PCB Repair Logs Vendetta
Forum Thread: Vendetta PCB Repair
A visual inspection of the board revealed that the mask ROM at 3K had been removed and socketed. It was a very rough job and had succeeded in breaking pin 4 off right at the plastic body.
Not having a suitable replacement EPROM I resorted to repairing the original by grinding away enough of the chips body to expose the metal that the broken leg was once attached to. I then soldered on a new leg then verifying the ROM against the mame set proved it was good.
A bit of grey coloured epoxy used to fill in the ground away plastic and it looks like a new one.
Now for the smoke test.
Up came the board test screen with 4F and 5F showing as bad these are the sound program ROM and ram these were both socketed already so I removed and tested both ok BUGGER!
Next to clean up the hatchet job the previous owner had made of fitting the ram socket surprisingly as bad as it looked all the tracks proved to be ok.
Suspiciously eyeing the custom chip and Z80 associated with the ROM and RAM at 4 and 5F I scoped all the pins of the Z80 and found pins 16 and 17 sitting at about 3.5v these pins were traced to the 74ls74 at 1G this was replaced and a socket fitted the board then passed all tests ok and booted yay!
So far so good but it still wont coin put the board into diagnostic mode [press the test button] and test inputs found coin 1 stuck on. The coin 1 edge connector pin was then traced through some kind of custom hybrid to a 74ls253 at 11A.
This chip had been replaced at some point in the past and unfortunately been soldered back in why don't people fit sockets? Carefully remove and fit a replacement and socket all now tests ok and the board works 100%.
Makes you wonder how a board can end up with two completely unrelated faults.