William Noble wrote:
now that you know the SCRs are bad (were the diodes also bad?) I'd suggest
you replace them with parts having a different form factor that is more
common - stud mounted diodes are common (I have some used ones for sale
soemwhere on my web page, but they are cheap), and most low power SCRs
nowadays mount via a single screw through a flange - your electronics supply
place can help you select modern parts that are electrically equivalent to
your old dead ones.

The diodes were dead short in on direction and both about 200 K ohms in the opposite.
That seemed OK to me but all the other diodes I had were in the 900 K ohm range so I
went ahead and ordered replacements


Check whatever was connected to the gate of the SCRs - it may have been hurt
also - typically SCRs fail short circuit, then blow an internal wire and go
open circuit (if they don't just explode their case)

Well I'll just have to see if replacing th four components does the trick or not.

Got quite a surprise today. Tried running one of my 60 volt DC motors (I thought they
were 90 volt motors) with a variac and my setup tripped the breaker in my power bar.
Checked and rechecked the circuits from the variac through the bridge and motor and
everything seemed logical. tried it again and again it tripped (not very smart
really). Then I happened to notice in small print on the very front of the variac
"360 cycles per minute" 6 HZ

Live and learn!

Thanks again
T


T
I de-soldered the four components and tested them all. I followed the test
guide for
the SCRs and wasn't totally sure they were shot until I tested an SCR from
an old
power supply. It behaved exactly as my instructions said it should. The
two SCRs in
the controller acted nothing like the good one. So I am confident that I
am on the
right track.

Had a little fun pressing the components out of the heat sinks, but I have
a set of
12 LC Vise Grips which have the reach to get in between the heat sinks and
with the
aid of a small pin taped to one jaw and a socket on the top end of the
component the
all pressed out slick as you could wish for. The internet instruction
suggested I
pry them out with a flat tip screw driver.

When pigs fly!!!

Will be 3 to 4 weeks to get the SCRs.

Gotta run