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(Topic ID: 253732)

MPU 100 Don't boot on first try


By oldschoolbob

1 year ago



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  • 252 posts
  • 10 Pinsiders participating
  • Latest reply 11 months ago by oldschoolbob
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    There are 252 posts in this topic. You are on page 2 of 6.
    #51 1 year ago

    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

    #52 1 year ago

    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

    #53 1 year ago

    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

    #54 1 year ago

    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

    #55 1 year ago
    Quoted from oldschoolbob:

    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.

    I always remove the components in the corroded area, clean the corroded copper traces with acid and tin them with solder to put some "meat on the bones" and protect the copper. Replace all IC sockets and pin headers - very rarely do those boards need any follow up diagnosis, they usually work first go.

    I see in your picture above some of the components in the "valid power" section have stale solder and tarnished copper pads. The components previously replaced before you got the board weren't cleanly solder attached to the copper pads.
    Shine a bright light from behind the board and closely inspect the pin area between the U8 socket and the board to get some idea of the work previously done and the current condition.

    Look at the solder joint on the right leg of the big R11 resistor. Is it making contact?

    To be honest, I'd remove those components in that area and clean then resolder tin the copper pads the components should be soldered to and install new components. If you feel this is too much work then at least reflow all those components for now (both top side and bottom side of the board) to see if it resolves.

    Quoted from oldschoolbob:

    Do you think the U7 or U11 sockets are bad?

    Pop the socket covers off and look at the state of the pin receptors.

    #56 1 year ago

    90% of battery damaged boards come to life and work 100% after replacing all IC sockets, replacing corroded parts, replacing headers, and cleaning up the copper tracks. When I would do there boards I wouldnt even attempt to diag beyond visual inspection before all that is done. It is kind of like redoing connectors. It sucks ass to do but if you want a reliability over long term and not possible continuous stream of new issues popping up it needs done.

    Those AUGAT sockets are not the worst ones but they are still crap. Add battery damage and they are totally unreliable. Battery damage will fester and hide under those closed from IC sockets.

    The order I would tackle MPUs....

    Desolder / cut everything out. Sometimes if the battery damage is bad enough you cannot desolder things first.

    Clean up the corrosion by stripping with an acid or sanding it off. Get any exposed copper shiny and nice so it will take new solder.

    Coat any exposed copper with solder. Using the vacuum of the desoldering gun you can apply a nice thin layer of solder on top of copper to protect if from tarnishing.

    Install the new parts and sockets.

    Clean the flux off

    test and diag the board (with less headache because the board is prepared).

    #57 1 year ago
    Quoted from oldschoolbob:

    ...supervisor he said they will replace it - it should be here Saturday. We'll see.
    Bob

    Good for you Bob!

    #58 1 year ago

    Bob,

    Adding to Barack's comments: Here's a good thread on cleaning battery acid off a PWB.

    https://pinside.com/pinball/forum/topic/stripping-battery-corrosion-with-a-strong-acid/page/2#post-5270047

    #59 1 year ago

    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
    #60 1 year ago
    Quoted from oldschoolbob:

    ...
    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.
    Bob[quoted image]

    Thanks for the kind words, many more smarter people here than me. I'm still just a newbie.

    As a precaution, make sure the iron isn't too hot. If you're energetic, I think they make 'rivets' (for lack of a better word) that can be used to fix a broken via pad (assuming it's just a two layer board). We use them them for when we route prototype designs, but not for thru hole parts since we use surface mounted parts exclusively. We use them to ties traces together between layers.

    In many years prior, we actually repaired loose traces with glue. This was an acceptable practice at the time, and worked rather well. Don't recall what glue we used, but I think it was an epoxy. Of course, we were very careful soldering on the repaired traces - but they did hold.

    #61 1 year ago

    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

    #62 1 year ago
    Quoted from oldschoolbob:

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

    LOL, I didn't even notice he started that thread. No doubt, I didn't pour it down the drain...or even have it in the house. Didn't need a lot of ZEP, just brushed some on, then rinsed well in the yard. Wore safety glasses, old clothes, and gloves too!

    #63 1 year ago
    Quoted from oldschoolbob:

    The problem I’m having (as did the previous owner) is the solder pads keep falling off

    Don't worry about the solder pads falling off the copper pads - it seems common for those late 70's Bally MPU boards. Just clean the copper pads and flux/retin with solder.

    #64 1 year ago

    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
    #65 1 year ago
    Quoted from oldschoolbob:

    It's not just the solder is missing but the entire pad. Nothing left to solder to.

