Topics

2465B Parametric Freq Measurement Error


joe@...
 

After successfully calibrating my 2465B, it reports "All tests passed" on start up. The question marks are all gone! My issue is with the parametric measurement of frequency. When I attempt to measure the frequency of a sine wave at frequencies higher than 10 MHz, the scope reports the frequency as 35.62 kHz. Any test frequency above 10 MHz gets the exact same report, 35.62 kHz. Below 10 MHz, it reports various incorrect values (i.e. a 4.89 MHz signal is reported as 6.35 MHz). At about 500 kHz and lower frequencies, the scope reports the correct frequency. I have replaced the PAL at U975 - no change. Any suggestions?


Chuck Harris <cfharris@...>
 

The parametric measurements use the trigger hybrid extensively,
and their performance is directly related to how well that hybrid
performs. Some are better than others.

-Chuck Harris

joe@reforyou.net wrote:

After successfully calibrating my 2465B, it reports "All tests passed" on start up. The question marks are all gone! My issue is with the parametric measurement of frequency. When I attempt to measure the frequency of a sine wave at frequencies higher than 10 MHz, the scope reports the frequency as 35.62 kHz. Any test frequency above 10 MHz gets the exact same report, 35.62 kHz. Below 10 MHz, it reports various incorrect values (i.e. a 4.89 MHz signal is reported as 6.35 MHz). At about 500 kHz and lower frequencies, the scope reports the correct frequency. I have replaced the PAL at U975 - no change. Any suggestions?




joe@...
 

If I replace the trigger hybrid, do I have to do the whole calibration again? Joseph Suste


Tony Fleming
 

Is my Tektronix 2465 DMS using the same part number or do I need a
different one?
Where would I find more information how to perform the replacement?
Thanks.
Tony

On Sun, Apr 28, 2019 at 8:43 PM Chuck Harris <cfharris@erols.com> wrote:

The parametric measurements use the trigger hybrid extensively,
and their performance is directly related to how well that hybrid
performs. Some are better than others.

-Chuck Harris

joe@reforyou.net wrote:
After successfully calibrating my 2465B, it reports "All tests passed"
on start up. The question marks are all gone! My issue is with the
parametric measurement of frequency. When I attempt to measure the
frequency of a sine wave at frequencies higher than 10 MHz, the scope
reports the frequency as 35.62 kHz. Any test frequency above 10 MHz gets
the exact same report, 35.62 kHz. Below 10 MHz, it reports various
incorrect values (i.e. a 4.89 MHz signal is reported as 6.35 MHz). At
about 500 kHz and lower frequencies, the scope reports the correct
frequency. I have replaced the PAL at U975 - no change. Any suggestions?






Chuck Harris <cfharris@...>
 

of course, but only cal03.

-Chuck Harris

joe@reforyou.net wrote:

If I replace the trigger hybrid, do I have to do the whole calibration again? Joseph Suste




Chuck Harris <cfharris@...>
 

All members of the 2465 family use interchangeable trigger hybrids.
To remove them, remove the four nuts at the corners of the module.

Tektronix considered them all to be "selected"... which I think meant
they tried them to see if they would work. the "-0X" suffix meant
changes in production usually... stuff like Tek vs Maxtek, or this
or that revision on their fabrication line...

I would suggest that your first attempted fix be to remove the module,
and clean the gold contacts with a Q-tip and IPA.

When you put the module back, seat it with finger pressure, and hold
it there as you finger tighten a pair of nuts on diagonal corners.
Then install the other pair of nuts. Tighten the nuts 1/4 turn past
where they just make contact. The tightness doesn't make or improve
electrical contact, so just 1/4 turn past the nut touching the hybrid
when it is touching the PCB.

I use one of the red plastic nutstarters that would be familiar to old
guys that built Heathkits. I wish I could find them new somewhere, but
I have enough to last my lifetime of used.

If cleaning the existing hybrid's contacts makes no improvement, then
swap in a hybrid from a working scope, and that should fix the problem.

-Chuck Harris

Tony Fleming wrote:

Is my Tektronix 2465 DMS using the same part number or do I need a
different one?
Where would I find more information how to perform the replacement?
Thanks.
Tony

On Sun, Apr 28, 2019 at 8:43 PM Chuck Harris <cfharris@erols.com> wrote:

The parametric measurements use the trigger hybrid extensively,
and their performance is directly related to how well that hybrid
performs. Some are better than others.

