开云体育

Hi,

Also have anyone transferred the 2445B NVRAM content into the 2445A SRAM?
There is a 2445B NVRAM file kindly uploaded by Mitchell Kobierowski in this forum. Technically it's possible to upload it into the 2445A SRAM (connect the voltage source via the current limiter while being in the ROM programmer tester and then bring it back to the A5 board). I hope it should fix the FAIL04 prompt and restore the calibration data integrity. Since my 2445a has option 05 (video triggering), I would have to recalibrate it later on together with CAL01, CAL02, CAL03.... but one at a time.

I wonder if doing CAL one at a time is possible at all..

Thank you,

All the Best,

Maxim

Hello Chuck,

Thank you for answering.

My 2445a repair/calibration project is the life long (almost 10 years, almost no time). I should of given up on it long before, but it's just not an approach of an engineer to give up on something which almost already works (put lots of hours already, but 2445a in my setup will be more of an artifact). I just wanted to understand how serious is the data integrity failure (FAIL04) and whether I can do the calibration in steps powering up the o-scope every time for the new CALxx routine?

I simply assumed that if the data integrity is OK then I can do the CAL routines selectively (therefore the idea was to get the calibration data w/o errors and then do one calibration routine by another). Otherwise I have to go from the beginning though the end non-stop otherwise nothing will be stored... So far whatever I have calibrated wasn't taken into account by o-scope since I didn't have the right set of equipment to perform the CAL ALL. For example I did perform CAL01 and CAL02 separately, then powered off the scope then I'm back to the same problems. Like it was not simply stored.

Have you managed to calibrate the 24xx scope in separate CAL sessions by having initially FAIL04?

Also do you know which CAL routing will contribute to the AUTO LVL trigger function. In my case channel 1 with the replaced hybrid has the offset too high on AUTO LVL, so trigger level isn't found automatically.

Thank you again and all the Best,

Maxim

Thank you very much for the detailed answer, Chuck,

So tihs means that actually I can do the calibration in separate steps by running the CALxx procedure from the beginning to the end. This will fix then the FAIL04 problem once all the calibration constants are updated and the checksum is OK for all of them.

Sending the scope from Europe to the US and back is more than 500 USD (including the taxes, customs etc) so its beyond the economical repairs. The battery is good, it's just our lab technician pulled out all the chips in the failed attempt to quickly repair the scope by reseating the ICs and clearly lost all the settings once the memory has lost its power. Then the scope was thrown to the company auction and I scored it for 150$. After that I had to replace the U200 hybrid, opamps around, etc. Looks like someone decided to probe HV with this scope. After recapping the power supply I decided to calibrate it, but I didn't have by that time the time mark generator. So now, I'm better prepared and can go slowly running the CAL routines one by one.

I'm going to re-run tonight the CAL01. Could you, please, tell me whether I always have to join the zoomed time marks around the Y axis in the middle of the screen. Sometimes two zoomed traces disagree more in the middle of the screen, The service manual only precises that the traces must be joined around the division 6 (screen center) only for the step 1. I assume that in order to align the signal timing they have to be precisely aligned at x10 zoom around the screen center (vertical axis). So I'll try re-running the CAL01 with the signal alignment around the screen center.

Thank you again and all the Best,

Maxim

Hello Chuck,

I have posted the photos from the CAL01 to the forum:
/g/TekScopes/album?id=74577

Could you, please, have a look and tell me if you see something not right?

I'll have to re-do the CAL01 with 7603 or 7834 scope as a bench scope this evening.

Thank you again,

Maxim

Hi Chuck,

Regarding the CAL01, I've followed your suggestion and counted the markers on the zoomed screen. The numbers do perfectly match. IMHO what looks like the rate problem is the long fall time of the time mark signal. Therefore the illuminated markers are not all the way down to the bottom.

Also I've run the calibration from step 17 to 23. I used both the Tektronix 7834 and LeCroy 9410 as the bench scope.

/g/TekScopes/photo/74577/14?p=Name,,,20,1,0,0

On LeCroy finally it was possible to reconstruct two signals to be superimposed. What was a bit shocking is that even on Tektronix 7834 using 7B53 timebase the 2445a stroboscopic display setup wasn't triggering that well (in some modes perfectly fine, in some not). So finally I've resorted to LeCroy, since its trigger was very stable.
Also since 7A18 amplifier has no 50 Ohm input termination I had to put the 50 Ohm terminators on a Tee connector just on the face of 7A18 (had no flow through terminated plugs). I looked and couldn't see any measurable reflections generated by such a setup...

So I wonder what's wrong and why I can't always see two signals to be superimposed (have to manipulate with the trigger level on 7B53 when changing the time mark rate).

Do you have a stable trigger with two displayed signals in all the steps from 17 to 23? What time mark generator are you using?

Thank you,

Maxim

Thank you Chuck,

Yesterday I've tried to get through CAL02, but I had LIMIT error problem. The DC balance walked automatically without generating any error message.
Then I've aligned two points for 10 horizontal divisions like this:
/g/TekScopes/photo/74577/16?p=Name,,,20,1,0,0
But then when the scope walked through the step 113 (I could see the beam jumping diagonally from the left bottom to the right top corner) it spit out LIMIT 113. I have pressed again on TRIGGER COUPLING button and it jumped immediately to the step 114. Then again, the story repeated with LIMIT error.

I wonder I the problem is with the hardware. Scope passes all the tests and generates FAIL04 3 (bad checksum). Otherwise the vertical amplifiers on all channels measure the input signal correctly (uncalibrated). The only problem I see is with AUTO LVL function (doesn't work for the channel 1), but I assume that it's addressed in the CAL03.

If I have the LIMIT error what do I have to do in the CAL02? The 2445a manual doesn't state what to do if the LIMIT ERROR is encountered (here is a nice re-written calibration procedure for 2465B):

If I advance the step after having LIMIT error is it assumed that the current step has failed and no calibration data is registered?

Thanks again,

Best regards,

Maxim

Chuck,

Thank you for checking the photo. There were 2 small problems: the photo is overexposed but also as you noticed the dots are not round, but rather oblong. The generator output doesn't seem to be noisy, but I'll try replacing it by another AWG and run the test again.

The main repair was made to the channel 1. But I don't really see any difference in terms of noise, offset etc when comparing the old "good" channels 2/3/4 and the repaired channel 1. After the repairs the channel 1 I received a hybrid U100 not from 2445a but from 2465a. Would it be the problem I don't really know.
I'll try advancing the test to the CHANNEL 2 calibration and see whether I'll have the same LIMIT error.

Regarding CAL/UNCAL state - this is all new to me. Are you referring to the R639 state, meaning that on the first go R638/R639 aren't set properly, so the state is UNCAL? But after running the first time through CAL02 on the second run the state is CAL, since the resistors are supposed to be set?

Thank you and all the Best,

Maxim