Alchemist power supply

[adrianjones]

Hi. I have purchased some quality replacement caps for the power supply of my Alchemist Pre amp(stand alone unit). I have so far changed 4 of the caps and notice that the PCB is blackened on the track side of a resistor on one channel (stereo amp) and less so on its opposite channel resistor. All these resistors measure 31/32 Ohm.
My question is, will the full replacement of all caps(16) reduce the heat being generated by the resistors, therefore, no need for concern? Or, do I need to replace the resistors?
The unit will be around 16 years old and has never been serviced before.
Thanks.

 

[JonSnell Electronic]

The capacitors will not keep the resistors cool. It is usual for power dissipating resistors soldered too close to the PCB to discolour the board.

 

[Mooly]

Discolouration of PB material is normal in the presence of heat. I wouldn't worry to much if the unit is working normally. Its also far from uncommon for commercial equipment to be poorly designed with regard to heat dissipation and the suitable rating of components used.

 

[adrianjones]

2 pics are attached. One of the darkened PCB and one with the new caps in place.
Many thanks for your replies.

 

[Mooly]

The discolouration from heat is normal, but as you mentioned earlier, it is very different to the other side. One possible reason (assuming the thing is basically OK and working) could be that the heat has dried out the caps and as such the resistor is seeing more ripple voltage across it which makes it run hotter.

 

[adrianjones]

Yes, that was my thought. The old caps were basic 85oC Nover. And being over 16 years old, maybe not so good. New caps are quality Vishay and Panasonic. Many thanks for your input.

 

[Mooly]

The caps you have fitted far exceed the original <NOVER> type

And good luck with the recap.

 

[adrianjones]

Just spent 3 hours enjoying some music. There was a very slight graininess before that is now totally gone. Also the sound seems generally improved in terms of treble detail and clarity. The power supply case did not get warm either, so all round I'm very pleased.

 

[Mooly]

That's great to hear you should be good to go for another couple of decades now