-Chuck Harris

joe@reforyou.net wrote:
After successfully calibrating my 2465B, it reports "All tests passed"
on start up. The question marks are all gone! My issue is with the
parametric measurement of frequency. When I attempt to measure the
frequency of a sine wave at frequencies higher than 10 MHz, the scope
reports the frequency as 35.62 kHz. Any test frequency above 10 MHz gets
the exact same report, 35.62 kHz. Below 10 MHz, it reports various
incorrect values (i.e. a 4.89 MHz signal is reported as 6.35 MHz). At
about 500 kHz and lower frequencies, the scope reports the correct
frequency. I have replaced the PAL at U975 - no change. Any suggestions?








Tom B
 

Hi Chuck,

I use one of the red plastic nutstarters that would be familiar to old
guys that built Heathkits. I wish I could find them new somewhere, but
I have enough to last my lifetime of used.
Like this: http://smallbear-electronics.mybigcommerce.com/nut-starter/

Tom


Chuck Harris <cfharris@...>
 

Exactly!

Have you tried their product?

-Chuck Harris

Tom B wrote:

Hi Chuck,

I use one of the red plastic nutstarters that would be familiar to old
guys that built Heathkits. I wish I could find them new somewhere, but
I have enough to last my lifetime of used.
Like this: http://smallbear-electronics.mybigcommerce.com/nut-starter/

Tom





Tom B
 

Hi Chuck,

Exactly!
Have you tried their product?
Nope. I found others for sale, but these were cheaper.

Tom


-Chuck Harris

Tom B wrote:
Hi Chuck,

I use one of the red plastic nutstarters that would be familiar to old
guys that built Heathkits. I wish I could find them new somewhere,
but
I have enough to last my lifetime of used.
Like this:


John Ferguson
 

Hi Chuck,

The parametric functions do not work on one of my 2445Bs, the one you didn't calibrate.? It also doesn't sync on signal on start-up but does work well manually.? I chased this around? on EVblog a few years back, but never arrived at what to look at.

Is it possible that cleaning up the contacts and gently re-seating a hybrid could resolve this? Would it make sense to buy a replacement hybrid just in case the clean-up doesn't produce the desired result?

best regards

john


Chuck Harris <cfharris@...>
 

Hi John,

Best would be to swap the trigger hybrid from one of your
2465 family scopes that does work into the one that doesn't
work, as a test. (as long as you restore the original to the
calibrated scope, there will be no affect on calibration.)

The trigger hybrid is crucial to everything in the parametric
functions.

An additional place to look would be to follow the signal from the
DAC to the trigger hybrid threshold inputs (TLA, TLB). The 4051's
and the TL072's and their associated sample and hold gate parts go
bad sometimes (U2521, U2520, U2420, C2421, C2621).

One repair/calibration blurs into the next. If you think I didn't
repair something correctly, send it back, and I will fix it gratis.

I know I tested the parametric functions on the unit I calibrated.
It is a standard part of the tektronix calibration routines.

-Chuck Harris

John Ferguson via Groups.Io wrote:


Hi Chuck,

The parametric functions do not work on one of my 2445Bs, the one you didn't
calibrate.? It also doesn't sync on signal on start-up but does work well manually.?
I chased this around? on EVblog a few years back, but never arrived at what to look at.

Is it possible that cleaning up the contacts and gently re-seating a hybrid could
resolve this? Would it make sense to buy a replacement hybrid just in case the
clean-up doesn't produce the desired result?

best regards

john




John Ferguson
 

Thanks Chuck,

Don't worry, you never saw this machine - it's sort of my beater.

best,

john

On 4/29/19 9:45 AM, Chuck Harris wrote:
Hi John,

Best would be to swap the trigger hybrid from one of your
2465 family scopes that does work into the one that doesn't
work, as a test. (as long as you restore the original to the
calibrated scope, there will be no affect on calibration.)

The trigger hybrid is crucial to everything in the parametric
functions.

An additional place to look would be to follow the signal from the
DAC to the trigger hybrid threshold inputs (TLA, TLB). The 4051's
and the TL072's and their associated sample and hold gate parts go
bad sometimes (U2521, U2520, U2420, C2421, C2621).

One repair/calibration blurs into the next. If you think I didn't
repair something correctly, send it back, and I will fix it gratis.

I know I tested the parametric functions on the unit I calibrated.
It is a standard part of the tektronix calibration routines.

-Chuck Harris

John Ferguson via Groups.Io wrote:
Hi Chuck,

The parametric functions do not work on one of my 2445Bs, the one you didn't
calibrate.? It also doesn't sync on signal on start-up but does work well manually.?
I chased this around? on EVblog a few years back, but never arrived at what to look at.

Is it possible that cleaning up the contacts and gently re-seating a hybrid could
resolve this? Would it make sense to buy a replacement hybrid just in case the
clean-up doesn't produce the desired result?

best regards

john