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Taito Space Invaders 3 Layer Repair Log #3


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When I powered up the board it was totally dead.

There was no output to the screen, no activity from the ROMs or CPU.

 

 

I started at the 'Clock Generator' and all was good there.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/Clock_zpsjpnn3nbt.jpg

 

 

 

Moving up the chip numbers I started to look at the four 74161's at [5] [6] [7] & [8].

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/20170306_213259_zpsnqpbagm8.jpg

 

 

 

Pin 15 had a pulse on [5] and [8] but was stuck low on [7] and [6]

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/Faulty%2074161_zpszhg75163.jpg

 

 

 

I removed, socketed and replaced [7] with a new 74161 and I now have a title screen, can clock up credits and play a game but have the graphics glitch as shown in the pics below.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/20170306_1825550_zpsptvyzkbw.jpg

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/20170306_182547_zpsraskiwmj.jpg

 

 

 

After rechecking the four 74161's I found that pin 14 on [6] had no output.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/fAULTY%2074161%206_zpsxkut2mvp.jpg

 

 

 

I removed it and put a socket in it's place butI didn't have any spare 74161's left so I desoldered one from a scrap board and tried it out.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/20170306_231555_zpsnrvfla8l.jpg

 

 

 

The game has a slightly different fault and pin 14 now has activity.

I checked the rest of the pins and everything is as it should be.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/20170306_231412_zps0ekle6nb.jpg

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/20170306_231508_zpswtvqg98t.jpg

 

 

 

Following on from pin 14 at [6] I then looked at what was happening at pins 5 & 6 on chip [1].

There was a pulse to pin 5 but the output at pin 6 was stuck high.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/Faulty%207400%201_zpsawmwn8yz.jpg

 

 

 

The 7404 chip was removed from [1], socketed and chip replaced with a new one.

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/20170307_011132_zpstenjbnzt.jpg

 

 

 

Hey presto!!!! Another Space Invaders PCB brought back to life.

A Space War Part Three at that... :cool:

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/20170307_011030_zpsprsvlrr2.jpg

 

 

http://i1038.photobucket.com/albums/a462/Kaizen088/Repair%20Logs/20170307_011105_zps2vdcepeb.jpg

 

 

I played a few games and P2 fires a missile immediately at the start and won't fire after that.

I've seen this before in a previous repair so should be an easy fix.

Will have the leave it there for tonight.

Edited by Kaizen
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