I recently acquired a Tek 422 AC/DC that so far has pwr sply issues. The history is it was supposedly working 20 yrs ago then put in storage. now it mine..beautiful condition, cute scope! low 8k sn I would really like to get it back in use..always wanted a tube front end!
I cannot check the indicator without the supply...gee.....wish I had the AC supply too! (circuit looks so much easier!)
so far-
i checked all resistors/diodes/xstrs/caps in circuit as best as possible.
I have found :
In the DC -DC converter Q1184 (2n1899) is bad. fuse had not blown. (possibly not run long enough to cause it to go).
i replaced both Q1184 and Q1174 with D1148 (appeared to be a reasonable sub, I had a matched pair, and matched fairly close to the one good xstr on my old sencore xstr tester, they are temporarily mounted just in case I can find 2n1899's). maybe my subs are a bad choice? is there a better one?
questions-
is there a problem with testing just the pwr sply section by defeating the DC interlock (pins 13-24)?
The supply appears to be a loop in a loop, I managed to test the Start circuit, the feedback and -12 supply ( it makes -8V at C of Q1154). (using exterior +/-12 to run the circuits)
Attached pwr per Calibration with 11.5V and have the oscillator functioning.
the oscillator (~7 khz ) did appear to want to start and circuit wants to run.
The big problem is too much current in the input circuit 4.5A at 12V input appears my sub for Q1174/84 is incorrect...they get really hot. and of course as input V rises so does current. it should not go over 2.5A (3A fuse).
the start circuit appears to be good. but one needs the osc to generate the +/-12 supplies that run the osc that drives the ........well big loop.
I am in need of someone who can suggest a good sub for the 2n1899.....mine is obviously wrong or possibly something else is haywire?
I really need some help.
thanks
Renée