DENON POA-6600A schematic wanted !!

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So.... then it was my turn.....

I got a flash shooting out of one of the speaker cables when I war removing it from an electrostatic speaker.
The amp got into protection mode and then back on.
But now it has now sound what so ever.
Turning the input level on the amp made the amp go into protection mode.

I opened it up and started to do do a fast fault finding by switching boards with the working amp.

Protection board= GOOD.
Input board= NOT GOOD.
Input board with the IC401 (NJM2068AD) was not working as it put the good amp into protection mode when using BALANCED input.

Finally when I put the healthy protection and input board (front part of amp) into the faulty amp, I got no sound and it got into protection mode.

So Amp-board= NOT GOOD either!

I stumbled upon a faulty zener diode D502 (HZ-15-2).
There may be some more faulty circuitry, but for now this is what I have found.

So, are there any GOOD equivalent parts for the NJM2068AD and the HZ15-2 zener?

Cheers from Sweden!

Jerker
 
Hi Ricardo,

regarding helping you to find original 2sa1492/2sc3856 I don't believe that I can help somehow. I live in Kosova and, all parts which I order are from asia - somewhere, don't know the origin precisely.

biasing diodes you have to replace only, not all. You point on those near zener diodes like, D511, D514, DS515, D516, D517, D518, D519, D520 these are 1S2076, and you can change them with 1n4148. Diodes D512 & D513 are zener HZ5C1 you can replace with BZX5V1 if you cannot find original ones.

OP's IC601 & IC602 you can change with NE5532, or NJM2068AD in both places, I did this on one broken amp like yours until I fix it then, I put new original ones. But, if you're sure that, those IC's are ok, don't change them. Eventhough, you can replace both IC's with M5238 when you finish fixing your amp.

TR601 is placed near R608 and C604 on your power amp board. Desolder it and check does it show short circuit, and if is ok put it back.

You can use 2SA1294/2SC3263 but, remember to not destroy all transistors on output, put just one pair on power amp board; example TR513 & TR514. You can always put any other cheaper trans there even fakes, just to see does it work. just make sure that bipolars you will use for testinga re not darlingtones.


replace all these electrolytes - is highly recommended:
C501, C507, C508, C523, C547, C601, C602 - 10uF/50V, you can replace with 10uf/63V;
C604 10uF/16V;
C516, C517 - bipolars 1uF/100V;
C524 22uF/100V;
C543 & C544 10uF/100V bipolars.

I don't know how old this amp is, therefore all these electrolytes are better to be replaced. condensers are pretty annoying and difficult to be sure that old ones are ok, regardless how much time you spent on measuring them.



bekim

Noteworthy is that C507 is bipolar!
And You forgot about the important C591 that is 10uF 35V.
This on the POA 6600A.

;)
 
Denon Poa 6600A Bias

Hello
Just looking for the POA6600a service manual (in English) as I only have the German version.
Having trouble understanding the German translation to set the bias level.
Would any one have details on biasing the amplifier correctly.

Thanks Dean

Hi Dean. Welcome to the wonderful world of Denon.Some of the most underrated amplifiers on the planet.
So I will translate and skip the boring parts.
Ok as the amp has Auto dc correction nothing there.
With no speakers connected and input on the front set to minimum 0 the following
Multimeter on points TP (TWO PINS ON PCB) SET TRIMMER VR501 FOR 1MV READING
AFTER 10 MINS SET VR501 8+- 1 MV I found that conservative and set it at 12 MV (better)
Now use a second multimeter on the speaker terminals
Now connect 1KHZ SINEWAVE ON RCA INPUT.If you have a RMS multimeter you simply choose a 1khz sine from a playback source then using your rms voltmeter measure the RCA and turn your source up or down to get 100mv AC.Plug this into the amp RCA
Now using the other multimeter on the speaker terminal turn up the input volume on the amp until the multimeter shows 2 V AC onthe speaker terminals.
Now on trimmer V502 set for 35+- 5 mv .I set it at 40 MV (sounds better) with a little more biasing Wait 15 minutes and readjust to 40 MV ON V502
This is your optical Class A biasing circuit working. T o cross check I use the following procedure which is not in the manual
The input in front is now at a posistion to produce 2 v acc at speakers .Now turn the input to full volume and confirm the bias jumps back to 12 MV AND SPEAKER OUTPUT should read 60 - 65 V output. Then turn it down again to 2 v and bias should return to 40mv.This will take some time as amp heats up if you turn the input volume to full at 1khz 100 MV AC
Thats it your amp will now run in class A biasing up to about 1 third volume the jump to class AB and when you have no input idle also jumps to class AB. You will notice the amp running cool on idle ,relatively warm when played to 1 third volume
Enjoy
 
