Scott Dorsey wrote:

Michael A. Terrell wrote:
tm wrote:


Are you sure it is not already a pulse width regulator? Those transistors
look like they are TO-220 packages, not TO-3.

I've seen 20W power resistors in TO-220 packages.

It does indeed look like a TO-220 from the pin spacing (since there are no
actual transistors in the photos, just spots from which they were removed).


All those photos only show one side. I full reverse engineering
should be done to draw a full schematic but I've never had my hands on
that module. It would probably take a couple of them, because ot the
potting.


But if it had been a PWM device, there would have been some filtering in
there, inductors and capacitors to keep the noise from getting into the
power lines. Designing clean and quiet PWM controllers is not quite as
trivial as some folks have made it out to be.

Have you looked at the National Semiconductor (Now part of T.I)
'Simple Switcher' series of controllers? Generally only one inductor
and a couple small electrolytics. A lot simpler than older designs, and
little noise because of the small footprint.


PWM has been around longer than SMT parts.

Maybe it is transients from the motor that are causing the failures.

This is possible, if it is the transistors that are failing. I don't see
any big protection diodes in there either.

If it's a RoHS soldering issue, though, I would not be surprised.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."


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