Elevator Action PCB Repair (from hell)

This pcb was bought from ebay years ago as untested when it arrived and I saw the state it was in it was stored away and been stored ever since. More recently I got a working Elevator Action pcb in a job lot of boards which reminded me about this one and having a working one could help narrow down which were the faulty layers by swapping on to the known working board.

Out of the five layers only the second one (sound board) worked correctly, even the tiny rom board on top was dead.

I didn't do a good job of documenting this repair as it was spread out over a week or so while waiting for parts and between doing other jobs. From the list of parts I had to replace you can see it was a bad one though, if I had known how many parts were bad and how long it would take to get running it would still be in storage or maybe the scrap pile. :)

 This is most of the bad chips, I forgot to save the 40193s.

The board had obviously had a nasty power spike or been hooked up incorrectly at some point as it wasn't just fujitsu ttls (although there were quite a few of those too). The ribbon cable that joins the security mcu board was even melted and had to be replaced.

I managed to reuse one of the original 40 way idc connectors but the other split so I had to replace it with a new 3M one. The originals are much nicer quality than the 3M but it does the job.

Here's a complete write up of every part replaced for those interested.

Top PCB (Small rom pcb)

3x CD40193 4bit counters which I had to order. UC10,11,13

Layer 3

2114 RAM - IC17,18

74LS157 - IC1,13,14,76

74LS86 - IC28,42,70

74LS374 - IC24,34,99

74LS10 - IC54

74LS74 - IC7

Layer 4

74LS138 - IC76

74LS157 - IC77

74LS32 - IC94

74LS74 - IC87,89,90,97

74LS374 - IC8

6116 RAM

Layer 5 (Security MCU / CPU board)

74LS245 - IC19

Ribbon cable

Repair complete.