You've given me some good ideas on things to check. Thanks for your
interest in my problem.

Some observations:

The 110V incandescent bulb stays lit all the time.
The board uses three Omron 24V relays to do its thing. One of them is an
open type, and its contacts are in good shape.
On the bench I can't hear any relays operate when shorting the up/down
button terminals.
I don't see any suspicious looking solder joints.
Don't see any burned up or darkened components.
Don't see any cracked or melted circuit board traces.
This opener has no optical safety sensors.
There is a 16-pin integrated circuit on the board made by TI. Cannot find
the number anywhere on the Web. Called TI. They could not identify it
either and concluded that it was an ASIC.

More questions:

What effect on the circuitry does the optical speed sensor on the motor
shaft have? Does its output need faked with the main board on the bench for
troubleshooting?
How do the up and down force limiters work?

wrote in message
ups.com...

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.