Controlled lamp diode Q

[Cryptkeeper]

Hay,
Theres a lamp around the whirlpool in my white water thats not working 100%
Its on most of the time and in test mode it comes on with 1 or 2 other lamps.
Would a busted diode at the lamp cause this problem or would the lamp not work at all?
Thanks

 

[Jay Walker]

It depends; if the diode's failed open-circuit, the lamp wouldn't work at all, but if its short-circuit (i.e. conducting in both directions), then current meant for other lamps could get in. If you've got a test meter, and the pcb's reachable, measure the diode on 'ohm' scale. It should be a low reading measured in one direction, and pretty much an open circuit in the other. There could also be short circuit connections between wires in the lamp 'matrix', which is where the 'single lamp' test comes in handy for working out which row/column might be affected.

 

[Cryptkeeper]

Ah yes,
I didn't consider it could fail to closed circuit.
Ive had one go before but the lamp was just out all the time.
I'll take it out later and test it.
Thanks Jay!

 

[Cryptkeeper]

So its not the diode,
tested good but i changed it anyway and same deal.
It comes on with every thing in its column .
any other tips before i get stuck into tracing wires?
Thanks

 

[aaronhicksuk]

Have you had the machine long? It could be something silly like a stray glob of solder shorting across a lamp holder. Try turning on whole rows/columns on at a time in the diagnostics to check for anomalies.

 

[Cryptkeeper]

Haven't had it long at all.
fairly certain this isnt a new problem.
I'll look into it again later with the row/column test

 

[elrikos]

IF the entire column lights with that lamp in single lamp test, trace the column back looking for shorts. There will be something somewhere. Also, find what row it's on and do the same on the row.

 

[Cryptkeeper]

IF the entire column lights with that lamp in single lamp test, trace the column back looking for shorts. There will be something somewhere. Also, find what row it's on and do the same on the row.

I didnt get a chance to look at it last night ,
Its actually opposite,The lamp in question (#5 waterfall) comes on with everything in its column .
2 of the lamps in that row are a ******* to get too because they're both on the mini playfield .

 

[aaronhicksuk]

I had a similar problem recently on one of my machines. Are there any other lamps illuminating when they shouldn't be or is it just that one? If you use single test mode what other lamps cause it to light? Particular attention should be paid to the lamps that cause it. It sounds like there must be a short somewhere, either in a diode or a lamp holder. I'd try to narrow down exactly which lamps cause the unwanted illumination and they check them for shorts. As mentioned before I've seen a small blob of solder that landed on a holder cause exactly what you have described.