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Old 19th February 2013, 05:36 PM   #1
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Default Hifonics Cronos

Got this amp for repair.

The original problem was broken legs of the output fets due to vibration.

This led to the explosion of several 10μF/250V MKT capacitors

After removing all fets-i plan to replace all of them-i powered the amp and

the relay clicks on and off, there were 74VDC on the output.

Then went back to the 3S module, where the auxiliary +12V supply is not

present, although i do have 25V getting in to the 7812, and the regulator

tests ok out of the circuit.

So, there is something shagging down +12V.

Could this be the two ics covered with polyester?
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Old 19th February 2013, 07:42 PM   #2
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Location: Louisiana
If they are pulling the voltage down, they would likely be getting hot.

Are you sure that the regulator is working properly? If you insert a 1 ohm resistor in series with the output leg (between the regulator and the board), what is the DC voltage across that resistor when the regulator is in the circuit?
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Old 26th February 2013, 10:00 AM   #3
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I spent quite some time trying to figure out this.
The regulator works perfectly, but there seems to be a short somewhere, and drags down its 12V output, so it gets very hot.
The same happened when i replaced the regulator with a new one.
On the other hand i cannot locate any parts getting hot.
Finally i had another amp and i swapped the 3S modules.
New problems came.
After replacing an open 4R7 resistor (R31), and re-doing a lot of soldering on the module,
when the amp powers up, there is a 10A current draw and one bank of fets is getting hot.
So i removed all 6 of them, and now it draws about 3A with green led on.
There is no output from the amp, but at least the relay stays on (no DC voltage)
As soon as i try to connect the RCAs, i hear a weird sound and the overload led comes on.

Last edited by ultra; 26th February 2013 at 10:03 AM. Reason: spelling
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Old 26th February 2013, 05:34 PM   #4
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What happens if you connect the RCAs then power the amp up?
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Old 26th February 2013, 06:48 PM   #5
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I removed the RCA connector as someone had done a not so good job with it.
Now, amp powers up and produces audio.
The increasing idle current made me suspect that something was not right.
Actually a bank of fets was overheating and after replacing an open gate resistor, everything works fine.
It draws steadily 3A at idle.
I ve tested the amp up to 110A with a 2 ohm load.
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