I have a Phase Linear 4000 series 2 that has an intermittent output on one channel. I had thought it was one of the pushbuttons at first as sometimes the channel would come back after cycling the buttons. My clue should have been that it never seemed to be the same button. Trying it last night I also had it work once when I put upwards pressure on the input cable of the source I was trying. My only other clue is that there is sound from both channels when switched to mono. This gets me thinking that it may possibly be a cold solder joint. So my questions are, should I trouble shoot with a non conductive probe to see if I can apply pressure to the board while it is running to at least get an idea of where this might be, or should I just carefully take it all apart and replace all electrolytics while I am in there and hope that I can find the problem? Also while I am in there are there any known tricks or upgrades I can perform such as transistors or opamps from this century? Also I dont want to break the bank, but I also dont want to cheap out, so would I be ok with just run of the mill brand name caps? Finally, should one upgrade one board at a time in a unit like this and test it or just go whole hog and take a chance? Thank you in advance for any input. ( :
The preamp likely uses 1970's carbon film resistors which are noisey compared to now low cost 1% metal film types. Don't waste your money on expensive bulk metal foil or caddocks ( i use them in my best system) as the phase linear circuit is too compromised with signal processing to benefit from them.
I had a similar vintage PL preamp some time back, but not the 4000. Maybe the 4000 is better but IMO the construction quality was run of the mill and the thing was physically difficult to work on. Component quality was uniformly below average. I wouldn't do anything beyond find the specific problem and fix it, trying not to do any additional damage in the process. You could have a cracked trace, bad solder joint or even a control IC that's pressure sensitive. My usual luck with these types of problems is that they get better just by messing around with it, making it impossible to find the root cause, but the unit is still too unreliable to use. Try tapping with a plastic rod, heat, freeze mist, flexing and a really good inspection of every joint and trace under bright light and a strong magnifier.
Thanks Conrad, from what I have read the lower numbered amps were actually better due to the lack of processing circuits. I have narrowed the area down to the board that the source selector is soldered to. Light flexing brought the channel in and out. You are also right in the fact that this is physically a very difficult amp to work on. It looks simple but it is not unlike a Rubik's Cube to take apart. I am going to do the obvious first and clean all pots and pushbuttons while I have it apart. I will also reseat any components that can be. I have looked closely at all the electrolytics and there is no bulging caps or any signs of leakage. Listening to it with the board flexed it is very quiet and still sounds decent after all these years. Once I have performed the cleanup I will do a listening and comparison against some other units I have accumulated and see if it warrants an upgrade.
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