Anyone been struggling with the POA 2400?

I see it is similar.

Mine is not working. I have measured every single component I have suspected to be faulty.
All electrolytics on amp board, opamps (with 5532 though), many transistors all diodes and zeners (except the 16V ones they do work)

At about 150VAC in I start to see oscillation and high bias. Also sound is very distorted. Except if I remove the opamps. Then signal is ok at low power and at higher power it goes into oscillation again.

Bought this amp because it was so cheap, 40€, but now I've spent like 100€ in parts alone :(

Sorry to intrude in this thread with a different model, but they are similar.

One thing, I did not have the predriver 2SC3334 and pair, so I substituted them with 2SC2705 and pair. Could that still cause some issues?
 
Denon POA 2400

JLITHEN

Denon POA 2400 is indeed a very good amplifier. Replacement amplifier at that level of audio and build quality will easily set you back about between 1500 and 2000 Euro and even then I'm not convinced it will be on the same level. So to spend a little money is well worth it.
Why don't you find the local Denon repair specialist and send it there. That is what I would do.
I had a similar problem with a Marantz PM 94 which I couldn't solve. Scouted around and found a repair shop that knew that model well. 1 week later it was repaired :D
BTW I have found the quality of those Denons of that era very good .SMC Capacitors etc. Are you sure it's not a simple dry solder joint problem.
I found that more than anything else to be the major problem on older Denon's,not component failure. Go through that PCB and check for dry solder
 
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Thanks for your tips.
I did solder through every joint and it did not help.

I bought this 2400 because it had been at some repair shop and they had only replaced power transistors and turned on and bang again. Big surprise :D
By using fake components and swapping them out randomly they also managed to blow up the working channel.

We really do not have many good repair guys in Finland. And paying 80€/h to someone who has no audio analyzer is something I will not do.
The few good ones we have tend to be busy.
Either I manage to fix the amp or sell it to someone who does :)
 
Well. I think I found it.
I desoldered the 2SA1360 pair and connected 32V 30mA over them.
One was fine, but every now and then the voltage over the other went down to 24V.
It was leaking 30mA at 24V.
I guess if I would have had more courage with my variac I would have found a smoking resistor that would have given me a clue earlier :)

Also the optical BIAS was unstable with NE5532 (at least like between 100 and 160V input) so I put back the original M5238 and it seemed fine.

I will do some biasing, testing and measuring soon.
Other channel was easy to bias.

So...the lesson. If these amps have fried outputs it might be that 4 stages have failed.
The parts are not available at your local supermarket, but if it saves a couple of hours of pondering then it is not a big deal to spend like 130€ on parts like I did anyway (I got a few extra drivers and output trannies for that also)
 
Yeaahhh:D

I'm glad it worked out. You have yourself a wonderful piece of audio gear there with amazing sound quality.
Btw I found if you change the bridge rectifier with a more modern one of 35 amp made a big difference. They Vishay ones are cheap and a 10 minute job to install
Enjoy ;)
 
I'm not gonna keep this amp...too low dist :)
 

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