PM-1.5 CARVER needs repair - help needed with how to proceed

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windeguy
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PM-1.5 CARVER needs repair - help needed with how to proceed

Post by windeguy » Thu Sep 25, 2014 4:29 pm

I have a CARVER PM-1.5 that needs repair. It had been a workhorse for many years but this week when I turned it on, it started up for about 1 second, I then heard a faint click and it blew the main fuse. It had never been worked on previously to my knowledge. After taking off the cover there is no obvious problem.

I am currently living in the Caribbean and it is not easy to send and receive heavy items like this back for repair, so I am looking at any diagnostic techniques that will be helpful with this model so I can attempt repairs myself. I did find a set of schematics on line for it and would like to know how to systematically proceed with finding the problem so I can resurrect it. I am a retired electrical engineer, primarily digital design so not an expert at analog, but I can certainly follow directions and I can solder (and un-solder) very well.

windeguy
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Re: PM-1.5 CARVER needs repair - help needed with how to pro

Post by windeguy » Fri Dec 19, 2014 7:46 am

I was able to repair the PM-1.5. It turned out to be one of the capacitors in the high voltage power supply that failed. Rather than go with new old stock, I went with a new part that was similar in specs to the original capacitor (slightly larger so I had to use tie wraps to hold them in place). I replaced the pair of high voltage caps from Mouser and the amp is working well again. \:D/

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TNRabbit
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Re: PM-1.5 CARVER needs repair - help needed with how to pro

Post by TNRabbit » Fri Dec 19, 2014 9:46 am

sorry we were no help! Glad you got it fixed~
TNRabbit
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Robert R
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Re: PM-1.5 CARVER needs repair - help needed with how to pro

Post by Robert R » Fri Dec 19, 2014 9:56 am

windeguy

Sorry you had so little response to your problem. Your amp happened to blow up at a time when many of us were returning from the Carverfest, and mostly thinking about the next one.

I'd suggest that you replace the nearby pair of somewhat smaller filter caps as well. And over time, every electrolytic in there is a potential problem - the little ones are all just as old, and they all fail sooner or later. A complete recap, perhaps done in stages, would be a great investment.

The service manual for your unit is posted on the carveraudio.com website. It has more than just schematics. You should check the bias adjustments, and also the level of DC on the speaker outputs, according to the manual's directions.

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radioeng2
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Re: PM-1.5 CARVER needs repair - help needed with how to pro

Post by radioeng2 » Fri Dec 19, 2014 11:46 am

Man....some help we all were. :rolleyes:

I'd second the idea of getting more electrolytics changed. Ones that are hammered hard, ones that are in physically hotter places, are the ones to change first'est.

When caps break down and isolation between stages is gone, components can also go. That's why it's good to be ahead of failure. Typical is for power supply filtering caps to be the first to go, due to being hit hard with sharp pulses of the diodes going on and off, and this results in usually just bad noticable hum. But other caps reaching end of life can have more dire effects. Easy to forget that when hummm is usually the first thing heard.

Mark
I was there "At the Fest!" Hope you were too!

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