Hello Group,
Moving on to the next issue (this one is minor... but annoying) on my recently acquired 7623A.
When I select any scale (either from Vertical amplifier or from Time Base) that requires 2 zeroes, it displays only one zero while the scope is still cold.
After warming up for - say - 5 to 10 minutes - it becomes normal.
While it's still cold, also, if I press IDENTIFY, the word identify doesn't show and instead, it shows (IIRC) a u symbol, in place of one of the zeros that are currently on display.
I narrowed down the temperature sensitivity to U2232, the "zeroes logic & memory" IC.
However, I`m not sure if the problem is in it, or if one of the signals coming into it is at a marginal level, and maybe when U2232 is cold, it's just misinterpreting the inputs which are marginal.
Fiddling with the "Column Match", or "Row Match" adjustments doesn't have any impact on the problem... it still "swallows" the second zero while cold, no matter what position those 2 adjustments are.
So, my questions to the group are:
1. Is there any Tek semiconductor manual available that shows what it has inside? The "Tek_Made_sm.pdf" available at TekWiki doesn't show it.
2. Does any of you guys have a broken readout board and would be willing to part this IC with me? I know that Sphere and Qservice have them, so I already have that as a last resort.
3. On my suspicion that the problem may *not* be at U2232, looking at the Column decoded signals that enters to it (and which are ultimately sampled at Time Slot 1 and memorized, to define whether it should add one zero, or two, or none), I find a little bit odd that the signals there don't really resemble "logic" levels, each (C1, C2, C3, C4 and C10) are sort of different from each other, and some of them really look much more analog signals then a digital signal with clearly distinct discrete levels.
I will try to take pictures from each one probed on my other scope and post it.
From what I understood, although the original Row and Columns signals are analog (OK. Discrete 10 levels analog signals)... after they are processed by the Row and Column decoders, those signals should have been translated into 10 different "logic" outputs, with only one output showing an "active" level, and all the other ones showing an "inactive" level (I don't say high or low because I`m not really sure if they're active high or active low).
Still, those "Column Decoded" digital signals (that don't look like digital) are the same ones going to the character generator IC matrix... And there doesn't seem to be a problem for the character generation circuitry, and all the displayed characters are correct, leading me to conclude that despite the Column signals don't look like what I expect... they might be correct anyway.
So my 3rd question: Can any of you take a look at the column decoded signals (the ones entering at pins 10,11,12,13 and 14 of U2232) and tell me if they look like digital signals, with clearly distinct "active" and "inactive" levels?
Thank you in advance for any input...
Rgrds,
Fabio
Fabio Trevisan