Hello, lots of good information here. Recently got a used TDS754A which was sold for parts but turned out there was nothing wrong with it. Retrofitted an LCD and replacement NVRAMs into it and it seems to work fine. Also recapped the PSU.
Does anybody know if there is a significant difference in speed (as in UI/menu speed, waveform update rate with long memory enabled etc.) between A, B and C variants of the 700 Series for example? I have noticed that my 754A waveform update rate gets REALLY slow when enabling the maximum sample memory (1M). The C and D have a newer processor but is it really worth it to source a C or D variant to gain a little bit of speed...
It is not so easy to answer your question because first we do not have any schematics of any C/D serie, only the TDS520B schematics has been available.
Since I've started this thread back in december 2019, I've purchased, repaired, reconditioned, hacked, upgraded, resold total of 9 tektronix TDS (510A 784C 540C 794D 520D 714L 784D and 754D). One of the most difficult repair was a fail BootROM which is synthetized in this thread
https://www.eevblog.com/forum/repair/major-boot-failure-tds784d/msg5133990/#msg5133990.
What I can tell you, some TDS A/B have a modern acquisition board (one PCB only) which seems to be roughly the same as the C/D versions so the question is how to interface with 68020 or 68040 processor boards with acquisition board HW and SW. Older A/B acquisition boards have 3 separate PCB's so I do recommend them, loose of time and very old firmware.
The repair of the TDS784D has taught me one key thing, namely the DRAM sits with the Kernel with A/B serie but outside C/D serie. Tektronix kept the same Kernel circuit then same control with Acquistion board in C/D but there is a special U1 chip which translates 68040 world to 68020 world. There is 68040 bus, processor, the graphics and display are the same as 68020 except there is no ASIC translator.
Attached again my hand sketched partial reverse engineering of C/D logic board then look the U1 chip and the DRAM which are outside kernel compared to A/B structure attached as well.
Intuitevely I'd tend to think 68040 are faster than 68020 even though their acquisition board are really the same HW/SW architecture for latest A/B's if and only if latest acquisition board single PCB. The advantage of 68040 firmware could be an optimized code from tekronix, for sure their firmware version is changed but the real question of speed when using 1M or 2M mode, not sure because these boards really are the same.
So either U1 chip introduces delay or slow down or tektronix really optimized the complete flow down thanks to 68040.
Note that I've never seen TDS754A acquition board, maybe you could open the blue cabinet and share a global view picture to see if it is monolithic PCB or old 3 parts.
Albert