Re: My 2465B has arrived + A5 Board leaky caps cleanup

Chuck Harris
 

Noise is endemic in electronics. It is related to the
temperature. The resistors, transistors, etc.. All make
a contribution to the noise.

The noise of a receiver is set by the noise of the front
end of the receiver. Once established, any further
amplification simply amplifies the noise... the signal to
noise ratio stays basically the same.... well, until overload.

When you have the scope in the higher gain positions, the
noise is being amplified, and is displayed as more fuzz.

Noise of this sort is called white noise. Its distribution
is fairly uniform across the frequency band of the scope.

If you run the scope at its full 350MHz bandwidth, it is
slurping in all of the front end's noise from DC to 350MHz,
and adding it to the trace, everywhere...

If you reduce the bandwidth of the scope, to say: 20MHz, there
is less overall noise to add into the trace, because there is
less overall bandwidth... the noise from 20MHz through 350MHz is
mostly blocked.

About the blink: Sorry, it has always been there with the
2465A and B models. It is not as apparent with the plain
model, mostly because the LED's are dimmer.

Wnen the LED's registers are loaded with the state of the
LED's on the panel, they all go into an LED ON state for
the duration of the load. It is a feature of the register
used.

CAL 05 is the routine that can read/set/reset the counters.
Its default position is to reset the counters. You can
set them to whatever you want... the technique requires
you to select the increment using the X10 button, and to
rotate the Delta Ref, and the Delta controls to make the
appropriate counter change... I know of nobody that does
this.

There is no specific manual for this option, but rather
there is the main instrument manual, and the GPIB options
manual.

GPIB on the 2465B is a complete waste for the usual user.
It only allows you to set the front panel controls, and
display some text on the screen. It does *not* allow you
to read anything that is derived from the CH1-4 inputs.

It's purpose is for use with the rack panel version of the
scope, when using the scope to do mindless calibration
and repair routines of military equipment. Basically, it
replaces the calibration manual with a computer as the
source of calibration information.

-Chuck Harris

tekscopegroup@... wrote:

Chuck as usual your explanations are outstanding. After reading them, just a few short extra questions/comments, bellow.

On Wed, Oct 31, 2018 at 09:49 PM, Chuck Harris wrote:
The design of the front panel is such that all of
the displays states are in registers that get strobed
whenever anything is changed on the front panel. That
shows up as a brief flash of all lights.

The 2465B uses 74F logic for those registers, the older
2465 used 74LS logic, and fairly dim LED's. The blink
is scarcely noticeable with the older 2465. The 2465B
uses much brighter LED's, and the blink is quite apparent.
I assumed that it was normal, but I was surprised to see the effect as it was never evident on any of the videos I'd seen before.

With 350MHz bandwidth comes a lot of ambient noise. Cut
the bandwidth, and you will cut the noise. That is why
the scope has the 20MHz bandwidth limit switch on the
front panel.
So it is normal to see some fuzziness on the traces at full bandwidth? I really have to go through this again, as I seem to remember the amount of fuzziness varied somewhat depending on the time/div setting, not sure that would be normal. I am still awaiting for the Mouser parts for the A5 board to arrive, and will confirm that once I have to put the scope back on the bench to work on replacing those parts.

The 2465B is not a frequency counter, and the A5 board's
10MHz reference has nothing to do with sweep or frequency
accuracy.

The way the 2465 family creates its sweep is by using a
miller integrator, and precision integration capacitors.
...snip...

Very nice explanation of the principle used to make the measurements, now I have much better understanding of the process.

It is standard practice of most sellers to remove all
calibration stickers, and stickers showing previous
ownership before the sale. Although I don't sell a lot
of scopes, when I do, I blow out the dust from the inside,
clean the outside, and the CRT, make any repairs, and
calibrate the scope, complete with zeroing the counters.
If I may ask, how do those hour and power cycle counters get zeroed out? I don't think I have seen the reset procedure explained in the service manual.

According to Manuel Maseda, Option 46 is the military
version of the scope (OS-288/G) that includes option 10
(IEEE-488), and 2 probes.
Is there a more specific service manual for this variant I should look for?
If you happen to know, are there any differences in the military version from the regular version?
Perhaps a sturdier build? or what where the military requirements?

Thanks again Chuck.

Alex



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