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k200b repair and info [message #2731]

Mon, 19 May 2003 12:15

Anonymous

A friend of mine had a k200b for a while that he stopped using when he got a fender bassman. I recently took it off of his hands for $50. It sat in his garage for a couple of years while he wasn't using it. I took it home and plugged it up to a 8ohm 4x12 cab. I got a loud hum and a little bit of guitar signal before it went dead. The unit still turns on, but i can't get it to put out any sound at all. There were no loud pops, flashes, or smoke. I opened it up and the fuse was okay. There is some rust on the transformer. and a lot of dust on everything else. If someone could give me some input on what the problem could be and how to fix it, it would be greatly appreciated. Also, the plate or sticker that had jack labels and information on the back has been removed. So if someone could clue me in on which output jacks are what and what the min/max ohm loads are it would be help me out alot. thanks

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Re: k200b repair and info [message #2734 is a reply to message #2731]

Mon, 19 May 2003 16:27

C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...

Senior Member

Hi, the cabinet is OK for that head. Kustoms like 4 ohms or HIGHER. I would suspect you have a K200A series amp. As far as the startup failure, my only guess would be a fuse mounted on the circuit board. That fuse is for the speaker output. That would be consistant with what you described. The amp has at least one output transistor that has shorted. The high current through the speaker caused the humming and then the fuse blew. You need to check the 4 output transistors on the bottom of the amp. Good luck

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Re: k200b repair and info [message #2735 is a reply to message #2734]

Mon, 19 May 2003 21:54

Anonymous

I checked the model number again, it is a k200B-5. I think i have solved part of the problem. I found burn marks on the back circuit board. It's fixable if i can get ahold of a schematic, but then i have to figure out why it fried. If anyone has any ideas on the problem it would help alot. thanx

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Re: k200b repair and info [message #2737 is a reply to message #2735]

Tue, 20 May 2003 09:07

C4ster
Messages: 686
Registered: June 2001
Location: Mukwonago, WI (Milwaukee...

Senior Member

Sorry about the K200A reference, but I still stand by the basic answer I gave. The circuit trace acted as a fuse and burned out. Does that trace go to the connector on the right side of the board and then with a blue wire to the 2 1/4" jacks on the back?? If it does then that is your speaker output. I still think there are shorted output transistor(s). You need to check out the transistors before you apply power again.

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Re: k200b repair and info [message #2744 is a reply to message #2737]

Thu, 22 May 2003 07:54

stevem
Messages: 4754
Registered: June 2004
Location: NY

Senior Member

Hi. If you got any type of sound out of the amp the first time you turned it on, and the fuse is still good now it must have been replaced at some time in the past with a larger fuse. Proof being the blown open circuit board trace( although I have seen them come open from being soldered on to many times)The hum you heard from the speakers is a sign of, in the least 1 bad output transistor or more and may be some shot driver transistors and open emitter resistors. The bridge diode rectifier near the power transformer has been known to fail all on its own, no less after being beaten up by high current draw from a shorted output section. I would also replace that with a new 25 amp bridge when you order up parts. Or better yet get 4 (6 to 8) amp super fast recovery diodes and use them to form the bridge. The make the amp sound much better, but you will have to mount them on a terminal strip leaving their leads long because they are part of their heat sink. Its worth the work!I have schematics for this amp. Send me a stamped self addressed envelope, and I will send you out copys. steven magnotti 548 yorkhill rd yorktown n.y 10598. PS their is only one glass fuse in any kustom amp, they do have a thermal circuit breaker mounted in the center of the output transisters.

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Re: k200b repair and info [message #2746 is a reply to message #2744]

Thu, 22 May 2003 18:40

Bill
Messages: 64
Registered: March 2002
Location: Kansas

Member

My K200a-2 has two glass fuses...one for power, right behind the power switch, and one to the right rear near the speaker output. All my B series only have one glass fuse--the one for power. Also has a thermal curcuit breaker. I got all my parts from Mouser Electronics and/or Radio Shack. Thrill Bill

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Re: k200b repair and info [message #2749 is a reply to message #2731]

Fri, 23 May 2003 07:37

stevem
Messages: 4754
Registered: June 2004
Location: NY

Senior Member

Hi, more info you asked for. The two speaker jacks are wired in parralle, you can use either/or. Minimum impedance is 4 ohms, cabs where normally 8 ohms. If you have a RCA jack on the back that is the preamp output.

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Re: k200b repair and info [message #4291 is a reply to message #2744]

Wed, 02 June 2004 09:58

Anonymous

Steven, Can I get a copy of the K200B 5 schematic from you please? Smoke

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