Just got a Tek 2465A, couple questions (how I screwed the calibration data)!!

[MarkL]

That's all I have, worth a try? 

An analog function generator?  Yikes.  I suppose any calibration is better than no calibration.

Try it, but the 2465A may not like any minute drift or instability the frequency is bound to have while the calibration is in progress, and the rise/fall time may not be sufficient.  If it doesn't like the signal, it will just fail the calibration, so no harm done.

Since your Rigol has a crystal timebase in it, I would at least set the frequency to 1MHz by measuring on the Rigol.

If it works you can compare 2465A CTT readings with the Rigol and repeat until it's as close as you can get it.  But it's always going to be "approximately right".  By comparison, the TG501 recommended by the service manual for calibration has a timebase accuracy of 0.00005%.  The CTT is specified for 0.0005% accuracy when calibrated with that timebase.

[MarkL]

Posted as I was typing my answer.

Great - glad it worked!

[alpher]

Actually I just realized that I've never thanked those that helped me with the whole affair.
So thanks to everyone involved especialy usuthu65, z01z and ofcourse MarkL  if you're ever in Mississauga beer's on me! 

I will probably try to calibrate the scope anyway but don't know when.
Will start another thread as I want to document the whole proces, reading the cal data of the ram as I proceed so we know what is what.

[MarkL]

You're welcome!  Although at times I felt I was distracting you from your original plan which, in the end, worked fine.  I might end up passing through Mississauga at some point.  We've always wanted to go camping in Canada.

But I'm not done yet.  I'm waiting for that used A5 board to get here and I hope it's working enough to boot.  I intend to strap it to a logic analyzer and make it give up its secrets.  I still want to know why the checksum wasn't matching and why the SRAM copy thing didn't work.

I do not like to end with unsolved mysteries.

[alpher]

Actually I put a step towards the calibration proces allready, here are a few pics:







Basicly what I did is I used the empty spot on the A5 board that Tek probably reserved for some sort memory expansion, never used it anyway (at least I haven't heard of it ever bein used).
Unfortunatelly Textronix in their wisdom thought of only 16kbits memory here, 24pin chip like 6116 or such.
So I had to improvise a few mods using kynar wire, anyway the idea was to have a zif socket there, so I can make a simple patch cable using 2 28pin sockets to connect it to programmer.
I  didn't feel at all comfortable pulling the eproms and nvram constantly during the "testing" phase.
The wear on the sockets an possibly the chip pins was a risk I did not like to take.
After I put the NVRAM chip I couldn't use the simple clip/cable (that was unreliable in the extreme anyway), I had to devise a way to read the RAM without pulling it everytime from the machined socket, risking a broken pin or such.
So we will see how it will work, I'm planning to do a quite a bit of memory reading during calibration procedure( at least once every step), we'll see how that goes.
As far as gear goes, so far I got his:



That does this:



That's a 50nS pulse, just look how sharp are the edges!, isn't that amazing.
500pS timebase :



As far as other stuff I may need I'm thinking of getting a new FY6800 or even older 6600 if it gets to be cheap enough.
May be enough to calibrate the scope.


PS MarkL , funny that you mentioned camping in Canada, the reason that I wont be doing the calibration anytime soon is this:



Bought this puppy before the winter and have to get it ready for the season, (lots of work), it's going to be the first season for me and my wife.
Cheers.

[tonedeak99]

Archer,

What a mess was created by replacing the battery.  I am thinking of doing just that to my 2465A CT but this is exactly my worry with doing it.  My scope works well, only has 5000 hours, and the battery reads 4v.  Could the points you chose to connect the backup battery have been the problem?

I'm thinking of following this process and points:
https://jestineyong.com/tektronix-2465a-dv-oscilloscope-memory-backup-battery-replacement/

I already took an EXER 02 video and I'm seriously considering backing up the SRAM with an GPIB interface adapter. I hope that GPIB can read and write the entire SRAM and not just the calibration area just in case it gets corrupted like it did for you.  Great job getting the whole mess fixed!

[alpher]

Worry not! I ended up calibrating the scope anyway, not to dificult in the end. Since your battery reads 4V i wouldn't worry at all.
Leave it alone.
 

[tonedeak99]

Like you, I'm just a hobbyist and don't have any of the fancy calibration equipment and couldn't afford it even if I wanted it.  What equipment did you use to calibrate?

[tggzzz]

Like you, I'm just a hobbyist and don't have any of the fancy calibration equipment and couldn't afford it even if I wanted it.  What equipment did you use to calibrate?

Vertical deflection is easy: just use a power supply and voltmeter.

Horizontal deflection is easy: just use any modern signal generator (or an old one with a frequency counter).

The trickier and more important adjustment is the step response. For that you need something with a risetime less than the scope's risetime with no overshoot and with a flat top. Hence the long running "show us your square wave" thread No, a simple pulse from an avalanche generator isn't sufficient, because the visible trace is the convolution of the (undefined) input pulse and the scope's response.

[alpher]

Like you, I'm just a hobbyist and don't have any of the fancy calibration equipment and couldn't afford it even if I wanted it.  What equipment did you use to calibrate?

Vertical deflection is easy: just use a power supply and voltmeter.

Horizontal deflection is easy: just use any modern signal generator (or an old one with a frequency counter).

The trickier and more important adjustment is the step response. For that you need something with a risetime less than the scope's risetime with no overshoot and with a flat top. Hence the long running "show us your square wave" thread No, a simple pulse from an avalanche generator isn't sufficient, because the visible trace is the convolution of the (undefined) input pulse and the scope's response.

To restore lost calibration constants you don't need any pulse generator.
I used the Tek prescribed stuff, all you really need is TG501 and PG506.


If you interested I'll sell it cheap.