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K100c-7 works intermittenly [message #24806]

Thu, 24 March 2016 12:10

natedriver
Messages: 35
Registered: March 2009

Member

So I have a slant plexi faced K100c-7 that just decides to not work on occasion. Last night at practice it just stops working. The light is on. I hear the wump when I turn
it on but no signal at all. I checked the cord from the guitar. Usually you can tap the plug and hear a little static. Nothing. Switched speaker cabs nothing. This has happened before and I switched cords and it worked. This time nothing. Bring it home works fine. Voltages are within in range. Am I dealing with a overheating issue? Its not hot in my room. I guess Ill have to wait til it happens again and just open it up right then and there to search for the issue. I just thought someone might have some insight. I am at a loss.
Thanks in advance for any help.

Nate

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Re: K100c-7 works intermittenly [message #24807 is a reply to message #24806]

Thu, 24 March 2016 12:53

Iowa Boy
Messages: 767
Registered: June 2014

Senior Member

You might have some corrosion on the input jack or one of the tangs may not be making contact on the tip of the cord. I'd check that first.

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Re: K100c-7 works intermittenly [message #24808 is a reply to message #24806]

Thu, 24 March 2016 12:57

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

The fact that the pilot lamp stays on rules out the thermal circuit breaker and the thump at turn on means that atleast the final section of the output stage is working , so this would leave a bad solder joint or a transistor failing .

When the amp does cut out does turning up or down the volume or treble control change the level of hiss heard from the speaker ?

[Updated on: Thu, 24 March 2016 13:01]

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Re: K100c-7 works intermittenly [message #24810 is a reply to message #24808]

Thu, 24 March 2016 13:41

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Agree with Steve. Dirty input jack or an intermittent cord could also be the problem.

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Re: K100c-7 works intermittenly [message #24812 is a reply to message #24806]

Thu, 24 March 2016 14:20

natedriver
Messages: 35
Registered: March 2009

Member

Thanks for the prompt responses. I will take your advice and go through my cords and troubleshoot again just to be sure I did not miss anything obvious.
I can hear the thump but the amp is pretty quiet compared to my other Kustom amps. I did fiddle with the volume and plugged into both high and low inputs as well as plugging into the other channels and could hear any noise. I even gave a couple whacks that would usually cause a reverb tank sound and nothing happened.
Thanks again for the help.

Nate

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Re: K100c-7 works intermittenly [message #24816 is a reply to message #24806]

Thu, 24 March 2016 17:47

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

More clues, that helps. To me it sounds like it might be a preamp power supply problem. The power amp still thumps, neither channel passes signal and no reverb crash.

The low voltage power supplies are located on the power amp pc board. Check to see that you have + and - 8 volts dc coming out of the regulators. Try probing the board with the well known chopstick and see if you can make the problem return.

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Re: K100c-7 works intermittenly [message #24817 is a reply to message #24812]

Thu, 24 March 2016 18:01

Shaun_Musings
Messages: 323
Registered: April 2009
Location: Reading, MA

Senior Member

I love using those old 1970s coil cords. One worked intermittently... I knew it was the cord because I have two of the same and a few others. One day I got sick of it going in and out, unscrewed it and pulled back the shielding to see like... three strands connected. Snip, solder, done, sounds like new!

Born on the Baaaaayou (Ok, in Massachusetts)

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Re: K100c-7 works intermittenly [message #24818 is a reply to message #24816]

Thu, 24 March 2016 18:02

Shaun_Musings
Messages: 323
Registered: April 2009
Location: Reading, MA

Senior Member

Oh, well the lack of reverb crash does narrow things a bit. One of my A4s had a loose wire connecting the output to the power supply...

Born on the Baaaaayou (Ok, in Massachusetts)

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Re: K100c-7 works intermittenly [message #24822 is a reply to message #24806]

Fri, 25 March 2016 06:13

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Coil cords are a failure waiting to happen from day one!
The strain placed on the connections is on average far greater then a regular type cord and some are molded without any strain releave to them!

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Re: K100c-7 works intermittenly [message #24827 is a reply to message #24806]

Fri, 25 March 2016 17:44

carlc
Messages: 143
Registered: July 2006
Location: Summerville, SC

Senior Member

I'm still using my original coil cord that I bought while i high school about 1966! Never been repaired; practice and gig with it.

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Re: K100c-7 works intermittenly [message #24828 is a reply to message #24806]

Sat, 26 March 2016 06:18

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

You would not want to travel in a air plane with the same percentage of failures that have befell coil cords I would think! Lol!
Many of them to this day have infearor sheilding also!

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