Another Phase Linear 3300 Series 2 Pre Amp

After running without incident for a week at low volume the left channel was dead when I turned the unit on this morning. As I recall the right channel was dead when I first energized the unit after reflowing the solder joints. I left the volume control at a low level and began exercising controls from left to right. The selector switch had no effect, but when I rotated the Bass control the left channel popped in. What I don't understand is that the Tone switch was in the out (open) position - assuming this takes the Bass and Treble controls out of the signal path so not sure why rotating the Bass control had any effect. I should probably stick to wrenching on old English cars.

I've attached a pic of the arsenal I've assembled based upon the input from you folks, and want to make sure I'm using the correct products. I'll flush/clean the 2 gang pots with Deoxit F and finish with a drop of the fader lube. I plan to remove them from the board to facilitate access for cleaning - thinking I might as well open them up for best cleaning and lube, or should I leave them closed? I'm not certain if all of the push button switch internals are all metal or include plastic components, so wondering if it's safe to flush them with the D5 or D100. Appreciate any advice. Will leave the Alps pot alone at this point.

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It is most likely that the physical motion of turning the tone pot restored a marginal PCB connection somewhere rather than the pot being involved.

This is fairly classic behavior on some PL preamps, particularly the infamous PL4000 preamp, marginal solder joints.
 
Thanks for that - makes sense. Does that suggest it's something immediately adjacent to the pot or could it be anywhere? I'll reflow everything I didn't touch the first time around. In the meantime I've already got the tone pots off the board so might as well clean them. Didn't realize how large the openings are adjacent to the board - thinking a simple flush might be enough.IMG_4094.JPG
 
It could be anywhere on the board that has an intermittent. However, it is not the tone pots if you have the switch in the OUT position. I would recommend a careful look under magnification of all the solder joints. They are approaching 50 years old...
 
Thanks - I'll do that. Not sure what they're called but what look like solder tracks on the PCB - is it possible for a crack to develop there?
 
Cracked traces can be extremely difficult to locate, especially if they are under the resist coating. Bright light from behind the board can help.
Only had this a couple times but I won't forget the struggle.
 
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