Calibrating my Tek 2445

[bob91343]

I acquired one of these and see that it's not very accurate, both in time and amplitude.  I fully expected an old time calibration procedure where one adjusts gain and so on but apparently they decided to modernize and make it self calibrating, sort of.

Can someone advise me how to accomplish this without risk?  Reading the procedure only confuses me at this point.

[tautech]

Manual link:
http://w140.com/tekwiki/images/5/5b/070-3829-00.pdf
Part 4 lists the gear required and part 5 has the procedures.
They are closely related to the 2465B family of which there is a big thread about them that should offer some guidance.
General consensus is the Service Manual is to be followed explicitly and the posts by member rf-loop offer his experiences of working on many in reply #14:
https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg73972/#msg73972

Maybe you could jump into that thread and seek help from others with this scope.

[rf+tech]

Hi bob91343,

Before anything, check the +10 Volt reference. Nearly all front panel potentiometers are supplied from this +10 Volt reference. The outputs of these pots are inputs to ADCs.

When the reference is off, so too will be accuracy and attenuator balance - the latter causing vertical trace shift when changing vertical Volt/division and variable vertical gain.

R1292 on A2 is to be set within 9.99 and 10.01 Vdc. Closely observe the voltage at A2 TP201 for any sign of drift. Nudge R1292 ever so slightly and again note any tendency for drift. I’ve now replaced noisy R1292 on three 24x5 scopes. This Bourns 1 kOhm pot has the proper lead spacing and orientation:

https://www.digikey.com/products/en?keywords=3386S-1-102LF

It should go without saying that all power supply voltages and ripple should be checked, per Table 5.1, section 5 page 2 of the manual.

Regards,

RF+ Tech

[bob91343]

Thanks for the replies.  When I get the nerve and enough time I will get into it.  The unit works well for the most part but is inaccurate.  The intensity setup seems to need some attention as well.

Power supply first, including reference.