On Aug 6, 10:33?am, "James Sweet" wrote:
The power supply,magnetron, and door switches are all quite simple.
Easy to diagnose (imho). Hard to believe that somehwere there isn't a
schematic for the display/control board. And I find it harder to
believe that the manufacturer of the SMD transistors would take the
time to print a number on them and it not be cross referenceable. I've
found cross for the good transistors, but the bad one illudes me.
Guess it rerally is a throw away item.

A schematic exists for the control board, but it will be an internal asset
to the company that designed the board. Many thransistors in this sort of
thing are house numbered for internal identification. What is wrong woth the
unit? You should be able to test components and diagnose the board without a
schematic. It's very rare for me to have one for anything I fix.

The unit is question is the display board. The other functions
(anunciator, key press, control) all work. Only the display is non-
functional (as far as I can tell).
The offending part was smoked. I pieced the parts back together to get
what i believe is the correct number. That's why I'm unable to tell if
it's a PQ40 or PO40 and the "4" is a guess as well. Most of the
body(SMD part) was held in place by silocone gell applied for other
reasons.
My next attempt will to be to try either an NPN or PNP (through hole
part) in it's place and see what happens. 3 pins, nine possible
combos, 2 types, should only take an hour or so.. That's assuming it's
not a vreg, vref, fet, or duel diode..... Sure mis sam's
photofacts )