Psychic 5 repair log #2

 PCB Repair Logs, Repair Logs  Comments Off on Psychic 5 repair log #2
Apr 102018
 

My beloved original pcb developed once again problems after the last repair log you can read here:

Psychic 5 repair log #1

This time, the overall colour palette was pinked and all text was missing

After some troubleshooting I found again a problem with a Fujitsu ttl 74ls08, same type and week/year of manufacturing of the one I changed on the old repair log!

 

After changing it, the game worked fine for some minutes and then it developed a new problem

 

Game lost sync and became bluish

Again I decided to concentrate on the only Fujitsu  74ls08 ttls which were present on the board until I found the faulty one.

Same week/year of manufacturing and same fault: dead outputs

In addition, I found another couple of Fujitsu 74ls08 which had dead outputs  and I decided to change all of them with good ones.

Now the game is 100% fixed but there are 3 more Fujitsu ttl waiting to be replaced. I ran out of parts otherwise I would have changed them immediately.

Psychic 5 repair log #1

 PCB Repair Logs, Repair Logs  6 Responses »
May 192016
 

Last year after a lot of research I succeded to buy at a good price an original board of Psychic 5 , one of my favourite game of all time, which was really in mint conditions.

 

psychic5

 

Some days ago I picked it up for a play and after some minutes the game developed this problem during attract mode:

psy5

psy3

psy2

 

After some more time the game was total yellowish:

psy4

 

Game hasn’t any schematics available and there are not any games known to me which have similar hardware and schematics available.

I could only go blind and try to find the reason of the fault.

So I started to short some signals of srams looking for palette changings and I found a couple of them at pos.6N and 6M, 16kbits.

The one at pos.6N had the first 4 data pins low and I was pretty sure either it was faulty or the 74ls245 connected to the data bits.

After desoldering, the sram 2018 was tested good in the programmer. That meant that the programmers didn’t use all data pins of the palette rams. The 74ls245 was good because it could drive correctly the signals without the ram installed.

I tested some TTLs nearby looking for strange signals but found nothing.

Decided to go brute force using my logic comparator and testing everything on the video board but starting with FUJITSU parts which are known to be very unreliable.

The logic comparator found a 74ls08 with all the outputs faulty

psy6

 

I double checked the outputs with a logic probe and they were all in the grey area (no good logic signal).

After changing it I fix the problem 100%

 

psy8

psy1

So FUJITSU brand proves once again to be really unreliable!