    You might have had some solder still attaching that pad to the header you were removing, so the pad pulled when you removed the header. Or if it was the other side, maybe too much heat for too long as Mark said or too much aggression with the solder sucker.

    If you're going to replace the components in that valid power area of the board, just cut them out and remove the leftovers like you did with the CPU socket.

    #66 1 year ago
    Quoted from oldschoolbob:

    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

    CAUTION! You always add acid to water, not the other way around! If you google why, you find:
    A large amount of heat is released when strong acids are mixed with water. Adding more acid releases more heat. If you add water to acid, you form an extremely concentrated solution of acid initially. So much heat is released that the solution may boil very violently, splashing concentrated acid out of the container!
    SO.....BE CAREFUL IF YOU ARE POURING STRONG ACID DOWN YOUR SINK DRAIN.
    I once cleaned the battery corrosion on a Bally MPU using acid and small acid brush. Let it set for less than a minute and rinsed the board in the kitchen sink. Worked like a charm.

    #67 1 year ago
    Quoted from Quench:

    You might have had some solder still attaching that pad to the header you were removing, so the pad pulled when you removed the header.

    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

    01 (resized).jpg
    #68 1 year ago
    Quoted from barakandl:

    90% of battery damaged boards come to life and work 100% after replacing all IC sockets, replacing corroded parts, replacing headers, and cleaning up the copper tracks. When I would do there boards I wouldnt even attempt to diag beyond visual inspection before all that is done. It is kind of like redoing connectors. It sucks ass to do but if you want a reliability over long term and not possible continuous stream of new issues popping up it needs done.
    Those AUGAT sockets are not the worst ones but they are still crap. Add battery damage and they are totally unreliable. Battery damage will fester and hide under those closed from IC sockets.
    The order I would tackle MPUs....
    Desolder / cut everything out. Sometimes if the battery damage is bad enough you cannot desolder things first.
    Clean up the corrosion by stripping with an acid or sanding it off. Get any exposed copper shiny and nice so it will take new solder.
    Coat any exposed copper with solder. Using the vacuum of the desoldering gun you can apply a nice thin layer of solder on top of copper to protect if from tarnishing.
    Install the new parts and sockets.
    Clean the flux off
    test and diag the board (with less headache because the board is prepared).

    I have seen people using clear wood finish over the copper and have tried that with wipe on poly. It seems to work fine, I did that to one a year and a half ago and still looks like I did it yesterday. I have done that to a few since then and all appear ok. I always wonder if there is a drawback when reworking something at a later date though? Also, what kind of acid would be best? After sanding I usually go over the area with Goof Off, that removes more hidden crud, then just Windex to clean away Goof Off so the poly won't have problems adhering.

    OT: (just so I have the history fixed correctly) When you first put out the NVRAM Bally/Stern replacement MPU it needed game roms (didn't it)? But now the new version is dipswitch selectable like the Altek, only around $50 bucks less, is that correct?

    #69 1 year ago
    Quoted from Mombo-number-5:

    I have seen people using clear wood finish over the copper and have tried that with wipe on poly. It seems to work fine, I did that to one a year and a half ago and still looks like I did it yesterday. I have done that to a few since then and all appear ok. I always wonder if there is a drawback when reworking something at a later date though? Also, what kind of acid would be best? After sanding I usually go over the area with Goof Off, that removes more hidden crud, then just Windex to clean away Goof Off so the poly won't have problems adhering.
    OT: (just so I have the history fixed correctly) When you first put out the NVRAM Bally/Stern replacement MPU it needed game roms (didn't it)? But now the new version is dipswitch selectable like the Altek, only around $50 bucks less, is that correct?

    Originally it was a single ROM. December 2018 started with universal combo ROM that includes software versions for all games. Bally games use custom software to enable freeplay, seven digit scoring, drop target down logic, bug fix, enhanced switch test etc.... depending on the game. Stern games all have free play options as well.

    #70 1 year ago
    Quoted from Mombo-number-5:

    OT: (just so I have the history fixed correctly) When you first put out the NVRAM Bally/Stern replacement MPU it needed game roms (didn't it)? But now the new version is dipswitch selectable like the Altek, only around $50 bucks less, is that correct?

    Andrew's combo rom has more room than the alltek allowing the extra variations of code, plus it has more ram and can take a 512 rom (giving homebrew coders address space of $1000-$FFFF for the rom, and $00-$FFF for the ram, minus $80-$ff which is system vectors)

    #71 1 year ago
    Quoted from oldschoolbob:

    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 feel your pain. The Stern boards were better chemically treated before they were solder bathed.
    Sometimes I'll try to desolder pin headers on a particular MPU board and the solder just doesn't want to clear effectively. In those cases I'll switch to using an iron to heat the pin and pull the pin out from the other side with pliers when the solder and plastic melt.

