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Author Topic: Taito Space Invaders PtII 3-Layer PCB Repair Log #1  (Read 4074 times)
Kaizen
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« on: February 26, 2017, 01:27:54 PM »


I was asked to look at this PCB (Space Invaders PtII Colour 3-layer)for fellow member on AA forum.
This was the screen output and the 12v fuse kept blowing.



I replaced the CPU and ROM's with tested working ones to rule them out, it made no difference.
With the 12v to the audio disconnected I powered the board up and started looking around.

There were a couple of lines stuck high on the roms.
I started at the CPU and found that there were two 7408's at 11 and 18 that weren't behaving correctly.
After socketing and replacing the chips there was life back in the board.
The 74LS157 below them had some dry solder joints so I reflowed them as well.








The next thing was to work out why the screen only displayed red.
A feature of SI Pt2 is when you get hit the screen turns red, there seemed to be an issue somewhere along that line.
Probing backwards from the 'bomb' line I could see the 74174 wasn't behaving correctly.
After socketing and replacing the chip I now had some colour.







Last thing to tackle was the sound, first thing to do was the identify the cause of the 12v fuse blowing.
A common issue with these PCB's is the Tantalums failing and going closed circuit causing a short to ground on the 12v (18v) audio supply.
I put a multimeter across the Tantalum next to the sound output amp (LM377) and sure enough it had a dead short across it.
After removing and replacing it, the 12v supply no longer blows the fuse and the audio has been restored.





There's some issues with the 'Trigger' sound (makes a short 'pop' sound) which I'll look at next.
When you press the fire button you could hear a short pop through the speaker there was a signal being generated but no audible 'Trigger' sound.
The most likely culprit was one of the LM3900's in the 'Trigger' circuit.
I started with number 35 which was on the end of the row.
Chip removed, socketed and a new one installed and fired the board up and all sounds are now working.
I'll socket and replace the rest of the LM3900's for preventative maintenance as well as the 4006 and 4030 CMOS chips.

https://youtu.be/JxwAUnRxNnY






« Last Edit: March 01, 2017, 06:40:12 AM by Kaizen » Logged
smarty
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« Reply #1 on: February 26, 2017, 03:00:19 PM »

Nice fix and well documented Smiley
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Andreas_AUT
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« Reply #2 on: February 26, 2017, 04:53:13 PM »

Great repair log, I really enjoy reading stuff like that!
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Pinge
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« Reply #3 on: February 26, 2017, 05:01:29 PM »

Awesome repairlog, thank you!

If anyone has a pcb like this for sale I want it, Im only missing the pcb for my coctail  lol
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Kaizen
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« Reply #4 on: February 26, 2017, 10:16:21 PM »

They don't come up very often, when they do they are overpriced or get snapped up quickliy.
This was my first repair of a dead spacies PCB.
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vernimark
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« Reply #5 on: March 03, 2017, 11:20:50 AM »

very interesting, thank you.
Actually I can't find the 3 layers schematics. Do you have a file to share?   Tongue
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Kaizen
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« Reply #6 on: March 03, 2017, 01:27:26 PM »

Link to schematics...

https://drive.google.com/open?id=0Bzy5XMBV05xGUzdJOWZENlk0Y0k




Link to Space Invaders Folder...

https://drive.google.com/folderview?id=0Bzy5XMBV05xGR2owWTZqbHBmVDg&usp=sharing
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vernimark
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« Reply #7 on: March 04, 2017, 01:59:45 AM »

Really thank you!
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Kaizen
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« Reply #8 on: March 04, 2017, 09:02:19 AM »

Many more schematics here...

http://s1038.photobucket.com/user/Kaizen088/library/SI%20Schematics?sort=3&page=1
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