I have been doing this too long to make these kind of mistakes. I was working on the playfield of my recently acquired Party zone and when I turned it back on, I had some sort of playfield short that blew out the red GI on the game. If you are unfamiliar with Party Zone, there are a set of GI lights that are all red.

I made sure the short is no longer there and I swapped the other GI legs and validated the playfield wiring is all good and the red lights up.

It’s clear the circuit on the WPC board was damaged, I get 6.2V from the other 2 GI legs and nothing from the Leg I shorted.
- I pulled the fuse at F10 and it is fine. (A little mad it didn’t blow the fuse)

The “red” GI is controlled by Q18 (triac)
- Triac Q18 appears to test fine as well as transistor Q17.
NOTE: I took out the heat sink screw in the pic.

Tested the triac the following way:
- connect the positive lead of multimeter to the MT1 terminal of triac and negative lead to the MT2 terminal of triac
- connect the MT1 and gate to positive lead and MT2 to negative lead.
- The multimeter showed a low resistance reading.
NOTE: Not sure if this test is applicable if this triac requires high gate voltage and current for triggering.

Could Q18 still be bad but tested ok? Something else I should be checking on the board?
- I don’t have a triac on hand to swap out and test, will have to order some.

Thoughts?

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Does it seem odd the fuse didn’t blow? I will order a couple triac’s tomorrow and hopefully get it mid week. Wondering if I could have damaged anything higher up in the board like a logic chip.

LOL! Makes me wonder if the fuse should have been a 4 amp or 3 amp fuse. Adds no value if it doesn’t blow.

I did. I found two led flasher bulbs that were damaged in the event too.
- Replaced them and they work fine.
- Checked all the switches and all 100%.
- No light matrix issues, no sound issues, no solenoid issues nothing else.
- Additionally the game doesn’t report any errors either.

I can double check, but that was the first thing I did when it happened was to see what got damaged.

I didn’t check the resistors, will definitely do that too. Like I shared above, the triac (using my multimeter). Tested fine and almost identical to the other triacs. Same for the driver transistors

These boards are old and rather than swapping a component and risking that I left a solder pad, I would rather buy a $2 part and wait for it to come in.

I will order a triac today. Good to have one in the supplies. Need to see what triac knowing the existing one is no longer made, I believe.

Thanks “Roamin” for the comment. Will let you know if I figure it out.

I pulled the board when I had the issue and did a continuity test on all of the traces from header pins back to the triac. I do not have a bench test where I can power the board and trace it like described. I can do some basic “live” tests while plugged in. Have to see what else I can do as you suggest from a troubleshoot check.

Question 1 on the fuse.
- Absolutely with a meter and outside the machine. Appreciate the question, I don’t assume anything either when helping folks.

Question 2 on testing the triac
I documented in the initial thread how tested it. I thought it was correct. Here it is again:
- connect the positive lead of multimeter to the MT1 terminal of triac and negative lead to the MT2 terminal of triac
- connect the MT1 and gate to positive lead and MT2 to negative lead. (You said this as well)
- The multimeter showed a low resistance reading.

NOTE: I also pulled the board for all tests I did.

I need to look more closely at your suggestions on testing without desolderimg. appreciate all the help!
- Let me know if the first two responses align with your questions and done properly.

I will try to do your isolation trouble shooting tonight and get back.

Well, I figured it out. It was not the TRIAC which I thought it really didn’t think it was bad after testing with my multimeter.

It ended up being the actual J115 ground wire (yellow-white) having a poor connection in its plug (Not the board side, but the plug itself) I tested back all of the traces and had great continuity everywhere and per chance checked them as well just being thorough, sure enough it had broken lose.

I wonder if the ground had a very bad connection and could a surge have made the barely bad connection finally fail. Just odd when I powered it on the came on and then went immediately out.

Thanks to this great community for sticking with me and providing additional thoughts to drive me to trace more.
Special shout out to emsrph and @roamin!