    The problem you may experience with this board is getting new solder to attach to the tarnished copper pads which might need to be cleaned beforehand - more work..

    Quoted from oldschoolbob:

    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.

    You're not using a desoldering gun to clear the holes? It helps to add a touch of solder to the pads before sucking.

    #72 1 year ago
    Quoted from Quench:

    The problem you may experience with this board is getting new solder to attach to the tarnished copper pads which might need to be cleaned beforehand

    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

    #73 1 year ago

    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
    #74 1 year ago
    Quoted from oldschoolbob:

    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.

    No way to get the pin out with tweezers?
    If you have a faulty chip, cut one of the legs where it comes out of the plastic and solder it onto the broken pin stub on that Stern ROM.

    Quoted from oldschoolbob:

    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.

    Question is also whether reseating the ROMs essentially got it working - i.e. one of the ROM sockets suspect?

    Quoted from oldschoolbob:

    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?

    Essentially what we were trying to see is whether the board was releasing the /RESET signal to the CPU (so it could wake up and start to boot process) when in fact power was detected as "valid" or not.
    The waveform snapshots you took the other day showed the same initial behavior between this Bally board and the Stern board. But we need to go further.

    Note you're getting a hell of a lot of noise on the blue signal (banded side of diode CR5). Maybe a grounding issue with the scopes probe?

    Hook up one of the scope probes to pin 40 of the CPU which is the /RESET line. Hook up the other scope probe to test point TP5 on the MPU board which is the 5 volt rail. What we want to see is when the /RESET line is released and goes from zero to 5 volts, that the 5 volt power rail is already steady at 5 volts. In other words, when the CPU is told to wake up and start running it must occur after power is stable. Otherwise the CPU will startup unpredictably and could cause solid LEDs on power-ups.

    #75 1 year ago
    Quoted from Quench:

    No way to get the pin out with tweezers?

    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.

    Quoted from Quench:

    If you have a faulty chip, cut one of the legs where it comes out of the plastic and solder it onto the broken pin stub on that Stern ROM.

    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.

    Quoted from Quench:

    one of the ROM sockets suspect?

    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?

    Quoted from Quench:

    Note you're getting a hell of a lot of noise on the blue signal (banded side of diode CR5). Maybe a grounding issue with the scopes probe?

    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.

    Quoted from Quench:

    Hook up one of the scope probes to pin 40 of the CPU

    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

    #76 1 year ago
    Quoted from Quench:

    Question is also whether reseating the ROMs essentially got it working

    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.

    #77 1 year ago
    Quoted from oldschoolbob:

    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.

    If you want to be creative, desolder that pin receptor, pull it out of the socket, reshape it and put it back in. Yes I've done this before...

    Quoted from Quench:

    If you have a faulty chip, cut one of the legs where it comes out of the plastic and solder it onto the broken pin stub on that Stern ROM.

    See pic below: The chip was a bit rough but you get the idea.

    Quoted from oldschoolbob:

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

    I always add a spot of new solder then suck it out with the desoldering gun.

    Quoted from oldschoolbob:

    I suspect the grounding issue. The ground wires on the probes are very short. So I connect a jumper wire to the TP4

    Sounds good. Sometimes those test point are so tarnished, getting a good connection can be tricky.

    Quoted from oldschoolbob:

    Would connecting to R139 do the same thing?

    Yes if that's easier, hook up the probe there to R139.

    Quoted from oldschoolbob:

    By the way - Amazon didn't ask for the old oscilloscope to be returned.

    Score!
    IMG_0056a.jpg

    #78 1 year ago

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

    #79 1 year ago

    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).JPGbally 02 (resized).jpgstern 02 (resized).jpg
    #80 1 year ago

    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

    #81 1 year ago
    Quoted from oldschoolbob:

    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?

    It's a paraphrasing of the theory of operation from the bally repair manual... pretty sure I wrote that section way back when pinwiki first came online. People were cutting and pasting Clay's stuff from pinrepair directly into the site, which would have gotten it shut down really quickly, so I specifically didn't reference his material at all and took it straight from the theory of operation instead, reworded in my own way of course.

    No measurements were ever taken to verify the manufacturer info and I never really thought about doing that either. My scope at the time was an ancient 90s textronics with a very jumpy and dim CRT which was really only useful in the gross comparison of timing (i.e., THIS signal is happening AFTER this signal). The Rigol I have now is much better.

    #82 1 year ago
    Quoted from slochar:

    My scope at the time was an ancient 90s textronics...

