Overheating Class A

[cln.white]

Hi, thanks for the replies. I have checked the two units I removed and the J162 reads very low resistance 140R across source and drain and the K1058 is dead. As far as the voltages go all measure 54.5V except the troublesome K1058/J162 pair where the J162 measures 33.4V

 

[cln.white]

Hi Here is a picture of the board. The problems are with the ones on the left of the picture

 

[AndrewT]

Clean off the soldered joints.
Check for shorting between the joints.
You can reduce the quantity of solder on many of the joints.
Check the 12 resistors to gate and from source.

Are those ferrites on the drain leads?

 

[cln.white]

The R47 resistor from source on J162 top left of picture dead. I will have to order, would I be better to change all to maintain balance? Yes, there is ferrites on all the drain leads, have read somewhere they are to combat oscillations.

 

[AndrewT]

You have spare resistors built into the PCB.

 

[cln.white]

OK, Now all reading around 54.6V.

 

[Eric]

Clean off the soldered joints.
Check for shorting between the joints.
You can reduce the quantity of solder on many of the joints.
Check the 12 resistors to gate and from source.

Exactly what I was going to say. Remove some of the solder from your FET legs and get some Flux Remover and clean up the PCB. I have had more than one problem from a sloppy solder joint that spilled just the smallest bit of solder across two pins, forming a short. On PCBs that have very narrow spacing around the pads, I run a very fine screwdriver between the pads after soldering, spray some flux remover, and inspect carefully under a bright light to make sure I didn't goof anything.

 

[cln.white]

Output at speaker terminals reading around 1R this is not right is it? What else to check? How do I test?

 

[Eric]

Following a short of the outputs, check your active parts - these tend to go first. Output transistors tend to be pretty robust, so it is likely they may OK. Check all diodes and all small signal transistors. Work backwards from the output and see what is "first" in the schematic and start there.