KB100 repair issues

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dc52322
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Joined: Tue Aug 09, 2022 6:59 am

KB100 repair issues

Post by dc52322 » Tue Aug 09, 2022 7:11 am

Hello,

I bought a KB100 at auction, had a broken POT knob, and reverb tank, and both switches, power, and ground(3way) needed to be replaced. I pulled it apart and replaced it, and now it does not work. Not sure what I did wrong, honestly. 98851152 build date 8-17-1989. The power light comes on, but no sound out of anything. It gets hot, especially on CP-5-25, double stack. See the image I circled https://drive.google.com/file/d/1mTBaEZ ... sp=sharing

Any help would be great.
Thanks
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Enzo
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Re: KB100 repair issues

Post by Enzo » Tue Aug 09, 2022 5:12 pm

Those two resistors are dropping resistors for the zener regulated 15v supplies. It is normal for them to heat up.

Um, your speaker wires are noy connected to the board.

With the board out like that, do not let the back of it touch the metal chassis.

Also do not operate the amp like that m0re than a few moments. The chassis is part of the heat sinking. The board needs to be mounted to the chassis for proper cooling.

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dak
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Re: KB100 repair issues

Post by dak » Wed Aug 10, 2022 10:31 am

Enzo wrote:
Tue Aug 09, 2022 5:12 pm
Those two resistors are dropping resistors for the zener regulated 15v supplies. It is normal for them to heat up.

Um, your speaker wires are noy connected to the board.

With the board out like that, do not let the back of it touch the metal chassis.

Also do not operate the amp like that m0re than a few moments. The chassis is part of the heat sinking. The board needs to be mounted to the chassis for proper cooling.
I would not be all that worried about the heat sinking. Apart from the thermal switch-off being next to the power transistors, the power amps I've looked at from that period were class B or barely AB. They would not produce significant heat without both a load and a relevant signal. Assuming that they are operating as intended, of course.

Having a speaker connected would of course help.

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