05-08-2012, 05:36 PM
(05-08-2012, 03:08 PM)Skywave Wrote: I might find the time today to have a further look and think about this.
Al.
And found a little time I did and looked a little harder I did too - and what did I find? Please read on - an 'interesting' tale . . .
Well for a start, C15 ('Suflex' type) was short-circuit! (Really weird: its capacitance value is spot-on, but put 1.5v. from an AVO on resistance range X1 across it - and phut: it's s/c! ) But the biggest mystery was TR4. The cct. lists this as a 2N3702, and indeed, that was what was fitted. When I replaced in 'on spec.', I didn't have one of those, so a consultation of the Towers Transistor book revealed that a BC212L was an equivalent: a few unused ones I have in stock. As usual, I checked the pin-outs of that and the 2N3702 prior to fitting the BC212L: both the same: the base connection is not the centre leg. However, now, today, a close exam. of the pcb revealed that the tracks and artwork are actually laid out for the centre leg to be the base.
So, out comes the BC212L, in goes a 2N2906 (an old favourite of mine). As a pro-tem measure, the s/c C15 has been replaced by a trimmer. Using the 'scope and adjusting that trimmer produced a nice 100 kHz narrow pulse train at Test Point 3. And a subsequent check (using the 'scope and a freq. counter) on the main R.F. O/P, with the calibrator set to 100 kHz, gave 100 kHz beats exactly where they are supposed to be. Hooray!So there we are - well, on that bit of the repair to the calibrator, anyway. But the point is this: when, in effect, you are given misleading / incorrect tech. data during a repair, it does not help!
Anyway, next steps: tidy up that bit and have a look at the 10 kHz divider. Then I'll report again (or ask for help . . . if necessary
).Al. / Aug. 5th. //
