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Conversion of 500MHz TDS744A to 1GHz TDS784A

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Jay_Diddy_B:
Hi,

Somebody asked for the TDS adjustment software.

It is attached to this message.

Regards,

Jay_Diddy_B

EB5AGV:
Hi all,

Thanks a lot for this thread!

Last year I bought a TDS 744A as part of a test-equipment lot buying. It came with a couple P6139A probes, the pouch and, free of charge, lots of dirt  ;)

I had not done more than powering it up and some basic checks. It worked, but needed cleaning. My usual digital oscilloscope is a DPO 3032, which is a 300MHz, 2.5Gs/s unit. So, except for the 500MHz bandwidth, the TDS 744A was a lesser unit and I didn't find any use for it at the moment.

But testerday, while looking for other info on a different project (a Tektronix CSA 8000 mainframe I am trying to get back to work), I stumbled upon this thread. Wow!!!. I was amazed to find I had a hidden treasure  :-+, as my 744A came without 1M option... which seemed to be also a configuration hack (and, yes, I have managed to activate it using just Keysight IO libraries and GPIB  :-DD)

So I took it out its casing and carefully cleaned it, including the keypads, as some keys were not working fine. The HORIZONTAL POSITION control also failed, so I took out all the front panel, dismantled and cleaned it. Now the oscilloscope looks like a close to new unit! (I will put some pictures later)

Well, once I performed the resistor mod and the capacitor removal, yes, the unit is shown as a 784A and now it reaches 4 Gs/s. I have run the SPC after a warm up period, and it has also worked fine. But there is a problem when the unit works at 4 Gs/s, which I think it is a matter of calibration. The test is simple: I put a 250MHz signal and activate only Channel 1. What the unit shows is a distorted signal. Then, if I activate Channel 2, so the sampling rate lowers to 2 Gs/s, the signal is an almost perfect sinusoid.

I need to setup a PC with a NI GPIB card to run the calibration software which I hope will solve this problem.

Regards,

JOSE

Jay_Diddy_B:
Hi Jose and the group,

I think that distortion will go away when you perform the calibration. At 4 GS/s all four ADCs are being used and the interleave timing has to be correct to get an undistorted sine wave. At 2GS/s the scope was calibrated when it was TDS 744A.

Regards,

Jay_Diddy_B

cncjerry:
I did the same upgrades to my 744, regularly run high frequencies into it and not only sine waves.  I haven't done the calibration and don't see any distortion like the new poster.

EB5AGV:

--- Quote from: cncjerry on July 27, 2015, 04:42:38 am ---I did the same upgrades to my 744, regularly run high frequencies into it and not only sine waves.  I haven't done the calibration and don't see any distortion like the new poster.

--- End quote ---

Yes, this is not unusual. Note that the compensation among samplers could be better in your unit without correction. Anyway, I doubt it is perfect, but probably lots less noticeable than on my unit.

All in all, I am happy with the experience. I hope I can fix it by calibration. If not, well, I can always revert the mod. It has been so far an interesting learning experience and a way to get back to life an old and tired unit  ;)

BTW, just adding Option 1M is already worth the effort  :-+

Regards,

JOSE

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