Gottlieb System1 Sound Question

xray2

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Can someone with one of the original Gottlieb System1 sound boards measure the voltage at the point show in red on the schematic for me. I am trying to help out a buddy but have no reference point for a working game.

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The zener diode being used as the voltage regulator is 13V so I'm going to guess around 12V at the point you highlighted. That makes sense in the context of the circuit.

It's a really simple board. I considered reproducing these but don't feel like getting sued by Gottlieb ;)

Hell... I might just do it anyway.
 
Yea Lindsey, my estimate was 11.5 under load but wanted to get a real world reading. Not looking to reproduce these so have at it.

I could still use a measured value from someone with a working board.
 
Yea Lindsey, my estimate was 11.5 under load but wanted to get a real world reading. Not looking to reproduce these so have at it.

I could still use a measured value from someone with a working board.

Sure... someone can go ahead and measure it. They'll find it at around 12V. Assuming their board is working correctly.

A better question is what are you reading on the board you're working on? It's not going to matter in this circuit if the voltage fluctuates a little bit. It should be obvious when measuring the voltage at that point if you have a problem. For example, 0V or 24V would indicate a problem with the power supply. 10V-12V doesn't. The only effect of a slight variation in voltage will be a shift in the pitch of the sound generation circuits.
 
I am helping someone remotely and do NOT have access to the board. Some of the information I receive is contradictory so I am double checking the data.

The board is comprised of cmos parts with a voltage range of about 4.5v to 18v so a half volt one way is no big deal. A voltage drop across the power feeds on the LM380 power amp would make a difference.

I honestly believe there may be nothing wrong with this board and the 24VDC power supply may be at fault. The 24VDC would have to vary widely for the 11-13VCD to be impacted here. Faulty wiring harness or connector is starting to sound like a high probability.

I sure wish all my friends had scopes, logic analyzers and the training to use them but unfortunately they simply do not.
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I am helping someone remotely and do NOT have access to the board. Some of the information I receive is contradictory so I am double checking the data.

That explains things. So... have the guy check the 24VDC at the input of the power supply and the output to VCC? What am I missing?

The board is comprised of cmos parts with a voltage range of about 4.5v to 18v so a half volt one way is no big deal.

Right. They're 555 timers. Fairly basic stuff. Not sure if the originals were CMOS though. They should be listed as LMC555 on the schematic if they are. Not that it really matters...

A voltage drop across the power feeds on the LM380 power amp would make a difference.

You're right. It will have the effect of raising or lowering the output volume slightly assuming that the voltage is within range (10V-22V according to the date sheet). Higher or lower and it will melt (higher) or not work at all (lower). Of course, the same logic applies to the 555 timers.

Shouldn't be too tough to check the voltage right at the amp with the game on. You could also just turn up the volume and listen for static. That's a good indicator that the amp is working.

I honestly believe there may be nothing wrong with this board and the 24VDC power supply may be at fault.

Have you had your friend check the input voltage? I would check at CR1 (1N4002 diode).

The 24VDC would have to vary widely for the 11-13VCD to be impacted here. Faulty wiring harness or connector is starting to sound like a high probability.

I agree. It would have to be either lower than around 14V or so high that it blew up the zener diode or something else.

I sure wish all my friends had scopes, logic analyzers and the training to use them but unfortunately they simply do not.
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The training to use them is the most important part :)

Unfortunately though, neither of those would be much use in solving this problem. Well... the scope would be useful if you had problems in the tone generation circuits but the power supply troubleshooting can be done with a $5 meter. You could also use a scope to see if there is anything coming out of the timer circuits to troubleshoot a possible amp problem. You could also use a cheap logic probe or small speaker, like headphones.

See... if I reproduced these I could just sell one and be done with it :)

Then he would find that the 24VDC was bad and want to return it. haha!
 
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but the power supply troubleshooting can be done with a $5 meter.

The problem is most likely with the cheap $5 meter in use. As you know, low cost DMM sample at a much slower rate than a quality meter. The voltage is averaged out and can swing wildly when not on a stable signal.

Believe me, I've been through all the normal stuff including reflowing headers. I probably could have resolved this in 5 minutes with some sort of telepresence device.

I do appreciate all the suggestions and bumps in the thread. Hopefully someone will offer up a measured value from an actual board under load. I have never owned any gottlieb pin and do not have access to this one so it's a pain.

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The problem is most likely with the cheap $5 meter in use. As you know, low cost DMM sample at a much slower rate than a quality meter. The voltage is averaged out and can swing wildly when not on a stable signal.

The same thing will happen with an expensive meter. If the voltage is all over the place then the readings will be all over the place. The only major problem I've found with cheaper meters is they're more susceptible to inaccuracies due to the battery in the meter getting weak. If the meter has fresh batteries and the 24VDC is all over the place then you can assume that there is a problem with the 24VDC supply.

The filter caps in the power supply section of the sound board could also cause ripple in the output voltage, though I wouldn't expect that to be detectable with a basic DC voltmeter. You could possibly check for ripple with the AC setting though this circuit should tolerate a lot of ripple.

I do appreciate all the suggestions and bumps in the thread. Hopefully someone will offer up a measured value from an actual board under load. I have never owned any gottlieb pin and do not have access to this one so it's a pain.
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No problem. I hope someone comes up with a metered voltage as well, though I already know what it SHOULD be :)
 
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