Silver Surfer wrote:

Need a schematic for the printed circuit board in my Craftsman garage door
opener. Did lots of Googling. Found nothing. Learned that The Chamberlain
Group makes the openers for Sears. Contacted them and asked for a
schematic. They said the board is proprietary,

I've found that 70% of the people who say "It's proprietary" simply
don't know.

Chamberlain has some real technicians who can sometimes be reached if
you ask a specific enough question, and I was once able to speak to one
by getting technical enough about a safety defect. But I doubt they'll
give you a schematic, and instead you'll have to trace out the pins
from the processor (probably Zilog or Microchip) to the relays. Most
of the failures tend to be from cracked solder joints (motor
vibration), a bad motor capacitor, leaky electrolytic capacitors, burnt
relay contacts (if you can't find new relays that fit, try substituting
the overhead lamp relay for one of the motor relays), or shorted relay
driver transistors and the diodes meant to protect them from relay coil
back EMF. Usually the back EMF won't damage the processor or control
circuitry. If your Sears/Chamberlain is like the one I bought in the
early 1990s and has 2 circuit boards, I wouldn't be surprised if the
pins that connect them together (like square wire wrap pins) have
corroded. If your door will open but not close, check for the wires
being broken right where they enter the optical receiver and sender
boxes. Also, just becuase the indicator light for them shines steadily
doesn't mean they're aligned well enough.