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Old 20th February 2003, 06:46 PM   #1
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Default Yes, I am a moron. Now what did I break?

Adcom GFA-555II. Unplugged RCA cable from preamp without checking to make sure Adcom was turned off. Very loud BZZZZZZZZZZZZZZZZZZZZZZZZT. Left channel of Adcom no longer works, right channel seems same as before.

Any ideas what I toasted guys?


Mark
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Old 20th February 2003, 06:55 PM   #2
Netlist is offline Netlist  Belgium
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Hi, Mark

I feel sorry for you
First thing to do: check the speaker connected to the bad channel
(Hope you didn't blow up your speaker!!)
Second thing: look for burned resistors, fuses.

Measure the output transistors. Measure for DC at the output.

Then post again.

/Hugo - Loves and hates it when things break; Loves it when his clients come in with broken stuff; Hates it when his stuff breaks
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Old 20th February 2003, 09:07 PM   #3
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That sucks. While I love the sound of most Adcom amps, sometimes I believe it is too easy to break 'em.

What you did should not have killed the amp. But that doesn't mean it didn't.
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Old 20th February 2003, 09:13 PM   #4
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Thanks guys.

Rail fuses are fine, measured both channels with a DMM with a music input signal. Got ~300mv rms on the working channel, ~10mv rms on the broken one (same reading as with the probes just hanging in the air, so I'm assuming there's zero actual output). Interesting thing it, the other channel has since stopped working also. sniff sniff


Mark
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Old 21st February 2003, 03:58 AM   #5
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Got a scope? Got a schematic? Dig in there buddy!
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Old 21st February 2003, 06:15 AM   #6
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I did the same thing to my GFA-545II about a month ago and it turned out to be blown fuse.

Did you check the fuse visually or with a meter?

My fuses looked perfect and I feared for the worse but when I tested them with a DMM, one had no continuity. Further scrutiny with the fuse held up to a light source revealed a break barely the width of a human hair. You could only see it with the fuse angled just right.
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Old 21st February 2003, 06:47 AM   #7
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Mark

Any LED's glowing on the front?
Oh, and try to use a variac as well

/hugo
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Old 21st February 2003, 08:12 AM   #8
Jay is offline Jay  Indonesia
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It is very unlikely that what you did to the RCA jack will damage anything else other than DC RAIL FUSES and SPEAKERS (or tweeter fuse if available). But there’s no fuse in woofer path, and you would have known if your woofer 100% blown (Meaning that it’s only the fuse)

As only L channel is broken, swapping the speakers and fuses from R to L should have located the problem. If not, you know where to go next.

If then the R is also broken, you may have done something wrong during “debugging”. R and L should totally be separated, right to the power supply (but if the power led is still glowing, then the PS is OK). Problem with RCA on the L should not be the reason for R to be damaged.

Shorting output during probing or “debugging” on R may or may not blow the fuse or even the transistor (depends on the circuit)

After pulling out fuses (from R channel) you may insert the broken ones, or the fuses damaged during this effort (it’s the metal ends of the fuse)

Mark, I think you owe Ultrachrome something.
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