Whitestar T3 - Flipper Fuse Blows When Button Held

[Menace]

Normally if the diode goes bad, it's bad. No in-between with them. And if the diode had gone bad, it would have taken out the drive transistor on the first flip.

There must be a small short somewhere along that flipper coil wiring somewhere that only gets triggered with vibration, which is why it's intermittent. This could be a tough one to track down... I friggin' HATE intermittent issues.

D

 

[retroactive85]

Well I went ahead and replaced the diode and have played many many successful games with no issue. The diode tested good at .6, but perhaps it was "leaky" and intermittently failing. I was reading the below article that might explain why the diode tested good with my digital multi meter but failed intermittently, and seeming more during multiball under heavy use. I'm going to give it a week of heavy play and if the fuse doesn't blow I'll assume I solved the problem.

http://www.electronicrepairguide.com/testing-diode.html

"If you don't get any reading either forward or reverse bias, the diode is considered open circuit.The real problem when testing a diode using the diode test function of a digital meter is that an open or leaky diode, the meter sometimes reads okay (0.6). This is due to the digital meter diode test output voltage (which you can measure the output test probe using another meter) is around 500mv to 2v. An analog meter set to x1 ohms range have output about 3V(remember the two 1.5V batteries you installed in the meter!). The 3V voltage is adequate to show you the accurate reading of a diode when under test."

 

[Menace]

Well, hopefully that's all it is but in all the years I've been fixing pinball machines I've never encountered a diode that would cause the behavior you're experiencing.

D

 

[retroactive85]

After replacing that diode I've played a significant number of games with no blown fuse, hours of play. I'm very hopeful that it did the trick.

I did find this thread on Pinside suggesting that perhaps diodes can cause this kind of issue - for what it's worth.
https://pinside.com/pinball/forum/topic/how-to-test-a-diode-on-coil

 

[sylvain]

Like Menace, I do not remember ever encountering a diode that is good sometimes and short-circuit other times,
in my numerous years of pinball machines and other electronics repairs.
Diodes are usually good, or short (and sometimes opened intermittently on Bally Solenoid Driver boards for instance)...

...Unless this was an incorrect diode (such as a zener) installed on the coil earlier...

Hope it is fixed!

Cheers,
- Sylvain.

 

[retroactive85]

Argh! After a solid week of play with no issues the fuse finally blew again.

I have a new coil on order... Hopefully that does the trick, I'm running out of things to try!

 

[Menace]

Is there any chance the coil has been rubbing against something? Any of the lugs close to something that it could possibly touch via vibration? I had a client's RCT that was intermittently blowing one of the coil fuses in the head, turns out the factory installed the kickback mech slightly off angle and it managed to rub up against a lane guide under the apron and over time rubbed through the insulation on the coil. It would only short out once in a while and I just happened to find the problem when I was adjusting the mech alignment.

I'd start looking for those types of issues in and around that coil if the replacement coil doesn't solve your problem.

D

 

[retroactive85]

Interestingly enough, not quite the same scenario but made me look closer, the "insulated" wire that runs to the kickback on T3 was rubbing against the coil stop and had worn through the black protective shrink tubing and exposed the two colored wires underneath. Now I believe the two wires underneath going to the kickback coil were uncompromised upon close inspection. By this I mean the colored tubing for each individual wire hadn't been worn through. I covered it with electrical tape to prevent any further wear.

I replaced the coil with a new one from Pinball Life. The game plays great so far, guess time will tell if there's still an issue.

 

[retroactive85]

Another 10 days gone by playing it a bunch and no blown flipper fuse. So either replacing the coil or insulating that kickback wire that was rubbing through to the coil stop did the trick. That was a good thing to note earlier Menace. That didn't turn out to be my problem exactly, but got me looking a little closer for possible shorts. Insulating that wire probably saved a lot more headaches for the future. Thanks for hanging in there with me guys. Happy flipping.