Galaga PCB repair...

modessitt

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Board does not boot - although on one occasion it reset two or three times then booted up. But then wouldn't boot again after that.

I've tested it both in the cab and on the bench - so it's not power related. I'm about to start pulling and cleaning chips, but I figured I'd ask if anyone has seen the image below and what it indicates. Looking through repair logs doesn't seem to match the descriptions and I haven't seen a pics site for troubleshooting Galaga screens (like is done with Pac-Man and DK).

Here's the pic after the initial scrambled character boot screen. This is where you normally see the cross hatch or ROM OK or the BOOM or whatever...

IMG_20120806_105234.jpg


Yes - the doofuses put an LCD in the cab...
 
Pulled and cleaned all chips - no change. About half the sockets appear to be new, including all the ones for the CPUs...
 
Which tells me what? Swap out some cpu's to see what happens? Do something with the logic probe?
 
Which tells me what? Swap out some cpu's to see what happens? Do something with the logic probe?

I usually start with new z80a cpu chips then look at the reset and all of the control lines. It looks like the cpu chips are trying to start.

Look at the custom chips and I have found the 07xx chip is usually bad on just about every cpu board I ever owned. I think I had two working out of 9.
 
Odd... I've never had a bad one and replace very few Z80 chips.

I do replace a few 08xx chips and a shitload of sockets and resistor packs.
 
I swapped out the 780C's and the Z80A and it didn't change anything.

Sometimes when I get this screen it will say ROM in the middle of the zeroes, like it's trying to do the ROM OK screen but fails. Even rarer, I might get a "EVERY 17000 POINTS" pop up in the bottom half of the zeroes.

Trying to find one of the extra Galaga boardsets that I know I have but can't find at the moment so I can start swapping chips to see if i can find the issue...
 
Replace the sockets and resistor packs first...

Then check the R/W lines coming from the 08xx to a small logic gate.
 
Replaced the ROM at 3E and it now boots up just fine, but no boom noise. Game plays fine with all sounds except the BOOM when you die. Resistor pack? If so, which one? Customer is trying to skimp and doesn't want to pay for a full rebuild of the board...
 
Replaced the ROM at 3E and it now boots up just fine, but no boom noise. Game plays fine with all sounds except the BOOM when you die. Resistor pack? If so, which one? Customer is trying to skimp and doesn't want to pay for a full rebuild of the board...

Steve, if memory serves.......it's the 54 custom (or associated chips).

Edward
 
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