HK 330c distorted right channel

[jbeech]

Hello,
I have a HK 330c with noticeable distortion on the right channel, unless I just have headphones plugged in with no speakers connected.
First thing I did was deoxit pots and switches. No change.
Next I checked the idle adjustment (service manual snippet attached).
For the left channel, the reading is 9mv
For the right, it shows 31mv.
Also while looking around I see a resistor that looks like it is burnt (attached).
After seeing that, I'm hesitant to just tweak the 31mv voltage to 10mv.
Should I just replace the resistor and re-check the voltage?
Would this be some symptom of the output transistor(s) going bad?

I do not have a scope, but I have a multimeter and soldering iron.
I have not replaced any components on this as of yet.

Thanks for any ideas!

 

[painttoad]

you probably have a bad output transistor on the right channel.

don't just replace the resistor. check the transistors first.

 

[jbeech]

you probably have a bad output transistor on the right channel.

don't just replace the resistor. check the transistors first.

Thank you for the advice

 

[dlucy]

The resistor that looks burnt is R419, a 220 ohm 1/2 watt resistor. You should replace it and R420, its complement in the opposite channel.

It is likely something let too much current through there and it got too hot. Q413 would be the the first device I'd check to see if it has shorted. And R425 and D407.

Sometimes the earlier HK 330's would have power-path resistors that were barely under spec... and would burn out over time. I don't recall seeing that in the 330c's, but it could be the case. More likely Q413 let through too much current... or D407 failed/is-failing and not doing whatever limiting it might be doing.

Remember: I'm no E.E. and there are many others here on AK who actually understand how this stuff actually works.

 

[jbeech]

The resistor that looks burnt is R419, a 220 ohm 1/2 watt resistor. You should replace it and R420, its complement in the opposite channel.

It is likely something let too much current through there and it got too hot. Q413 would be the the first device I'd check to see if it has shorted. And R425 and D407.

Sometimes the earlier HK 330's would have power-path resistors that were barely under spec... and would burn out over time. I don't recall seeing that in the 330c's, but it could be the case. More likely Q413 let through too much current... or D407 failed/is-failing and not doing whatever limiting it might be doing.

Remember: I'm no E.E. and there are many others here on AK who actually understand how this stuff actually works.

Thanks so much! I'm going to run through your suggestions.

 

[jbeech]

Tested R419 and it actually was in tolerance. Going to replace it anyway, along with R420.
Q413 tests good.
D407 tests good.
would it benefit me to check the other transistors on that channel? There are 7 more minus the output transistors.