repairing k150-8 plexi [message #24179] |
Sat, 28 November 2015 10:13 |
natedriver
Messages: 35 Registered: March 2009
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I have a k150-8 plexi head that is blowing fuses. I built a bulb limiter. I am getting 55v and -55v off the filter caps. the schematic for board 5032 shows 39.5v and -39.5v.
Am I missing something here? Any help would be appreciated before I move foward with trouble shooting the power amp board thanks. Nate
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Re: repairing k150-8 plexi [message #24180 is a reply to message #24179] |
Sat, 28 November 2015 12:19 |
chicagobill
Messages: 2006 Registered: April 2003
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The power supply is normally somewhere around +&- 40vdc, so with a light bulb limiter it should be less than that. The 55 volts that you are getting is much higher than expected.
What is the line voltage coming in from the wall? Is the power transformer original to the amp?
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Re: repairing k150-8 plexi [message #24182 is a reply to message #24179] |
Sat, 28 November 2015 21:33 |
chicagobill
Messages: 2006 Registered: April 2003
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Is the power supply disconnected from the rest of the amp? Is your meter accurate?
It really doesn't make that much of a difference, if the voltage are high, they're high.
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Re: repairing k150-8 plexi [message #24192 is a reply to message #24179] |
Mon, 30 November 2015 06:30 |
stevem
Messages: 4772 Registered: June 2004 Location: NY
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There is something not right with your readings your posting up.
I opened up my k150 and then took readings at the input to the diode bridge I had 95.6 volts ac, and you had 48.7, this sounds to me like your where measuring each ac output leg of the power transformer to ground, not across both legs?
On my amp when I measured those legs to ground, then I got a reading of 48.3 volts ac.
Your high DC voltage readings across each main filter should make for high ac voltage readings also as you check back from the DC portion of the power supply to the power transformer.
Your DC voltage readings on the filters are some 16 volts too high, mine with the amp working at idle are 41.9 and 41.7 on the negative rail .
[Updated on: Mon, 30 November 2015 06:32] Report message to a moderator
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Re: repairing k150-8 plexi [message #24328 is a reply to message #24179] |
Mon, 04 January 2016 15:00 |
chicagobill
Messages: 2006 Registered: April 2003
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Senior Member |
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The preamp supplies are supposed to be plus and minus 8 volts, so you have a problem with the positive 8 volt regulator circuit.
Test transistors Q9-11-12-13 on PC5032, as well as diode CR10. While you are there you can also check the resistors and caps in the same circuit.
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