Hi Jerrold, This reply is a little disjointed, but that's how it came
back to me...
I'd disconnect the various plugs in the unit, turn it on and then start
reconnecting plugs until I found the one that pops the fuse. Then at
least you've isolated the problem down to a section.
One thing just hit me: I did a job in north Jersey a couple of
years back and the unit was constantly blowing fuses. The problem
ended up being a combination of problems including a defective toggle
switch and shorted diodes in the drive motor circuitry.
The switch was broken internally. Since direct replacements are no
longer available, I had to fashion new contacts from an old toggle
switch that had the same basic design. That took about an hour.
Now it's coming back to me. The problem started when a toddler tried
to physically stop the roll from rewinding. That caused an overload
in the bridge rectifier (up by the drive motor circuitry) and shorted
out one or two of the diodes (can't remember for sure, but I think it
was two diodes). That problem in turn caused the power switch to arc.
(I remember the customer's son telling me it arced every time just
before the fuse blew out. He had tried replacing the fuse a number of
times before calling me in to troubleshoot the unit. I remember I was
a bit unsure of myself and told them that if I couldn't find and fix
the problem, I wouldn't charge them for the 130 mile round-trip or my
time. That will make you determined!)
So I'd start by unsoldering the diodes and checking the back-to-front
and front-to-back resistance. It might be that simple. As I recall,
one of the diodes that's in parallel with a charging capacitor was also
The two things that made the job difficult were the confined space and
the unavailability of direct replacement parts. I used parts from
Radio Shack and they worked fine. Make sure you have some good heat
sinks (I used clamping forceps) when unsoldering and soldering the
diodes and a soldering iron with a fine tip. It's cramped in there.
Hope this helps,
John A. Tuttle