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.
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....
and 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....
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.
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.
Oh and it's looks like the sockets were stock.
One sheared input pot and one open circuit feedback pot. Great design, cheap pots ;) Dr. Lee had some very advanced thinking for the time in the design. Very interesting origins of the company too. Worth a bit of read....
unfortunately the new pots did not fit the old knobs...so two units got an upgrade to metal knobs...
cool picture. those knobs get me every time!