Thanks for all the suggestions. I think I've figured out what
happened, a bit far-fetched but here goes:

By taking the square-root of the primary to secondary inductance
ratios, we get a step-down ratio of nearly 5, which implies a step-
down ratio to 24 volts. Which is what we measure the transformer
providing.

Now that tranny goes into a full-wave bridge, then thru a SCR to the
12-volt nicad pack and 16V 470F capacitor.

A completely non-sensical situation.

Now a couple more observations:

(a) The transformer doesnt smell cooked, but it does have a few
droplets of varnish oozing out.
(b) Somebody replaced the dual AC line fuse holders with a single
fuse holder.
(c) The unit arrived with no fuse caps or fuses in the AC line fuse
holders.
(d) The nicads, although overheated and with 1983 date codes, are in
good electrical condition.
(e) These 1502's tend to get very beat up, as they're meant for
portable use in the field. This one looks like-new.
Not a scratch or scuff anywhere.



The only explanation I can come up with is:

(1) The guys at Tek wound the transformer wrong. Twice as many turns
on the secondary than required. They slapped the "0151-xxx" tek
sticker on it anyway.

(2) The transformer had just enough primary resistance to limit the
primary current to around one amp average.

(3) The nicad pack (remember, it looks overheated) acted like enough
of a zener to clamp the voltage to about 14 to 16 volts.

(4) The rest of the power supply aged very quickly with the
overvoltage, frying a transistor and a zener.

(5) ... and the unit ran just long enough for Tek to calibrate and
ship it.

(6) Since then it's been blowing AC line fuses every few minutes, bad
enough so someone rewired it to use just ONE line fuse.

(7) It's been used very little, probably put on a shelf as a
unreliable fuse-blower. That explains the good nicads and the
pristine condition.


Weird, but I don't see any other logical explanation!

You'd think Tek would have caught this, especially on such a pricey
unit.