[TenTec] More OT: Acoustic Switching PS Noise

[Kim Elmore]

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./