Galaga boots up to 00000s

mrsodapop

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Hi all,
I just got a Galaga dropped off for some work, and it also has a booting issue.
When powered on it has the usual boot up strange graphics show for about 3-5 sec., than for a split second you see the star field and text: RAM OK. Then the screen displays all 0s.
I removed and cleaned the legs on all socketed ICs and also edge connector with no change. I checked the voltage on the PCB(5.2vdc). It also looks like someone has installed several new IC sockets(very professional job). Any ideas?
Thanks for any advise
Aaron
 
Sounds like the 3rd Priority CPU may be having issues. Swap the Z80s around and see what happens.
 
I think your on to something. The board seems to only have one Z80A. I have not been able(so far) to find another known working Z80A laying around, but did find a unknown Z80. I installed the Z80 in place of the Z80A, and now game seems to reboot 2-3 times, and than locks up on star field with text RAM OK. I am still searching around for a Z80A(I must have one around with all my junk on the shelves), than will let you know what I find.
Thanks
Aaron
 
I think your on to something. The board seems to only have one Z80A. I have not been able(so far) to find another known working Z80A laying around, but did find a unknown Z80. I installed the Z80 in place of the Z80A, and now game seems to reboot 2-3 times, and than locks up on star field with text RAM OK. I am still searching around for a Z80A(I must have one around with all my junk on the shelves), than will let you know what I find.
Thanks
Aaron

I am not sure but I think a regular z80 will work in all but the first priority cpu. The first priority has to be a z80a or faster.
 
I went out after checking schem. and found the other 2 Z80s have been replaced with NEC D780c-1. Is this an acceptable replacement? I tried swapping all 3 around and had pretty much the same as listed above(locks on RAM OK).
Thanks for any advise
Aaron
 
Yes, that NEC is fast enough.

Anything that causes the 2nd or 3rd CPU to not boot properly will cause the symptoms you are experiencing. This could be a problem with the R/W signal, the 8xx chips, CPUs, ROMs, or even the 6xx chip.

Raymond
 
I am not sure but I think a regular z80 will work in all but the first priority cpu. The first priority has to be a z80a or faster.

Z80s have been replaced with NEC D780c-1.

Yes, that NEC is fast enough.

For future reference:
Z80 = NEC D780C = 2.5MHz max
Z80A = NEC D780C-1 = 4.0MHz max
Z80B = NEC D780C-2 = 6.0MHz max

ALL 3 CPUs in Galaga are clocked at 3MHz, and thus should be, according to Hoyle, the "A" (or "-1") variety (or faster). I have no idea where the nasty rumors otherwise got started.
 
Thanks for the great info guys! It looks like this is getting beyond my capabilities, so I have one last question. Could you guys recommend someone to repair this board(s).
Thanks for your time
Aaron
 
I've seen the all 0s before ages ago. designed a sub board to handle it. All it does is flex some critical timing parameters for the common RAM.

they might be out now but check with Eldorado Games and see if they have the sub board. Remind them it was Tony's fun solution for wierd behaviors on the board.

If they are out, will see about another run then ship it out there. Haven't done that repair in years since I started the home pinball mpu.
 
For future reference:
Z80 = NEC D780C = 2.5MHz max
Z80A = NEC D780C-1 = 4.0MHz max
Z80B = NEC D780C-2 = 6.0MHz max

ALL 3 CPUs in Galaga are clocked at 3MHz, and thus should be, according to Hoyle, the "A" (or "-1") variety (or faster). I have no idea where the nasty rumors otherwise got started.

Before it was kind of vague, now it is crystal clear.

I do have a z80 cpu chip and then it has some numbers on it. Riptor seen it also and said 'that is a z80a' I looked at him and he said 'trust me'. He knows much more about parts than I do. That is where my confusion came from, the chip will have something like z80 on it then some other numbers I assume are the clock speed. You really Really REALLY have to watch the part numbers and if you are unsure ask someone who sells them.
 
Well I am a dumbass!

The problems I have been having with several of the cpu board were the fact that not all of the chips were z80a or faster. Many of the cpu board I have are working and I spent lots of time looking for trace issues that were not there. Now that I got this through my thick skull I can now move onto other board sets that don't work. Thanks guys, you save what little sanity I have left.

You have no idea how much time I spent on the cpu board sets for no real good reason.

*mental note* Galaga = z80a or faster.
 
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