Hi Ricardo,
The base voltages are seldom equal in magnitude, referenced to ground especially. NPN and PNP transistors do not have the same E-B drop. If you want to measure things like this, you must measure from a common point, and common ground is not that point. There are many measurements that do not use ground as a common reference. You seem to be stuck on using ground for a reference, this will hinder you.
Do you have the complete manual? Read it again if you do. Bias current readings are taken with no load connected and at zero signal level. That means no input, volume control to minimum and speakers turned off. Then and only then you will get a meaningful reading. Expect readings less than 100 mV DC for bias. Always refer to the manual if at all possible.
TR500 and TR501 (2SK184C) are your differential pair. There are two more pairs following that could affect this. TR502 and TR503 (smugged) and TR504 and TR505 (2SA1321). All these pairs must be matched for gain. This may be beyond your ability to test. The main pair to check would be TR500 and TR501. These are J-FETs and you want to measure transconductance, like a vacuum tube. The other pairs would have to be further out of balance to affect the offset this much, but it is possible considering you lost the output transistors. Do not touch these parts unless you know exactly what you are doing. You could order a matched pair if you can find someone who has them and will match them for you. Just sticking a pair of new parts in is not really a good plan.
Your soldering skills will be very important. Consider the circuit board as the very most expensive component there is in that amp. Keep in mind that is is also not a straight forward amplifier. A seasoned audio repair technician can tell you that by looking at the schematic.
If anyone has a clean copy of this schematic and the set up instructions, it would be most appreciated. What I have is terrible.
-Chris
The base voltages are seldom equal in magnitude, referenced to ground especially. NPN and PNP transistors do not have the same E-B drop. If you want to measure things like this, you must measure from a common point, and common ground is not that point. There are many measurements that do not use ground as a common reference. You seem to be stuck on using ground for a reference, this will hinder you.
Do you have the complete manual? Read it again if you do. Bias current readings are taken with no load connected and at zero signal level. That means no input, volume control to minimum and speakers turned off. Then and only then you will get a meaningful reading. Expect readings less than 100 mV DC for bias. Always refer to the manual if at all possible.
TR500 and TR501 (2SK184C) are your differential pair. There are two more pairs following that could affect this. TR502 and TR503 (smugged) and TR504 and TR505 (2SA1321). All these pairs must be matched for gain. This may be beyond your ability to test. The main pair to check would be TR500 and TR501. These are J-FETs and you want to measure transconductance, like a vacuum tube. The other pairs would have to be further out of balance to affect the offset this much, but it is possible considering you lost the output transistors. Do not touch these parts unless you know exactly what you are doing. You could order a matched pair if you can find someone who has them and will match them for you. Just sticking a pair of new parts in is not really a good plan.
Your soldering skills will be very important. Consider the circuit board as the very most expensive component there is in that amp. Keep in mind that is is also not a straight forward amplifier. A seasoned audio repair technician can tell you that by looking at the schematic.
If anyone has a clean copy of this schematic and the set up instructions, it would be most appreciated. What I have is terrible.
Only in that it may possibly increase the amount of distortion generated. This depends on many factors, so this is as general as I can get.
-Chris
Just soldered more two trannies....... After two seconds I heard a pop...... All trannies are now shorted and one of them opened/cracked.
After removing the blown trannies, I turned the amp on and now the bases of the trannies all have -1.04 V
I believe something bad happened but can not identify what.
This is beggining to be very distressfull.
After removing the blown trannies, I turned the amp on and now the bases of the trannies all have -1.04 V
I believe something bad happened but can not identify what.
This is beggining to be very distressfull.
Hi Ricardo,
The main problem is very simple. You are inexperienced and are attempting to service a complicated amplifier. A high power one at that. I can't even remember what test equipment you have, but I know it's not as much as a properly equipped service shop has. Then there is a possibility that you are not getting "real" transistors. What I am trying to explain to you is that this is far more difficult for you, than it would be for an experienced person with the proper equipment. So, yes. I expect you to have a more difficult time of it.
Remember. There is no magic. Everything follows the laws of physics and wishful thinking will get you into trouble. Deal with facts only, and write them down. Never write down an assumption or conclusion.
At this point, I suggest you look at this as a brand new repair. Test each part and write down the results. There is no shortcut.
Sorry you are having a tough time with it.
-Chris
It's next to impossible to foresee what may happen next when troubleshooting over the web. The major problem is that it isn't in front of me and there are many clues that we don't get. There is also the manner in which you are powering the unit up in. I generally use a variac and other methods that allow me to catch problems before more damage occurs.
The main problem is very simple. You are inexperienced and are attempting to service a complicated amplifier. A high power one at that. I can't even remember what test equipment you have, but I know it's not as much as a properly equipped service shop has. Then there is a possibility that you are not getting "real" transistors. What I am trying to explain to you is that this is far more difficult for you, than it would be for an experienced person with the proper equipment. So, yes. I expect you to have a more difficult time of it.
