Galaga playing but no graphics, only star field

Bullwinkle

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I'm working on a galaga. The game plays sorta blind. I can coin up and start a game but I get the star field only with no other graphics. I did re-seat the 04xx chip which didn't help. I realize it could be the socket or a dead chip. Is there anything else I should check before replacing the socket?

Thanks

Tom
 
See if your problem changes if you switch the three z80's around on the main pcb.
I've seen a similar symptom on Galaga pcb's showing just the starfield.
The pcb I was working on would not start a game...but I thought, why not.
Good luck on getting it going...
 
See if your problem changes if you switch the three z80's around on the main pcb.
I've seen a similar symptom on Galaga pcb's showing just the starfield.
The pcb I was working on would not start a game...but I thought, why not.
Good luck on getting it going...

The first z80 is actually a z80a and if you put in a regular z80, it will not work. If they are all z80a you are good to go with the test.
 
Well, here's what I have and what I've done. The 3 Z80s are identical..however not sure which ones they are but assuming this board worked before...I'd assume z80a. They are all NEC D780C -1 x1Z695-152. I moved them all around to no avail.

I also moved a 04xx chip from another board I have into this one and it didn't change anything either. Now, when I boot the machine, I get no boot up sequence (the whitish screen with what looks like garbled trash, then the grid,then the upsidedown screen, etc... ).. I get none of that. Is that more indicative of a z80 issue (assuming all mine are z80a)

Am I looking at sockets at this point? I have replaced the interconnect cable, I have not replaced the resistor packs yet but intend to..what's the most likely culprit at this point? I dont think it makes a difference, but it is a bosconian CPU board (yes it has galaga roms in it)... assuming they must use the same board.

Thanks
 
I looked up those CPUs and they are 4MHz parts so OK.

And the Galaga and Bosconian CPU boards are interchangeable but not the video boards.

Sounds like you went backwards. I would reverse the changes you made and see what happens.

Got a known working board that uses Z80? I would test each one or swap in known good ones.
 
I think one those is bad. Do you have an extra D780C/Z80a that will allow you to test out each one?
I've seen this condition on one of my boardsets as well.
 
I looked up those CPUs and they are 4MHz parts so OK.

And the Galaga and Bosconian CPU boards are interchangeable but not the video boards.

Sounds like you went backwards. I would reverse the changes you made and see what happens.

Got a known working board that uses Z80? I would test each one or swap in known good ones.

I should probably have said that the first thing I did was change the interconnect...then I put the new 04x chip in, when it didn't make a difference I put the old one back in place. Then I swapped the z80s around. I have not put those back to the original spots yet, but I can, where there was no change, not sure if there's a reason to at this point. I was leaning towards a z80 socket replacement. Is there any one z80 that has more to do with displaying graphics than any of the others? OR, is there a ROM that has more to do with graphics that may need to be looked at?

Thanks
 
I should probably have said that the first thing I did was change the interconnect...then I put the new 04x chip in, when it didn't make a difference I put the old one back in place. Then I swapped the z80s around. I have not put those back to the original spots yet, but I can, where there was no change, not sure if there's a reason to at this point. I was leaning towards a z80 socket replacement. Is there any one z80 that has more to do with displaying graphics than any of the others? OR, is there a ROM that has more to do with graphics that may need to be looked at?

Thanks

It is my understanding the first z80 is the one the does most of the tests, Then the other z80s chips start up. You can watch this with a logic probe, when it first starts there will be nothing much on the others. After about 8-10 secs. the others will spring to life and the pins will go from chirp chirp to a wirlwind of activity.

These bords usually have problems with the resistor packs and I would bet you have a broken one somewhere. Look carefuly where they attach to the ceramic body for pins pulling away or broken pins right at the body.

edit: put everything back to where it was playing blind and if it is playing blind your roms are good (most likely)
 
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It is my understanding the first z80 is the one the does most of the tests, Then the other z80s chips start up. You can watch this with a logic probe, when it first starts there will be nothing much on the others. After about 8-10 secs. the others will spring to life and the pins will go from chirp chirp to a wirlwind of activity.

These bords usually have problems with the resistor packs and I would bet you have a broken one somewhere. Look carefuly where they attach to the ceramic body for pins pulling away or broken pins right at the body.

edit: put everything back to where it was playing blind and if it is playing blind your roms are good (most likely)

Yes... First Z80 does all the self tests up to the explosion sound then kicks off the other 2. They are held down in reset until those tests are finished. If they don't start up properly then the watchdog timer kicks the main CPU in the head and resets it.

If it truly plays blind then check the video board for issues. 5B, 5M, and 5N on the video board is where I would start.

RJ
 
If it truly plays blind then check the video board for issues. 5B, 5M, and 5N on the video board is where I would start.

RJ

It does indeed play blind...will look at those locations. I actually have a 2nd boardset that I believe has issues on the cpu board..so I will try hooking that video board up and see if that clears the issue

Thanks
 
I looked up those CPUs and they are 4MHz parts so OK.

And the Galaga and Bosconian CPU boards are interchangeable but not the video boards.

Sounds like you went backwards. I would reverse the changes you made and see what happens.

Got a known working board that uses Z80? I would test each one or swap in known good ones.

just remember this when you change the boards.
 
I have had a similar issue where the background of stars are there and the enemies and player is there but not the score or any text and the tractor beam were missing.

Would this be caused by one of the secondary Z80s failing? I couldn't get into it much because it is intermittent.
 
I have had a similar issue where the background of stars are there and the enemies and player is there but not the score or any text and the tractor beam were missing.

Would this be caused by one of the secondary Z80s failing? I couldn't get into it much because it is intermittent.

If they are Zilog I would just go ahead and replace them....I really really HATE them. I spent more time than I should have finding a problem that was there and then not. Turned out to be a marginal Zilog Z80 chip. Watch it, some are z80 others are z80a, and z80b.
 
I have had a similar issue where the background of stars are there and the enemies and player is there but not the score or any text and the tractor beam were missing.

Would this be caused by one of the secondary Z80s failing? I couldn't get into it much because it is intermittent.

No. If those fail the watchdog should knock the main CPU over the head.
 
OK, I have made it past just having the starfield..now I have part of the game... looks like 2 of the same images. Any suggestions on what might cause new scenario? I should mention the tube produces a nice clear picture..the camera is crap

Thanks,

Tom
 

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Not sure... If I were troubleshooting it I'd check the 04xx, 00xx, and the 07xx chips first.

Oh, and on the missing graphics one, the 02xx

Did you break any pins off on the customs when swapping those around? Double check!
 
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