| Two K150-2 Heads - #1 Overheats, #2 No Sound [message #13807] |
Sun, 30 May 2010 00:01  |
Goonak
Messages: 19
Registered: April 2010
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Junior Member |
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Hi all - after successfully fixing my Kustom Sinderwinder with the gracious help of this forum I now could use some help in fixing a couple of K150-2 heads that I have.
#1
I bought #1 on ebay a few weeks ago. It was sold as a fully functioning amp (minus burnt out pilot lamps, which I've since replaced). Anyway, everything worked fine, all controls, all effects for a couple of weeks. Recently it's started to overheat after 45 mins to an hour of playing. The back of the chassis gradually gets very hot to the touch. Eventually the amp turns itself off. After a few minutes it turns back on.
I searched previous posts here on the site and found a thread about checking the thermal circuit breaker connection and the bias diode connection. I checked them and they both seem properly connected. However I don't know if they need to be replaced. What should I be testing to figure out what's wrong with this head?
#2
I also picked up a second K150-2 head via ebay recently. I bought this one fully knowing that it wasn't working as my hope was to fix it, or at least use it for parts. This second head powers up, but I get get no signal from it. Where should I start with the diagnosis for #2?
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| Re: Two K150-2 Heads - #1 Overheats, #2 No Sound [message #13819 is a reply to message #13807] |
Tue, 01 June 2010 14:00  |
chicagobill
Messages: 2005
Registered: April 2003
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Senior Member |
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The overheating power amp is usually a bias problem. If you have checked each of the diodes in the bias string, check the driver transistors. Also make sure that the diode that attaches to the heatsink is held firmly in place in the little metal clip.
When the power amp overheats, it opens the thermal circuit breaker located on the heatsink, shutting off the entire amp. When the amp cools down, the breaker closes and the amp will power up again.
As for the second amp, try sending a signal directly into the power amp and see if there is any output.
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| Re: Two K150-2 Heads - #1 Overheats, #2 No Sound [message #13865 is a reply to message #13807] |
Fri, 04 June 2010 12:08 |
chicagobill
Messages: 2005
Registered: April 2003
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Senior Member |
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In my experience, smoke can cause all sorts of damage to electronics, but I couldn't tell you any specific thing that would cause your overheating.
Smoke carries with it any number of things that can be corrosive or just plain dirty. Pleat's comments about the connectors comes to play here as the smoke could easily cause the Molex contacts to become iffy. If smoke has gotten into the pots, they will need cleaning.
You should clean out the chassis and pc boards as best you can and you should pay particular attention to the chassis grounds (any place that there is an electrical connection to the chassis).
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| Re: Two K150-2 Heads - #1 Overheats, #2 No Sound [message #13873 is a reply to message #13807] |
Sat, 05 June 2010 14:00 |
chicagobill
Messages: 2005
Registered: April 2003
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Senior Member |
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The output transistors are drawing too much current and are causing the amp to overheat. If you have a meter, it's time to start checking things on the power amp.
I'd start by checking the three diodes in the bias section. These are the two white cased CR1 and CR2 and the metal cased one CR3 that clips onto the heat sink. Check for bad connections to that heatsink mounted one as well.
If all of the diodes check ok, then carefully start taking voltage readings on the power amp board and compare them to what you see on the schematic.
Remember that working on any amp while it's turned on and plugged into the wall is dangerous, and should be done with extreme care. If this is beyond your abilities, then stop and take the amp to a qualified tech.
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| Re: Two K150-2 Heads - #1 Overheats, #2 No Sound [message #13908 is a reply to message #13807] |
Mon, 07 June 2010 07:14 |
stevem
Messages: 4746
Registered: June 2004
Location: NY
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Senior Member |
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The picture of that amp is odd as so many of the those now brown looking orange drop caps make me think that all the boards cam out of another amp that was in a fire or something, the rest of the amp just looks too clean.
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