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Weak signal (one side) [message #24077]

Tue, 27 October 2015 16:52

Fatstrat1991
Messages: 6
Registered: October 2015
Location: Louisiana

Junior Member

What's up guys? Newbie here to the forum. I'm currently trying to repair a Kustom K100 C-8. The left input works just fine, the right side doesn't. The right side inputs are going to a preamp PC1400. I took the output from the other preamp and wired it to the power amp where the 1400 is supposed to go in, and once again, works perfectly. Leading me to believe the problem is somewhere on the PC1400. With a guitar into the side that doesn't work, if I turn the volume pot to about 9 o'clock I can get a very faint sound, but anything above or below that is silent. I thought it might be the pot, but I took an ohm reading and it measured from 0-15K just like I assumed it should. Any idea what could be going wrong here? Thanks for any help

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Re: Weak signal (one side) [message #24078 is a reply to message #24077]

Tue, 27 October 2015 22:40

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

Welcome to the place. If you have a meter with a diode test function, use it to test the transistors on the board. The usual suspects are the first two transistors at the input.

Another typical problem is broken solder joints and open electrolytic capacitors.

Let us know what you find out.

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Re: Weak signal (one side) [message #24079 is a reply to message #24078]

Wed, 28 October 2015 09:00

Fatstrat1991
Messages: 6
Registered: October 2015
Location: Louisiana

Junior Member

Thanks alot for the quick reply. I had a feeling it was a transistor, but after three hours of soldering, testing, and taking apart I decided to walk away for the day. Lol... I'll definitely be checking those transistors and let you know what fixes the problem. Thanks again

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Re: Weak signal (one side) [message #24082 is a reply to message #24077]

Thu, 29 October 2015 06:25

stevem
Messages: 4775
Registered: June 2004
Location: NY

Senior Member

Once you have taken the time to remove the original transistors on that preamp board don't even take the added time to test them, just replace them as that board has less then $1.50 in transistors on it and the new ones make far less noise.
Be sure to leave the leads as long as you can as they will help keep the transistor cooler by acting like a heat sink .

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Re: Weak signal (one side) [message #24109 is a reply to message #24082]

Fri, 30 October 2015 18:42

Fatstrat1991
Messages: 6
Registered: October 2015
Location: Louisiana

Junior Member

Stevem, I've looked everywhere I could think of on the Internet for replacement transistors but can't seem to find any to match the specs of the ones in the amp... Anywhere special that I should be looking? Thanks for the advice too btw, makes sense!

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Re: Weak signal (one side) [message #24110 is a reply to message #24077]

Fri, 30 October 2015 20:18

chicagobill
Messages: 2006
Registered: April 2003

Senior Member

The basic transistors in all Kustom amps are not all that special. The maximum voltage that they ever see is no more than 20 volts or so.

You can use basic 2N3904 and 2N3906. I tend to use 2N4401 and 2N4402 because I use them in other things, so I stock them in quantity.

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Re: Weak signal (one side) [message #24112 is a reply to message #24110]

Sat, 31 October 2015 16:00

Fatstrat1991
Messages: 6
Registered: October 2015
Location: Louisiana

Junior Member

Thanks chicagobill!

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Re: Weak signal (one side) [message #24123 is a reply to message #24112]

Mon, 02 November 2015 22:38

Fatstrat1991
Messages: 6
Registered: October 2015
Location: Louisiana

Junior Member

I would like to say thanks to everyone for the great advice. I replaced all transistors on the PC1400 with two 2N3906's and four 2N3904's. I put a couple in backwards at first, but once I referred to the schematic, I was able to get the amp running and playing in tip top shape. A huge thanks to everyone for advice and the quick replies. If I can help anyone with some information, just ask.

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