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Denon POA 6600 Thread

Bratwurst7s said:
So, to do a small review here.

This amp is actually the first one that I unpacked. It went on the bench, passed the dim bulb test, was opened, put on the mains and the idle current was adjusted after 10 minutes to the stated 8mV.

Later, when I was having problems with the second amp I put this one back on the bench with the intention of taking a great many voltage measurements and comparing them to the misbehaving amp to get a better picture of where that amp was having problems. It warmed up about 20 minutes on the bench after opening it up.

I was sitting there looking at the schematic deciding where to start and just like that R536 flashed, burned and smoked. This is a 1k ohm fusible. The trace from one end of that part runs to R562 (47 ohm fusible) and then to the output trace that all of the output transistors feed into.

The other end of R536 goes to the junction of C520 (33pF) and pin 2 of IC501 (NJM082BD).

Something pulled a lot of current through that resistor.
It has just now been replaced with a Vishay RN60 1k part.

Next I pulled R562. Being only a 47 ohm fusible I would guess that it would have burned first if there was a shorted transistor etc on that end of the trace. It tested at 46.5 ohms. Now replaced with a RN60 47 ohm.

Next I went back in the other direction and pulled C520. It tested at 32pF. Replaced with a TDK MLCC C0G part.
Lastly for today I pulled IC501 and replaced it with a socket.
I still don't know how to bench test an op-amp.

That's it for today, the new Mark Knopfler CD arrived in the post today and now it's time to check that out.

:beerchug:,
James
Click to expand...
Sucky poo...did ya spill your brew on it? :dunno: . Seems oddly random.
 
Bratwurst7s said:
Made a bit of progress today and checked everything in and around the idle current section all the way over to the edge of the voltage amp section. Also tested and sorted matched sets of 5 each of KSA1381 and KSC3503 to get ready for the voltage amp section.

The 2 14.8v zeners (D506, 507) tested low at about 14.4v, found a pair of new ones that tested at 14.75v.
Everything else checked very nominal.
Fusible resistors were replaced with 1/4w Vishay RN60, the rest with SFR25 except for the 4 1w MOX, those were re-installed.
Caramic caps and a couple of mylar were replaced with MLCC C0G.
C518 and 519, 220µF/25v were replaced with Panasonic FM 35v.

View attachment 3176888

Tomorrow I'll start looking through the voltage amp section.

:beerchug:,
James
Click to expand...
I'll go sift through the thread for the schematic. I doubt you need my help though. Ya seem more experienced.
 
Sifted through it. I'd swap diode farm D510 through D514, all of them. TR 510 might be worth an out of ckt test. Good luck.:beerchug:

Also wanted to verify C524 & C525 are a polarized type, vice a Wima bipolar jones.

Redneck out
 
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Soundscape said:
I'll go sift through the thread for the schematic. I doubt you need my help though. Ya seem more experienced.
Click to expand...
Actually, reading your posts, I think that you are more experienced at circuit troubleshooting, or at least better at at it. What I am doing could best be described as a brute force method.

I see no good reason for that resistor to have burned without something along that trace pulling way too much current. The trace is bookended by fusible resistor R562 on one end (47ohm) and op-amp IC501 on the other. The resistor is good and I would think that little thing would have burned first if the problem was at that end.

Every single part around IC501 checked good, all the way over to C524, 525, except for the op-amp itself. I would love to know a way to test one of those with a DMM.

C524 and 525 were replaced with a 1µF/100v Wima. You thinking that this is a position where a polarized cap is required? I did put Wima's there in the other amp and it seems to be working fine now. I would have to order elcos for that. I haven't had an elco smaller than 10µF in my benchstock for a long time now.

All small signal diodes are getting replaced, and other than a couple on the front panel board the zeners are getting replaced also.

Yesterday I worked almost the entire voltage amp section, just a few resistors and caps nearby CN12 and CN13 to check. Then I will shift over to IC502 and friends. So far every single part has tested nominal except for that one burnt resistor and the 2x low performing 14.8v zeners.

:beerchug:,
James
 
Bratwurst7s said:
Last step with the power supply board was to add some Panasonic ECW 0.01µF poly film caps in parallel with the main filter caps and re-solder the rest of the connections.

View attachment 3174938View attachment 3174939

Cheers,
James
Click to expand...
Should I start doing this in amps that didn't do it originally?

side note: even though I subscribed to y'alls threads, it seems like AK only sends me notifications when it feels like it. I double checked my notification settings, there must be something I'm missing.
 
analogwisdom said:
Should I start doing this in amps that didn't do it originally?

side note: even though I subscribed to y'alls threads, it seems like AK only sends me notifications when it feels like it. I double checked my notification settings, there must be something I'm missing.
Click to expand...
Well, the theory is that the little film caps should filter out high frequency noise that the large value filter caps are not so good at doing. I view it as a low cost "it might help and shouldn't hurt" mod.

