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Old 9th December 2008, 03:12 AM   #1
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Default strange input/turn on problem

I have a cheap Pyle amp I received from a friend, described as non working from purchase. I pulled the covers, and found a fried ground trace. I fixed this, put power to it and promptly fried a IRFZ44N. The only replacement I had handy was an old SK device from a Kenwood KAC somethingorother. I powered it up again, and NO SMOKE! That's good. But, of course, another problem came up.

I inserted this amp into my test system in my minivan, running a 10" sub. When the system turns on, everything powers up, but all I get is faint alternator whine. As soon as I unplug the RCAs from the problem amp, my headunit starts outputting signal. Plug the RCAs back in (hot) and the amp plays fine.

I am new at diagnosing and fixing amps, advice and help is appreciated.

Ben
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Old 9th December 2008, 03:39 AM   #2
jol50 is offline jol50  United States
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Is there any current on the RCA shields of the amp, unhooked but on? So you mean if you plug the RCA into the amp only after you turn it all on then it works?
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Old 9th December 2008, 03:51 AM   #3
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If I unplug the repaired amp, everything works. Everything works fine with another amp in the same spot.
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Old 9th December 2008, 04:21 AM   #4
jol50 is offline jol50  United States
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I guess I would test the outputs in the amp to start with, or see if it has rail voltage from power supply. I don't know what a PS does if you put just any part in, I only use replacements or a known sub. You can test the speaker outputs too, there should be little current on speakers with no RCA hooked to amp. If there is then output might be bad.

Often things blow for a reason, you never know if the reason is in the rest of the amp or was something that happened outside the amp. That one might be inside the amp yet, like the outputs.
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Old 9th December 2008, 04:33 AM   #5
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Unplug the RCA cable from the bad amp and use a volt meter to see if there is a substantial amount of DC voltage on the shield of the RCA jack of the amp. Black meter lead to the chassis of the vehicle and red lead on the outer part of the RCA jack.
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Old 9th December 2008, 08:01 PM   #6
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No dc on RCA ground, but I did notice large (~.070V) DC on the speaker terminals...bridged into 4 ohms. This is with the RCAs plugged back in.

I used the SK mosfet because it was the only thing I had handy, and it's only a Pyle that already didn't work, so why not? Want to mail me the right part, if you have one handy?

There were some wire clippings that had found their way onto the board before the solder dip at the factory. I think this is what caused the initial trace burn.

This is the order of events:

1. Fixed burned trace.
2. Put power on.
3. IRFZ44N in power supply goes poof.
4. Remove amp and fix solder bridges, and insert SK K2421 in place of burned IRFZ44N
5. Put power on.
6. Power good, no sound.
7. Unplug RCAs
8. Sound comes on in the rest of the system.
9. Plug RCAs back in, sub comes on.

Thanks for the help,
Ben
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Old 10th December 2008, 01:48 AM   #7
jol50 is offline jol50  United States
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IRFZ44 are very common and cheap, you can get them anywhere.

I still don't understand, you are saying the audio for this amp does not come on until you unplug RCA and plug back in?

.07v is a little high but not surprising for that amp I guess, not likely to matter with a sub.
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Old 10th December 2008, 02:04 AM   #8
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Let me describe the setup:

Factory Ford 2DIN tape/cd, front channels to passive xover to tweeters.
rear channels into LOC to 4 channel amp.
four channel amp bridged to 8ohm mids.
line out from four channel to Pyle amp.
Pyle amp bridged to 4ohm sub.

Everything in the install is solid, ie no issues before Pyle amp.

I start the vehicle, turn on the deck. Only sound is quiet alt whine. Amps turn on, but just alt whine. With everything still on, I unplug the RCAs going to the Pyle, and my tweeters and mids start working. I plug the RCAs back into the Pyle (with a slight thump ), and the sub works. The deck doesn't like something the amp is doing at turn on.

And a switch in the turn on line to the Pyle does nothing.
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Old 10th December 2008, 04:41 AM   #9
jol50 is offline jol50  United States
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Guess I would check the grounds then look at the LOC. Does it have gains on it? I have not used one in very long time, but my only guess is the factory HU does not like the load maybe? I'm not sure. I assume you mean you trigger the amps with a switch to turn on...and it does not make them come on with the pyle in there? (when it does this)
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Old 10th December 2008, 05:16 AM   #10
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do you know if your ford has a factory amp? if so that might be your problem. you might have to run all new speaker wire to the speakers if u didnt already
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