Repairing Denon AVR-1602

Brannigan · 24th October 2005, 03:46 PM

I'm repairing a Denon AVR-1602 surround receiver for a friend and I've replaced the broken parts (fuse and two transistors). Do I have to adjust the trimmer pots? (And how?) There's one trimmer pot for each channel.

anatech · 24th October 2005, 05:26 PM

Hi Brannigan,
Questions. What transistors did you replace? Did you check any others and how?

-Chris

Brannigan · 24th October 2005, 06:11 PM

Chris,

I checked all the transistors mounted on the big heatsink and then I replaced Q101SL (2SD389) and Q103SL (2SB1559).

I used a DMM to measure resistance between the different transistor legs. The broken transistors had close to 0 ohms resistance between two legs.

anatech · 24th October 2005, 06:18 PM

Hi Brannigan,
I would recommend you replace the drivers as well. Possibly the bias transistor also. Did you check the emitter resistors, as well as the resistor between the bases?

Once you have done that, adjust the control to make the voltage across the emitter resistors the same as the other channel. Recheck every 15 min for an hour. I don't have the manual, so I can't advise you more than that.

-Chris

Brannigan · 24th October 2005, 08:45 PM

Chris,

I'm not familiar with amp designs, so basically I've just been poking around with a DMM looking for broken parts. I haven't checked any resistors.

I forgot to mention that the amp is working, but you still recommend I replace the drivers and bias transistor?

anatech · 24th October 2005, 09:37 PM

Hi Brannigan,
I got that feeling, hence my questions.

Normally I check transistors for leakage. I replace one stage back from the last damaged part. Since you can't check for leakage, just change the drivers and bias. We know for sure excessive current went through them. Test diodes and other transistors using your diode check function, there should be a small transistor to sense over current through an emitter resistor, a few resistors between. Check the low value resistors, up to 1K0, for opens. They may look fine and still be open.

That should do it. Light bulb in series when you turn it on the first time. I use a variac and do testing as I increase voltage.

I wish you luck.

-Chris

Brannigan · 25th October 2005, 10:23 PM

Chris,

Thanks for you help

I've checked all diodes and most resistors. Some resistors are very low values, so I'll check the voltage across those once I've put the amp back together.

Do you have any suggestions for where I can find 2SD947 transistors? I've only found these at MCM, but they have a $250 minimum on international orders.

I've put together an approximate schematic of the output stage.

anatech · 25th October 2005, 10:28 PM

Hi Brannigan,
Is there a distributor for Denon in your country? Why not just order the spares from there? Check how much a manual is, it may not be that expensive.

If the parts come from Denon, they will not be fakes. The really low value resistors are probably the emitter resistors. You measure across these to determine bias current.

-Chris

Brannigan · 25th October 2005, 10:40 PM

Yes, there's a distributor. I've emailed them about a service manual (I have the user manual), but I never got a reply. I'll give them a call tomorrow.

anatech · 25th October 2005, 10:50 PM

Good, I think that would make your life a lot easier. You might find a good friendly tech there to give you a hand if needed. We will here as well, that goes without saying.

-Chris

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24th October 2005, 05:26 PM	#2
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Brannigan, Questions. What transistors did you replace? Did you check any others and how? -Chris

24th October 2005, 06:11 PM	#3
Brannigan diyAudio Member Join Date: Jul 2003 Location: Norway, west coast	Chris, I checked all the transistors mounted on the big heatsink and then I replaced Q101SL (2SD389) and Q103SL (2SB1559). I used a DMM to measure resistance between the different transistor legs. The broken transistors had close to 0 ohms resistance between two legs.

24th October 2005, 06:18 PM	#4
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Brannigan, I would recommend you replace the drivers as well. Possibly the bias transistor also. Did you check the emitter resistors, as well as the resistor between the bases? Once you have done that, adjust the control to make the voltage across the emitter resistors the same as the other channel. Recheck every 15 min for an hour. I don't have the manual, so I can't advise you more than that. -Chris

24th October 2005, 08:45 PM	#5
Brannigan diyAudio Member Join Date: Jul 2003 Location: Norway, west coast	Chris, I'm not familiar with amp designs, so basically I've just been poking around with a DMM looking for broken parts. I haven't checked any resistors. I forgot to mention that the amp is working, but you still recommend I replace the drivers and bias transistor?

24th October 2005, 09:37 PM	#6
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Brannigan, I got that feeling, hence my questions. Normally I check transistors for leakage. I replace one stage back from the last damaged part. Since you can't check for leakage, just change the drivers and bias. We know for sure excessive current went through them. Test diodes and other transistors using your diode check function, there should be a small transistor to sense over current through an emitter resistor, a few resistors between. Check the low value resistors, up to 1K0, for opens. They may look fine and still be open. That should do it. Light bulb in series when you turn it on the first time. I use a variac and do testing as I increase voltage. I wish you luck. -Chris

25th October 2005, 10:28 PM	#8
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Hi Brannigan, Is there a distributor for Denon in your country? Why not just order the spares from there? Check how much a manual is, it may not be that expensive. If the parts come from Denon, they will not be fakes. The really low value resistors are probably the emitter resistors. You measure across these to determine bias current. -Chris

25th October 2005, 10:40 PM	#9
Brannigan diyAudio Member Join Date: Jul 2003 Location: Norway, west coast	Yes, there's a distributor. I've emailed them about a service manual (I have the user manual), but I never got a reply. I'll give them a call tomorrow.

25th October 2005, 10:50 PM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	Good, I think that would make your life a lot easier. You might find a good friendly tech there to give you a hand if needed. We will here as well, that goes without saying. -Chris

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