As far as notifications goes, I notice that there are times that I don't get any and then later they come in a flood.

LOL, recently, after over 10 years of being here, I just started to explore the buttons and tabs at the top of the AK menu banner. :biggrin: And discovered that I had 49 pages of watched threads. Seems that I forgot that replying or posting in a thread automatically adds it to the watched list. After 3 days of unwatching stuff I am down to 14 pages. Another day or so and that should be under control.

:beerchug:,
James
 
The voltage amp section and DC servo section have now been completely worked. As before, so far every part has checked out good, nominal even. Replacement choices are as earlier also.

DSC02611.JPG

I would have liked to replace C501 and 508 with 10µF Wimas. But they would have overhung the 2 zener diodes D501, 502 and I was concerned about creating a heat trap. Btw, those 2 "14.8v" veners were not as low reading as the 2 on the other end of the section, both were about 14.6v.

DSC02613.JPGDSC02614.JPG

Next up is the pre-driver/driver section, then the protection section. After that a run through the outputs and everything around them. With a little luck I will be done with the board in 3 days.

:beerchug:,
James
 
Nashou66 said:
Why not move the Zeners to the underside , keep them a little above the board. Then you'll have enough room for the 10uf Wima's .

Athanasios
Click to expand...
Good idea. I might do that.
Of course, then the 2 amps will be different. I won't be able to sleep at night without doing the same to the other amp. :biggrin:

:beerchug:,
James
 
Soundscape said:
Yes sir...C523 as well
Click to expand...
OK, very good to know, thanks!

Just to help an old mechanic understand can you share some of the secrets of knowing that about these positions? Because I would never have twigged to that and this seems like a good chance to learn something.

Based on your advice I swapped C523 with a Panasonic FR 10µF/50v.
C524 & 525, I could temp re-install the originals until I can buy some elcos so that I can test the amp. They aren't great, tested at about 900nF and 5.9 and 7.5 ohms ESR.

I found some Kemet 1µF/100v elcos that look decent.
https://www.mouser.de/ProductDetail/KEMET/ESL105M100AC3AA?qs=HXFqYaX1Q2x0RWu/YCFzZA==

But that will have to wait until I'm back from vacation.

Cheers,
James
 
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Looks like I found a reason for that resistor burning. And at the same time it looks like I will get to find out if the KTA1659A and KTC4370A are good drivers for this amp.

TR512 2SA968B driver is shorted. I haven't gotten TR511 out yet, the screw to the heat sink is very tight and it looks like I'll have to de-solder the heat sink with it to get it out.
Both pre-drivers tested ok but got replaced.

I haven't gotten to the outputs yet.

Cheers,
James
 
I wrote something incorrect yesterday, the DC servo section was not completely finished, I hadn't replaced all of those diodes. That is finished now, as well as most of the driver section.

DSC02615.JPG

Cheers,
James
 
Note for the next person:
There is a sneaky little diode, D527, that is hard to find. In the schematic it is nearby TR551. It's actual physical position is far from there.

That little devil has snuck right between the legs of TR510.
When preparing a new part for that position bend the legs a bit asymmetrically so that the glass body of the diode is directly between the transistor legs to insure that there is no chance of a short.
You will have to remove TR510 to replace the diode.

DSC02617.JPG

Cheers,
James

edit: I hate it when I look at one of my photos and see parts that are not neatly lined up with the rest of the troops. That just burns my butt.
 
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I just took a detour and looked over the 3rd, damaged amp. I'm thinking that it looks repairable. There are a couple of damaged traces to fix but they don't look terrible.

Someone has done lots of things in there. It has been at least partly re-capped, mostly with Roederstein, which are actually not bad. Whoever it was put a 22µF63v cap in place of C524, one of those 1µF things that we were talking about. :dunno:
The drivers have been replaced with ISC 2SA1006 and 2SC2336, which are not a completely bad choice I think, 25w, but only 80mhz.
They unwrapped the wire wrap posts, so that sux.
2 of the outputs have been replaced with ISC parts, one in each bank, and both are shorted.

I'm thinking that after I get some other projects out of the way I will revisit this thing, late summer or Fall, and get it working.

Cheers,
James

edit: corrected 2SC2336, I wrote the wrong number (2236)
 
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