I put a Carver M-1.5t on the bench yesterday. The chief complaint was that it was a fuse popper. I thought that was pretty odd, as this Carver amp has a protection circuit in it to shut it down under excessive current conditions.
Based on my extensive experience with Carver amps <ha!>, I figured the problem had to be on the primary side of the PT, perhaps in the diac/triac on the magnetic field whatzit regulation board. The triac had a telltale brown spot at the M1 lead, so I did some power-off testing, thinking that this had to be the problem. It wasn't.
So I ran through the amp wtih my diode checker and found that all of the transistors in the amp tested OK. All of them. things were getting to the point that I had to test the amp powered-on. I called it a night and put off the rest of the testing until this afternoon.
Much to my surprise, today I powered up the amp on a variac and it didn't pull current. So I powered it up with full voltage and no load, and it just sat there with the running lights on. No protection circuits triggered. No fuses popped. What?
I calibrated the high voltage rail on the PSU board and dialed it up from 108 to 124VDC. Then I calibrated the bias on both channels, which were reading 0.1 mV. I set it to 3.4 mV and traced some small signals into no load. So far so good. Then I gradually increased the signal to full power at no load. 72 VAC when the clipping indicator came on.
Eventually, I worked my way up to 72 VAC RMS into 8R on each channel. That's the rated output of 650W RMS. The amp is now doing a burn-in test with real music as I type this.
Sometimes you just get lucky.
Based on my extensive experience with Carver amps <ha!>, I figured the problem had to be on the primary side of the PT, perhaps in the diac/triac on the magnetic field whatzit regulation board. The triac had a telltale brown spot at the M1 lead, so I did some power-off testing, thinking that this had to be the problem. It wasn't.
So I ran through the amp wtih my diode checker and found that all of the transistors in the amp tested OK. All of them. things were getting to the point that I had to test the amp powered-on. I called it a night and put off the rest of the testing until this afternoon.
Much to my surprise, today I powered up the amp on a variac and it didn't pull current. So I powered it up with full voltage and no load, and it just sat there with the running lights on. No protection circuits triggered. No fuses popped. What?
I calibrated the high voltage rail on the PSU board and dialed it up from 108 to 124VDC. Then I calibrated the bias on both channels, which were reading 0.1 mV. I set it to 3.4 mV and traced some small signals into no load. So far so good. Then I gradually increased the signal to full power at no load. 72 VAC when the clipping indicator came on.
Eventually, I worked my way up to 72 VAC RMS into 8R on each channel. That's the rated output of 650W RMS. The amp is now doing a burn-in test with real music as I type this.
Sometimes you just get lucky.
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