Re: 475 Time Base Setting Problem

John Clark

Thanks Raymond,
I believe I need a Time Mark Generator for that and, unfortunately, I'm flying blind there as I don't have one.

I'm still planning on disassembling and cleaning the cam switches but I want to make sure I check all possibilities when I'm in there so I don't have to go back in again after a cleaning and re-check. Obviously I'll check R1083 and R1084 but I don't think they're open...out of tolerance maybe, but not open. I'm just puzzled. One check indicates R1083/R1084 or Switch 9 are open yet another check indicates they're not.


Date: Fri, 6 Nov 2015 06:20:35 -0800
Subject: [TekScopes] Re: 475 Time Base Setting Problem

> However, even if it was out of its detent it would still get some amount of voltage from R1070, right?

Sure, anything between +50 V and +15 V.

Either R1083 or R1084 has effectively gone o/c. is my hunch

Definitely, since sw. pos. 9 and its circuit still is a strong candidate. The sudden and complete failure of the affected timings speaks for a broken R over a bad switch contact.

It may still be worthwhile to check whether the working tim/div settings are correct within a few %.. If they are, I wouldn't worry about the close-to-zero (wrong?) voltage you find even at those apparently working speeds.

After all, there might be a failure somewhere in the integrator that allows it to operate at all but the highest-ohmic settings. If most timings are ok, that possibility becomes very unlikely.


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