So I just replaced the transistor (Q5) on my Stern RCT again tonight. First the OPTO receiver stopped functioning (a week after I replaced it) but the switches on that column were still working. Then I went to play today and found that none of those switches were working. Upon testing the switch row/column pins with a jumper wire while in switch test mode, I found that sure enough, the pin associated with transistor Q5 was not registering any switches.

So I cleanly desoldered the 'old' one, removed all solder from the points, and very nicely soldered in a replacement. Everything works great now except for the opto, which I have ordered another $40 replacement board from Marco, to arrive tomorrow or Saturday.

I'm hoping it was just a bad part, but I'm concerned something else is causing this issue. I checked voltage to the opto and it's +4.9ish VDC, inline with other +5 connections around the unit. The opto definitely isn't working though, as I can pass my finger through and the LED indicator light does not illuminate like it did when I first installed it.

My family is really enjoying this game, and we are looking forward to adding more (you guys said nobody can have just one - now I understand why.) But I'd really like to have something that works relatively reliably!

Any ideas or assistance is appreciated! I did replace the ROMs with new display and CPU ROMs, and there is a provision in there for failed OPTOs, so I'm going to play a little while and see if it doesn't work acceptably without the opto installed.

Thanks!
Adam

Replaced it, left Opto out of system. Played for 30 minutes fine and then it blew another transistor. Maddening!!!

Sorry I'll have to check. Spoke with Chaz at Stern and he says it's something injecting voltage into the line and blowing the transistor. This would make perfect sense and explain why I'm going through optos. I'll bet the same spike is blowing the Opto.

I pulled the 'column' switch plug and minitored voltage on the pins. They all get around 3.1v until a switch is activated, at which time they are registering around 3.3v. This is the same with the series of switches which is causing the transistor failure.

I'm curious if I could insert a fuse inline on this circuit to at least catch it before it blows the transistor? I also wonder if a failed diode on any of the switches could cause this kind of a spike? I have visually inspected every connection I can find and see no obvious issues. Unfortunately it looks like there aren't many options for help in DFW. BUT I'm sure learning a lot about pinball, very quickly!

Thanks for any ideas you have! My wife actually loves this machine - and I need that wife acceptance factor to be able to buy more!

Adam

Thank you guys for the notes. I will check the voltage again when I get home. Obviously hesitant to replace the transistor yet as I'm sure it'll just blow again.

Wayout440 - I noticed that the opto was not working, but the rest of the microswitches WERE working (all on the same column.) So I pulled the opto and played the unit for 30 minutes. During that time (in the middle of a game) the rear switches all stopped working that are on the same column. So my hypothesis (and I'm so new at this it's ridiculous) - something spiked on the wire that killed the opto, which was more sensitive than the transistor on the White Star CPU board. After playing, a subsequent 'spike' killed the transistor (Q5) which prevented any of those switches from registering due to the blown transistor.

So I don't think it's on the board, and I think that $500 for a new board would just result in a blown transistor on a brand new board.

So if it's likely not a diode, and not anything on the main board (assumptions here) - then there must be some area / plug where this particular column line is arcing or shorting with a higher voltage line in the same harness connector? I WANT to learn this thing, and I WANT to fix it myself... I just wish I had gone to school for electrical engineering :-/

Thanks again guys for your replies. I really appreciate it.

Ok thanks! I will look at that. There is a pop-up target immediately in front of the opto board, and appears to be wired to the circuit. I've looked at it and sure haven't found anything yet, but there's a gremlin somewhere, and it needs to die.

Will spend some more quality time with the flashlight and manual this afternoon. Also going to hook up my multimeter to ground and then to the connector for the column switches, unplugged from the game, and have my wife play the game while I watch the voltage to see if it ever spikes above to 3.3v mark where the others go. maybe if I can get a readout on a higher voltage I could better determine if it's a solenoid voltage level or GI lamp, etc as you mention.

Well. 6 transistors into it. This poor CPU board can't take much more. Had someone out today, I had found a switch that was missing a diode all-together and wasn't working. He replaced that, and I had replaced the transistor, so it worked for 30 minutes, he left (after I paid him over $200 for the hour he was here) and 30 minutes later it blew again.

I'm about to toss this thing out of a window! It's tons of fun WHEN IT WORKS. New troll doll installed, some LEDs, legs, etc. It looks and sounds great, but not having those rear microswitches when that transistor blows is a deal killer.

Sigh. Why are there no experts in DFW anymore?!?

Great advice guys. thank you! I pulled the opto, put a new transistor in, and it's been playing ok again without the opto installed. That's really weird to me, as the opto receiver board has been replaced twice with new ones. I'll give it a week and if it's still working ok I'll dig some more.

Luckily it appears this was enough of a problem that in the latest ROM (which i just installed) - it has full workarounds for that Opto being out of the system.