[sdiy] Need help about how to service an amp

Jean-Pierre Desrochers jpdesroc at oricom.ca
Sun Apr 4 00:40:21 CEST 2021



Here is the link for the good schematic and PCB layout:


There are KB100 schematics showing on Google which actually are
KBA100 schematics so not the one you need..


I've been working on music instruments for many years..

Here is a list of what you could do:

Since it's powering up that means there are no shorts caused by shorted power transistors (Q101, Q105).

Many times this ‘no sound problem’ on both the output speaker and headphone jack

Is caused by jacks connected between the preamp section
and the power amp section.

These jacks have normally closed contacts that carry
the signal through them when there are no plug connected in them.
These contacts get dirty when these jacks are not used
and cut the signal completely from reaching the final output stage..

In  the case of the KB100 there are 2 jacks to check for:

Front Pre-EQ patch jack

Rear PWR AMP IN jack

You can first feed the PWR AMP IN jack with some audio source
and check if there is sound at the speaker. If so the internal contact is dirty and
need to be cleaned.
Do the same test on the EQ patch jack at the front.





De : Synth-diy [mailto:synth-diy-bounces at synth-diy.org] De la part de Jean Bender via Synth-diy
Envoyé : 3 avril 2021 14:52
À : SDIY List
Objet : [sdiy] Need help about how to service an amp


Hi list !


A friend gave me a Peavey KB100, not working, i mean it's powering up but no sound, even in the headphone output.


Well, i realise in don't know from where to start when you have to service an amp. Is there a specific way to work once you have check all the basics (fuses, power supply, and visual check up around caps and chips) ?


Do i need, for example to simulate the speaker impedance if i disconnect it from the board for troubleshooting the circuit ?


So this thread is more to have tips, readings about this kind of thing, since i don't feel really comfortable working on it from scratch knowledge !


Thanks per advance



Jean Bender <https://hearthis.at/jean-bender/> 

Hak Lofi Record <http://h.a.k.free.fr/> 


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