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?
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?
Attachments
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?
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?
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.
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.
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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.
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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