P2100 - is this bad?

bought it off ebay. 10A main fuse was blown. Replaced fuse and powered up with dim bulb connected to tuner and old speakers. Light seemed to stay bright. No sound and no click. Checking the schematic looks like no output relay but just fuses? Maybe this is common with pro amps, but I'm unwise in their ways. Got this to use with some new (old) Magnepans that are supposed to be current hogs. Anyway I checked the power cord and expected more resistance than that. I thought there might be a short, maybe in the power line cap.
 
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My M-2 measures less than 1 Ω across the power plug.
 
Also verify that the two thermal switches have continuity when cold.
 
Transistors and thermal switches are good. The XLR inputs have a switch that swaps pins 2 and 3. I bought a Monoprice XLR to RCA cable where the XLR pin 1 goes to the RCA tip, and XLR 2 and 3 go to the ground ring. It looks like this cable shorts out the Yamaha inputs in either position. Maybe the table and pictures make this more clear. What gives? Seems like there should be a protocol that either the Yamaha or the cable is ignoring.

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The spec sheet for the monoprice cable shows that the tip shoud be XLR pin 2 (instead of 1 like mine). That checks with the Yamaha schematic, so I resoldered the XLR end of the cable. Unfortunately that didn't do the trick and I'm still without sound. Measured the power cable hot and neutral wires just as they enter the unit (before the switch) and get 125VAC when switched off, dropping to 1.5VAC when switched on. The transformer has no hum or vibration at all, and there are 0V at the main caps and the rectifier bridge.
 
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Check the bridge rectifier. Bought a P2200 a while back for scrap metal prices. A shorted diode in the bridge rectifier was the only thing that prevented it from working. Was blowing the main fuse at power on if memory serves me.
 
Check the bridge rectifier. Bought a P2200 a while back for scrap metal prices. The a shorted diode in the bridge rectifier was the only thing that prevented it from working. Was blowing the main fuse at power on if memory serves me.
That would sure do it...
 
The fuse didn't blow but I have it on my bulb tester (60W lamp) and only had it on for 30 seconds or so. Seems like a shorted diode on the output would make the transformer work hard and hum. Think its time to unsolder the diode?
 
Seems an RCA to a ¼" TS phone plug adapter would be an easier way to get a test signal into the unit for the first time. Fewer questions, but you are beyond that. Hope you get it working properly.
 
Transistors and thermal switches are good. The XLR inputs have a switch that swaps pins 2 and 3. I bought a Monoprice XLR to RCA cable where the XLR pin 1 goes to the RCA tip, and XLR 2 and 3 go to the ground ring. ...

I'd generally not ever expect RCA pin to go to XLR pin 1.

Typically RCA pin would go to XLR pin 2, then shell usually to XLR 1+3.
 
The transformer seems OK - I measured the secondary at 73VAC (+/- 36.5) so right on spec. Whew.
Looks like a bad bridge rectifier - thanks for the tip Whoaru99. Anyone have suggestions on a stouter replacement? The original was 25A and I'm finding 35A units but they all seem unbranded.

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Well looks like we found another bad bridge rectifier. Anyone have suggestions on a stouter replacement? The transformer seems OK - I measured the secondary at 73VAC (+/- 36.5) so right on spec. Whew.

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Awesome save..Rectifier is much easier to find. What P/N is printed on it.
 
Yes the old one is a KBH2504. I'll order the parts:
GBPC3506-E4/51 (Vishay 35A rectifier)
ECQ-E6103KFB (Panasonic .01uf/630V snubbers)


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