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