Those resistors were likely overheating because the gates of one or more output transistors were charged and there was current flowing through the protection circuit components. With the rest of the components back in the circuit, this shouldn't be a problem. Remove the jumpers before replacing the rest of the components. Don't power it up again until you've replaced everything that's missing.
Yes, the supply seems to be OK.
Yes, the supply seems to be OK.
From all the excitement I forgot to check this part:
LM317T input pin measures: 52V
LM317T output pin measures: 20.8V
LM317T adjust pin measures: 19.5V
LM337T input pin measures: -52V
LM337T output pin measures: -19.4V
LM337T adjust pin measures: -18V
I've also measured the OP-AMPs input voltage:
All TL072C's measure 34.7V between pin 4 (Vcc-) and 8 (Vcc+).
The LM833M measure 34.7V also between pin 4 (Vcc-) and 8 (Vcc+).
The Right speaker output measure -34.4V
The Left speaker output measure -0.006V
Also checked voltage from TL494C and LM339D:
TL494C between pin 7 (Vcc) and 12 (GND) measures 19.88V
LM339D between pin 3 (Vcc) and 12 (GND) measures 19.88V
I've got the amplifier on for about 5 minutes now and the following parts are warm/hot:
Voltage Regulators. LM317T is hotter then LM337T.
The OP-AMPs are warm but not hot.
TL494C is also warm, warmer then the OP-AMPs.
LM339D next to the TL494C is cool.
Power supply FETs are warm but not hot. The toroid is also warming up but its not hot.
All output FET's are cool.
After about 10 minutes, the amp draws 1.144A (Voltage supplied at B+ and GND = 13.07V).
Have a good weekend
Perry Babin said:
LM317T input pin measures: 52V
LM317T output pin measures: 20.8V
LM317T adjust pin measures: 19.5V
LM337T input pin measures: -52V
LM337T output pin measures: -19.4V
LM337T adjust pin measures: -18V
I've also measured the OP-AMPs input voltage:
All TL072C's measure 34.7V between pin 4 (Vcc-) and 8 (Vcc+).
The LM833M measure 34.7V also between pin 4 (Vcc-) and 8 (Vcc+).
The Right speaker output measure -34.4V
The Left speaker output measure -0.006V
Also checked voltage from TL494C and LM339D:
TL494C between pin 7 (Vcc) and 12 (GND) measures 19.88V
LM339D between pin 3 (Vcc) and 12 (GND) measures 19.88V
I've got the amplifier on for about 5 minutes now and the following parts are warm/hot:
Voltage Regulators. LM317T is hotter then LM337T.
The OP-AMPs are warm but not hot.
TL494C is also warm, warmer then the OP-AMPs.
LM339D next to the TL494C is cool.
Power supply FETs are warm but not hot. The toroid is also warming up but its not hot.
All output FET's are cool.
After about 10 minutes, the amp draws 1.144A (Voltage supplied at B+ and GND = 13.07V).
Have a good weekend
The output from the regulators seems high. I'd expect it to be ~15v. Measure directly across the output and adjust pins. Do you have ~1.25v on each regulator?
With the jumpers in place, you shouldn't have -36v on the outputs unless you have a defective output transistor. Confirm that R44 and R48 are within tolerance (amp off, confirm that voltage across speaker terminals is essentially 0v).
With the jumpers in place, you shouldn't have -36v on the outputs unless you have a defective output transistor. Confirm that R44 and R48 are within tolerance (amp off, confirm that voltage across speaker terminals is essentially 0v).
The result of my previous post were done with all the missing components still out. I didn't notice that you replied.
Voltage measured between Output and Adjust:
LM317T = 1.24V
LM337T = 1.24V
I've removed the jumpers on the Right and measured the FETs (in circuit). I get somewhat the same results as in Post #58
The resistors measure:
R44 [5111] = 5.12K ohm
R48 [5111] = 5.11K ohm
Voltage measured between Output and Adjust:
LM317T = 1.24V
LM337T = 1.24V
I've removed the jumpers on the Right and measured the FETs (in circuit). I get somewhat the same results as in Post #58
The resistors measure:
R44 [5111] = 5.12K ohm
R48 [5111] = 5.11K ohm
Done some testing
Unhooked all Drain leads from the circuit on the Right outputs (IRF9640, IRF640), Source and Gate are still connected.
When I power up the amp, with the jumpers in place and all of the Drains out of the circuit I measure 0.012V on the right speaker output.
