PCB Repair Logs Wec Le Mans 24
Wec Le Mans 24
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| PCB Image | Reserved |
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| Pin Out | Reserved |
Repairer: Womble
Forum Thread: Wec Le Mans 24 PCB Repair
I fixed this board for Scratcha years ago, he has since sold the cabinet to Genie, whose daughter loves the game until it died on her mid race. The game apparently locked up and gave the following screen...
...which stays on the screen for about 5 seconds until the game resets itself, rinse and repeat.
Having met this board before I know it is peppered with Fujitsu TTL chips, hundreds of them. All the faults originally were bad Fujitsu TTLs so I guessed it had lost some more. I was expecting it to just be one, but in fact there were a few. The 74LS07 at 17E was missing all its outputs but replacing that did not have any effect with the board in its current state. I had quickly gone over the board with the logic probe looking for the tell tale signs of bad Fujitsu TTLs - floating outputs but aside from the LS07 there were none.
The simplest option is to resort to using my logic comparator for 14 and 16 pin ICs, as input pins that are disconnected internally leave the chip doing the wrong thing but looking like it is getting the correct signals externally. this threw up a number of 74LS174s as having bad timing so about 8 of those across both boards got replaced, again with no effect. Setting up the comparator for each chip type is pretty boring so I idly decided to dump the mask ROMs on the CPU board, and found the ROMs at 17H and 23H were bad, they dumped but their contents did not match the MAME set, the ones at 18H and 21H did. So a couple of 27c512s had the correct contents programmed and they were installed, no change.
Back to the logic comparator and after going through a dozen or so chip types I got round to the 74LS153s and found the one at 25E had both its outputs stuck low...
... piggy backing a good one had no effect as it was presumably shorted internally to ground.
So this chip was de-soldered
and a Hitachi LS153 was installed. Where possibly I always use Hitachi TTLs salvaged from scrap as I have never actually met a dead one on any board, and its not like they are an uncommon make either, very robust chips I reckon!
Anyway - new chip in, power on and....
...shes back!
Not quite 100% yet tho, there is glitching in the kerb detail and the road markings...
... the black lines in the white sections of kerb, and the black bars in the gaps between the white road markings should not be there! When I originally fixed this there was a fault where the road markings were completely missing and I tracked this to a trio of LS166s on the CPU board, one of which was totally shot before.
I vaguely remembered struggling to find a replacement chip at the time as 166s are not common at all on arcade boards. This was clearly an early repair of mine as I gave up installing sockets for TTL replacement chips quite early one. Partially because I was chewing through a lot of sockets and also as when you have a desolder station the main benefit of being able to get the chip off again is never a problem. I pinched the Motorola chip, tested it on my EPROM burner and then used it as the comparator source, which showed that the LS166 on the right of the three was giving errors on its output. Judging by the fault and the comparator error I would say it has actually lost one of its input legs internally so the output pattern is missing the feed from that pin. The chip although socketed is probably the original one from the board as its marking match the original one on the left, I never put Fujitsu TTLs back on the board if I can help it but originally I could only find a single 166 to fix the dead one, and today the only scrap board I have with 166s uses... yep - Fujitsus.
So it had to be a Fujitsu again, not sure what the white square on the chip denotes, possibly "pin 1", havent seen or noticed that before.
Reassembled and powered up...
...all road faults gone.
One weird thing with this board is that it is a two board set, with three 50 way ribbon cables connecting the two board, but the lower board does not get its power from the upper board where the JAMMA connector is, as is the case in every other board set I have ever met. It seems that it takes its power from the steering mechanism in the cabinet as there are no pinheaders for a power feed on this board. To work on this outside the cabinet you have to solder a power feed to the board, the simplest place is to the smoothing electrolytic cap in the corner, its a pain but it works.
UPDATE - found a tube of new 74LS166 chips while looking for something else, so have whipped the last remaining original Fujitsu 166 off the board, and replaced the two in sockets so there is a set of 3 new ones.
They are probably ones I bought after struggling to find a single one for the fix back in 2008/2009, ironic that they have ended up on the same board.
