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Gallag PCB missing explosion sound


Kaizen

Question

I have a Gallag PCB the has the explosion sound missing.

It's not there at boot up and also missing when your ship gets hit.

All other sounds are fine, I have a second board which I've swapped the roms into and the explosion sound is there at startup (it has other issues but the sound is definitely there ) on that board.

I've spent a bit of time over the weekend reading up on the Galaga boards but wasn't much help.

Can anyone point me in the right direction as to where in a Gallag board the explosion sound is generated.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Arcade%20PCB/20161004_061920_zpsnfkuuthf.jpg

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Looks as if you may be missing a rom from the board as the empty socket is populated on my two boards with a rom labeled G2 which contains the cpu code.

I also think the gallag boards used an extra 4th z80 cpu to emulate the explosion sound, so check to see if they are all good as well.

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I believe the explosion sound is not stored in ROM, on a Galaga board it is generated by a custom IC @ 6M. The Gallag bootleg won't have the custom IC, but instead some logic ICs or a PROM or something as a substitute.

 

Looking at the Galaga schematics, the outputs from 6M go through a heap of resistors and caps then to the op-amp and amp. If the Gallag board has an op-amp, you should be able to follow the inputs back and find where they come from.

 

My guess is the location to the right of the top most CPU.

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I've found the 4066 to the right and slightly below the top Z80 gets a high at pins 8-9 & 11 when the ship is hit but pin 12 stays low so switch D doesn't close allowing the output through pin 11.

The Op Amp is above the 4066.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Arcade%20PCB/20161004_061920_zpsnfkuuthf.jpg

 

That's about as far as I got tonight...

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Random%20Crap/CD4066%20-%20Pin%20Assignment_zpsaw3atg2s.jpg

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I pulled out my Gallag board, looks like this, spot the difference ->

 

http://members.aussiebroadband.com.au/kanem/pic/gallagalag.jpg

 

Looks like your board is missing the LM324, which is the op-amp I was referring to in the Galaga schematics. All the pics on google of Gallag boards appear to have it, strange that yours doesn't seem to have ever had one.

 

Maybe solder one in and see what happens.

 

Also looks like you're missing all of the decoupling caps too :blink:

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Looks like your board is missing the LM324, which is the op-amp I was referring to in the Galaga schematics. All the pics on google of Gallag boards appear to have it, strange that yours doesn't seem to have ever had one.

 

Maybe solder one in and see what happens.

 

Also looks like you're missing all of the decoupling caps too :blink:

The board was fully functional before storing it for 12 months...

 

Does the RGB-S come out of the edge connector on your board??

If so which pins?

I have another similar board but it has no riser board and RGB-S comes out of the edge connector.

It has MGG-703A written on it.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Gallag%20PCB/20161005_193206_zpssrnsq174.jpg

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Gallag%20PCB/20161005_193236_zpshlmk2uf0.jpg

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Does the RGB-S come out of the edge connector on your board??

 

No, has the plug on the video board.

 

I have another similar board but it has no riser board and RGB-S comes out of the edge connector.

It has MGG-703A written on it.

 

That has an interesting layout, they moved the amp section to the top :unsure

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