    My one and only scope I ever owned was a Heathkit I built in the 60's. If yours was ancient, mine must have been prehistoric. OMG.

    #83 1 year ago
    Quoted from oldschoolbob:

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

    Ha! too late, been sniffing too much solder flux and acid fumes from these boards

    Quoted from oldschoolbob:

    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.

    Phew, that's a relief that you got to the bottom of the problem. Looks like those suspect ROMs are Lectronamo/Nugent PROMs.

    Quoted from oldschoolbob:

    My question is why does the 5V look so high?

    Did you accidentally flick the x10 switch on the scopes probe? Or do you have some other setting on the oscilloscope for amplitude division/correction?
    When you connect both the blue and yellow probes to TP5 on the MPU board, they should obviously read the same voltage.

    The scope pics are interesting. I wonder if it was just a glitch or if there's something relevant about that blue skinny line spike on the Bally /RESET line.

    Quoted from oldschoolbob:

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

    Well, the snapshot images don't tell you the moment you powered on the system. You probably need another snapshot of the 12V rail vs the R139 /RESET line. The moment the 12V rail starts to rise tells you when you applied power and then see how long it takes for the /RESET line to release and go high.

    By the way, incase you don't know, when you see signals on the schematics with a line over them, the line indicates those signals are logically active low, ie. they are active when at zero volts. So when I type a forward slash "/" in front of RESET, I'm indicating that reset signal is active low. When the reset signal goes to logic high (5 volts) the system is no longer in reset mode.

    Quoted from JethroP:

    My one and only scope I ever owned was a Heathkit I built in the 60's. If yours was ancient, mine must have been prehistoric. OMG.

    Oh dear, I thought I was the only one still using a CRO (Cathode Ray Oscilloscope)!

    #84 1 year ago
    Quoted from Quench:

    Oh dear, I thought I was the only one still using a CRO (Cathode Ray Oscilloscope)!

    You are still using yours?! Haha, my Heathkit is long gone. The newer scopes are really nice....smaller and lighter. But I've just gotten by all these years without one, so have never replaced it.

    #85 1 year ago

    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

    #86 1 year ago

    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

    stern 001 (resized).jpg
    #87 1 year ago
    Quoted from oldschoolbob:

    Who knows, I may learn to use this thing after all.

    I think you already have

    I just looked up the Motorola 6800 CPU datasheet. With respect to the speed that this CPU runs on these boards, the calculation says the CPU must stay in reset a minimum of 16us (micro seconds) after 5 volts has stabilised, so the 8ms you're measuring is plenty of time.

    #88 1 year ago

    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

    IMG_3960a (resized).jpgIMG_3959 (resized).JPGIMG_3959a (resized).jpgIMG_3956 (resized).JPG
    #89 1 year ago

    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.

    #90 1 year ago

    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

    #91 1 year ago

    Check to see if you have a factory reset on your scope and go that route first.

    Encoders do fail, but they are rated for 10 of thousands (or more) uses.

    #92 1 year ago

    If all the potentiometers are the only front panel items not working then look for common signals to them all and back trace.

    Might be worth disconnecting the flat ribbon cable to the front panel board and reconnecting it.
    To do so lift one side of the black cloth tape holding the cable to the female receptor.
    On each side the receptor there are brown tabs. Push the brown tabs outwards (towards the cable) about 1/16" and then the flat cable will be free to remove. Resinsert the cable and push the brown tabs back into position to lock the cable in.

    #93 1 year ago

    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.

    Quoted from Quench:

    then look for common signals to them all and back trace.

    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

    #94 1 year ago
    Quoted from oldschoolbob:

    I don't think this scope has a "factory" reset...

    The 'Default Setup' button is the factory reset (for what it's worth)...

    #95 12 months ago

    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

    #96 12 months ago
    Quoted from oldschoolbob:

    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

    Just pressing the button sets it to default. I assume 'Cancel' will return it to the prior setting. If you were already at default settings, then I suppose it looks like it didn't do anything.

    #97 12 months ago

    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
    #98 12 months ago

    So the common signals from the pots go to the chip at location UF2 which is a 74HC4051. Google the 74HC4051 datasheet and look up what the pin functions are to try and get some sort of idea what its purpose in this circuit is.
    Note, UF2 on that diagram is split into two parts. You've highlighted "UF2A" and if you look above it one of the four yellow blocks is "UF2B".

    #99 12 months ago
    Quoted from Quench:

    Note, UF2 on that diagram is split into two parts. You've highlighted "UF2A" and if you look above it one of the four yellow blocks is "UF2B".

    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

    #100 12 months ago

    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

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