Suspect Denon Power supply issue

[lottathought]

I am very new to the world of troubleshooting electronics...so please be patient with me. I got my hands on a Denon 3802. It appears to be in protection mode. The unit is getting power and has the red standby light. When you try to turn it on however, the display does not light up and the red on/standby light just starts to flash. I have read that Denon installed 4 surge protecting resistors in the power supply that are known to fail. So far so good.. Here is where I am running into a problem and am probably showing my newness. I have no idea where the 4 resisters are...or where to find the schematics to track them down. And I am not sure how to test a Denon power supply to see if that could be the trouble. As this was supposed to be a common issue for Denon, I am hoping somebody could point me in the right direction.

[Khron]

Re: Suspect Denon Power supply issue

I've managed to find 11 of the 15 pages of schematics of this receiver. The only "surge protecting resistors" that i've been able to spot upon a quick perusal are R503 and R504 (page 9, right edge of section A) - 0.1ohm / 5watt. They look like they're used more like some current-sense shunt.

You might also wanna run a check on all the fuses - they might offer an indication where the fault might be located, in case it is indeed some overload-damage of some sort.

EDIT: Now i noticed there's a few resistors in the speaker output section as well (page 8), although they're much less likely to have "gone".

[lottathought]

Re: Suspect Denon Power supply issue

Thank you so much for this. I have checked all the fuses. They seem to be fine. I have a feeling that this is going to be a long term project. I am learning as much about how test as any actual troubleshooting here. But that is why I got this receiver.

[Khron]

Re: Suspect Denon Power supply issue

What about that pair of power resistors on the +59v rail?

I hope you've at least got a multimeter of some sort.

If all the fuses are fine, you might wanna check if all the voltages are around the values they're supposed to be.

Do any of the relays click on when the receiver's supposed to "power up"? You might wanna check for DC on the "input" side of the output relays.

[lottathought]

Re: Suspect Denon Power supply issue

Khron666...yes I do have a multimeter. I have a Fluke 87v. Yes,I know it is overkill and I will likely never fully grow into it....LOL It is a little hard to explain but although I have never done much of this, it is in my blood. I strongly suspect that I will be troubleshooting electrical equipment for a long time and wanted a solid machine. I will have to get back to you on the voltages. The relay does click at startup. But it then the on/standby starts to flash and there is never a display.

[Khron]

Re: Suspect Denon Power supply issue

I don't suppose the owner's manual has a list of flash / error codes, does it?

[lottathought]

Re: Suspect Denon Power supply issue

The display never lights up. Even if there were an error code readout, there is no way to see it.

[Khron]

Re: Suspect Denon Power supply issue

I meant about that stand-by led flashing

[redwire]

Re: Suspect Denon Power supply issue

lottathought, there are many ways to troubleshoot. Make sure you have small sharp probes for the Fluke, lest you slip and cause damage. It takes patience

I would start by measuring and recording all power supply voltages. There's a lot of them. Just at the connectors. The red traces on the schematics highlight the power paths too. Find a good ground point and then just roam around with your positive multimeter probe only, it's easier. Troubles with the power amps outputs and +/-59V rails are the first place to look.
"Surge protecting resistors" is poorly translated Japanese for "fusible resistors" but I didn't see any (grey box and ! symbol on schematic).
The protect system is fairly complex, based on overtemp and any channel having too much DC offset. It would be hairier to troubleshoot back from that.
Ignore the flashing red light, it just tells you there is trouble "somewhere". I would think the display should come up but it might not have power too, although the CPU is up.

Khron666 thanks for posting the schematics.

[Franco76]

Re: Suspect Denon Power supply issue

Hi there

1. Check that the main trafo works. Measure ohm across the input plug on the trafo (below 20 Ohm.).
2. If the trafo is ok. Then check the output transistors isen't shorted.

My bet is one of the two is faulty.
Happy hunting!

[dwu]

Re: Suspect Denon Power supply issue

New to this board, not sure if this is the right spot to post.
I have what seems like the same problem with an AVR 486. Changed all power supply capacitors. I suspect when I had rewiring done in my house they reversed my rear channel wires and something blew. Tried the standard reset, no luck. Powers on the get that flashing red light