K-250 [message #13599] |
Sat, 08 May 2010 20:44 |
cassent5150
Messages: 341 Registered: August 2009
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Senior Member |
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I'm working on a 5065 output board for a k250 I picked up to restore. A cap (C shorted apparently and burned 3 of the resistors around it. I have a schematic but could realy use a clear ledgable one if anyone could sent me one. The resistors I believe to be all 470 ohm ( resistors 13, 15 and 16 )as best as I can tell. They burn the board pretty bad, but I replaced them and the cap (I didn't have a 27mf 35v and replaced it with the closest one I had, 33mf 35v). I pulled a licon power switch from another amp and powered her up. Everything works (Channels 1, 2,also reverb and trem/vibro),but she's heating up those resistors I replaced and the sound distorts a bit as you crank up the volume. Would the 33mf cap I installed cause this (too big or in backwards) or are we looking elsewhere? Steve C
Steve C
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Re: K-250 [message #13635 is a reply to message #13624] |
Mon, 10 May 2010 22:58 |
cassent5150
Messages: 341 Registered: August 2009
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Senior Member |
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all 6 diodes check good I have another board and pulled a cap out of it. Caps are correct (27mf 35v) now. I pulled 2 of the power transisters out of the chassis cause they were giving me bad readings, but out of the chassis they were fine. I replaced the 38735 next to C-8 and thats where I'm quiting for the night. Now I have a hum and the .51 5W power resistor next to the plug from the pre-amps is getting hot. I would think I put a transistor in backwards, but I got the plugs exactly the way they came off and I don't believe you can put the transistors in wrong because of the offset pining. So now I'm scratching my head!!!! I got a Kasino 250 head that works fine and I'm guesing thats the same on the inside so I'll open it up and use it for a comparison and maybe figure this out that way. Steve C
Steve C
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Re: K-250 [message #13639 is a reply to message #13599] |
Tue, 11 May 2010 12:06 |
chicagobill
Messages: 2005 Registered: April 2003
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Senior Member |
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Read the speaker output for dc voltage, that's my guess for the hum and overheating resistor. If you do find anything over a volt, unplug the speaker, as it will eventually destroy the voice coil.
Check all of the transistors on the board.
To check the output transistors, just pull off the black plastic plug and test with your meter. No need to remove them or to unhook the red lead.
Be sure to test the 4 driver transistors as well. These may be harder to test in circuit, but test in circuit first and if you get really odd readings then either pull the plug on the related output transistor and test again, or unsolder the base and emitter leads and test.
Is this the amp from eBay that Kevin M was selling? If it was, I saw the photos of the pc board. How did you clean-up the burnt areas? If the charred areas are too bad, they will conduct current and cause circuit failures.
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Re: K-250 [message #13640 is a reply to message #13639] |
Tue, 11 May 2010 20:27 |
cassent5150
Messages: 341 Registered: August 2009
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Senior Member |
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Yes, its that one from Keven M. I scraped most of the chared area with a flat screw driver and brushed it with a stiff tooth brush to get any loose stuff off. All the solder lines were intact. I was thinking about the 2 power transistors I pulled out. Why do they apear to be apposing each other yet the offset pining only seems to alow you to install the one way? I'm thinking that I didn't put them back in the same hole they came out of. I don't know how that would change things, but other than that I really didn't change anything else and it worked ok before I pulled them out to check them. Steve C
Steve C
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Re: K-250 [message #13643 is a reply to message #13642] |
Wed, 12 May 2010 09:07 |
cassent5150
Messages: 341 Registered: August 2009
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Senior Member |
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This is going to a bigger fix than I have time for right now. I have a couple good boards in a K-II SRS slave amp I bought a while back and I'm just going to replace the whole board, get it going, grab my Strat, take her for a spin on a few different cabinets and see how she drives. I'll deal with this later when I have more time to really go through it. Thanks for the testing tip, "man that is WAY KOOL". I've been pulling them out of the board to test them and you sure are right, its a friggen pain in the #@$%^ if ya know what I mean. You can bet I'll be making some use of that tip.
AGAIN: You guys are the BOMB!!!
Steve C
Steve C
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