2246 Mod A Repair Question

Dave Trainor

Guys, need to ask for some advise. Here is the background:
Ex-USMC 2246 Mod 6 Scope 1998 warranty date.

Purchased by me in 2007, been working perfectly and passed all checks and
to the best of my calibration capabilities (TM500 modules) been working
perfectly for my needs in Ham Radio Repair.

Week after Christmas, Turn On - Pop sizzle sound, horizontal trace
jumped vertically, scope turned off. Smell of letting the smoke out of
something, not strong but distinct.

Attempts to turn on, result in the whirr/click of the PS resetting itself
over and over, scope never powers up.

Ah-Ha I said power supply failure. Found good website of fellow who
recapped a 2245 and had the mouser part numbers and so on - bought the
caps, re-capped the unit.

Same result, whir/whine/click.

Found a 2246 1Y on E-place and bought it, it had been dropped obviously
on left corner enough to break plastic rear, but seller says it powers on.

Arrived, swapped power supply, same whir/click. Hey lets put my
re-capped power supply in the dropped unit - whoh it wooers it up no
problem, but that scope took damage to mainboard and maybe CRT not sure.
However I now have one recapped power supply, and one fro the damaged
scope both are good.

Tried swapping Processor Boards, 1Y and Mod A can be swapped same
connector location. Makes no difference, the problem is not isolated to
the mainboard. The dropped unit has a cracked and obviously damaged
mainboard no help in board swapping there.

Found and bout a 2246 Tektronix mainboard on E_play again. It arrives,
its a 2246 board, not mod A or even 1Y - connector cables are different
lengths to the processor board, but hey it powers up and does show a blue
dot center of screen but its obviously not going to work as I need a 1Y or
Mod A board replacement. Was fun swapping mainboards. Proved I could dd

So after this novel, I have a 2246 Mod A mainboard that has some type of
short preventing the power supply from coming up, after repeated scans
with 10X magnification and nose not a single part that looks like it went
bad. Power supply filter caps are electrolytic, every parts looks good to
both visual and smell test. It will not power up to preform ay testing.

How DO I proceed in trying to fix this? I like the scope. I should be
able to fix this even as a long time IT guy an only a amateur tech but I
can make Voltagee readings if the power supply won¹t start when connected.
No way to know, is the the +15, -15, +5, -5 or other supply that¹s
shorted and causing it not to start.

Any ideas? Or Anyone need a very nice 2246 ModA CRT? Really giving up
is frustrating. Just not sure what else I can do.

Sorry for the lengthy novel. Full story nothing held back. If I should
give up just tell me.

73 - Dave N8ZFM

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