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Lexicon PCM 41- 3 units Various Repairs

3 PCM 41 units in for repairs.  These are some of my favourite delays, many fond memories playing with these in feedback.  

PCM 41 Face

PCM 41 Top Cover off

pcm 41 bottom cover off

The first unit had a blow cap in the -ve power supply rail. Clearly someone had previously replaced the power supply filter caps...I will clean ip that repair a bit.  I don't like to the old silicon on the pcb...and the would prefer a cleaner solder job....

pcm 41 bad capand yes the blown cap is pretty  obvious ;)  I also don't like the regulator sockets used.

It also had a broken 4 pin pot... yes four pins...the fourth pin being the center tap of the rheostat. 

Interesting design, very impressive actually....

Comments

Link555 Wed, 07/14/2021 - 05:56

In reply to by paulears

paulears wrote: Was the socketed regulator original? I’ve not seen that before, but as many were run so near the limit, it’s quite a good idea as retested replacements messes up the board doesn’t it.

I am not a big fan of socketing voltage regulators, sockets introduce impedance and can affect the thermal dissipation. As well with the constant thermal expansion and contraction of turning the unit on and off, it doesn't take long to loosen the contact points.

Given a proper design that take into account the thermal dissipation requirements of a regulator a properly soldered will last far longer than a socketed IC...IMHO.