Denon Amplifier PMA 720 AE packed in

[Marco Murray]

Hi there experts,
I have a Denon Amplifier PMA 720 AE and it's suddenly stopped working.
It's approx 4 yrs old.
It gets played loud occasionally.
Decided to play some music, sound was very low, turned it up louder, burning smell, switched it off.
Would no longer operate.
Checked speaker wires for any shorts but they were ok.
Removed lid.
Fuse F901 F2.5AL 250V had blown.
Replaced it. It blew again immediately.
Dismantled amp.
Looks like some small components have failed (pictures attached) but not sure if they are as a result of a more fundamental problem eg output transistors blown ?
Any advice gratefully received.
I'm handy with a soldering iron and have a multimeter but by no means am I an expert !
I'm happy to have a go at fixing it.
Thanks.

 

[duke37]

Have you sound a schematic (circuit diagram)?
Mono or stereo?
The resistors may be still in this world, they are designed to get hot.
The trouble could be in the output stage but if the amp is stereo and both channels are faulty, then it could be in the power supply.

How far are you from Matlock?

 

[Greenbriggs9]

Good evening. Did you get it working ? Mine has done the same

 

[Marco Murray]

Hi,
It's been a long time since I posted!
As it happens I did fix it.
Replaced all 4 main output transistors (don't forget the thermal paste) and re-soldered the burned out bits.
Can't remember if I replaced the overheated resistors. Think I did.
Still going strong, although I've added a hidden stopper underneath the main volume control knob to mechanically prevent anyone from turning the volume up too high. Kids haven't sussed it yet !
I reckon the original issue was caused by poor connections on cheap dodgy banana plugs from... guess where ?
Lesson learned.
Hope this helps.