I have a Roland KC100 keyboard amp that died on me. First,
I started noticing an annoying low level ring from the
speaker when my keyboard was hooked up. I thought at first
it was a ground loop, but I couldn't get it to go away.
Then, the amp started cutting out for brief stretches of
2 or 3 seconds. The sound would die out and the power light
would fade off. But it would usually come back on by itself.
When it didn't come back, I could sometimes get it back by
jostling the unit. Finally, it died altogether. When I power
on, I hear a faint "power on" sound from the speakers, but
I get no sound from my inputs anymore.

A guy in a local music store told me, "Sounds like you blew
a capacitor in your amp."

Does anyone here have a good idea of what might have happened?

I have no experience with such things, but I'm hoping I
might be able to do the repair myself, to save the $100 or
so a shop would charge me. Does anyone have any comment on
how advisable that would be or how I'd go about figuring out
how to fix it?

"Hamad bin Turki Salami" wrote in
message news
I have a Roland KC100 keyboard amp that died on me. First,
I started noticing an annoying low level ring from the
speaker when my keyboard was hooked up. I thought at first
it was a ground loop, but I couldn't get it to go away.
Then, the amp started cutting out for brief stretches of
2 or 3 seconds. The sound would die out and the power light
would fade off. But it would usually come back on by itself.
When it didn't come back, I could sometimes get it back by
jostling the unit. Finally, it died altogether. When I power
on, I hear a faint "power on" sound from the speakers, but
I get no sound from my inputs anymore.


A guy in a local music store told me, "Sounds like you blew
a capacitor in your amp."

Does anyone here have a good idea of what might have happened?

I have no experience with such things, but I'm hoping I
might be able to do the repair myself, to save the $100 or
so a shop would charge me. Does anyone have any comment on
how advisable that would be or how I'd go about figuring out
how to fix it?


Your problem is almost certainly one of simple dry joints. On group
equipment, these commonly occur on the front preamp board, where the power
supply from the rear power amp board comes in, and is zenered down by two
damned great wirewound resistors, and two zener diodes, to provide the (
typically ) +/- 15v supplies for the preamp ICs. The power on LED is also
usually fed from one of these rails.

I would suggest that you open the thing up, and run it open, providing you
are confident enough to do so without risking electric shock, and then
gently tap and poke components using a long plastic stick, such as a
ballpoint pen. Go for any large components, as these suffer transport
vibration when you carry the thing to gigs, which can result in fractured
solder joints, and anything which looks as though it runs hot, and may have
discoloured the board material in the area.

Chances are that you will rapidly find the area or exact component that
causes it to go on and off, when disturbed. If you don't then know how to
locate the exact component or bad joint, you can at least then take it to
someone who does, and point them to where the problem is.

Don't be afraid to at least have a go, it's the only way to learn. The only
area that you should be careful to steer away from for your personal safety
with this type of equipment, is any exposed wiring where the power cable
comes in, or on the back of the power switch. Avoid attempting repairs to
tubed kit though, as there can, and usually will, be very high and dangerous
voltages present. Good luck with it

Arfa

"Hamad bin Turki Salami" bravely wrote to "All" (17 Dec 05 00:49:13)
--- on the heady topic of "Keyboard amp died"

HbTS From: Hamad bin Turki Salami
HbTS Xref: core-easynews sci.electronics.repair:351712

HbTS I have a Roland KC100 keyboard amp that died on me. First,
HbTS I started noticing an annoying low level ring from the
HbTS speaker when my keyboard was hooked up. I thought at first
HbTS it was a ground loop, but I couldn't get it to go away.
HbTS Then, the amp started cutting out for brief stretches of
HbTS 2 or 3 seconds. The sound would die out and the power light
HbTS would fade off. But it would usually come back on by itself.
HbTS When it didn't come back, I could sometimes get it back by
HbTS jostling the unit. Finally, it died altogether. When I power
HbTS on, I hear a faint "power on" sound from the speakers, but
HbTS I get no sound from my inputs anymore.

HbTS A guy in a local music store told me, "Sounds like you blew
HbTS a capacitor in your amp."

HbTS Does anyone here have a good idea of what might have happened?

HbTS I have no experience with such things, but I'm hoping I
HbTS might be able to do the repair myself, to save the $100 or
HbTS so a shop would charge me. Does anyone have any comment on
HbTS how advisable that would be or how I'd go about figuring out
HbTS how to fix it?


