Corrado Tomaselli

No background in electronics. Learned everything by reading pdf books and expecially Video game logic Vol 1 by Atari and in general early Atari and Williams arcade manuals

Apr 142018
 

Got a Black Tiger for a repair which had a colour problem on some graphics

It lacked some shades of colour

I decided to look around the palette rams @6C and 6D until I found a fixed address line

Tracing back I found an 74ls157 @5D with an output stuck low.

After checking the inputs I found one of them stuck low and according to its truth table, the output is always low.

Tracing back I found a 74ls273 witth Q3 output low and D3 input oscillating.

Piggybacking a good one restored the correct colours.

After changing it , the game was completely fixed

 

Apr 102018
 

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

Psychic 5 repair log

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.

Vanguard repair log

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Feb 242018
 

Bought this classic as not tested but luckily it was working except the missile sound was completely missing.

Looking at the schematics I found this

 

 

In the game there are only two missile sounds.

Shot A is your ship missile sound, while Shot B is the one from some enemies

IC37 is an LM3900 op amp which is very unreliable and infact after changing it , the missile sound was restored

Labyrinth Runner repair log

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Feb 242018
 

The game was working good except the sprites were all missing some lines

 

The board is using some unreliable drams 41464 from Fujitsu similar to the ones used on Konami Haunted Castle or CPS1 A board.

I bought some units from Aliexpress , put some handmade socktes and changed both to be 100% sure

Turned out only one of the two was faulty, in anycase the graphics were 100% fixed

Joust repair log

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Feb 242018
 

I bought a Joust boardset declared 100% working.

When I tested it  all the coin inputs didn’t work

I ran the test and infact they were all activated

I was not worried because  I was sure it was the 6821P PIA on the romboard.

After replacing it didn’t fix the problem.

Looking at the schematic there are also some 4066 CMOS chips involved.

I desoldered the one used by the three coins inputs and after testing it on my programmer it was declared good.

I decided to add a socket and test another one on board

Luckily the problem was fixed and it turns  out my programmer is not reliable in testing CMOS devices.