Author Topic: Tek 2465A question  (Read 1209 times)

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Offline GerryR

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Re: Tek 2465A question
« Reply #25 on: October 17, 2019, 11:56:04 am »
Another question or two for those in the know:  At the beginning of the Cal 02 procedure, it states to connect a 0.5 V standard-amplitude signal to CH 1 and to use CH 2 Position to vertically position the "trace" to within 1 division of the center graticule line, and then to use the CH 1 Position and Volts/DIV VAR controls to obtain a 10-division horizontal signal.  I don't get a "trace," only 2 dots.  I can position the dots with the controls to put one dot on the first graticule line and the other on the 10th.
Question 1: "Is this "normal," or am I doing something wrong?"  I've read and re-read the procedures and can't find any references to this.

Also, at the beginning of the Cal 01 procedure, it states that, "Upon entering Cal 01, the Input Coupling is automatically set to 50  \$\Omega\$ DC ....."  This doesn't appear to be true for the other Cal procedures (2,3,4,etc) as I had to install a terminator on my generator to get the actual levels called out in the test procedures (monitored on another scope).
Question 2: "Is this correct, or am I missing something here, as well?

Thanks in advance for any input!

Gerry

Still learning; good judgment come from experience, which comes from bad judgment!!
 

Offline jonpaul

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Re: Tek 2465A question
« Reply #26 on: October 17, 2019, 09:15:31 pm »
Gerry many thanks for the note

Been thru the CAL proceedure a few times, great learning curve and many details and pitfalls.

On groups.io TEKSCOPES  much more about this, especially TEK pros like Chuck H.

On eevblog see the 65 page 2465B teardown thread.

About the out of limit message, no further information is provided and usually its the generator signal at fault or proceedure is not precisely followed.

Just re-read and do that step over.....and over....eventually one gets it!

Bon courage et bon chance


Jon



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Offline jonpaul

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Re: Tek 2465A question
« Reply #27 on: October 17, 2019, 09:22:52 pm »
Gerry just saw the 2 new questions

Question 1/ Trace/ dots....my recollection is the dots are the "trace" but may depend on intensity setting.

Question 2/ CAL 01 Term.....

Normally the 246xB INTERNAL 50 OHM term setting is used. Is is set automatically in some steps.

Any external termination will not be as good a VSWR or transient response.

I  never saw that problem.

Enjoy


Jon
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Offline GerryR

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Re: Tek 2465A question
« Reply #28 on: October 20, 2019, 05:16:30 pm »
A little update.  I was having problems with  CH 2 during calibration (CAL 02).  When I got to step 130, I would get a limit error.  In normal mode, CH 2 relay would not switch when going from the 500 mV to 1 V  scale.  I checked out the logic to make sure the shift registers and relay drivers were functioning, which they were, and then proceeded to remove the attenuator.  I checked out the individual relays and found one that would not transition from one state to the other.  I dismantled the relay and found burrs on the sides of the "rocker-contact."  I removed the burrs with a fine diamond file, re-installed and tested; relay was then fully functional.  I re-installed the attenuator into the scope, powered it up, and now the relay changes state when going from 500 mV to 1 V.  I haven't rerun CAL 02 to see if that problem went away with the relay fix; tomorrow is another day.  Pictures attached if anyone is interested.

The last photo shows part of the ceramic substrate of the attenuator with some "dark areas" on the left side.  They look like traces of carbon (though they don't rub off) but I'm not familiar enough with these attenuators to know if this is normal.  Any input is welcomed.
Still learning; good judgment come from experience, which comes from bad judgment!!
 

Online med6753

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Re: Tek 2465A question
« Reply #29 on: October 20, 2019, 06:00:00 pm »
Wow, you really ventured in deep. Good fix!  :-+

Dunno about those dark areas on the substrate. It almost looks like arc tracks to me but that makes no sense because the attenuator would blown sky high.  :-DD 
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Offline GerryR

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Re: Tek 2465A question
« Reply #30 on: October 20, 2019, 06:13:20 pm »
That's what I thought at first, but nothing rubs off like you would expect from a carbon track.  Well, testing will tell all.
Still learning; good judgment come from experience, which comes from bad judgment!!
 

Offline jonpaul

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Re: Tek 2465A question
« Reply #31 on: October 20, 2019, 07:01:16 pm »
Gerry kudos for the attenuator relay job, and fine macrophotographie.

The "carbon" areas could be the normal laser trimming of thick film attenuator resistance.

Notice how only certain resistors are affected and how deterministic the carbon areas are?

But never opened one up so this is just speculation.

Perhaps one of the TEK mavens or retired engineers can comment?

Just the ramblings of a retired EE

Jon
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Offline GerryR

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Re: Tek 2465A question
« Reply #32 on: October 20, 2019, 09:59:13 pm »
Believe it or not, my left hand was holding a 5X eye loop over the substrate, while my camera was in my right hand taking the picture; nothing fancy!
Still learning; good judgment come from experience, which comes from bad judgment!!
 

Offline jonpaul

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Re: Tek 2465A question
« Reply #33 on: October 21, 2019, 11:49:12 am »
Gerry looking again at the last photo, I am now sure the blackened areas are from trimming of the thick film attenuator resistors, and not due to overload.

Jon
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Offline GerryR

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Re: Tek 2465A question
« Reply #34 on: October 21, 2019, 12:04:49 pm »
I believe you are correct.  I powered up the 'scope and the attenuator is responding correctly on every scale.  Now back to the re-calibration.  :)
Still learning; good judgment come from experience, which comes from bad judgment!!
 

Offline GerryR

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Re: Tek 2465A question
« Reply #35 on: October 21, 2019, 03:51:08 pm »
Well, that CH 2 relay was what preventing full calibration of the 'scope.  The dreaded out-of-cal ???????? are gone.  Picture below.  I now know more about the 2465A internals than I ever wanted to know, all thanks to some mishap during a battery change.  Thank you all for all your support!
Still learning; good judgment come from experience, which comes from bad judgment!!
 

Offline jonpaul

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Re: Tek 2465A question
« Reply #36 on: October 21, 2019, 04:07:27 pm »
Gerry: GOOD JOB, especially on the relay repair and learning the CAL procedure.

If you look on the 2465 teardown thread, and groups.io, you will see many notes for backup of the NVRAM, battery replacement, etc.

Even after CAl, I would recheck H and V cal and the measurement routines as a double check.

Easy to miss  the transient and CRT CAL.

Enjoy,



Jon
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Offline GerryR

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Re: Tek 2465A question
« Reply #37 on: October 21, 2019, 07:13:26 pm »
I have been through the teardown thread and on groups.io.  In fact, I followed the procedure for changing out the battery, but something went wrong, and as I stated earlier in this thread, I believe laying the control board down on an anti-static mat may have done me in.  I had a problem with that several years back and cooked a cmos circuit while working on a similar mat when I powered it up.  It's fine when working on non-powered boards, but the battery to the ram slipped my mind.  Oh well, I'm back up and running and learned a lot along the way.

I really intend to go through the full cal procedure again, but want to use the 'scope for awhile to get used to its operation and potential.  I have a circuit that I need to build that will utilize this 'scopes bandwidth, but one of these days (I sound like Pa Kettle!) I'll be back into the calibration, again.
Still learning; good judgment come from experience, which comes from bad judgment!!
 


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