Tektronix 7603 scope behavior when readout board is missing

Greetings:

I just acquired a Tek 7603 scope with 7A18 dual-trace vert. and 7B53A
timebase plugins but upon internal inspection and cleaning discovered
that the readout board (when facing the front of the instrument it is
found on the upper right side midway along the length) is missing, as
are all interconnecting cables it uses.

The display is very corrupted: odd blanking and sawtooth displays
appear with no vertical input and horizontal sweep width changes with
timebase selection in a drastic way. A vertical input signal modulates
the strange displays in a fashion that suggests the vertical section
is functional and the vertical position controls do work.

The plugins are supposed to be in operating condition.

The internal logic timeshares the display between readout and
waveforms and is rather complex and implemented in Tek custom
hybrid ICs and a mix of TTL and CMOS. I would really
appreciate a report of the behavior on a working 7600 series scope
when the readout board is disconnected; the service manual describes
various voltage measurements with the board removed so it is
permissible to do so and power the instrument (but no mention is
made of the scope's behavior with the board removed).

Many thanks to anyone willing to do this.

Regards,

Michael

 

Post what options were sold as part of this scope. Some were sold
without readouts, the fact there are no connectors indicates that
possibly the readout option was deleted.

IMHO, (and this is just a WAG) the problem you are reporting is not
related to the readout...

 

Digging through Internet archives this morning I noticed a few posts
from folks seeking the readout board for 760x scopes with a mention
that 'Option 01' was a cost-reduced version sans this board so evidently
the scope should work without it (if properly optioned?). I was not
sure if any cable modifications would be needed if the board were
removed from a scope not-so-optioned.

And indeed I now discover an "Option 1" label on the bottom of the
left bay so this scope never had the board.

Its problems are elsewhere.

Thanks,

Michael

 

<snippety>

There is a Tektronix group on Yahoo groups that is loaded with very
experienced 'Tekkies.' You would do well to take your query there.

Off the top of my head, I would say two things.

(1) Get the service manuals for your 'scope frame, AND both plug-
ins. It will be nearly impossible to troubleshoot or service without
them.

(2) Check your power supply section for bad filter caps, correct
voltages, noise, etc. Ironically enough, you will likely need a known-
working 'scope to fix this one.

Happy tweaking.

 

The problem was a defective C811 (14000 uf / 25v), the -18V filter
capacitor for the -15V supply.

Scope works well now.

Regards,

Michael

 

Sounds good to my repair eperience. Due to own experience bad/dried
filter caps in the LV pwr supply of Tek 76xx is often a problem. I had
more than 50 of these for repair, and most of these due to cap
problems.

Good luck with your fresh repaired scope, it is a nice instrument
(with and without readout option).


hth,
Andreas