Re: Tektronix 577 crawling dots and CRT noise


Dave Voorhis
 

On 21 Apr 2020, at 19:29, Eric <ericsp@...> wrote:

I wonder if something is oscillating or out of alignment. At 0V collector there should be little to no deflection in any mode I know from talking to some people here that adjusting the storage / tube sections of the D1 is quite an undertaking and very fiddly adjustment.
I just went through the calibration procedure, or at least most of it, on my 577 because I replaced the faded CRT with a used unit. I don’t know (nor did the previous owner) if it came from another 577 or a 5111 ’scope, which I think uses the same CRT?

The whole calibration seemed fiddly and questionable. Just about everything seemed to be described poorly and seemed more difficult than it should be, but who am I to argue with Tektronix?

Storage went from working well with the old CRT — though the live trace was almost invisible due to the weakness of the CRT — to a nice bright, sharp trace on the new CRT but no storage before calibration, and barely adequate storage after calibration. It seems unreasonably insensitive — it requires considerable trace brightness to work at all — and tends to leave blank spots (though not consistently, so perhaps not target burn?) and if adjusted for greater sensitivity the background fades up unusably, won’t erase consistently or fully, etc.

Both carefully following the calibration instructions and using ad-hack tweak-it-to-work-as-best-it-can wind up with the same results.

I suspect the replacement CRT might have worn out storage internals, though I’m not familiar enough with failure modes in analog storage ’scopes (despite having a 549, a 564, and a 7623) to assess it.

Advice on that would be appreciated.

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