This amp will power up and produce good audio.After about 15mins it goes off.5mins later it will come back on and repeat the cycle.Am not sure if it is thermal problem but i lift the two thermistor away from the heat sink but saw no change in the cycle.Any idea what is happening there?
Does the power supply shut off?
Do you lose oscillation on the output transistors or does the oscillation remain and the audio mutes?
Do you lose oscillation on the output transistors or does the oscillation remain and the audio mutes?
I will assume the power supply shuts off because power let also goes off.I will check it tomorrow to make sure.
I forgot to check the signal on the outputs.
working
1:4.37
2:4.37
3:15.02
4:0.286
5:1.654
6:3.786
7:4.97
8:0.683
9:1.272
10:4.97
11:7.15
12:0.001
13:4.36
14:0.001
shutdown
1:3.702
2:3.688
3:12.43
4:0.001
5:1.421
6:4.12
7:4.31
8:0.185
9:0.185
10:4.32
11:7.76
12:0.001
13:3.714
14:0.001
working
1:4.37
2:4.37
3:15.02
4:0.286
5:1.654
6:3.786
7:4.97
8:0.683
9:1.272
10:4.97
11:7.15
12:0.001
13:4.36
14:0.001
shutdown
1:3.702
2:3.688
3:12.43
4:0.001
5:1.421
6:4.12
7:4.31
8:0.185
9:0.185
10:4.32
11:7.76
12:0.001
13:3.714
14:0.001
What is the DC voltage on the two resistors R63 and R73? Black probe on ground, read probe on the 4 terminals of the two resistors. 4 voltage readings.
Sorry. I missed this.
One problem that I see is that there is inconsistent readings on pin 5. It connects to the point where R63 and R73 connect. When the amp shuts down, the voltage isn't the same on the two resistors as well as pin 5. Were the readings in error or is the problem causing the inconsistent readings causing the shutdown?
One problem that I see is that there is inconsistent readings on pin 5. It connects to the point where R63 and R73 connect. When the amp shuts down, the voltage isn't the same on the two resistors as well as pin 5. Were the readings in error or is the problem causing the inconsistent readings causing the shutdown?
I think the readings drift because the amp is slowly recovering from what shut it down.Taking the reading is a challenge because the amp recovers very fast when i remove the bottom cover.
I pull both thermistor just to make sure they not triggering the shutdown.Maybe an IC is thermally shunting down?
I pull both thermistor just to make sure they not triggering the shutdown.Maybe an IC is thermally shunting down?
The board is out of the sink,I will mount it tomorrow to take reading.I found D19 burn open would that indicate something or it is part of another circuit?
D19 is between the preamp and primary grounds. It generally fails when a 12v source contacts the RCA shield.
Are you referring to the SG3526? It should not be getting really hot.
Is the IC shutting down due to a change of voltage on one of its input pins?
Are you sure that you don't have any defective power supply driver transistors?
What is the DC voltage on pin 18 of the 3526?
Is the IC shutting down due to a change of voltage on one of its input pins?
Are you sure that you don't have any defective power supply driver transistors?
What is the DC voltage on pin 18 of the 3526?
Went back to this amp today.I see good gate signal on all PS FET.
SG3526
working --- shutdown
1:4.96 ----- 4.23
2:3.778 ---- 0.002
3:4.22 ------ 0.109
4:4.69 ------- 0.008
5:4.18-------- 0.022
6:0.001------- 0.000
7:0.001 ------ 0.000
8:4.33 --------3.365 pulsing to about 3.772
9:3.735 ------ 3.082
10:1.995 ----- 1.794
11:0.003------- 0.002
12:4.63 -------- 4.15
13:6.66 -------- 0.001
14:15.65 -------12.59
15:0.001 ------- 0.000
16:6.67 --------- 0.001
17:15.67 --------12.59
18:4.96 ----------4.33
SG3526
working --- shutdown
1:4.96 ----- 4.23
2:3.778 ---- 0.002
3:4.22 ------ 0.109
4:4.69 ------- 0.008
5:4.18-------- 0.022
6:0.001------- 0.000
7:0.001 ------ 0.000
8:4.33 --------3.365 pulsing to about 3.772
9:3.735 ------ 3.082
10:1.995 ----- 1.794
11:0.003------- 0.002
12:4.63 -------- 4.15
13:6.66 -------- 0.001
14:15.65 -------12.59
15:0.001 ------- 0.000
16:6.67 --------- 0.001
17:15.67 --------12.59
18:4.96 ----------4.33
Last edited:
I'm going to have to try to check an amp I have here. There seem to be several problems. I'm going to try to replicate the shutdown to see how the voltages change.
I think the IC may be defective. I checked the voltage with and without B+ as well as with the shutdown pin grounded and the regulated output on pin 18 was a constant 5.01v.
It could be that the regulated voltage is being pulled down, causing the IC to shutdown but that wouldn't make the IC overheat?
Do you have another IC to replace this one?
If you replace it, you may have to temporarily remove R34 if the new IC won't function.
It could be that the regulated voltage is being pulled down, causing the IC to shutdown but that wouldn't make the IC overheat?
Do you have another IC to replace this one?
If you replace it, you may have to temporarily remove R34 if the new IC won't function.
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