Re: 2465A channel 2 problems


Are you saying that the scope CH 1 & 2 inputs will be in 50 ohm mode for all the Cal procedures? I did check the inputs in normal mode when switched to 50 ohms, and they are both OK, right at 50 ohms.. I haven't checked their state when in the different Cal procedures; I'll be back at it a little later.

Also, I don't hear CH 2 relays clicking when going from the 500 mV to the 1 V scale; OK from 50 mV to 100 mV. The inputs stay at 1 M throughout the ranges for both CH 1 and CH 2, but I expect that particular relay isn't being activated for CH 2, so it is stuck in the 500 mV range and showing a "good" 1 M input.

I'll have to look at the schematic and see if I can jumper the proper relay to activate the 1 V scale change. They are OC Darlington's, so that may tell me whether it is the attenuator module relays or if the software or the drivers are the problem. Any other suggestions are welcome!


----- Original Message -----
From: "Chuck Harris" <cfharris@...>
To: <>
Sent: Thursday, October 17, 2019 8:56 AM
Subject: Re: [TekScopes] 2465A channel 2 problems

Hi Gerry,

First, you are not supposed to get a trace, just a pair
of dots, approximately 10 divisions apart.

This is a crucial step, as it affects all future steps.

I would suggest that you always put it in VAR mode, as it
will always give you an adjustable range to hit the mark.

But note: It is most important that the VAR knob be back
in its click before you start the next, and all subsequent,
steps. If you do not do this, you will achieve out-of-range.

If you repeat this step after having done it recently, you
will usually find that the dots are perfectly spaced.

There is no linkage between the 50 ohm annunciator light and
the 50 ohm relay in the preamp. Unless your preamp is broken,
it is in 50 ohm mode.

As a test, when the scope is in normal mode, put the preamps
in 50 ohm mode, and measure them with an ohmmeter. If they
are other than 50 ohm, you have the ever popular burned out
50 ohm load. Unless you are very clever you will be replacing
your preamp, as the resistor is printed on the ceramic substrate.

-Chuck Harris

GerryR wrote:
Another question or two for those in the know: At the beginning of the Cal 02 procedure, it states to connect a 0.5 V standard-amplitude signal to CH 1 and to use CH 2 Position to vertically position the "trace" to within 1 division of the center graticule line, and then to use the CH 1 Position and Volts/DIV VAR controls to obtain a 10-division horizontal signal. I don't get a "trace," only 2 dots. I can position the dots with the controls to put one dot on the first graticule line and the other on the 10th.
Question 1: "Is this "normal," or am I doing something wrong?" I've read and re-read the procedures and can't find any references to this.

Also, at the beginning of the Cal 01 procedure, it states that, "Upon entering Cal 01, the Input Coupling is automatically set to 50 ohm DC ....." This doesn't appear to be true for the other Cal procedures (2,3,4,etc), as I had to install a terminator on my generator to get the actual levels called out in the test procedures (monitored on another scope).
Question 2: "Is this correct, or am I missing something here, as well?

Thanks in advance for any input!


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