Re: Tek 2467B Erratic Intensity controls


The comparator U2510, an LM311, is used to compare the DAC output to pot
readings, and the MPU uses this with successive approximation to make a
software ADC. This is described in the “Theory of Operation” section.

The trigger hybrid is not involved in pot scanning, though otherwise it
works the way Chuck describes it.

On Sat, Nov 30, 2019 at 04:49 Chuck Harris <> wrote:

There is no ADC part in the 2465 family scopes.

There is a DAC that is used as a part of an ADC
that is made from the DAC, CPU, MUX's, Sample and
Hold cells, and the trigger hybrid. The trigger
hybrid is used as the comparator that compares the
DAC output to the pot's wiper voltage.

The voltages get to the trigger hybrid by way of
a pair of muxes.

The capacitors referred to in the post are on the
A5 controller card on scopes with serial numbers
greater than B049999.

They are ordinary power supply bypass capacitors,
that because of the abuse of their being soldered
to the board by an oven, leak electrolyte all over
themselves, and the circuit board. The electrolyte
is highly corrosive to copper, and highly conductive
to electricity. It eats the copper traces, and
shorts out other components and traces.

They are the only surface mount electrolytic capacitors
on the board. Three are near the DAC, and the other is
on a distant corner.

If your A5 controller board has these capacitors, you
must replace them before anything else the scope does
will make much sense... Assuming that they haven't been
replaced already.

-Chuck Harris

peter bunge wrote:
Thanks Chuck, I was following the signal path from the two Intensity pots
on the 2467B schematic, sheets 5 and 2. They do not go to an ADC input
I'm sure they must. There is something missing on the schematic, and I
looked at several.
Do you know what capacitors are referred to in this post:
Did you solve the capacitor leak problem on A5 logic board? Cause all
settings are under dependance of the DAC and when resistor connections
corroded everything goes wrong, including display points appearing, and
intensity dimming.

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