Just a small analogy to outline the problem:
If you had no experience of brain surgery would you really even
consider attempting it to save money?

Similarly, sophisticated electronics require knowledge to diagnose and
tactile skills to make a repair. There is a steep learning curve to
each too. It isn't brain surgery however but it can't be done without
any experience at all. Forget DIY, send it to the shop.

A*s*i*m*o*v

.... [] - Please write your complaint legibly in that box.

Asimov wrote:

Similarly, sophisticated electronics require knowledge to diagnose and
tactile skills to make a repair. There is a steep learning curve to
each too. It isn't brain surgery however but it can't be done without
any experience at all. Forget DIY, send it to the shop.


If you know how to solder already, it doesn't take a great deal of
additional skill to open up a piece of gear and replace all the big
electrolytic caps. Caps are usually a good bet for some reason if
you're stumped, especially if the noise you're talking about is of the
60Hz variety. It's kind of like replacing the plugs and wires before
you try to troubleshoot your ignition system. I wouldn't hesitate to do
this kind of job with a $5 iron from RadioShack.

If you're not experienced at all with this kind of work, though, $100
sounds cheap for an easy and guaranteed solution. If you have to buy
two caps and a soldering iron, and a roll of solder and a braid, you
might spend half that before you know it'll fix the problem.

Success! I gathered some tools and my 4 year old son and
I opened the amp up and took a look. I figured at the
very least I could teach him the little I know about
electronics. But following your advice, I quickly
located a transistor with two cracked solder joints.
After resealing those, the amp came back to life.

I saved $100 and had some fun with my son, so it turned
out to be a good gamble.

Thanks for the advice.

On Sat, 17 Dec 2005 13:25:41 +0000, Arfa Daily wrote:
Your problem is almost certainly one of simple dry joints. On group
equipment, these commonly occur on the front preamp board, where the power
supply from the rear power amp board comes in, and is zenered down by two
damned great wirewound resistors, and two zener diodes, to provide the (
typically ) +/- 15v supplies for the preamp ICs. The power on LED is also
usually fed from one of these rails.

I would suggest that you open the thing up, and run it open, providing you
are confident enough to do so without risking electric shock, and then
gently tap and poke components using a long plastic stick, such as a
ballpoint pen. Go for any large components, as these suffer transport
vibration when you carry the thing to gigs, which can result in fractured
solder joints, and anything which looks as though it runs hot, and may have
discoloured the board material in the area.

Chances are that you will rapidly find the area or exact component that
causes it to go on and off, when disturbed. If you don't then know how to
locate the exact component or bad joint, you can at least then take it to
someone who does, and point them to where the problem is.

Don't be afraid to at least have a go, it's the only way to learn. The only
area that you should be careful to steer away from for your personal safety
with this type of equipment, is any exposed wiring where the power cable
comes in, or on the back of the power switch. Avoid attempting repairs to
tubed kit though, as there can, and usually will, be very high and dangerous
voltages present. Good luck with it

Arfa

Hamad bin Turki Salami wrote:

I saved $100 and had some fun with my son, so it turned
out to be a good gamble.


Your son is convinced you're an electronics sorceror now, too.

wrote:

Hamad bin Turki Salami wrote:


I saved $100 and had some fun with my son, so it turned
out to be a good gamble.



Your son is convinced you're an electronics sorceror now, too.

Soon all his son's friends will be coming to him for repairs. :-)

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form .

"Hamad bin Turki Salami" wrote in
message news
Success! I gathered some tools and my 4 year old son and
I opened the amp up and took a look. I figured at the
very least I could teach him the little I know about
electronics. But following your advice, I quickly
located a transistor with two cracked solder joints.
After resealing those, the amp came back to life.

I saved $100 and had some fun with my son, so it turned
out to be a good gamble.

Thanks for the advice.



Glad to have been of help. What the group's all about ...

Arfa

On Mon, 19 Dec 2005 14:03:07 -0800, wrote:


Hamad bin Turki Salami wrote:

I saved $100 and had some fun with my son, so it turned
out to be a good gamble.


Your son is convinced you're an electronics sorceror now, too.

I think he's ready to take his share of credit. The problem is,
he can't wait for things to break now.