Re: Tektronix 2235 grief


Jim Yanik wrote:
BFoelsch <BFoelsch@xxxxxxxxxxxxxxxxxxxxxx> wrote in
news:ju3sf29bov9mhpcuqm7d8uc5l315jhu5d4@xxxxxxx:

Was given a Tek 2235, option 2 (what's that?) in decent shape, with
one problem.



Opt. 2 is AFAIR a change in the preregulator board (power supply).


Poking around inside, I found a little assembly, P/N 307-1013-00 that
is labelled 10X and 100X . Apparently this assembly contains some
compensating capacitors for the attenuator.

In any event, touching this assembly, exerting the slightest force in
any direction clears up the problem, which quickly returns as soon as
I remove the pressure. I don't think the problem is the switch
contacts, as pressing down and wiggling the switch cam doesn't do
much.
...snipp..
Perhaps a bad solder joint at the pin/substrate interface?
Or a fractured SMD cap.
I believe regular solder will not work here,but don't have any
alternatives,either.Possibly some low-temp stuff like Chip-Quik may work
without destroying the metallization on the substrate.

The other alternative is to find a replacement thickfilm.
Sphere in Canada may have new parts for this,or cannabalize from a parts
scope.


I canibalized 7A18 that where otherwise unrepairable for these, or
unrepairable 465 scopes. The x10 and x100 ceramics were useful for me,
but of course it is some time effort necessary to bring parts in.


(I always wondered if one could make a small PCB using SMD resistors and
caps instead of the ceramic thickfilm,to replace one of these.)

Was the method tof these times, Jim. You can find these a lot in
instruments of this age. Nowadays, when you look for the 0.002 ct
optimization, for a 60 to 100 MHz scope you would manufacture with PCB
made in China.


hth,
Andreas

.

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