Remember. There is no magic. Everything follows the laws of physics and wishful thinking will get you into trouble. Deal with facts only, and write them down. Never write down an assumption or conclusion.
At this point, I suggest you look at this as a brand new repair. Test each part and write down the results. There is no shortcut.
Sorry you are having a tough time with it.
-Chris
Thank you Chris.
I believe I will be succesfull in the end.
Please note that I got this amp alreday broken and it does not operate for more than 5 years.
Several atempts have been done by more or less "enlightened" locals, so the board is heavily damaged with most of the transistors soldered to pieces of wire due to the lack of copper in the board.
Yesterday it played all afternoon with only two trannies....
Now i believe i will need to replace almos everything.
Can the board be properly rebuilt ?
As I have one working unit and could apreciate it´s beautifull sound, I really want to redo the broken one.
Note:
I have nice schematics and operating instructions.
All are pdf... if you please leave me your e-mail
Ricardo
I believe I will be succesfull in the end.
Please note that I got this amp alreday broken and it does not operate for more than 5 years.
Several atempts have been done by more or less "enlightened" locals, so the board is heavily damaged with most of the transistors soldered to pieces of wire due to the lack of copper in the board.
Yesterday it played all afternoon with only two trannies....
Now i believe i will need to replace almos everything.
Can the board be properly rebuilt ?
As I have one working unit and could apreciate it´s beautifull sound, I really want to redo the broken one.
Note:
I have nice schematics and operating instructions.
All are pdf... if you please leave me your e-mail
Ricardo
re,re
Hello Ricardo,
Your attemt to repair your poa and everytime blew some trannies, can be easily brought back to nearly zero.
All you have to do is put a very normal bulb (60w 230v) in series with your amplifier (the mains i mean).
This way you can very easily check all in and outputs without blowing any transistors.
If it gets to hot to handle for the amplifier the lamp simply will start to glow.
When finally repair is done and everything is working normal.
Change the bulb with a higher one (150-200w) now you can still check if the amplifier behaves normal and you even can put a tiny load on it.
When then the amplifier still works as it should be you can remove the bulb and sart enyoing the amp.
Greetings Pieter
Hello Ricardo,
Your attemt to repair your poa and everytime blew some trannies, can be easily brought back to nearly zero.
All you have to do is put a very normal bulb (60w 230v) in series with your amplifier (the mains i mean).
This way you can very easily check all in and outputs without blowing any transistors.
If it gets to hot to handle for the amplifier the lamp simply will start to glow.
When finally repair is done and everything is working normal.
Change the bulb with a higher one (150-200w) now you can still check if the amplifier behaves normal and you even can put a tiny load on it.
When then the amplifier still works as it should be you can remove the bulb and sart enyoing the amp.
Greetings Pieter
Denon POA6600
Hello Folks,
I was reading this thread with interest since I have one 6600 on my desk now.
Completely "kaput" as the owner told me. To be short: I hate these amps (lol).
For easy inspection: Undo the + and - supply from the poweramp. Remove both IC's. Undo the 15v conn. (cn12) and check for proper voltages. If ok, reconnect and Power the darn board with + and - 15 volts (cn12, only input stage is powered) Now you can measure the complete input stage(s) upon strange behavior. If all seems okay, put in ic501 and, if all is still fine, put in ic502. This is where I am now.
I found that this 6600 has had some repair attempts. I have replaced the 2sk184's as one of them was dead (!) This is the base (heart) of the amplifier. If it goes wrong here already it will probably ruin following stages as voltages are quite high. Several other transistors have been replaced. I think I have renewed the whole input stage. Replace with originals only (!) And .. do not forget to test the electrolytes. The one here had a faulty c519. Replace them all with descent ones. Compare values found against the schematic. If all is fine you can start checking the output stage, which isn't too difficult.
If you still are in need of the original POA6600 schematic, ak, service manual, let me know. I will scan it and sent it to you.
Hello Folks,
I was reading this thread with interest since I have one 6600 on my desk now.
Completely "kaput" as the owner told me. To be short: I hate these amps (lol).
For easy inspection: Undo the + and - supply from the poweramp. Remove both IC's. Undo the 15v conn. (cn12) and check for proper voltages. If ok, reconnect and Power the darn board with + and - 15 volts (cn12, only input stage is powered) Now you can measure the complete input stage(s) upon strange behavior. If all seems okay, put in ic501 and, if all is still fine, put in ic502. This is where I am now.
I found that this 6600 has had some repair attempts. I have replaced the 2sk184's as one of them was dead (!) This is the base (heart) of the amplifier. If it goes wrong here already it will probably ruin following stages as voltages are quite high. Several other transistors have been replaced. I think I have renewed the whole input stage. Replace with originals only (!) And .. do not forget to test the electrolytes. The one here had a faulty c519. Replace them all with descent ones. Compare values found against the schematic. If all is fine you can start checking the output stage, which isn't too difficult.
If you still are in need of the original POA6600 schematic, ak, service manual, let me know. I will scan it and sent it to you.
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