KBA 100 tech info

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brianguitars
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KBA 100 tech info

Post by brianguitars » Sat Sep 04, 2021 3:33 pm

I have a KBA100 combo amp that has a problem, now giving me the silent treatment. Is a schematic available ?, I would have liked to get my hands on a schematic before taking the unit apart and trouble shooting.

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Enzo
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Re: KBA 100 tech info

Post by Enzo » Wed Sep 08, 2021 11:13 am

I don't have that one handy, but [email protected] would.


But why wait? If your car wouldn't start, would you buy the service manual first? I'd be looking for empty gas tanks, dead batteries, etc. A silent amp is probably the easiest problem in an amp. Oh sure, it could be something weird, but first, are the wires on the speaker still? Does the speaker work? Do th power lights come on? Is there any background hum or noise to let you know it is trying to work? You have an insert/patch jack on the front, poke a plug in and out of that a couple times, any help? On the rear is the loop - Preamp Out and Power Amp In jacks. Poke the power amp jack, any help? Better yet, plug a spare cord from send to return there, aanything? You can test the power amp by simply plugging your instrument or other test signal into that power amp jack. There is a headphones jack, got sound there?

And if you can use a schematic, you can at least check for blown fuses inside, and for that matter basic power supply voltages. I am sure the op amps inside run on 15vDC supplies positive and negative. And the power amp, who knows, somewhere in the 35-50v on each polarity. I suspect those will either be missing or right. It is not likely that a 40v rail will be at oh 12v or something.

Yes, I like to have the drawings, but most repairs do not require them.

RHP
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Re: KBA 100 tech info

Post by RHP » Sun Mar 13, 2022 6:25 pm

Hi, I thought I would just revive this thread rather then start a new one since I'm have the same problem with the same amp.
This one I bought new in about '95-96. Never had a problem with it but it has been sitting in the same climate controlled room for at least 15 years.
When I went to try it out today the light comes on but no sound from any of the three channels, nothing from the headphones, and I did try working the jacks on the effects loop and nothing.
I did take the chassis out and the three fuses were good, I had 120vac on one of them and 19vac on the other two. There are no signs of anything burnt or melted. I ran a cable from the pre-amp out to anther amp and it does put out from there.
Any advice on where to go from here would be appreciated. The amp really doesn't owe me anything but I would hate to trash it since it still looks brand new.

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Enzo
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Re: KBA 100 tech info

Post by Enzo » Tue Mar 15, 2022 2:58 am

Hi.
Generally it is better to start new threads for new amps. It can get confusing working on more than one amp in a thread. but this one never got going and that was half a year ago, so...

If the light comes on, then the mains fuse is OK. That is 120vAC. When you are checking fuses, don't measure the voltage to ground, measure end to end of a fuse. A good fuse has zero volts end to end. (remember, a good fuse is really just a wire in a glass tube) An open fuse - a bad one - will have different voltages on each end. And so a voltage will appear end to and.

Same things I mention3d before. Is there any thump or pop when you flip power on? Is there any little hum or hiss in the speaker telling us it wants to work? Are the wires still on the speaker and board connections? Test the speaker itself with a 9-volt battery. A good one will pop when you touch the battery to the terminals.

Your preamp seems to be working, so the low voltages are all present. Did you plug a signal into the power amp in jack? Or the FX return if that is what it has?

It may need a repair now and then, but these amps ought to run forever.

RHP
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Re: KBA 100 tech info

Post by RHP » Tue Mar 15, 2022 7:24 am

Hi Enzo, thanks for the feedback, I did run a jumper from the pre-amp out to power amp in but no go.
The speaker tests okay but no snap, crackle or pop, nothing when hooked up to amp. I also checked the continuity of the speaker wires from the main board through the board with the headphone jack .
Without knowing what else to check for on the circuit board the only thing I think of to do is remove the board from the chassis a see if I can find a cold solder joint somewhere but that involves removing all the nobs and jacks from the front panel and that could very well be the end for this thing.

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Re: KBA 100 tech info

Post by RHP » Tue Mar 15, 2022 10:38 am

And it's fixed, I was getting ready to tear it apart but decided check all of the plugs first. I unplugged everything that could be unplugged and the plugged them back in and voila !!! I making noise.
Thanks

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