With the amp powered off and the Drain disconnected from the circuit, I've checked the output FETs.
Results:
IRF640's measure ~.520 (D- , S+)
IRF9640's measure between 1.020 and 1.042 (D+, S-)
With the Drain leads of the IRF640's back in circuit and the jumper in place I powered the amp back up. I measure -0.012V on the right speaker output.
Unhooked the Drain leads of the IRF640's from the circuit and connected the Drain leads of the IRF9640's. Powered the amp up with the jumpers in place and measured -34.3V on the right speaker output.
So one or more IRF9640's are causing the right speaker output to rise to ~-34V.
With all the Drain legs of the output FETs pulled out of the circuit, I connected the Drain legs one by one back in the circuit to check which one is the culprit.
Results (Drain connected from / measured right speaker output):
Q311 = -0.12V
Q312 = -0.12V
Q313 = -0.12V
Q314 = -29.8V
Q315 = -33.4V
It seems that Q314 and Q315 are both the cause of this matter or some of the components connected to them.
Cut Q314 and Q315 completely out of the circuit and measured them.
Results (D+, S-):
Q314 = 1.020
Q315 = 1.047
With those two out of the circuit, I measured the Gate resistor and the resistor connected to the Source. They are all good.
Installed two new IRF9640’s and powered the amp up with only those two connected to the circuit (Jumper wire also connected). I measure 0.012V on the right speaker output
.
With all the other Drain legs back in circuit and the amp powered up (with the jumper in connected) I measure 0.012V on the right speaker output.
So now the speaker output voltages are:
Left: -0.006V
Right: 0.012V
What you think? Any good?
Unhooked all Drain leads from the circuit on the Right outputs (IRF9640, IRF640), Source and Gate are still connected.
When I power up the amp, with the jumpers in place and all of the Drains out of the circuit I measure 0.012V on the right speaker output.
With the amp powered off and the Drain disconnected from the circuit, I've checked the output FETs.
Results:
IRF640's measure ~.520 (D- , S+)
IRF9640's measure between 1.020 and 1.042 (D+, S-)
With the Drain leads of the IRF640's back in circuit and the jumper in place I powered the amp back up. I measure -0.012V on the right speaker output.
Unhooked the Drain leads of the IRF640's from the circuit and connected the Drain leads of the IRF9640's. Powered the amp up with the jumpers in place and measured -34.3V on the right speaker output.
So one or more IRF9640's are causing the right speaker output to rise to ~-34V.
With all the Drain legs of the output FETs pulled out of the circuit, I connected the Drain legs one by one back in the circuit to check which one is the culprit.
Results (Drain connected from / measured right speaker output):
Q311 = -0.12V
Q312 = -0.12V
Q313 = -0.12V
Q314 = -29.8V
Q315 = -33.4V
It seems that Q314 and Q315 are both the cause of this matter or some of the components connected to them.
Cut Q314 and Q315 completely out of the circuit and measured them.
Results (D+, S-):
Q314 = 1.020
Q315 = 1.047
With those two out of the circuit, I measured the Gate resistor and the resistor connected to the Source. They are all good.
Installed two new IRF9640’s and powered the amp up with only those two connected to the circuit (Jumper wire also connected). I measure 0.012V on the right speaker output
.With all the other Drain legs back in circuit and the amp powered up (with the jumper in connected) I measure 0.012V on the right speaker output.
So now the speaker output voltages are:
Left: -0.006V
Right: 0.012V
What you think? Any good?
All missing parts are now in. Removed the jumper wires and powered it up. Also replaced D20, D21 and U3 because the leads had broken off.
(note that the new rectifiers are STTH1502's and not STRP1520D's)
At start up its draws 3A for about 2 seconds (charging caps), then its at idle current but quickly after the current dropped to idle it suddenly draws 3A for an instant and then goes back to idle. It keeps repeating the last part over and over again (draw 3A, idle, 3A, idle, 3A idle etc.).
My multimeter isn't fast enough to check the speaker output but for what I can see it doesn't go beyond 0.046V (left) and -0.019 (right).
What could be causing the amp to go in this cycle 3A, idle, 3A etc. ?
Is it because the new rectifiers are from a different type?
Yes it produces audio but only for an instant (because of the cycle).
The blue potentiometers on the pcb are turned counter clockwise and the gains are both in center position.
