Bally Squawk & Talk issues, please help...

keithsarcade

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I am noticing a loud background noise from my Mr. & Mrs. Pac-Man pinball. The problem seems to be somewhere in the Squawk & Talk PCB. Tried the MPU in another game and it checks out. The S&T also seems to have a jumper wire attached near the heat sink, looks like someones "attempt" at this repair. I can attach this jumper to ground and the background static will go away, but then after a few seconds I get no sound at all. I don't see any bad solder joints or cracks, I did replace the pots with no success, and I have reseated all chips. Also if the static gets worse at times, the displays go crazy.

Anyone have any idea what might be causing this? Caps maybe?
 
I am noticing a loud background noise from my Mr. & Mrs. Pac-Man pinball. The problem seems to be somewhere in the Squawk & Talk PCB. Tried the MPU in another game and it checks out. The S&T also seems to have a jumper wire attached near the heat sink, looks like someones "attempt" at this repair. I can attach this jumper to ground and the background static will go away, but then after a few seconds I get no sound at all. I don't see any bad solder joints or cracks, I did replace the pots with no success, and I have reseated all chips. Also if the static gets worse at times, the displays go crazy.

Anyone have any idea what might be causing this? Caps maybe?
If the displays are going crazy also do you think you could have a power supply issue?
 
Looks like the Solenoid driver PCB is the real culprit. I can put another one in and the static goes away. Displays are still going nuts if I disconnect that jumper wire on the S&T. Can anyone with a Mr. & Mrs. Pac chime in, does yours have a jumper wire?

I'm guessing caps for the Solenoid Driver?
 
My guess is you have excessive ripple on the high voltage cap (the large "horizontal" one above the plastic high voltage section cover), top left of the board. This is the cap that smooths the high voltage for the displays, and can very well cause High frequency static interference as well.

Replace it and you should be good to go. Not sure why the S&T jumper relates to this, I think the cap will fix you up.

Chris
 
OK, got some work done today so here goes. First I worked on the Solenoid Driver, replaced both caps as well as the 25k HV pot for good measure. Put it in, no difference. Then I focused on the S&T. I was informed by an expert that common culprits are caps C16 and C22 IIRC. They are weird looking 4.7uf 25v caps. His advice was to up these to 6.8uf running 16v or higher. Bob Roberts then informs me that theres a 10uf susbstitue that should also work fine. So I went ahead and replaced those 2 funny looking caps with 10uf 16v caps. The noise immediately went away, but I feel my success might be short lived. I've had the game on for 3 hours now and am noticing a faint buzz coming back. Nowhere near as loud as it was, and I can live with it if it doesnt get any worse, but if it does, something must be causing this, wouldnt you think? It seems to be loudest when the "B...A...L...L...Y..." flash on the pac-maze, and especially noticeable with the red lamps. Like I said, nowhere near as bad as it was, but still there.

Any advice?
 
OK, got some work done today so here goes. First I worked on the Solenoid Driver, replaced both caps as well as the 25k HV pot for good measure. Put it in, no difference. Then I focused on the S&T. I was informed by an expert that common culprits are caps C16 and C22 IIRC. They are weird looking 4.7uf 25v caps. His advice was to up these to 6.8uf running 16v or higher. Bob Roberts then informs me that theres a 10uf susbstitue that should also work fine. So I went ahead and replaced those 2 funny looking caps with 10uf 16v caps. The noise immediately went away, but I feel my success might be short lived. I've had the game on for 3 hours now and am noticing a faint buzz coming back. Nowhere near as loud as it was, and I can live with it if it doesnt get any worse, but if it does, something must be causing this, wouldnt you think? It seems to be loudest when the "B...A...L...L...Y..." flash on the pac-maze, and especially noticeable with the red lamps. Like I said, nowhere near as bad as it was, but still there.

Any advice?

Not sure on your exact issue, but I have a Bally Spectrum that had a slight buzz (especially w/ the speech), and I did a cap kit on the S&T board - problem fixed.

I don't know if you know this or not, but Ed @ Great Plains Electronics has cap kits for the S&T boards...
 
Good to know. So far I have replaced those 2 caps and both volume pots. I guess a full cap kit would be beneficial. I had it on all evening again and the light buzz is still there as it gradually warms up, but its still nowhere near as bad as before.
 
A recap of the S&T board is always the first step in improving sound issues. Other items that can affect the sound/speech path include the pots, the LM3900's, and the amp. From there it gets cagey....

Chris
 
Just an update for future reference, buzz came back louder. I still havent done a full cap job, but I did replace several more caps, mainly the larger ones as well as the 10uf. No background static at all now, and it sounds better than ever. I also confirmed after doing this that the jumper wire I was referring to was indeed someone's answer to attempt to fix it, I cut it off and the games been going all day now without any issues.
 
On the S&T boards, nine times out of ten, what I have seen was bad electrolytic capacitors. Replace all of them. Also check for cold solder joints at the connector pins.
 
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