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

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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

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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

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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