Jump to content
Due to a large amount of spamers, accounts will now have to be approved by the Admins so please be patient. ×
IGNORED

Taito Space Invaders 3 Layer Repair Log #1


Recommended Posts

I was asked to look at this PCB (Space Invaders PtII Colour 3-layer)for another AA member.

This was the screen output and the 12v fuse kept blowing.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/DaveFJedi%20SI%20PCB%20Repair/SCREEN%20GARBLE_zpsxydgkytl.jpg

 

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] (;7] and [16] on the schematic below) 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.

 

 

http://i1038.photobucket.com/albums/a462/Kaizen088/DaveFJedi%20SI%20PCB%20Repair/7408x2%20faulty_zpsnkmum0u9.jpg

 

http://i1038.photobucket.com/albums/a462/Kaizen088/DaveFJedi%20SI%20PCB%20Repair/20170226_193505_zpsw1q5peng.jpg

 

http://i1038.photobucket.com/albums/a462/Kaizen088/DaveFJedi%20SI%20PCB%20Repair/20170226_142104_zpspirtnn3z.jpg

 

 

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.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/DaveFJedi%20SI%20PCB%20Repair/74174%20faulty_zpslbtyhhoz.jpg

 

http://i1038.photobucket.com/albums/a462/Kaizen088/DaveFJedi%20SI%20PCB%20Repair/20170226_193445_zpswfuxt99k.jpg

 

http://i1038.photobucket.com/albums/a462/Kaizen088/DaveFJedi%20SI%20PCB%20Repair/20170226_193156_zpstpthanxn.jpg

 

 

Last thing was the sound, first thing to tackle was 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.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/DaveFJedi%20SI%20PCB%20Repair/10uF%20Tantalum%20faulty_zpsz9gjnvub.jpg

 

http://i1038.photobucket.com/albums/a462/Kaizen088/DaveFJedi%20SI%20PCB%20Repair/20170226_205116_zpsazehcbrx.jpg

 

There's some issues with the missile sound (works but not correct sound) which I'll get to tomorrow.

Edited by Kaizen
Link to comment
Share on other sites

I set to work on the audio issue today.

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.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/DaveFJedi%20SI%20PCB%20Repair/faulty%20LM3900_zps7qaeezjl.jpg

 

http://i1038.photobucket.com/albums/a462/Kaizen088/DaveFJedi%20SI%20PCB%20Repair/20170227_201632_zpsv2xaf7fh.jpg

 

Edited by Kaizen
Link to comment
Share on other sites

  • 3 months later...
  • 1 month later...

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...