Harman Kardon HK3500 low/no output

[xslntx]

I recently picked up a Harman Kardon HK3500 on CL listed as non-working. I was told it was playing music fine, then shut off with a little bit of smoke. I opened it up and found a blown fuse, a shorted output transistor and a resistor burned beyond recognition.

Here's what I've done so far

Outputs
2SA1265 -> 2SA1492
2SC3182 -> 2SC3856
Q413 2SC945 -> KSC1845FTA
Q415 2SD667A -> KSC2383YTA
Q417 2SB647A -> KSA1013YTA
Burned resistor R441, 0.6w 82ohm
C27, replaced due to being badly scorched from the resistor.
R439 also got toasty and was 13 ohm over spec so I replaced that.

Everything I changed on that channel I did on the other as well, minus the burnt resistor and capacitor.

I went ahead and checked and adjusted the idle current to as close to 40mv as I could (it's within spec). There's no significant DC being outputted on the speaker terminals.

Audio plays fine, but hollow sounding, at near-minimum volume. But increasing it beyond say 1/4 turn causes the output to cut out, and the heatsink feels, to me anyway, warmer than it should be. Within 5 minutes of being powered on I would expect it to still be room temp, but it gets slightly warmer.

Could someone help point me in the right direction here? Happy to attach photos and take further measurements. I have the service manual in front of me but I honestly don't know enough about this stuff to know what my next steps are.

 

[Ray Gianelli]

I recently picked up a Harman Kardon HK3500 on CL listed as non-working. I was told it was playing music fine, then shut off with a little bit of smoke. I opened it up and found a blown fuse, a shorted output transistor and a resistor burned beyond recognition.

Here's what I've done so far

Outputs
2SA1265 -> 2SA1492
2SC3182 -> 2SC3856
Q413 2SC945 -> KSC1845FTA
Q415 2SD667A -> KSC2383YTA
Q417 2SB647A -> KSC1013YTA
Burned resistor R441, 0.6w 82ohm
C27, replaced due to being badly scorched from the resistor.
R439 also got toasty and was 13 ohm over spec so I replaced that.

Everything I changed on that channel I did on the other as well, minus the burnt resistor and capacitor.

I went ahead and checked and adjusted the idle current to as close to 40mv as I could (it's within spec). There's no significant DC being outputted on the speaker terminals.

Audio plays fine, but hollow sounding, at near-minimum volume. But increasing it beyond say 1/4 turn causes the output to cut out, and the heatsink feels, to me anyway, warmer than it should be. Within 5 minutes of being powered on I would expect it to still be room temp, but it gets slightly warmer.

Could someone help point me in the right direction here? Happy to attach photos and take further measurements. I have the service manual in front of me but I honestly don't know enough about this stuff to know what my next steps are.

If your list of replacements is correct Q417 is a problem, as it's a PNP and you've listed its replacement as an NPN.

Since this is just your 2nd post I was going to welcome you to AK, but I see your join date was 2011. Truly a man of few words!

 

[xslntx]

If your list of replacements is correct Q417 is a problem, as it's a PNP and you've listed its replacement as an NPN.

Since this is just your 2nd post I was going to welcome you to AK, but I see your join date was 2011. Truly a man of few words!

Thank you for your help. I mistyped the replacement, it is a KSA1013YTA, I've updated the post.

Funny enough when I went to register I found out I had done so way back then and not remembered.