need help onkyo m-5000 and m-5140

[ostie01]

Hi, everybody. I have 2 Onkyo power amplifier M-5000 and M5140.
Both have problem with power transistors.The transistor number is STK 4044 V (15 pins transistor). I bought 4 new transistor to replace those that were burned. When I turned on the amp and hookup a preamp , it played well at low volume but as soon as I crank up the volume maybe 1/3 of power, the transistor make a loud pop and smoke came out.I can let it play for hours at low volume and the transistors do not come hot at all.I have the servive manual but could not find any clue. They are very simple amp with very limited number of components on the main board.All the circuitry are inside the transistors. There's no bias adjustment.I know that these kind of power amp are not very high end but would like to find out what's going on .I don't want to replace those expensives transistors before I can find out what the problem is. A little help will be appreciate is somebody out there know that kind of amplifier. I like to repair power amp and I have fixed a lot of other brands like harman kardon , cambridge sony es and yamaha and many more but this is the first time this happen to me.

[onkyofan]

Still having trouble?

What ohm speakers are you running? These amps CANNOT handle 4 ohm loads. Speakers need to be 8 ohms.

I've repaired a few of these and have never had any trouble after repair.

Did you replace the heatsink compound between the transistor pack and the heatsink when you reinstalled the transistor pack?

These are very stable amps.

Hope some of this helps.

[ostie01]

Hi, thanks for the help, I have solved my problem with a new soldering iron and by grounding each pin before touching it with the iron tip. Thanks