I evidently have an opto problem on my MB:

When I turn the game on, I get a Test Report to check switches 74 (pos 5), switch 77 (pos 2), and switch 78 (pos 1).

After I run Drac Test (in T-19), the DMD reads that Drac Pos 1 SW is broken--however, running a Single Switch test in T-3, reveals that 4 of the 5 switches are working perfectly: namely, switches 74 (pos 5), 76 (pos 3), 77 (pos 2), and 78 (pos 1)--they all open and close perfectly when I test them with a tool.

However, I have found a problem with Switch 75 (pos 4): it is currently staying permanently closed.

Earlier (in a T-3 test of Switch 75; pos 4), the switch was continuously cycling on its own from being closed to being open.

I thought it may be a connector problem, so I re-seated all the wires with an IDC insertion tool at the IDC connector to the PCB under the Drac Trac (Defender Switch PCB Assembly A-21402) but that didn't help. On a long-shot, I also re-inserted all the wires on the IDCs leading to the 16-Opto PCB to no avail.

So what's going on here?

A bad opto at U2 on PCB assembly A-21402? A bad transistor on PCB assembly A-21402?

I haven't yet inspected all the transistor pins with a magnifier to check for a cracked pin--I thought I'd stop and ask for help at this point.

Many thanks in advance.

Update:

Someone suggested I reflow the solder on the opto in question--which I just did--but it didn't work in this case.

The opto is no longer cycling in T-3, it's just staying closed. Surmising the opto itself is bad?

Should I just replace the slot opto itself or the entire PCB (A-21402)?

Reason I ask is I heard Williams used specially selected Opto's that had a higher sink current than normal (the photo transistor)--and that a standard slot-opto will only work for a short amount of time before failing.

A search for the ID numbers on the optos turned up nothing (KAT00091 QT742), and the only 5-pin slot optos I could find were 5490-14575-00 at Competitive Products (just like this one that's out-of-stock at Bay Area):

http://bayareaamusements.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=OP-5490-14575-00

Should I use it or track down a board?

That is unless anyone has any original optos you'd sell (used ones are fine)?

Thanks in advance.

In case anyone else ever runs into this problem, just thought I'd post the resolution: a new repro standard slot opto in the PCB did the trick...well, for now that is--I'll report back if it fails because of the issue mentioned above (pruported higher sink current than normal on the originals).

Longshot, but if anyone has any working original 5-leg slot optos or the entire PCB itself (dead or alive) please LMK.