Do GI triacs ever fail?

[good_buddy83]

According to the Marvin Pinball book, he states that when diagnosing GI issues it is never the triac and he has never seen one fail. My issue is I think I have a bad triac on a GI string and I am curious if anyone else have ever come across this.

Here is the issue, working on troubleshooting a few minor bugs on the Getaway and there is one GI string in the back box that won't light. I checked J115 and the connector was burnt pretty bad (to the point it fell apart when taking the board off). So I rebuilt the connector and the pins on the board. Powered back on and no dice. I pulled the board, check continuity on the board traces on the problem circuit. All fine. This part of the board looks brand new, no heat damage what so ever. Board back in, powered on not lights.

Now getting smarter I tried to multi-meter it at the fuse. Yup power gets from the transformer to the board, from the board to both sides of the fuse. I felt the triac heat sinks after being powered on and all are warm except for the one in question. Knowing I already checked the trace I know power is getting to the triad. I am 95% sure it is the triac, but I am doubting myself because Marvin's says it is never the triac. What the hell?! Let me know your thoughts. I am curious. I am worried I am missing something.

Oh and yes I checked for voltage at the connector leaving the board and there is no power at the pins, so I am certain it is a board issue. Let me know.

 

[good_buddy83]

Oh and the only reason I haven't replaced the triac yet is because they are not supposed to fail and I don't have any on hand. I have to wait until Monday to hit up the local electronics shop anyway, so it gives me some time to think before doing something drastic.

 

[Menace]

I've never come across a bad triac in my travels. It's always been a header / connector pin issue, cold solder, broken trace, bad fuse or holder etc etc etc.

D

 

[good_buddy83]

Picked up a new triac today. I'll keep you posted. I'll feel stupid if it is something else, but I am out of ideas.

 

[good_buddy83]

Re: Do GI triacs ever fail? NO! they do not.

Well don't I feel stupid!

I checked the voltage at the triac tabs before I pulled it. All of them read 1 except for the bad on in question, it reads 6.8 plus it is cold. That tells me the triac is not turning on like it should, but definately is connected to power. Changed the triac and no help. So I tried changing the pre tranisistor as well and no help. I have a hard time getting a meter into the areas around the triac and pre transistor, but following the board trace the next stop is U1, some kind of IC chip I know nothing about. Really could this be the problem? From the IC chip is goes straight back to the CPU via ribbon cable. Any chance this is a ribbon cable? This is way too much work for one string of backbox GI's, but it bothers me to know end that the machine thinks it is smarter than me.

Really open to suggestions now, as I now feel like idiot for changing the triac. I guess everyone was right and it is never the triac. Stupid :FP:

Anyone who can offer help it would be greatly appreciated.

 

[Menace]

Well, if you happen to have another machine you could always swap the ribbon cable to eliminate that. Have you also rung out all of the traces from the gi string all the way back to the ribbon cable? (schematics are your best friends for this) Always start with the easy stuff first and work towards the hardest.

Keep us posted.

D

 

[good_buddy83]

OK I am running out of options. Changed the ribbon cable and it is not that. For some reason the triac refuses to turn on. It does not heat up, and yet there is power to it. I am starting to suspect the LS374 chip (I think those numbers might be wrong I am guessing) but it is the rectangular chip that tells the triac to turn on. Does these ever fail? Is there a chance of failure at the CPU board? To recap, the triac has been changed and the pre-drive transistor has been changed. I checked for continuity on all the traces. Even the resistors are registering in range, I am thinking of metering the LS374 chip, but I am worried about getting a probe on there with out shorting anything out as it is tight. Anyone have any better ideas? This issue is getting the better of me.

 

[Menace]

The LS chips can and do fail, but if you want to rule out the CPU portion of the equation you could always install the driver board in another game to test. At least then you know the issue is on the driver board and the only part left in the chain is that LS chip. (this is assuming you have another WPC game to test the driver PCB in)

D

 

[good_buddy83]

Thanks Menace,

I have the getaway sitting next to an Addams Family, so I'll make the power board switch and see what we have. I am betting on it being the chip, but I'll be a little smarter and rule everything else out first. Any tips on replacing this chip? Looks like a lot of pins and has me a little concerned. Let me know. Thanks.

 

[Menace]

The only thing I can stress to you is if you've never done any sort of PCB re-work before, best to have someone experienced handle it. (Just ask Wong lol)

Not sure where you're located, but if it comes down to it I could handle the repair for you.

D