One can turn 4ch a B/W TDS5xx into a full featured TDS784 with external colour screen, so a 2ch model 5xx model would be convertable to the highest end 2ch 7xx model.
Didn't even know there was such a thing as a mere 2 channel 700 scopes ?!
Maybe...
So all the known hacks will work with them - max out the BW by removing the capacitors, change model # by moving the zero ohm resistors, unlock options. Most probably the 2M (largest memory) option won't work since there's not enough memory, but 1M (medium memory) and others (like Math and FFT) work.
IMHO InstaVu (or DPO as it was called later) isn't that useful, otherwise I don't know from which model revisions on this was available, but for sure different for 5xx and 7xx.
If you basically want a real GHz scope, IMO this still is an option. If you want a versatile and modern scope with large memory etc., but e.g. 200MHz is enough, you'd better go for a modern Siglent or similar.
My 544A has been fixed cap wise, it's rock solid now.. the last thing I want is to mess with it.
I don't see how Tek would have put expensive 2GSps H/W in a 500 scope and limit it to 1GSps...
As for B/W, increasing it why not but then what... scope would not be calibrated at all, like, at all, for that. F/W would not allow for faster sweep speeds either, so not much point.
That would require I guess putting a 700 F/W into it, I don't see how that can go smoothly, or at all, and even then.. I would then have no sig gen to calibrate it with anyways.
And again ,no Instavu no matter what. No big memory either, no hard disk, no X Y Z...
I just don't see the point in messing with my poor 544A. I will just get a 784D when I can afford it and that's it... then sell the 544A and call it a day.
I don't want a high-speed scope, I have a TDS694C for that, 4x3GHz 10GSps on each channel. But it's not a general purpose scope, 50ohms 5Vrms only and low memory. As for bottom of the barrel (or not) cheap chinese scopes, not my cup of tea, they just don't cut it for me, to each their own I guess. For general purpose work I have my 4x200MHz Fluke/Philips "Combiscope" that works just fine. The 694 for high BW stuff.
The goal of the TDS 784D, presently my 544A, is to fill the gap between the Combiscope and 694C. As better performing and featured as the Combiscope as possible, while still being a general purpose scope (1M inputs, wide input voltage range, memory, features...). In that department the 784D fully optioned up seems like the best there was at the time from Tek, and it's available. The 794D of course would be even better but I find it's much rarer than the 784D, so I am willing to compromise a bit !