BIG problems

One more thing to check on the chassis, Jer alluded to it earlier. Check the bridge rectifier for shorts. It's the 1-1/2 " sqare thing by the PS caps. There are 4 diodes in it.
 
laatsch55 said:
One more thing to check on the chassis, Jer alluded to it earlier. Check the bridge rectifier for shorts. It's the 1-1/2 " sqare thing by the PS caps. There are 4 diodes in it.
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I measured the DC coming off the caps earlier and IIRC it was in the order of +85v 0v -85v
Can the bridge still be defective?
 
No, not with those numbers. Most of the semiconductors on the driver board can be checked in circuit for shorts or opens, EXCEPT D13, and you already checked them. You are looking for a shorted Q7, Q10, Q5, Q4-Q1. 1-4 are doubtful . check every diode on that board as many tie directly to the plus and minus rails....
 
What's the datecode on the XPL's?? If you want to go back stock I have a few. All new MJ21196's would only be 60.00....... You'll want to keep the RCA-410's they are the best driver for any output we've found. I'll senda replacement for the burnt one.
 
laatsch55 said:
What's the datecode on the XPL's?? If you want to go back stock I have a few. All new MJ21196's would only be 60.00....... You'll want to keep the RCA-410's they are the best driver for any output we've found. I'll senda replacement for the burnt one.
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7334 for the most part. How do they compare as outputs? That would be the least expensive route for sure. I imagine things would be weird with XPLs on one channel an MJs on another, no?
I will take you up on the 410 offer, very kind of you.
 
laatsch55 said:
No, not with those numbers. Most of the semiconductors on the driver board can be checked in circuit for shorts or opens, EXCEPT D13, and you already checked them. You are looking for a shorted Q7, Q10, Q5, Q4-Q1. 1-4 are doubtful . check every diode on that board as many tie directly to the plus and minus rails....
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That board is intimidating, a PL 14a BTW. I`m a little apprehensive maneuvering it with all the short and seemingly brittle wires and traces. In circuit testing would be easier for sure. That will have to wait till the morning. You had me check D13 out of circuit which checked out normally but not with the .79 both way measurement you expected though..
 
Correct on D13, in circuit it tests .79 each way.
 
Michael F said:
7334 for the most part. How do they compare as outputs? That would be the least expensive route for sure. I imagine things would be weird with XPLs on one channel an MJs on another, no?
I will take you up on the 410 offer, very kind of you.
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I've seen a lot weirder combos than that.The MJ21196's are the best to be had. They are a dedicated audio part, the MJ 15024's are GP and a little noiser, well , a lot noisier. Not that you can hear it, but the AP can see it, so it's a consideration.
 
No, you did right, D13 HAS TO BE checked out of circuit.
 
A 1N4148 is not supposed to let current go both ways, due to the matrix interconnections, you have to isolate it from those other influences
 
laatsch55 said:
No, you did right, D13 HAS TO BE checked out of circuit.
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OK, checked in and out of circuit, got ya. I`m debating whether or not to replace D 14,15 since they are already "half out" and nasty looking, same with D 13, looks to be of the 1n4148 variety
 
Michael F said:
Would that be back to back diodes across C6? Which kind?
Was there not some debate over C6 value as well, while I`m in there...
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1N4148 back to back
470uF 25v bypassed with 0.01uF to 1uF polypropylene non polar 63V cap
 
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