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.
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 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.
Edit: Left it on for 10 minutes and it got extremely hot. I did some more checking and R433 is way off, 859 ohms instead of 1.5k. Re-checked idle current and it was also off by 23mv and the pot was bottomed out so I'll replace that.
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.
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 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.
Edit: Left it on for 10 minutes and it got extremely hot. I did some more checking and R433 is way off, 859 ohms instead of 1.5k. Re-checked idle current and it was also off by 23mv and the pot was bottomed out so I'll replace that.
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