(Topic ID: 21939)

TECH--MB Drac Trac Opto Problem


7 years ago

Topic Stats

  • 3 posts
  • 1 Pinsider participating
  • Latest reply 7 years ago by NM
  • Topic is favorited by 2 Pinsiders


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#1 7 years ago

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.

#2 7 years ago


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):


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.

1 week later
#3 7 years ago

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.

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