Who is our resident Q*bert troubleshooting guru?

Better yet, just post your problem here. It's kinda what the forum is for.

That way, if Riptor is able to help, everyone can learn. Or perhaps someone else can help, too.
 
Better yet, just post your problem here. It's kinda what the forum is for.

That way, if Riptor is able to help, everyone can learn. Or perhaps someone else can help, too.

I agree, I look through the posts in the repair section a dozen or more times a day. If I have any advice I will post it.
So what seems to be the ailment?
 
I have two different Q*bert boards, both of which have issues. I was hoping to combine components from both into one good board, but I'm not sure which should be the donor and which the board to restore. I've reflowed the filter board, rebuilt the PS board with the exception of the D26 diode, which I've ordered a replacement for (the current diode reads 33v, I've ordered a 27v replacement), and I've removed the faulty LM379S just in case it was causing a voltage drop while I wait for the replacement to arrive.

As far as the individual issues, rather than explain it, I'll show you.

This is my first board...



...which glitches in random ways. Sometimes the foreground shows up fine and the background glitches, other times the background is fine and the foreground glitched, and sometimes both glitch. The only thing consistent is the manner in which certain things glitch, like the 888888s across the top of the test screen, the weird box instead of the arrow on the aforementioned screen, etc. Test mode flip flops around (I've replaced the old toggle and pushbutton switches on the cab to no avail).


And the second board:



This board does some really weird stuff. Test mode comes up without any flip flopping. Object Priority screen onloy shows blue boxes in place of the discs, and the bottom row appears at the top of the screen, partially offscreen. Out of test mode, the screen has a reddish tint to it, and the screen flips around, first upside down, then upside down flipped, then right side up, and finally right side up flipped. Foreground characters either do not appear or appear as blocks.

The first board's had a cap kit installed, has no battery acid damage and has had all the IC and board contacts cleaned and polished, including the harness connector. Second board hasn't had a cap kit yet (I just received it from a fellow KLOVer yesterday) and hasn't had the contacts cleaned yet, but there isn't any acid damage here either thankfully.

Hope that's enough to start off with. Let me know if you need any more info.
 
BTW Rip, I ordered the sound amp and 27v diode from you :p

Yep, its boxed up and going out in the morning.

If the boards dont have acid damage they are worth fixing. If they do have acid damage its just a matter of how much. First thing I would do is is measure the 5v on the main pcb. Qberts have quite a bit of voltage drop from the power supply to the main board and they will glitch if its too low. I found that most need the pot on the power supply almost all the way up. Dont bother measuring on the ps itself, its at the mainboard that counts.
If your voltage is confirmed I would verify the eproms.
 
Where is the pot on the PS located? I looked all around and didn't find one.

EDIT: Do you mean VR1 on the PS board itself?
 
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Where is the pot on the PS located? I looked all around and didn't find one.

EDIT: Do you mean VR1 on the PS board itself?

Yes VR1, its the only pot on the power supply. It adjusts the +5, all other voltages are non-adjustable.

"Okay my Q*bert must be different from others out in the wild. Mine has the single blue cap on the PS and no pot, yet it has the LM379S on the sound board."

It was a factory mod which makes the power supply output around 20-24v. It was designed to run the LM379S replacment amp which is a TDA2002 and cant handle the 30v. However, the LM379S runs just fine with the modified power supply. The only problem is the knocker doesnt work too well.
The modified power supply will still have a pot on it. The only thing changed were a couple components in the 30v section.
 
Here's my board where the battery pack was at. Not sure if you'd consider this acid damage or not, it looks fine to me:

1031481.jpg
 
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The pic is not big enough, can you post a bigger one :)

There is minimal acid damage there, no problem. I have seen them where almost half the board was destroyed.
 
The pic is not big enough, can you post a bigger one :)

There is minimal acid damage there, no problem. I have seen them where almost half the board was destroyed.

haha sorry, forgot to size it down a bit in ImageShack. Fixed pic is up.

So, I took the second board with the flipped screens, cleaned and reseated all pullable ICs, upped the voltage on the PS a bit, and no effect.

Where would be my next likely candidate?
 
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