NO, do not replace the polypropylene caps!
For a start, if I do not see any electrolytic capacitors with visible damage, I would replace none.
What I would do, is connect an oscilloscope and find out what is wrong with the amp.
Replacing components at random is not a good idea.
For a start, if I do not see any electrolytic capacitors with visible damage, I would replace none.
What I would do, is connect an oscilloscope and find out what is wrong with the amp.
Replacing components at random is not a good idea.
Well can't "test" the caps, so it would be a start and have no info on ageing of these film caps.
Film caps are the last thing that can go wrong in an amplifier.
I don't remember that I had to replace one in the last 30 years.
(exepted transient suppressor class X or Y capacitors).
I don't remember that I had to replace one in the last 30 years.
(exepted transient suppressor class X or Y capacitors).
Silmic II, eh? They were not cheaping out on parts quality there.
Do you have any way of scoping the various supply voltages, in addition to measuring their DC values?
If the unit has that many hours on it, I would give any filter capacitors, the solder joints of regulator series transistors and those transistors themselves a good look. (Denon gear from this time is quite notorious for bad solder joints.) If you suspect a cap is degraded in ESR, solder a known-good one of approximately the same capacitance and a high enough voltage rating in parallel.
I don't remember the signal flow in these offhand - if the volume pot is the last thing ahead of the power amp and it still hums with volume turned down, chances are it's one of the Big Guys. If the volume is still followed by tone stages or anything else that involved the lower voltages, caps there would be suspect as well.
Do you have any way of scoping the various supply voltages, in addition to measuring their DC values?
If the unit has that many hours on it, I would give any filter capacitors, the solder joints of regulator series transistors and those transistors themselves a good look. (Denon gear from this time is quite notorious for bad solder joints.) If you suspect a cap is degraded in ESR, solder a known-good one of approximately the same capacitance and a high enough voltage rating in parallel.
I don't remember the signal flow in these offhand - if the volume pot is the last thing ahead of the power amp and it still hums with volume turned down, chances are it's one of the Big Guys. If the volume is still followed by tone stages or anything else that involved the lower voltages, caps there would be suspect as well.
Also without the tone/volume control (P. direct) the output stage makes buzzes/hums/noise. And with the tone/volume control it increases significantly: so it has problems and it's age.
The control unit (board 3707-2) is beneath the two giant transformers (too heavy too handle), and can only be reached by completely dismantling the amp (no separate access or visual...).
Sofar the most practical thing seems to me to bite the bullet recap it (for the next 14 years), and then partly reassemble and measure it.
If interested i can upload photo's.
The control unit (board 3707-2) is beneath the two giant transformers (too heavy too handle), and can only be reached by completely dismantling the amp (no separate access or visual...).
Sofar the most practical thing seems to me to bite the bullet recap it (for the next 14 years), and then partly reassemble and measure it.
If interested i can upload photo's.
Do you have normal (non distorted) sound and normal power output apart from the buzzing noise?
Does the hum or noise varies with the volume control?
Put a scope on the big power elco's and also on the voltage regulator board.
You need a schematic for a start.
Replacing components at random has no sense at all.
Does the hum or noise varies with the volume control?
Put a scope on the big power elco's and also on the voltage regulator board.
You need a schematic for a start.
Replacing components at random has no sense at all.
Item is 15-20years old filled with quality caps, I don't see the need for a recap, as pointed out above, better to fix the problem rather than random component replacement.
Sure, hum on both channels can be caused by tired power supply caps. It can also be caused by tired voltage regulators and,,,and,,,
How about a more systematic approach, run some basic tests and collect observations/symptoms...
Is hum mains 50/60Hz or rectified 100/120Hz? (probably 100/120Hz)
Does the unit have pre-out/main-in RCA connectors (didn't see them on the schematic)
Connect external pre/power amps ans note if hum remains
Do you have an oscilloscope? Both mine need work, in the meantime I've picked up a signal tracer on the bay for AUD35, ok for binary yes/no testing...
Suggest basic health check of power supply, measure dc voltages
Sure, hum on both channels can be caused by tired power supply caps. It can also be caused by tired voltage regulators and,,,and,,,
How about a more systematic approach, run some basic tests and collect observations/symptoms...
Is hum mains 50/60Hz or rectified 100/120Hz? (probably 100/120Hz)
Does the unit have pre-out/main-in RCA connectors (didn't see them on the schematic)
Connect external pre/power amps ans note if hum remains
Do you have an oscilloscope? Both mine need work, in the meantime I've picked up a signal tracer on the bay for AUD35, ok for binary yes/no testing...
Suggest basic health check of power supply, measure dc voltages