Harman Kardon PM635 sound problem

[Lynyrd]

Hello.
Integrated amplifier HARMAN KARDON PM 635.
Strange problem.
Power on.The amplifier sounds clear, no problem. But after 1-2 minutes, the sound slowly disappears on both channels. After turning off for 10 minutes, the sound reappears for a few seconds and then slowly disappears again.

No bad soldering.

SM

HARMAN KARDON PM635 OWNER'S MANUAL Pdf Download | ManualsLib


Thank you.

 

[duncan2]

Certainly sounds like the typical result of a HR soldered connection.

But you have eliminated that so------- next on my list would be a faulty resistor .

 

[Lynyrd]

Ок, where I need to check this resistor?
now there is no sound at all

 

[nigelwright7557]

Check all the resistors for value.
Some might read oddly if in parallel with other devices.

My first stop is always a careful visual inspection. Look for bad soldered joints.
Check all connectors are tight.

Then start looking at voltages starting at power supply end.

 

[Lynyrd]

No bad soldering

 

[Lynyrd]

the sound appeared again

 

[Lynyrd]

No bad connection,no blown parts

 

[duncan2]

Thats a good point by Nigel , if you are now saying ---"no sound at all " is the amplifier still powered up ?

Voltages are ( approx ) 38 volts+/- DC .

If no voltages then check fuses for HR connections.

Schematic available on HiFi engine.

 

[Lynyrd]

Amplifier power on.
The fuse is ok.
Service manual on Poste #1
Now the sound is very good,but after 1-2 minutes nothing

 

[Mark Tillotson]

Perhaps its time for the cold-spray or insulated poking stick? Somethings heat sensitive in there, could be a cracked pcb trace, dry solder joint, damaged component, the first step is track down the sensitive part...

 

[Lynyrd]

NO BAD SOLDERING,NO BAD CONTACT !!!!!!!

No no no!

 

[duncan2]

What Mark was trying to point out was the logical engineering way to locate a fault like yours ,even TV engineers use spray or a heat gun to aim heat at different parts of a circuit to bring on the fault quicker.

Coolant spray can sometimes restore a faulty circuit long enough to locate the area of a fault but you seem pretty adamant that nowhere on your amplifier is faulty --yet you complain it cuts out and that I take it is with the power supply in good working order --yes ?

Clip on your meter to the plus and negative supply lines AT the OUTPUT --run your amplifier and watch your meter .

Try and remember we are working virtually not sitting at a workbench with a host of test equipment connected to your amplifier .

 

[bucks bunny]

NO BAD SOLDERING,NO BAD CONTACT !!!!!!!

No no no!

So you really did resolder every joint? You did not? Than this is an assumption only

 

[Lynyrd]

Yes all soldering points verified

 

[Lynyrd]

I m all veryfied, nothing..no bad soldering,no bad contact

 

[Lynyrd]

I'll go now turn on the amplifier

 

[Lynyrd]

Very good sound
but disappeared after 30 seconds

 

[Lynyrd]

and how should I cool these parts

 

[duncan2]

And did you do as I asked in post #12 ----- clip on your multi-meter to prove its not a power supply failure at the output supply to the output transistors ?

Cool the parts with a freezer spray.

 

[Lynyrd]

where should i place multimeter