Galaga board issue

Bullwinkle

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OK, picked up this non working Galaga board. Previous owner mentioned there were video issues with it and only tried reseating socketed chips but that just made it worse. So I figured sockets and replaced all sockets on the CPU board. Next I just took a quick once over on the socketed chips on both boards and noticed the custom chip at 4M on the video board is in backwards! popped it out and put it in properly but my guess is, it was powered up this way (probably what made it worse). I also am going to guess that whatever voltage was applied to this chip going up the wrong pin probably did the chip in. I don't have a galaga machine, but do have a JAMMA to Galaga adapter so I hooked it up to see what I have. Yeah, video issues for certain.

1. Is it possible the custom chip survived

2. Is there anyplace I can procure the chip for that location

3. The video below shows what I'm getting now. I have replaced all sockets on the CPU board, but not the video board yet. I've also reflowed solder on the CPU board. Any suggestions on where to start looking?

 
I'm not a galaga expert, but i have repaired a few, i can tell you its getting mostly through the boot cycle and then resetting. I'd start by testing the roms, it could easily just be a bad rom at this point.
From there, i'd start looking at the rams.
As far as the customs go, without digging out the schematics, i'm not familiar with what that particular one does - but i know a few have been replicated. JROK and FPGA arcade come to mind - as well as pulling one off of another older junk namco pcb.
 
The likely hood that a custom chip survived reverse voltage is slim at best.

You might want to post in the Wanted section of this board to find a replacement chip.
 
Those customs are fragile at the best of times, reverse polarity will have destroyed the chip, 99% certainty. From memory the 4M custom on the video board would have the number 05xx on it. That's the starfield generator, the game will work without, minus the starfield effect obviously. The xx in the number is the chip revision so any 05xx custom will work as a replacement.

4M on the CPU board is a 40pin chip - thats a Z80, or it should be, if a custom has been jammed in there then that is a problem.
 
Those customs are fragile at the best of times, reverse polarity will have destroyed the chip, 99% certainty. From memory the 4M custom on the video board would have the number 05xx on it. That's the starfield generator, the game will work without, minus the starfield effect obviously. The xx in the number is the chip revision so any 05xx custom will work as a replacement.

4M on the CPU board is a 40pin chip - thats a Z80, or it should be, if a custom has been jammed in there then that is a problem.

I'll start looking for a replacement on that. It was on the Vid board... the 3 z80-As on the CPU are in tact and I have many to throw in their place if they turn out bad.

Easy enough for me to burn a set of roms and I have plenty of rams to replace what's there. So from the sound of it, you suspect the issue is on the CPU board somewhere. That at least narrows it down half way. (other than the custom starfield generator)

Thank you guys for giving me a starting point. ...much appreciated

Tom
 
The sockets, ribbon cable and the resistor network packages are the prime candidates on these boards. Worth replacing them all, but the fault could be on either board still.
 
The sockets, ribbon cable and the resistor network packages are the prime candidates on these boards. Worth replacing them all, but the fault could be on either board still.

epically if they have the flat ceramic resistor packs. Also, you might want to check the dip switches. I had one that did not work that had a screen like that and it turned out that one of the Dips had switch #3 turned on. I think I settled on dip set 1 4=on and dip set 2 4&8=on, all others off.
 
Yeah,

DIP switches will cause the board to constantly reboot if they are set wrong...

Those pesky flat ceramic resistor packs are notorious for causing problems on the boards too. They pop their legs loose and stop making connection. They are used to help "pull up" various data bus and other connections and when they break the logic levels go screwy.

Check the reset lines. The main CPU will run then after the self tests the 2 sub CPUs will have their reset lines go high and they start running. If either of them aren't working then the watchdog timer will smack the main CPU and self tests start over again.

If the main CPU is stuck in reset then check for bad connections to the EPROMs (or for bad EPROMs) and to the main SRAM chip on the video board. It's common for one of the address/data lines to lose signal by having a bad trace from replacing sockets (VERY easy to pull traces) or resistor packs.

