Re: 2465B - Weak Readout Intensity


On Fri, Jan 24, 2020 at 01:12 AM, satbeginner wrote:

The 2465x uses what I call a "fly by wire" control system.
The sample and hold circuits are build using a simple opamp circuit.
The output of the analog switch charges a capacitor, and the high input
impedance of the opamp keeps it at the presented level.
The opamp shifts the level depending on what the functionality needs.

I have seen these sample capacitors go bad as well as the opamps. (TLO72???)
Thank you for pointing this out! This illuminates an entire section of the DAC "fly by wire" circuit that I have heretofore overlooked.
Certainly before I go to the monumental effort of performing a CRT swap, I will sniff my way carefully thought this MUX'd sample-and-hold circuitry.

I have ordered a CRT, which hopefully will be of the 2465A/B flavor, but I'd be nothing but glad to just put it up on a shelf or resell it instead of having to install it!

Also let me add my "+" to the massively informative, if not exasperatingly long and multilayered EEVBlog "2465B Teardown" thread. I spent hours pouring over that thread—hours well spent for anyone diving into a 2565B restoration. It was that thread that essentially illustrated the finer points of repairing the later model A5 board with its notorious leaky 'lytics.

- Scott

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