On the positive and negative voltage feeds to the output transistors , if you cant find that then on the power supply itself although that doesn't cover all possibilities, you just watch for a voltage drop when it goes faulty.
as you descripted, both channel begin to fade after 2 mins.
It could be something that trigger the protection circuit, the protection circuit controls the input power supply of both channel.
download the schematic from the following website which need no signup.
HARMAN-KARDON PM635 SM Service Manual download, schematics, eeprom, repair info for electronics experts
according to the schematic
check Q1, Q2, Q3, Q4, (protection circuit)
check the voltages when turn on and sounds normal..
check the voltages when the sound fade away.. no sound.
if the voltages appear different, find the bad component.
It could be something that trigger the protection circuit, the protection circuit controls the input power supply of both channel.
download the schematic from the following website which need no signup.
HARMAN-KARDON PM635 SM Service Manual download, schematics, eeprom, repair info for electronics experts
according to the schematic
check Q1, Q2, Q3, Q4, (protection circuit)
check the voltages when turn on and sounds normal..
check the voltages when the sound fade away.. no sound.
if the voltages appear different, find the bad component.
i think it is more a muteing circuit.......
a protection system has relays inside that cut off the psu-unit or so.....
i would measure all voltages in that circuit and look for bad electrolytic caps.
a protection system has relays inside that cut off the psu-unit or so.....
i would measure all voltages in that circuit and look for bad electrolytic caps.
A relay cuts off the output to the loudspeakers depending on the circuit design for large DC offset /over current/delay at switch on to stop "thump " in loudspeakers and various other faults .
In processor controlled amplifiers this can become quite complicated as digital circuits control its function.
You can also get relays in the power supply to safeguard the amplifier or even the mains transformer --many many different circuits exist.
Modern solid state amplifiers have electronic power supplies that do all the functions of a relay.
In processor controlled amplifiers this can become quite complicated as digital circuits control its function.
You can also get relays in the power supply to safeguard the amplifier or even the mains transformer --many many different circuits exist.
Modern solid state amplifiers have electronic power supplies that do all the functions of a relay.
I put this in a separate post as I just missed your last post .
If the voltage stays on and you say no soldering problems then its down to loss of signal due to a faulty component.
As this cuts off both channels then the fault must be near the input .
If the voltage stays on and you say no soldering problems then its down to loss of signal due to a faulty component.
As this cuts off both channels then the fault must be near the input .
Lynyrd
its very nice of you to say please.
did you follow the suggestion on #22,
(its a suggestion not an instruction, I am old but still learning.)
In the protection circuit, where you locate the difference in voltages between normal stage and no sound stage, the fault will be easier to find.
When overcurrent is detected, the protection circuit can shut off the current supply to the input diff. of both channels and thus no output. this amp is protected in this way,
but when components fail, the protection circuit could cause no sound.
if it happens after 2 mins, C8 and other components in the protection circuit could be the culprit.
According to the schematic, in the protection circuit
Q3 collector pin supply current to the input diff. of both amps via two 68k resistor, R11,R12.
when Q3 is cut off, no current to the input diff. thus no output---no sound.
R8, R9 provide a turn on -0.6v bias to Q3 when normal. if this -0.6v not present then Q3 shut off. .. no sound.
R4, R5, Q1 provide a -2.5v supply to R8 68k to turn Q3 on.
if this -2.5v not present then Q3 shut off. no sound.
when Q2 was turned on by Q4 via R6 4.7k,R7 47k resistor,
minus2.5 volt would be shorted to ground.
no -2.5v, no -0.6v to Q3, Q3 shut off......no sound.
Q5, Q6 detect the output current,
when overcurrent was detected, Q5 Q6 would be triggered to turn on,
Q4 is turned on via R13 R15 R16 R21, provided by the current of Q5 or Q6 or both.
D5, D7, C6 provide a -5.4v supply for the protection circuit and all led.
any failure of the components in the protection circuit could cause malfunction and cause no sound.
(please point out wherever there is not correct .)
its very nice of you to say please.
did you follow the suggestion on #22,
(its a suggestion not an instruction, I am old but still learning.)
In the protection circuit, where you locate the difference in voltages between normal stage and no sound stage, the fault will be easier to find.
When overcurrent is detected, the protection circuit can shut off the current supply to the input diff. of both channels and thus no output. this amp is protected in this way,
but when components fail, the protection circuit could cause no sound.
if it happens after 2 mins, C8 and other components in the protection circuit could be the culprit.
According to the schematic, in the protection circuit
Q3 collector pin supply current to the input diff. of both amps via two 68k resistor, R11,R12.
when Q3 is cut off, no current to the input diff. thus no output---no sound.