It's also common to short traces on the top side of the board under the sockets if you didn't desolder them cleanly.

RJ
 
Well, I started to look into grabbing roms from MAME.. my CPU board has roms labeled as follows:

3N = GG1 3N
3M = GG2 3M
3L = 3400C
3K = 3500D
3J = 3600E
3E = GG2-7 3E

and the vid board has

4L = 2600J
4F = 2700K
4D = 2800L

I want to make sure I have no intermixed sets on the board so My question now is, which Midway Rev should I burn and does it matter? Also, can I use namco roms on a midway board?

As for the resistor packs, I have not replaced them but did find a link on how to do it. It is on my list of things to do. I've already replaced the ribbon cable with a new cable and replaced all sockets on the CPU (havent done the vid board yet...thinking tonight for that). Will also be doing the ram replacement (removing the 8 2147s and replacing them with 2 2148s).

I've also tested the voltage at the cap next to the power connector on the CPU board and it tests at 5.2vdc per the guide on Arcadeshop.com

RJ & Kb0jjn, I had seen a post on the dip switches and messed with those as well to no avail, but that could mean they're is one totally dead switch too. Keeping that in mind as I move forward. As for traces, I'm comfortable with soldering/desoldering but still check to make sure all traces are in tact before putting the new socket in place. This was actually one of the easiest boards I've worked on for soldering (my previous being missile command, millipede and (gulp) an MCR boardset (of which I can't mention or I burst into tears) ;D

Hopefully I'll get this running soon.

Thanks for all the suggestions
 
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LOL ... no offense taken, I'm not sure what my mental block is with that as I'm usually fairly competent with spelling & grammar. That one bothered you, eh? I try not to let other peoples spelling / grammar miscues bother me. Less stress that way. :D
 
I sent mine to Chanelmaniac for testing so I don't really know what they are or should be but he probably could tell you. If I remember right mine all had the xx00 names on them.
3200a
3300b
3400c
3600e
etc.
The video board ones are labeled correctly but don't let that fool you. The labels could be wrong or the chips could be bad. That is why I sent mine out for testing. Also my eprom programmer (Needham's pb-10) is giving me diffrent checksums then the mame files.
There are proms also that need to be looked at and I have no possible way to check them once out of the board.

The first two don't look like they came from the same set.
gg1 would be one set
gg2 wolud be set two


Well, I started to look into grabbing roms from MAME.. my CPU board has roms labeled as follows:

3N = GG1 3N
3M = GG2 3M
3L = 3400C
3K = 3500D
3J = 3600E
3E = GG2-7 3E

and the vid board has

4L = 2600J
4F = 2700K
4D = 2800L

I want to make sure I have no intermixed sets on the board so My question now is, which Midway Rev should I burn and does it matter? Also, can I use namco roms on a midway board?

As for the resistor packs, I have not replaced them but did find a link on how to do it. It is on my list of things to do. I've already replaced the ribbon cable with a new cable and replaced all sockets on the CPU (havent done the vid board yet...thinking tonight for that). Will also be doing the ram replacement (removing the 8 2147s and replacing them with 2 2148s).

I've also tested the voltage at the cap next to the power connector on the CPU board and it tests at 5.2vdc per the guide on Arcadeshop.com

RJ & Kb0jjn, I had seen a post on the dip switches and messed with those as well to no avail, but that could mean they're is one totally dead switch too. Keeping that in mind as I move forward. As for traces, I'm comfortable with soldering/desoldering but still check to make sure all traces are in tact before putting the new socket in place. This was actually one of the easiest boards I've worked on for soldering (my previous being missile command, millipede and (gulp) an MCR boardset (of which I can't mention or I burst into tears) ;D

Hopefully I'll get this running soon.

Thanks for all the suggestions
 
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