Roland KC-500

[quarterdollar]

The amp has output but very low, any suggestions.
Thanks

[J M Fahey]

What does that exactly mean?
> it has the volume of a tabletop radio or less
> neighbours hate me but the drummer and guitar pllayer drown me when rehearsing or playing me
> What instrument(s) are you amplifying (a guitar straight into an input that expects a keyboard will be weak)

Most amps have preamp out and power amp in, althoughn they sometimes label themm otherwise, such as loop out/in , effects send/receive, etc.
Yours seems to have something called "stereo out/in" .
Also a dedicated line out only.

Send thge line out into another known good amplifier power in and viceversa, so as to check which is the weak acting part in your amp, either the preamp or the power amp.

Google around and link data, such as user manuals, (hopefully) a schematic, etc.

[gui_tarzan]

Here ya go. Set 1.

[gui_tarzan]

Set 2.

[Jazz P Bass]

To add, these amps are a major challenge simply to access the boards.

To get to the power amp (which is bolted to the bottom of the enclosure) the grille must be removed.
Then the speaker.

And if any work is to be performed on the preamp, the above must be applied to remove the preamp connectors. (as they are attached to the power amp.)

Worlds of fun to be had on this one.

[gui_tarzan]

Yep, I've got a KC-350 apart right now. Pain in the butt.

[quarterdollar]

Thanks For your help
All channels have low output with volume and master volume set @ 10
I have checked power supply board and The -15 volts and +15 volts are good +vcc @ 54 volts -vcc @ 54 volts.
I would think the power supply board is working.
Are you telling me the preamp board is mounted behind the speaker in the cabinet?
This is my first Roland KC-500 amp I have worked on.
Mainly restore old tube amp. fender ampeg
Retired from GE did Bio- medical electronics for thirty years,just trying to help a friend out with her amp.

[Enzo]

Before taking a million voltage readings, isolate the problem. Ther is a preamp and a power amp. First, try plugging a spare cord from send to return on those loop jacks. ANy help?

Plug some headphones into the phones jack, does that sound OK?

You have various preamp outputs, so do they sound OK? Or do all those have the diminished output?

Plug a signal into that IN jack of the loop pair. Does that come out the speaker OK?

What we want to do, and should be able to simply enough, is determine if the problem is in the preamp or the power amp. No point rummaging around in one section if the trouble is in the other.


If in the preamp, and all channels are affected, then look down at the master volume and EQ staqes as a good starting point. And if the power amp, my first suspect would be the mute circuit,.

[Jazz P Bass]

[QUOTE=quarterdollar;363177]Are you telling me the preamp board is mounted behind the speaker in the cabinet?
\QUOTE]

No.
The preamp connectors are on the power amp board (which is inside the enclosure).
Follow Enzo's advise & try to narrow it down.

[quarterdollar]

Thanks for your help.
I have the amp. working now 1mf cap
thanks

[Jazz P Bass]

Thanks for your help.
I have the amp. working now 1mf cap
thanks

For posterity, can you indicate which 1uf capacitor, where?

[quarterdollar]

C227 or C226 in the muting circuit