[TenTec] REPORT: 252 POWER SUPPLY

[Mike Souhrada]

Well guys the power supply is now working as it should. 
Tnx to a number of list members I was able to FINALLY fix the
problem and get 13.0 VDC regulated required. 

Suggestions for others with this problem:
1. Use a VTVM for testing voltages. I found that my DVM 
   did not show minor excursions that I could see with
   the VTVM.
   My VTVM showed a slow climb in voltage on the base
   of the pass transistor and then a quick drop to the
   6 VDC level.
   Concluded that one or more of the switching transistors
   Q2;Q3 were breaking down at =~ 9VDC. Changed both.
2. I also changed all of the 1000 mf @25 V caps to 50VDC
   R/S didn't have enough of the 25's and @ $2 each no big
   difference. But there is an added protection now. R/S PN 272-1047
   I noticed the votage test with my Eico 950 bridge simply didn't
   "look right" compared to many other tests. Although, they appeared
   to pass.
3. None of the fixed resistors were out of tolerance.
   I noted some were 5%.
4. For some reason the variable R8 was 2000 OHM not
   100 as specified. I replace with what I had-a 200 OHM device.
5. Q1 the pass transistor was replaced w/ ECG 181
   The previous owner used the lighter 2N3055 for some dumb reason.
   That's the correct device for the 9 A model 251.
6. Q2;Q3 were changed from my junk box replacements.
7. Q5 the SCR was replaced automatically w/o test.
8. Total cost to repair- about $8

The main clue was the base voltage of Q1- should be 13 VDC. Which
lead back up the string to Q3 which was defective.
BTW I have the 252 model;I was working with the 252M schematic. There
were differences. A couple of 2N5128's were used instead of the 
MPSV01's. Not sure if the previous owner changed or if TT did in
production.
Now that its fixed I'd slick through another pretty fast. If you
have this problem would be glad to help further.

The Triton II is now cranking out  80-85 Watts, pretty close to
specs. However, the manual does not give a clue on setting R8 for
the 100 Watt output it should have. May still need a tweak but 
for my money 80 Watts is plenty.

So tnx again for the replies to my post. Couldn't have repaired it
as fast w/o your help.

Mike
Le Claire, IA
Hometown of Buffalo Bill

--
FAQ on WWW:               http://www.contesting.com/tentecfaq.htm
Submissions:              tentec@contesting.com
Administrative requests:  tentec-REQUEST@contesting.com
Problems:                 owner-tentec@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm