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Old 09-27-2020, 03:54 PM   #5
re-atari
Senior Member
 
Join Date: Oct 2010
Posts: 102
Default Re: Denon AVR-X2000 mainboard caps bulging

Hi Momaka, many thanx for your insights, it's always a pleasure to read your posts on Badcaps!

The X2 cap is indeed placed across the AC input of the standby PSU. I have attached page 121 of the service manual, showing its schematic. I wanted to encircle the culprit cap (c4143) in the schematic, but sadly after the last Nitro Pro update I cannot edit pdf's anymore...

I'm in 230V territory (EU), our wall sockets carry 3 wires, brown (phase), blue (neutral) and yellow/green (GND). One strange thing is that the receiver's AC input socket does not have a GND pin, only phase and neutral are connected. I don't know how the previous owner had the receiver hooked up, he possibly had it earthed through the tuner's coax lead. Cable radio/TV is standard in my country, so just about every home has a coax wall socket.

The internals of the receiver don't appear to have been excessively and prolongedly overheated. There's no visible massive discoloration on the PCB's or on the cooling heatsinks. Besides that, I would expect the cooling paste on the output transistors to be dried out then as well, and that's not the case. The regulators are bolted to the steel bottom halve of the receiver housing for cooling, and the steel isn't discolored there either.
There is a tiny spot on the mainboard PCB that looks slightly discolored. It's the area where r4025, r4026, r4027 are situated (see service manual pag. 127). They are three 1,1K resistors that are connected in series immediately after the positive lead of ELNA cap c4052. The resistors all measure in spec, as do r4029 (10K), d4007 (1SS133) and zd4002 (ZJ6.8B, a 6,8V zener) that come after them. These components produce the Mute+7V signal. The discoloration may very well have been caused by a possible power surge, which is what you suspect has happened.

Curiosity already got the better of me, so I disassembled my working AVR-X2000 to swap boards. This showed that only the mainboard of the failing receiver is at fault causing it to not start up, all other boards are OK. I took my investigation one step further and desoldered the two bulging large ELNA caps. This wasn't easy, as the bottom of the cans was stuck to the mainboard PCB with some kind of white silicone glue, but in the end I got them out undamaged. I was astonished to find both caps measured completely in spec: 11 mF (or 11.000 uF) on my M4070 LCR meter and an ESR of 0,018Ohm on my MESR-100!

I had been thinking of measuring the voltages that the five 78XX and 79XX regulators put out beforehand, just to exclude obvious and easy to fix faults there. Decided doing these measurements wouldn't be easy, though, as the regulators are quite hard to reach. And now I had come this far in my fault search, I really didn't want to inadvertently make a short circuit with my test leads and potentially turn an only partially defective receiver into a complete total loss. And as none of the regulators showed a short between IN, OUT and GND, I suspected they would be OK, so let them be for the moment and started desoldering the large caps. Sadly this didn't identify the culprit :-(

That leaves the million dollar question which component(s) on the mainboard could be preventing the receiver from starting up. I did some measurements on the various components on both mainboard PCB's and compared the readings, but got no differences. And as it looks like the two large ELNA caps are not the reason the receiver didn't start up after all, I'm now no step further. Very awkward.

I agree with you, that the material Denon used for making the PCB's (Phenol) sucks big time. I mean, pertinax has already been around for more than 40 years, why would a serious manufacturer even think of using Phenol.
Denon did use pertinax for the CPU board, probably because it's a double sided PCB, whereas all other boards are single sided. Must probably have something to do with cutting cost corners...
Attached Files
File Type: pdf Denon AVR-E400 & X2000 service manual pag. 121.pdf (643.0 KB, 2 views)

Last edited by re-atari; 09-27-2020 at 03:58 PM..
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