[TenTec] More OT: Acoustic Switching PS Noise

[Wade Staggs]

*The transistor that is getting hot, may be doing that because it is leaky.
Or in other words has developed leakage between any of the 3 elements to
another. You may be able to remove both transistors and check them on the
RX1 scale of your DVM or Analog Meter. Standard Diode test back and forth
between the Base and Collector and the Base and Emitter. I would also
suggest moving the meter to something like the Rx1K scale in the Ohm Meter
setting and checking both transistors for leakage/resistance. The
resistance between the base to collector and base to emitter and such all
the way around on the RX1K Scale of your DVM or VOM should have an infinite
reading on that scale. Transistors are Cheap. My advise would be to check
this out before something avalanches and takes out several components.
Also, check the Capacitors in circuit if, you can find a friend with an ESR
Meter. Look closely at the Capacitors to see if any have a Domed look at
the top or are leaking at the bottom. Best of Luck with it my Friend.*
*                                           73 from Wade/KJ4WS*



On Sat, Jun 28, 2014 at 7:49 AM, Kim Elmore <cw_de_n5op at sbcglobal.net>
wrote:

> I'd post this somewhere else, but I don't know where that would be, so I
> avail myself of your collective wisdom yet again. Recall that I noticed a
> lot of acoustic "singing" from a small switching PS transformer on the
> PIEXX microprocessor board installed in my TS-930S.
>
> I removed the heat shrink tubing that had been holding the transformer
> halves together and installed the clip that is now used (very clever clip)
> and that helped but did not eliminate the problem. There are two small
> MOSFET transistors at the heart of the switching supply and I found that
> one gets VERY hot -- too hot to touch while the other does not. After about
> 30 min of operation, the transformer also gets uncomfortably hot. This can
> only be caused by excessive current somewhere. What I don't understand is
> why only one transistor gets hot and not both. I touched each capacitor and
> found none to be even particularly warm, and none show signs of swelling.
>
> I have a note in to PIEXX, who makes the board, to see what insights they
> can add. The board is shipped without a schematic, so getting one of those
> would be helpful.  Is what I've described indicative of a common switching
> PS failure, or is it just weird?
>
> Kim N5OP
>
> --
>
> Kim Elmore, Ph.D. (Adj. Assoc. Prof., OU School of Meteorology, CCM, PP
> SEL/MEL/Glider, N5OP, 2nd Class Radiotelegraph, GROL)
>
> /"In theory there is no difference between theory and practice. But, in
> practice, there is." //-- Attributed to many people; it's so true that it
> doesn't matter who said it./
>
> _______________________________________________
> TenTec mailing list
> TenTec at contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>