Roland KC350

[Hipnote]

Hi Folks,

New here/ old otherwise. While setting up for a rehearsal I slipped with my keyboard amp on ice and it and I suffered a concussion. I am recovering, but the amp isn't doing so good. As part of my concussion therapy I would like to diagnose the problem. About all I can tell you is, that it does not turn on. No light, but I hear a thump when turning the switch from off to on. I am a pretty determined and sharp guy. Can anybody walk me through some diagnostics? I have a DMM and a basic understanding of electronics. I have built several vintage HI FI and guitar amps. But have no formal training. Not afraid to learn. I will be very patient.

Peace

[52 Bill]

Welcome to the place. I hope that you are feeling better soon. And I hope that your amp will be better soon as well.

The fact that you hear the power amp thump when you turn on the power switch, leads me to believe that the problem is in the preamp or the low voltage power supply. This would also explain the lack of the pilot light from lighting up.

Search this forum and you will find the service manual for your amp. It will also contain information for the KC-550 amp. In it you will find all of the information of how to take your amp apart and how to find the fuses for the low voltage power supply. It may be that when the amp was dropped the fuses were damaged or they may have fallen out of their holders. It could also be as simple as a loose cable that connects the preamp chassis to the power supply.

Let us know what you find out and if you have any questions.

[Jazz P Bass]

KC 350

To add: these amps are a nightmare to get apart.

The speaker grill & the speaker must be removed.
Then the power amp/ power supply assembly can be accessed for removal. (it is mounted to the bottom of the cabinet) There are a dozen cable ties holding all of the wire bundles together. These must be removed.

Once you have the amp/ power supply assembly out of the unit, check/ resolder the main componenets.(capacitors, voltage regulators, headers)

As stated, it sounds like a 'low voltage supply' problem.

[Hipnote]

Thank you for the kind welcome

To add: these amps are a nightmare to get apart.

The speaker grill & the speaker must be removed.
Then the power amp/ power supply assembly can be accessed for removal. (it is mounted to the bottom of the cabinet) There are a dozen cable ties holding all of the wire bundles together. These must be removed.

Once you have the amp/ power supply assembly out of the unit, check/ resolder the main componenets.(capacitors, voltage regulators, headers)

As stated, it sounds like a 'low voltage supply' problem.

I will study the documents and the forum this weekend and get into it next week.

Thank you so much !!

[Hipnote]

Hi guys,
I studied and prepared myself with the info you supplied and.......
It was an easy fix :-). After getting to the power amp( which was a nightmare) upon visual inspection I could see a cable unplugged. Went through all connections and its all good again. Darn it !
I was so looking forward to doing some more in depth study. Lol

So I got these two other amps :-) they are like opposites. One is a kalamazoo bass 30. The preamp tubes when you turn it on light up, but remain cold. Amp has sound but weak. The other is a Vox vt 40 plus that upon turn amp on there is a loud snapping sound in speaker. Very consistent snap. Snap. Snap. I will read up. Would love some basics though of reading voltages and following schematics. I got the kalamazoo one but can not find the vox.

Peace and thank you guys so much!

[The Dude]

I would recommend you start separate threads for each amp to avoid confusion. Each will have its own set of issues. Glad you got the KC fixed and good luck on the others.

[Jazz P Bass]

I hope you have the same luck with the Vox VT40.

It is basically a computer with an output chip.

[Hipnote]

Yucky !