R8, R9 provide a turn on -0.6v bias to Q3 when normal. if this -0.6v not present then Q3 shut off. .. no sound.
R4, R5, Q1 provide a -2.5v supply to R8 68k to turn Q3 on.
if this -2.5v not present then Q3 shut off. no sound.
when Q2 was turned on by Q4 via R6 4.7k,R7 47k resistor,
minus2.5 volt would be shorted to ground.
no -2.5v, no -0.6v to Q3, Q3 shut off......no sound.
Q5, Q6 detect the output current,
when overcurrent was detected, Q5 Q6 would be triggered to turn on,
Q4 is turned on via R13 R15 R16 R21, provided by the current of Q5 or Q6 or both.
D5, D7, C6 provide a -5.4v supply for the protection circuit and all led.
any failure of the components in the protection circuit could cause malfunction and cause no sound.
(please point out wherever there is not correct .)
I think that Q1 is faulty.
-5.4v input ok,but no -2.5v and no sound
When Q1 is cold -2.5v ok and sound o.k.
-5.4v input ok,but no -2.5v and no sound
When Q1 is cold -2.5v ok and sound o.k.
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Interesting
please note
the culprit could be any component in the protection circuit, of course other areas too,
to find the faults, it needs your skill and patience to locate it.
please note
the culprit could be any component in the protection circuit, of course other areas too,
to find the faults, it needs your skill and patience to locate it.
when no sound after 2 mins,
check the voltage at the joint of R4, R22 and D6. (-5.4v)
if no voltage or lower.
check the D6 zener HZ6A.. and R4, R22..
check the joint of R22, R24 -5.4v
check the voltage at the joint of R4, R22 and D6. (-5.4v)
if no voltage or lower.
check the D6 zener HZ6A.. and R4, R22..
check the joint of R22, R24 -5.4v
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Hi, please check capacitors C405 (left channel) and C406 (right ch.).
These are 220uF / 6.3V and known to be troublesome.
Replace them anyway with the same capacitance, but higher voltage.
Something like 200uF / 35V will do.
These are 220uF / 6.3V and known to be troublesome.
Replace them anyway with the same capacitance, but higher voltage.
Something like 200uF / 35V will do.
According to the schematic,
in the protection circuit
A: Q3 supply current to the input diff. of both amps via two 68k resistor, R11,R12.
B: when Q3 is cut off, no current to the input diff. thus no output--- no sound.
C: R8, R9 provide a turn on -0.6v bias to Q3 when normal.
if this -0.6v not present then Q3 shut off. .. no sound.
D: R4, R5, Q1 provide a -2.5v supply to R8 68k to turn Q3 on.
if this -2.5v not present then Q3 shut off. no sound.
E: when Q2 was turned on by Q4 via R6 4.7k,R7 47k resistor,
minus2.5 volt would be shorted to ground.. no sound.
( if Q4 was defective, leakage...., it would turn on Q2..) no sound.
F: no -2.5v, no -0.6v to Q3, Q3 shut off......no sound.
G: Q5, Q6 detect the output current,
when overcurrent was detected, Q5 Q6 would be triggered to turn on,
Q4 would turned on via R13 R15 R16 R21,
provided by the current of Q5 or Q6 or both.
H: D5, D7, C6 provide a -5.4v supply for the protection circuit and all led.
if no -5.4v, no sound.
I: R22, D6 zener, if no -5.4v..... no sound.
any failure of the components in the protection circuit could cause malfunction and no sound.
(please point out whatever incorrect .)
in the protection circuit
A: Q3 supply current to the input diff. of both amps via two 68k resistor, R11,R12.
B: when Q3 is cut off, no current to the input diff. thus no output--- no sound.
C: R8, R9 provide a turn on -0.6v bias to Q3 when normal.
if this -0.6v not present then Q3 shut off. .. no sound.
D: R4, R5, Q1 provide a -2.5v supply to R8 68k to turn Q3 on.
if this -2.5v not present then Q3 shut off. no sound.
E: when Q2 was turned on by Q4 via R6 4.7k,R7 47k resistor,
minus2.5 volt would be shorted to ground.. no sound.
( if Q4 was defective, leakage...., it would turn on Q2..) no sound.
F: no -2.5v, no -0.6v to Q3, Q3 shut off......no sound.
G: Q5, Q6 detect the output current,
when overcurrent was detected, Q5 Q6 would be triggered to turn on,
Q4 would turned on via R13 R15 R16 R21,
provided by the current of Q5 or Q6 or both.
H: D5, D7, C6 provide a -5.4v supply for the protection circuit and all led.
if no -5.4v, no sound.
I: R22, D6 zener, if no -5.4v..... no sound.
any failure of the components in the protection circuit could cause malfunction and no sound.
(please point out whatever incorrect .)