Tek TDS 744A -> TDS 784A upgrade hack!

Hi, all,

Just wanted to report success in upgrading my TDS 744A scope (500 MHz, 2 gigasamples) to a much swoopier TDS 784A (1 GHz, 4 gigasamples). It now identifies itself as a TDS 784A everywhere except the printing on the bezel. Passes all self-tests and SPC.

Turns out you just have to remove four 5.4 pF caps from the ADC inputs and one zero-ohm jumper, both on the acq board.

I was a bit worried about what the step response was going to look like, but it's actually reasonably decent. The input signal was from an 11802 mainframe and SD-24 TDR plugin (17 ps rise time).

Thanks to the estimable JW (TestPlus) for walking me through it. The screen is a bit brighter now too, but the contrast pot is now cranked all the way, so there isn't a lot more juice available.

BTW there's some Bad Info on the EEVblog forum thread about this--they tell you to remove R1064, but that gets you 1 Gs/s (export mode) and not

4 Gs/s (TDS 784A mode). For that you have to remove R1061.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Phil Hobbs
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Nice.

I see that you had to go 34 years into the future to get that screen shot - do we all have to wait that long?

(See timestamp)

kevin

Reply to
kevin93

Yeah, SD-24 is a fabulous pulse generator. Well, the rising edge is fabulous; the falling edge isn't.

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John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  
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John Larkin

I've always been ahead of my time. ;)

(see )

Cheers

Phil

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Dr Philip C D Hobbs 
Principal Consultant 
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Phil Hobbs

You're welcome. I've done this on a number of TDS700 scopes that I've sold, and never had any complaints about step response, although I don't have a fancy SD-24 like some folks do to test it. ;)

I run the Tek field adjustment software to calibrate it, though. I'm guessing that you didn't?

PS: I'm not the right guy to repair your HP 3585A, I don't work on those ancient boat anchors anymore and I tossed all my service info on all that stuff years ago. I do know a guy in Texas that might be, and he has a climate-controller cal lab in his house with a 3458A and lots of other good stuff. If you want his contact info, let me know.

Lastly, I do have lots of hacks for scopes, but only ones newer than 1995 or so; nothing on your list, sorry.

Reply to
JW

One other thing, Phil, did you get a capture before the operation by any chance?

Reply to
JW

Not so far. It seems to require ancient hardware that I don't have. It passes the frequency response self test, and there aren't a lot of edge artifacts due to the interleaving being off, so I'll probably just leave it alone.

The 3585A is a nice instrument for low frequency stuff. What I really want is a 100 MHz bandwidth dynamic signal analyzer. I'll try digging out my 70820A and see what it can do--it has a 40-GHz sampling front end and a 10-MHz instantaneous bandwidth FFT back end.

Well, one of these days my ship will come in. ;)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

Nope, but it was a bit under a nanosecond.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

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