(note that the new rectifiers are STTH1502's and not STRP1520D's)
At start up its draws 3A for about 2 seconds (charging caps), then its at idle current but quickly after the current dropped to idle it suddenly draws 3A for an instant and then goes back to idle. It keeps repeating the last part over and over again (draw 3A, idle, 3A, idle, 3A idle etc.).
My multimeter isn't fast enough to check the speaker output but for what I can see it doesn't go beyond 0.046V (left) and -0.019 (right).
What could be causing the amp to go in this cycle 3A, idle, 3A etc. ?
Is it because the new rectifiers are from a different type?
Yes it produces audio but only for an instant (because of the cycle).
The blue potentiometers on the pcb are turned counter clockwise and the gains are both in center position.
Try it again but at the lowest volume possible (or with no input signal). It could be shutting down because the output current demand is dragging the 12v power supply voltage down too far.
If that's not it and if the blue pots are fully counter-clockwise, measure the DC voltage across each of the 0.1 ohm resistors to see if one has a higher voltage. The voltage will pulse so you'll have to hold the meter on each resistor for several seconds.
Also monitor the temperature of each channel's outputs to see if one channel (or even one FET) is getting hotter than the other.
If that's not it and if the blue pots are fully counter-clockwise, measure the DC voltage across each of the 0.1 ohm resistors to see if one has a higher voltage. The voltage will pulse so you'll have to hold the meter on each resistor for several seconds.
Also monitor the temperature of each channel's outputs to see if one channel (or even one FET) is getting hotter than the other.
I think I spotted the problem.
First I had the Bias adjust pots (?) fully counterclockwise like this:
With them in center position, the amp powers up and stays on. Music plays crisp, no distortion.
I guess I had the pots clockwise instead of counterclockwise. Now the output FETs aren't running as hot as they did before like in the picture.
What do you think?
The only thing that rapidly heats up now is voltage regulator U3 (LM317T).
First I had the Bias adjust pots (?) fully counterclockwise like this:
With them in center position, the amp powers up and stays on. Music plays crisp, no distortion.
I guess I had the pots clockwise instead of counterclockwise. Now the output FETs aren't running as hot as they did before like in the picture.
What do you think?
The only thing that rapidly heats up now is voltage regulator U3 (LM317T).
It appears to be working properly. The regulators will run hotter than the rest of the components at idle. When you get them clamped to the sink, they will operate at much lower temperatures.
Don't play it for more than a few seconds until you have the transistors soldered to the MEHSA strip and have the strip clamped to the sink.
You'll have to remove the old heatsink compound and replace it with new compound.
Don't play it for more than a few seconds until you have the transistors soldered to the MEHSA strip and have the strip clamped to the sink.
You'll have to remove the old heatsink compound and replace it with new compound.
Sorry for the late reply.
Here is a complete overview of the parts that I renewed:
Green: Components that were defective or needed to be replaced.
Blue: Components needed to be replaced because a leg had broken of or that I wanted to have replaced with fresh new ones.
Purple: Fixed burnt/broken trace
I've got the amp in my car, and it plays great !!
I couldn't have done the repair without the guidance of Perry Babin
. I can't thank you enough for helping me.
Here is a complete overview of the parts that I renewed:
Green: Components that were defective or needed to be replaced.
Blue: Components needed to be replaced because a leg had broken of or that I wanted to have replaced with fresh new ones.
Purple: Fixed burnt/broken trace
I've got the amp in my car, and it plays great !!
I couldn't have done the repair without the guidance of Perry Babin
. I can't thank you enough for helping me.woutzor & Perry Babin
I've been following this with considerable interest, I often see amps on ebay which are faulty and go for very little and wonder if I could fix one. This thread has been very informative and the large pictures really help to illustrate what can be a rather confusing aspect of posts on the forums.
Quite a considerable number of components were replaced, can I ask how much the replacement parts cost in total?
I've been following this with considerable interest, I often see amps on ebay which are faulty and go for very little and wonder if I could fix one. This thread has been very informative and the large pictures really help to illustrate what can be a rather confusing aspect of posts on the forums.
Quite a considerable number of components were replaced, can I ask how much the replacement parts cost in total?
These amps (800a2 and similar models) destroy more parts than any other amp their size. Most amps can be repaired much more easily.
If you're buying amps to resell for profit, it's difficult to do via eBay. If you simply want a few more amps to use, buying cheap amps and repairing them is a good option.
If you're buying amps to resell for profit, it's difficult to do via eBay. If you simply want a few more amps to use, buying cheap amps and repairing them is a good option.
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