Gorf/WOW/Space Zap/Roto sound amp tantalums!

*pat on the head*
Go have Ralf do "your" next project.
as soon as you finish your next project. zing
the sad thing is you could have used this thread as a learning experience and no one would have cared. "oh i see i didn't know those caps are known to be defective" "yes electrolytic caps would be just fine for an audio amp"
"pat on head while rubbing belly" "sit on toilet while eating a twinkie" "brag about unfinished projects you did 15 years ago"
 
I guess if you want to get pedantic, they aren't defective, since that would point to them not being right from the get go, but no harm in replacing parts that are failing due to being end of life, like Atari big blues
 
i just picked up a working space zap yesterday thanks Ari Friedman (id tag your klov name if i knew it)
haven't checked for burned caps yet but probably not motivated enough to replace them before they go bad.
it has little board on the cpu socket that negates the need for the rom board. never knew this board existed
 
haven't checked for burned caps yet but probably not motivated enough to replace them before they go bad.
it has little board on the cpu socket that negates the need for the rom board. never knew this board existed

You should, probably preaching to the choir, but you don't want to mess around with astrocade games and power, the custom chips aren't cheap. Cap the power supply too, probably replace the big series pass transistor of it hasn't been done yet.
 
I guess if you want to get pedantic, they aren't defective, since that would point to them not being right from the get go, but no harm in replacing parts that are failing due to being end of life, like Atari big blues
some would fight to the death over that statement. i understand the logic of preventive maintenance by replacing parts with a limited shelf life but i myself often ride big blue till the wheels fall off. if a healthy game starts resetting at the first few minutes after powering on i will replace the big blue as a shot gun before looking any further as it doesn't hurt to do so.
 
You should, probably preaching to the choir, but you don't want to mess around with astrocade games and power, the custom chips aren't cheap. Cap the power supply too, probably replace the big series pass transistor of it hasn't been done yet.
previous owner installed a switcher kit. this might not be not good for the custom chip due to incorrect voltage. makes you wonder if some of the issues with customs is because someone (upgraded ) the power supply.
 
It would be interesting to know if Astrocade hardware customs were common failures back in the 80s when they were routed and powered up for hours on end.

Jason
 
I was working on a Space Zap that had a 90s Dell Dimension era PC power supply in it (???) and had an extra linear power supply to drop in and fix all the wire nutted nightmare, game was kind of ok. until those AMI customs (both data and address) crapped out. but by this point a few months back I had the Arcadeshop switching power supply kit for it... something goes pop sizzle. I was talking to @KPW66 about it and he just asks "was it the middle caps on the ram cards?" and I said "yeah, how did you know?" the answer, like IBM PCs, "the +12V caps are the ones that go" now everything makes more sense LOL

it's wild that I have 2 Gorfs running on Arcadeshop power supplies that never had any such issues but that Space Zap did. so I can't say I agree with the linear power supply being shitty or whatever the theory is to cause the tantalum caps to blow.

hopefully I'm done with this job before those Astrocade games go on the fritz again.
 
At least we have toledoflyer's data custom fpga replacement. I have one on standby for my wizard, when I eventually get a space zap, I'll have to get another.
 
previous owner installed a switcher kit. this might not be not good for the custom chip due to incorrect voltage. makes you wonder if some of the issues with customs is because someone (upgraded ) the power supply.
Yeah, the customs are run off the 12v, and when folks install switchers, the 12v line ends up too high and makes the customs run hotter...
 
Here are my observations and thoughts.... YMMV

I have repaired over 200 of these board sets (Gorf, WoW, Robby, Space Zap, and Extra Bases). The tantalums fail often at this point, but it is almost always the caps on the 12v rail that fail. This happens with both the original PS as well as switchers. On my bench supply the voltage is set precisely at 12.00v, and it still happens.

It's gotten to the point where I will not even test a board set anymore on my bench without first replacing the caps on the 12v rail. It's just not worth the headache for if the rupture of the cap is pointed down towards the board it can actually do some significant damage to the board and/or traces. I'm too old for fireworks on my bench (it reminds me of a "flower" firework).

I've replaced all the tants (16 on Gorf, for example, not including the one on the Amp board), on every set I've done. I replace them with electrolytics and have never had an issue nor complaint. I'm sure we could argue the original intent of why the engineers chose the tants for this application, and many other Bally Midway applications, and there probably was a valid reason, but that would be out of my knowledge area or interest quite frankly. But again, the electrolytics work fine.

As for the customs, I'm not sure I am a big believer of the mildly "over-voltage" theory. I'm sure if the 12v is cranked way up over 12.00v then it can cook them, but it's my experience that switchers do not typically run super high on the 12v as long as the 5v is dialed in. The on-board regulation circuit is very crude, but it usually holds fine. Even when the customs die the voltage is still at the prescribed setting if the 12v input is accurate.

Moreover, the single I/O applications (Space Zap, Extra Bases) run that I/O custom at 10v whereas the dual I/O' applications (Gorf, WoW, Robby) pull that down to 8.5v. As such, I suspect the VGG voltage on these customs have an acceptable range and are a bit more lenient then we give them credit for.

That all said, I am a firm believer in heat killing these customs (and, yes, I do understand that heat can be related to voltage), and especially a killer for the Data custom. It's odd that the earliest production CPU board version ("C") and every later release has the through-holes. Could that have been for a heat sink to be zip-tied to the Data custom? or maybe that was for a daughter board instead of a custom?? but either way Bally did not install a heat sink on the Data custom until the later production run of the later games (Gorf). Either they got lazy or cheap but it eventually caught up to them. Of all the dead Data customs I have seen (probably at least 80-100 of that variety), I think only two had the factory heat sink installed. So, that heat sink really did/does make a difference.

Since there are almost as many failures on the other two chip varieties (Address and I/O), I also have been wondering lately if the fact that AMI was the partner here (and not another vendor) also contributes to the failure rate. This is pure speculation but if I use the high failure rate of AMI's 6821 PIA chips as compared to other vendors, perhaps they just didn't have the best quality in their 40-pin DIP manufacturing process?? Again, pure speculation here but it does make you ponder. Maybe if another partner was chosen by Bally we would have less failures..... maybe....
 
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