I'm sorry Reg, I thought you had a "C" model.
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I agree, they are fun to play with.
I will try to check my "C" for the information
Reginald Beardsley via Groups.Io wrote:
My scope is an 11801. That should be visible in the screen photo I posted. Based on the dates on parts it is 1989 production. It is enough different from the 11801C that it was obvious from the meager information in the service manual for the 11801C that I needed an actual an 11801 manual. Zenith was kind enough to furnish a scan of the 11801 service manual, which is now available online, but I bought a paper copy.
I currently am triggering off a square wave on one channel of the 33622A while displaying a ramp from the other channel. There is a periodic jitter in the time base, so even with an external trigger I cannot get a stable sweep. In 1024 point mode at 1 ps/div it appears that there are 4-5 subsweeps before it repeats. As a result the trace oscillates back and forth over a span of about 1.3 ps as it drifts across the screen. In 5120 point mode it seems to have just 2 subsweeps with ~1 ps dither between them.
When the OXO heater kicks on everything jumps out of sync for a while. It may well be that the mystery NVRAM calibration constants are intended to correct the time offset between the sweeps. IIRC my timebase ROMS have a 1991 or 1992 date, so it is possible that my scope had a FW update and could be corrected if I knew where and what values to write with a PROM programmer.
If someone has an 11801C or other newer model open I'd appreciate version and date information on the timebase board ROMS. But if anyone knows *anything* about this I'm very interested in investigating. I've got another 11801x in CA at my sister's house which I'm waiting for her to ship to me. I have had more fun with my 11801 than any other piece of test gear I've bought. Being able to see reflections from each side of a high grade SMA-F to N-F adapter is quite amazing.