Re: 485 No Trace - more progress

Robert Simpson

May have found something. Right after the Zin test point, with intensity turned full down on both scopes, At Q1742 collector- good scope 5.4V bad scope 12.7V. There is zener there. Will try and lift a lead and test. I can use an external power supply with series resistor and see if the zener is working.

--- In, David wrote:

I printed up the 475 and 485 schematics on 11x17 paper and added them
to my big 3 ring binder of test equipment I do not have a few days
ago. I sometimes scan in schematics from the paper manuals that I
have just so I can mark them up with colored pens.

At some future time, I may pick up a broken 465B or similar just so I
do not miss out on all of the fun and I have an idea for a circuit
which could replace the tunnel diodes that I would like to try.

I have lucked out with all of my oscilloscopes in not having to delve
into the ALT/CHOP/Z-Axis logic. I have however diagnosed a couple of
Tektronix universal timer/counters which involved reverse engineering
the logic circuits.

On Fri, 01 Feb 2013 02:50:47 -0000, "Robert"

Thanks for the tip. It will help. I just bought up that part of the cicuit to look at. In fact I am just printing out the layout for note takeing.
Note, nothing on beam finder either.

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