I test the amp in my car where existing working amp is working fine and then I just remove that one and hook up this one. That way I know all sources are fine.
With no RCAs plugged into the amp and the black probe on the chassis ground terminal, how much DC voltage do you have on the input RCA shields?
Do you have positive and negative regulated voltage on the op-amps?
Do you have positive and negative regulated voltage on the op-amps?
am getting none. no voltage
I don't know how to test for voltage at op-amps but am planning on changing them anyway
I noticed that one resistor did run little hot and one leg of it goes to 14 leg IC labeled TL074CN
One more thing, is that amp turns on by just putting positive and negative without the remote connected, is that a simptom of shorted REC402, the part that looks like FET? because without remote connected amp turns on and I can read 3v at the remote port.
Before you do anything else, you should take photos of the parts you couldn't identify in the other amp. If this amp has problems similar to the other amp, the same parts could burn.
The rectifier shouldn't have anything to do with the amp powering up without the remote turn on.
Measure the DC voltage on the center legs of the rectifier (black probe on chassis ground). What do you have there?
For the 8 pin op-amps, you would measure the DC voltage on pins 4 and 8. On the 14 pin op-amps, you would measure the voltage on pins 4 and 11. Again, black probe on the chassis ground.
When measuring the voltage on the rectifiers and the op-amps, apply 12v to the remote turn on terminal.
The rectifier shouldn't have anything to do with the amp powering up without the remote turn on.
Measure the DC voltage on the center legs of the rectifier (black probe on chassis ground). What do you have there?
For the 8 pin op-amps, you would measure the DC voltage on pins 4 and 8. On the 14 pin op-amps, you would measure the voltage on pins 4 and 11. Again, black probe on the chassis ground.
When measuring the voltage on the rectifiers and the op-amps, apply 12v to the remote turn on terminal.
but amp turns on without remote connected so I fear if I conect it something will give. On rectifier the heat sink screw was lose so I suspect they ran hot?
Today the first MTX152 got done and tested OK, I saw from the second amp what values resistors are so I put them in there and the amp works fine, I did not bridge it and am afraid of pushing it too much.
Now the second amp, the amp turns on without the remote, it works but it got very hot, then I turned the volume up a bit and the fuse blew, which means the power suply FEt is toast. Something is shorted in there, why would amp be turned on by just putting positive and negative without remote? I just teared it appart pulled all the FEts and tested them all, the right chanel outputs failed and I just installed original factory replacement IRF540. So something else is making them go bad
Now the second amp, the amp turns on without the remote, it works but it got very hot, then I turned the volume up a bit and the fuse blew, which means the power suply FEt is toast. Something is shorted in there, why would amp be turned on by just putting positive and negative without remote? I just teared it appart pulled all the FEts and tested them all, the right chanel outputs failed and I just installed original factory replacement IRF540. So something else is making them go bad
There are a number of things that could make the amp power up with no remote. You're likely going to have to trace the circuit back to the components that feed the LM339 and the TL494 to determine what's driving it on. If you want help troubleshooting it, post the DC voltages on all of the pins for the two ICs (preferebly with AND without remote voltage applied). Before you can do that, you'll have to either find the fault that's killing the outputs or you'll have to remove the outputs from that channel.
494
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:
339
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Whenever you power up an amp, you REALLY need to have the power semiconductors tightly clamped to the heatsink and have either a current limiter or a small fuse in the B+ line to protect the amp.
The new transistor may have a lower threshold than the older transistors. If that's the case and you didn't adjust the bias/idle current, that could have caused the output to fail.
494
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Pin 15:
Pin 16:
339
Pin 1:
Pin 2:
Pin 3:
Pin 4:
Pin 5:
Pin 6:
Pin 7:
Pin 8:
Pin 9:
Pin 10:
Pin 11:
Pin 12:
Pin 13:
Pin 14:
Whenever you power up an amp, you REALLY need to have the power semiconductors tightly clamped to the heatsink and have either a current limiter or a small fuse in the B+ line to protect the amp.
The new transistor may have a lower threshold than the older transistors. If that's the case and you didn't adjust the bias/idle current, that could have caused the output to fail.
Now I removed the power supply FETs as well as all output FETs, can I power on the amp and then check the voltage on 494 and 399 pins? Or do I have to have FETs installed?
This is wierd because this amp only had a problem with outputs destorting but it worked fine at lower levels, but after I took it appart and then put it back together the power transistors blew and after that I have this problem, Am on my last FETs, if I blow these then it would be too much to fix. I already spent money on it, I changed the OP amps on it.
This is wierd because this amp only had a problem with outputs destorting but it worked fine at lower levels, but after I took it appart and then put it back together the power transistors blew and after that I have this problem, Am on my last FETs, if I blow these then it would be too much to fix. I already spent money on it, I changed the OP amps on it.
I don't think it will cause any problems if you remove the FETs. Post the numbers and we'll see.
with power FETs out the amp did not turn on the LED.
