.

This scope has run/stop. Would that get me the full cycle?

I also have save / recall.

U1 pin 1

pic_9_1 (resized).jpg

Could this be one full cycle? I was expecting 63 cycles.

This is U1 p1 - it's saved in scope memory.

I don't see the pause.

pic_9_2 (resized).jpg

I thought when I save it to scope memory I could recall it and change the settings. For some reason it won't do that.

U1 P1 at 400 us:

pic_9_3 (resized).jpg

Mark you're right - scope setting was on 10X - probe was 1X.

I thought single seq. would catch all pulses but it didn't - I'll try again.

when I hit save/recall it says Ref - Setup - CSV . what should I be using. I thought Ref.

When I recall (see post 127) I can change the horz and vert settings but it don't change the graph on the screen.

When I hit F7 it does allow me to change the window but when I hit F7 I loose the graph.

U1 P1 single seq.

pic_9_4 (resized).jpg

pic_9_5 (resized).jpg

I think this is it

pic_9_6 (resized).jpg

I count 3 pulses down - 24 up

pic_9_7 (resized).jpg

ground is probably not the best but there isn't much to connect to.

IMG_3995 (resized).JPG

IMG_3987 (resized).JPG

if I change the sweep time I think we'll lose the pulses.

Instead I moved the window and got 4 shots.

pic_9_8 (resized).jpg

pic_9_9 (resized).jpg

pic_9_10 (resized).jpg

pic_9_11 (resized).jpg

Thanks Mark

Both at the same time?

I knew you'd say that.

It MAY be possible for me to hold both probes at the same time (not easy but possible) but I can't press the save button. Maybe my wife can push it but it'll have to wait - she went to bed already.

I'll need to set the time base and voltage before I attempt this. Any idea what I'll need to set it at?

Ever think you guys would be teaching long distance? The education I'm getting is amazing.

Thanks guys.

Bob

Pushing the record button would be about her limit.

What are you doing tomorrow? How soon can you get here?

I’m not in the shop yet.

Didn’t we decide the problem is probably U2 P9 (C) is being held low causing X4, X5, X6 not to work properly. If I check U2 pins 9 , 10 , 11 and they all show basically the same Then can we assume U1 is doing its job? And if I compare U2 P9 ,10,11 to U3 P9, 10,11 and they look about the same also means U1 is working?

If everything looks right on those pins – then the problem has to be in U2. Right?

Quench, to answer your question from a while back – No, I don’t have a hot air gun. Expensive tool for just one job and I doubt I’ll work on SMDs again (I hope). I was thinking of using ChipQuick. The problem I see is installing the new chip. Holding it in place while soldering the legs. Would BluTack (silly putty stuff) or temperature resistant tape work?

I’m heading down to the shop soon.

Bob

U2 P9:

pic_10_7 (resized).jpg

U2 P10:

pic_10_8 (resized).jpg

U2 P11:

pic_10_9 (resized).jpg

U3 P9:

pic_12_1 (resized).jpg

U3 P10:

pic_12_2 (resized).jpg

U3 P11:

pic_12_3 (resized).jpg

It looks like (to me) we have activity on all those pins. They are getting their signal from U1. So we can assume U1 is working. We can also assume U3 is working because all switches going through U3 are working.

Could it be something in U2 is causing "C" to be held low? Or something in U2 is broken and not letting the signal get out?

I'm no expert but this is just my guess.

Bob

U2 P1:

pic_13_1 (resized).jpg

U2 P2:

pic_13_2 (resized).jpg

U2 P3:

pic_13_3 (resized).jpg

U2 P5:

pic_13_4 (resized).jpg

I don't know if this means anything but the traces on P1, P2, P3 seems to be moving - like it's constantly changing. The trace on P5 is never changing. It's the same every time I test it. Does that tell us anything?

Bob

I've read over all the posts regarding this scope and this is about the best advise.

What I need to do is order some 4051's and 393's. They're cheap so I'll get several incase I screw some up. But there must be a zillion different sizes and shapes of them available. I have no clue what I need to order.

Below are some photos and some rough measurements. Can someone please tell me what to order?

Thanks

Bob

S20191028_0003 (resized).jpg

U1 size (resized).jpg

U2 size (resized).jpg

Here's a couple more photos. I'm pretty sure it's soldered securely. I think that's glare from the lights.

I do have a micrometer but it was easier to get in there with my vernier caliper. The drawings above were the best I could do. (dang, that's small)

I agree the TSSOP is the best match. But when I went to order it, it don't say what package. Just see data sheet - and that shows dozens of sizes.

Is Mouser the best supplier? Where would you order from?

Thanks

Bob

IMG_3975 (resized).JPG

S20191028_0006 (resized).jpg

Thanks Dave

I think I bought from Mouser before but their site is very confusing for a dummy like me - Seems like a great place for professionals though.

I might look a digi-key.

Bob

I just looked at digi-key - 5,151 items (207 pages)

https://www.digikey.com/products/en/integrated-circuits-ics/interface-analog-switches-multiplexers-demultiplexers/747?k=&pkeyword=&sv=0&sf=0&FV=-8%7C747&quantity=&ColumnSort=0&page=1&stock=1&pageSize=25

I guess a real professional could filter out what he needs - but I have no idea what to look for.

Mouser is about the same.

We need an electronics store for dummies.

I think it’s more complicated to find the correct part than to figure out what part is bad.

