Yeah, it will need a full cal regardless...I changed out the CRT from the 7903 parts unit I have. I do have good quality non-inductive resistors on hand.
Since I have two identical vertical amplifiers thanks to the parts unit, I did the resistor swap on one of them. It did help a little, but it's not the whole issue. Unfortunately, the vertical output IC on the original amplifier that was in the scope is very much bad. And the output IC on the board from the parts unit already had crap high frequency response because it looks like a gorilla bodged together the little output wires that go to the CRT vertical deflection inputs. The ones on the bad output IC are single wires; the working one has about three sloppily soldered together...which cannot be a good impedance match at all.
I hate to say it, but I may need another vertical amplifier board with known-good ICs altogether.
Sean
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On Tue, Jan 26, 2021 at 10:41 AM, Nick Shipman wrote:
Hi Sean,
A bit of drift shouldn't be a big problem if both resistors in a pair do it
by the same amount ¡ª it's when one differs from the other that you'll get
the trace shifting up or down. But with any drift the overall sensitivity
will change to some degree, so you might want to look at the vertical
calibration once you're happy with the trace positioning.
Make sure you use non-inductive resistors for the replacements, try to get
ones of about the same size, and avoid bending anything (I seem to remember
it's all a bit 3-D here). It'd be a shame to spoil that amazing performance.
Regards,
Nick
