Quote:
Originally Posted by YamahaFreak
Did some preliminary testing. In the attached image, the circled diodes test shorted (same readings both ways) and the one circled resistor is open. I haven't looked up how to test caps and transistors with my meter yet.
I'd assume a totally shorted rectifier is a pretty bad thing, hopefully the whole unit isn't toast.
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The 4 diodes make up the full wave rectifier circuit you will read something both ways. Probably OK but to test you'd need to de-solder one end of each and test individually. The resistor you have circled is a very high meg-Ohm resistor can't quite tell if the 2nd band is brown or violet, but regardless it looks like either 2.1 or 2.7 meg Ohms and provides a static electricity path to ground from the cold side to the hot side. Never seen one there fail. It's going to read open unless you have your meter set on the highest Ohms scale.
The diode though, and Q901 and Q902 I would be suspicious of. And anything else in that cooked area. It's been getting way too hot there.
You need an ESR meter to test all the caps. If you plan on doing this sort of thing as a hobby (or a living☺) you need to get one, not just to fix this machine. Said it before: Electrolytic capacitors are the bane of electronics!
And yes if those 4 diodes that make the full-wave AC rectifier are all shorted it probably took a nasty power surge or lightning hit.