Here’s the 4051 that I think I need.

https://www.mouser.com/ProductDetail/595-CD74HC4051QPWRQ1

The specifications show Package/Case = TSSOP-16. The data sheet shows TSSOP-16 is pretty close to my measurements. I think this is the correct part.

Here’s the 393 that I think I need.

https://www.mouser.com/ProductDetail/595-SN74HC393PWR

The specifications show Package/Case = TSSOP-14. But the data sheet doesn’t show TSSOP-14. The data sheet shows PW (R-PDSO-G14). Which is pretty close to my measurements. (See screen scan). Is this the correct part? Is PW (R-PDSO-G14) the same as TSSOP-14?

You guys that do this every day are amazing.

Thanks

Bob

393 case (resized).JPG

When you compare the price of the parts (0.38 to 0.86) to the cost to ship (7.99) - I may as well get plenty.

I looked at Nexperia parts but which one do I need? Or which one is best? I'm sure there's a difference but I sure don't know.

4051:

https://www.mouser.com/ProductDetail/771-74HC4051PW-T

https://www.mouser.com/ProductDetail/771-74HCT4051PW-T

https://www.mouser.com/ProductDetail/771-74LV4051PW-T

https://www.mouser.com/ProductDetail/771-74HC4051PW

https://www.mouser.com/ProductDetail/771-74HCT4051PW

https://www.mouser.com/ProductDetail/771-LV4051PW112

393:

https://www.mouser.com/ProductDetail/771-HCT393PW118

https://www.mouser.com/ProductDetail/771-LV393PW118

https://www.mouser.com/ProductDetail/771-HC393PW118

https://www.mouser.com/ProductDetail/771-HC393PW112

https://www.mouser.com/ProductDetail/771-LV393PW112

Why so many?

That's what I been worrying about for the last week. I'm thinking about getting these:

https://www.amazon.com/gp/product/B00OK0MAX6/ref=ox_sc_act_title_1

Thanks

Bob

Thanks Quench,

I've ordered 6 each of the 4051 parts and 3 each of the 393 parts. I'm afraid if I drop one I'll loose it.

mouser (resized).JPG

I have one of those magnifying lamps but could never get used to using it. I'll let you know how the glasses work.

amazon (resized).JPG

Working outdoors is out of the question now. We're coming into winter here - high today was 45* F - next week we're looking at 30's and 40's.

I hope you're right. I've watched dozens of videos. My plan is to use ChipQuik to remove the old part - never used it before but it looks pretty easy.

You, Quench, and everyone suggests tacking down the corners first. My concern is holding the part in place while I tack it down. I've had good success using Blu Tack (it's like silly putty) to hold headers straight and IC sockets flat. I'm hoping to use it to hold the part in place while I tack the corners. Or maybe use the heat tape.

The solder I use is Kester 63/37 .031. I've had good luck using it. Do they make a thinner solder?

Many people have said that surface mounted is easier and faster than thru-hole. I guess it depends on how many you screw up.

Thanks guys. I'll let you know when the parts arrive. Maybe you all can stop by and show me how easy it is.

Bob

On order - thanks

https://www.amazon.com/gp/product/B0019UZP7I/ref=ox_sc_act_title_6

I just found 0.015 on Amazon:

https://www.amazon.com/gp/product/B076GHCZZ1/ref=ox_sc_act_title_2

I think it's the same as what I been using but thinner.

That's strange - I have some solder wick (Radio Shack I think). I always complained it was too thin and don't absorb much solder.

Thanks guys - maybe I can do this.

Bob

Here's Dave using ChipQuik.

What worries me most about the ChipQuik is that it mixes with the solder so every bit of it must be removed before attaching the new part.

Mark suggested a while back to use two soldering irons. I might give that a try first.

On thru-hole parts I usually set my iron to 650*F (344*C) Should I use less heat for SMD parts?

I'm looking forward to getting those glasses and practice board.

Maybe this weekend.

Thanks

Bob

Parts from Mouser arrived today. When I opened them my first thought was they sent the wrong parts. These are way too small. Then I went to the shop and compared them - nope - they're the correct parts OK. I sure hope those magnifying glasses work.

The problem today is we have machines that can do this sort of stuff that a human can't do.

We'll see.

Bob

IMG_3997 (resized).JPG

IMG_4003 (resized).JPG

S20191107_0002 (resized).jpg

S20191107_0003 (resized).jpg

This guy makes it look so easy.

He says "piece of cake"

One of my biggest concerns is lifting a pad. My track record hasn't been very good lately. A lifted pad on this board would be game over. I doubt it could ever be repaired. I'm leaning toward Mark's suggestion of using two irons.

I plan on working on the practice board a lot when it gets here. Both installing and removing parts. Also thinking very seriously about using the Blu-Tack to hold the IC's in place. I'm not too sure I'm steady enough to hold it.

Bob

I received the magnifier glasses today. My first impression so far - You can't use both lenses at the same time. You have to close one eye. This may or may not be a problem but you can't get stereo vision. The biggest problem I see is the focal length is very short. About 1.5 inches (38 mm) with the 10X lense. The 25X is even shorter. (Hope I don't burn my nose). And you can't adjust the length. I would have prefered more like 6 inches focal length.

I haven't tried these under actual workbench conditions yet. The practice board should be here tomorrow.

https://www.amazon.com/gp/product/B00OK0MAX6/ref=ppx_yo_dt_b_asin_title_o01_s01

Bob