Help troubleshooting a Denon POA-1500

Capacitance should always stay the same unless you really know what you're doing.

Don't you need C9? That's a 220uF 25v. I have some nice Panasonic FC's in that value I'd send you for free if you'd like. Might have some 47uF as well, I don't remember.
I have the cap in my hand and on the side it says 47. Judging by the soldering, it looks to be factory but doesn't match the schematics that I have.
 
I scanned the list in the service manual and it seems the schematic and the list are in disagreement. But installed and list match, schematic is the odd man out.
caps.jpg
 
I can pop the top of mine if you want to know what is installed- Nate, you can do the same.

Personally, I'd go with the 220uF and bypass it with a small film or leave it at 47uF, there's plenty of room and caps are a lot smaller than the were in 1983. The zener reg supply runs both channels diff front ends. Perhaps they specified 220uF, but there was too much zener noise in the front end, so they went with a smaller value with less inductance at HF.

1500.JPG

The 3.9K 2W resistor would have survived a shorted cap to ground, it would have dissipated around 1.1W in that situation, so it shouldn't be cooked. :)
 
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I can pop the top of mine if you want to know what is installed- Nate, you can do the same.

Personally, I'd go with the 220uF and bypass it with a small film or leave it at 47uF, there's plenty of room and caps are a lot smaller than the were in 1983. The zener reg supply runs both channels diff front ends. Perhaps they specified 220uF, but there was too much zener noise in the front end, so they went with a smaller value with less inductance at HF.

View attachment 1281585

The 3.9K 2W resistor would have survived a shorted cap to ground, it would have dissipated around 1.1W in that situation, so it shouldn't be cooked. :)

I picked up pairs of both the 220uF and the 47uF caps on the way home today, so I can install either. There is plenty of room in that area and the 220 would fit no problem. I was just waiting to hear which was the better candidate. Thanks for helping me get this far, I feel like this old girl might sing tonight.
 
IT'S ALIVE! My gut said put the 47uF caps back since thats what I took out, and all my rails have their power. I plugged in speakers and a source and the needles began to dance!! No noise at idle, and everything is very balanced and clear. She's a real gem.

Thanks for all the help guys, not only have I learned a bunch about troubleshooting circuits, but I also fixed the amp!

I also ordered the 2SC2655 transistors, 4.7K resistors, and new 60ma lamps to replace the burnt out meter lamps. Then she should be good as new.
 
Well done. I liked your logical and considered approach and the willingness to listen. You have repaired a lovely amplifier for the cost of a capacitor and learned a whole lot.

Do the lamp mod- my amps have never blown bulbs since.

Show us some pics of the pair when she's all lit up later. Cheers. :)
 
@restorer-john - is there a good reason this amp has transistors involved in the lamp circuit? (As opposed to them simply running off one of the rail voltages.) I was wondering if an LED swap would be more difficult on this amp than some others because of the complicated lamp setup.
 
Looks like I got excited a little too soon. While the amp is doing great, it seems my pre-amp is now plagued with gremlins. I did, however, find what I'm assuming wrecked my amp in the first place. I am getting a lot of "noise" or "feedback" out of the speakers when I plug in anything into the inputs. I've swapped interconnects and sources and the issue is the same. I attempted to see if it was still transmitting the source despite the noise, but when I would turn the volume knob the amp would immediately go into thermal mode. Needless to say, I turned everything off and disconnected everything before I re-ruined my amp.

I'll also likely start a new thread since this is a completely different topic and will aid others when they search. I'll link the new thread below.

http://audiokarma.org/forums/index.php?threads/denon-pra-1000-problems.838138/
 
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