KA-6000 Oscillating?

A couple germanium diodes. 1N60. Transistors appear to all be silicon.
Ah, good! I read up on this one a while ago, because I was considering buying one. My friend still has it.

So my information was getting a little rusty in my mind. Why I stayed away from saying too much.

And good to know all parts are still available. If I ever do decide to pick it up, I will be in a good spot.

Another thing I’ve remembered is the preamp section has a lower output than normal, and I assume the amp section has a related higher input. One warning I heard about was to be very careful when matching with other components as you can easily push it into overload due to the lower preamp output level.
 
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...Another thing I’ve remembered is the preamp section has a lower output than normal, and I assume the amp section has a related higher output. One warning I heard about was to be very careful when matching with other components as you can easily push it into overload due to the lower preamp output level.
That is true. The "preamp" section has a gain of about -5.5dB. The amplifier section is approximately 46dB, IIRC.
 
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So uhh, I just took the power amp board off and...I think I figured out why the right channel wasn't working...this is after I stripped away the ruined resistors and caps.

Mx5jxCd.jpg
 
Not sure where to go from here...I must've ****ed up and shorted something because the new resistors also catch on fire. Is it the output transistor?
 
That means you just replaced a symptom of your problem. Something else is drawing so much power your resister is burning up.
 
Yeah, I'm aware of that, but would it be the output transistors that is sucking up that much power? I can't think of anything else that would be broke
 
but would it be the output transistors that is sucking up that much power?
If the OP transistor(s) are faulty usually they'll either stay stone cold, or get very hot, or blow fuses. Blown driver transistors can cause damage like that, but I am a bit surprised at the scale of damage - it must have been smoking and smelling a lot during/after that event. :(

High time you built yourself a Dim Bulb Tester (DBT). ;)
 
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So I replaced all the drivers, turned it on and no more resistor pop! However, the left side got really hot and then the fuse popped. Stuck again...
 
So I found out what it was: Q5 died, so I replaced it. The voltage from the casing of Q5 to ground is ~55V and the voltage from the casing of Q7 to ground is ~25V. That...doesn't seem right.
 
you didn't say but i'd do:
build a dbt and use it
clean the burned board and verify all foil traces are not broken. I use lacquer thinner but others have magic solvent. the search button will help you here.
replace all parts in the burned area
bring up on DBT
test power supply voltages

report back with updates and pics of the cleaned areas

your posts seem like 'i found a bad part and replace it and it still is broken'. think about creating a plan to get this working and implement plan.

i'll try to take a look at the schematic and post ideas of attack. once the ps is working, you can measure collector voltages at prudent places and narrow down the problem.

I'm assuming you have the basic test equipment (scope, function generator, a few volt meters, dbt). it should be easy to get this working and posting bumps probably will get ignored.

create a plan and post it.

if do you find something off, include a schematic bit of the affected area. you need to provide as much info as you can for others to help.
 
See, thing is, I'm a complete newb to this hobby so I'm just struggling through this process. I have no clue where to start and what to do because it's so complicated to me so that's why I'm posting this. I had no idea what a dim bulb tester was or that it could help me until you mentioned it, for example. I also had no idea that the foil traces could be burnt away. Forgive me for my noobness!
 
Kinda late, but there is a thread where the motorboating on a KA-6000 was cured by cleaning and resetting the board corrected the problem.
http://www.audiokarma.org/forums/in...-6000-output-transistors.11751/#post-12425751
Also, if you haven't done so already, replace 2sc458 transistors. (ksc1845 usual replacements)


Don’t replace the 2SC458 with KSC1845. The gain is too high and it can cause motor boating.
The OP said they would use KSC1815. Those work correctly in this situation.

If you have it narrowed to the amp. Recap the amp and test every transistor. Then check every resistor. You can compare working side to broken side in circuit. Any in the broken side that don’t measure the same as the working side are suspect. Retest them with one leg lifted. They may be ok because the circuit there is wonky. Test ever diode. All this can be done unpowered. Just do comparing checks side to side.

Once everything seems OK, then fire it up on the dim bulb tester and start comparing voltage side to side.

Getting at things while assembled may be a challenge. It’s been a while since I rebuilt one of those and I’ve forgotten the chassis arrangement.
 
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