Here are the test results:
494
1-22.2mv
2-4.46v
3-62.5mv
4-4.3mv
5-1.48v
6-3.32v
7-3.6mv
8-11.45v
9-3.7mv
10-4.92v
11-4.92v
12-4.92v
13-11.72
14-11.18
15-6.6mv
16-3.5v
----------------
399
1-4.72v
2-4.72v
3-11.74v
4-4.92v
5-6.91v
6-3.63v
7-4.92v
8-4.71v
9-2.3mv
10-1.9mv
11-3.37v
12-4.69v
13-3.37v
14-0.42v
let me know what to do next
Here are the test results:
494
1-22.2mv
2-4.46v
3-62.5mv
4-4.3mv
5-1.48v
6-3.32v
7-3.6mv
8-11.45v
9-3.7mv
10-4.92v
11-4.92v
12-4.92v
13-11.72
14-11.18
15-6.6mv
16-3.5v
----------------
399
1-4.72v
2-4.72v
3-11.74v
4-4.92v
5-6.91v
6-3.63v
7-4.92v
8-4.71v
9-2.3mv
10-1.9mv
11-3.37v
12-4.69v
13-3.37v
14-0.42v
let me know what to do next
I don't think you have the pin numbering correct. Copy and paste the list of pin numbers I posted and type the numbers in place. Don't use dashes.
tested with automotive battery that has voltage of 12.4
494
Pin 1: 22.2milivolts
Pin 2: 4.46v
Pin 3: 62.5milivolts
Pin 4: 4.3milivolts
Pin 5: 1.48v
Pin 6: 3.32v
Pin 7: 3.6v
Pin 8: 11.45v
Pin 9: 3.5v
Pin 10: 6.6milivolt
Pin 11: 11.18v
Pin 12: 11.72v
Pin 13: 4.92v
Pin 14: 4.92v
Pin 15: 4.92v
Pin 16: 3.7milivolts
339
Pin 1: 4.72v
Pin 2: 4.72v
Pin 3: 11.74v
Pin 4: 4.92v
Pin 5: 6.91v
Pin 6: 3.63v
Pin 7: 4.92v
Pin 8: 0.42v
Pin 9: 3.37v
Pin 10: 4.69v
Pin 11: 3.37v
Pin 12: 1.9milivolt
Pin 13: 2.3milivolt
Pin 14: 4.71v
does this make sense?
494
Pin 1: 22.2milivolts
Pin 2: 4.46v
Pin 3: 62.5milivolts
Pin 4: 4.3milivolts
Pin 5: 1.48v
Pin 6: 3.32v
Pin 7: 3.6v
Pin 8: 11.45v
Pin 9: 3.5v
Pin 10: 6.6milivolt
Pin 11: 11.18v
Pin 12: 11.72v
Pin 13: 4.92v
Pin 14: 4.92v
Pin 15: 4.92v
Pin 16: 3.7milivolts
339
Pin 1: 4.72v
Pin 2: 4.72v
Pin 3: 11.74v
Pin 4: 4.92v
Pin 5: 6.91v
Pin 6: 3.63v
Pin 7: 4.92v
Pin 8: 0.42v
Pin 9: 3.37v
Pin 10: 4.69v
Pin 11: 3.37v
Pin 12: 1.9milivolt
Pin 13: 2.3milivolt
Pin 14: 4.71v
does this make sense?
You need to determine why pin 7 on the 494 has 3.6v. It should be at ground (0 ohms to the ground terminal of the amp). No pin on the amp should be lower than pin 7. If there's a burned trace, you need to repair it. Don't run a wire back to the ground terminal (not as a permanent repair - would be OK for testing).
Did you have the black meter probe on the ground terminal of the amp?
After looking at the other numbers, it's probably 3.6mv. If you post the voltage as 0.036v, it will prevent errors.
Did you have the black meter probe on the ground terminal of the amp?
After looking at the other numbers, it's probably 3.6mv. If you post the voltage as 0.036v, it will prevent errors.
Correction:
3.6mv = 0.0036v, not 0.036v.
I guess I should have said it will HELP prevent errors. 🙁
Is the voltage on pin 9 3.5v? or is it 0.0035v?
3.6mv = 0.0036v, not 0.036v.
I guess I should have said it will HELP prevent errors. 🙁
Is the voltage on pin 9 3.5v? or is it 0.0035v?
yes pin 9 is .0035v I red it wrong, I had to use better DVOM, and in my opinion that means no voltage present at that pin.
If 9 is at ground. Everything looks OK. Now you need to post the numbers with no remote voltage applied.
results are the same remote on or off, maybe I need to install the power FETs to get different results?
The voltages should change (especially on the 339) with/without the remote voltage. If you go from 3v (which I think you stated you had on the remote terminal with no remote voltage applied), the voltage on the 339 should change significantly. Check it again.
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