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k150-8 [message #14395] Fri, 24 September 2010 13:11 Go to next message
Bill
Messages: 64
Registered: March 2002
Location: Kansas
Member
I bought a k150-8, non working, pilot light works, no sound at speakers. Found someone had reversed the monitor and speaker outputs on the output board, wired the speakers as a short. I fixed these things and now have signal all the way through the amp, but it has a whoop-whoop-whoop sound, that is not affected by the volume or other controls,puts out about 20 volts ac--don't see any dc. Someone has replaced one driver with an SK3024, and the thermal diode was replaced by a 116 diode, and not placed in the chassis heat sink. Three other transistors have been changed on the premap board. I will try to isolate where it's coming from--either preamp or power board first.
Bill C
Re: k150-8 [message #14398 is a reply to message #14395] Fri, 24 September 2010 14:37 Go to previous messageGo to next message
Bill
Messages: 64
Registered: March 2002
Location: Kansas
Member
Update on the k150-8 project.
With all boards installed normal, I have 89.3.vdc at the power iputs of the board. Voltage at the preamps is 9.5v on the red/positive side, and 3.87 volts on the negative.

With the power cut off the right preamp it is 10.62v positive and 2.76 vlots negative.

With both preamps cut off it is 12.56 volts positive and 1.4 volts negative.

Looks like I have a power regulator problem, too.
Bill C
Re: k150-8 [message #14399 is a reply to message #14395] Fri, 24 September 2010 14:49 Go to previous messageGo to next message
chicagobill
Messages: 1949
Registered: April 2003
Senior Member
That's strange that the negative supply gets lower as you unhook more load from it.

I guess you're right that there is a problem in the regulator circuit. As I recall, the positive supply is set by the circuit values, and the negative supply tracks the positive supply. I'd check the transistors and the tantalum caps in there first.
Re: k150-8 [message #14403 is a reply to message #14399] Fri, 24 September 2010 17:31 Go to previous messageGo to next message
Bill
Messages: 64
Registered: March 2002
Location: Kansas
Member
Thanks Bill,
So far I've only found the second driver was bad, so replaced that, and went ahead and put in the correct thermal diode (1n3754). Will try the power board now and see what changes.
Have a good weekend, and thanks for your help.
Bill C
Re: k150-8 [message #14404 is a reply to message #14403] Fri, 24 September 2010 17:59 Go to previous messageGo to next message
Bill
Messages: 64
Registered: March 2002
Location: Kansas
Member
Well,
Believe it or not, that fixed the problem. Everything works now.
Re: k150-8 [message #14433 is a reply to message #14395] Sun, 26 September 2010 13:53 Go to previous message
stevem is currently offline  stevem
Messages: 4272
Registered: June 2004
Location: NY
Senior Member
Glad to hear it, good job there!
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