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

Chuck Harris
 

Hi Alex,

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.

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.

Working amounts of power supply ripple are not generally
noticeable. Large amounts, usually cause erratic operation.
An example of erratic operation would be trigger jitter.

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.

The way it measures frequency is rather convoluted, but
depends entirely on the sweep accuracy.

Think of it this way, the sweep is generated by charging
a capacitor with a constant current. It is correlated
to both the graticules, and the cursors during calibration.

The frequency measuring method uses the trigger hybrid
and a DAC to measure the zero crossing points of the
waveform, and uses the delay sweep to measure the time
between the zero crossing points. The CPU then performs
the inversion, and the display shows that number as the
frequency. It is not a frequency counter!

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.

It would look as you are describing your scope, regardless
of how old it really is. If I cannot repair it, and clean
it up to that degree, it becomes a parts source.

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.

-Chuck

tekscopegroup@... wrote:

On Tue, Oct 30, 2018 at 01:11 PM, Chuck Harris wrote:

For what it's worth, the power cycle counter, and on time counter
are meant to be reset after every calibration. They are there to
let the technician know how long it has really been since the last
calibration... as opposed to whatever the customer says..

They don't mean much to a customer. If you see really low numbers,
it simply means the scope saw little use since its last calibration.

-Chuck Harris
Hi Chuck, this certainly makes a lot of sense. Thanks for clarifying it, never heard this simple and logical explanation from anyone else, other that people being very happy when they see low numbers on those counters on a newly acquired scope. This one does not have any past cal stickers at all, so wonder if it ever was calibrated after being purchased.

Since I am new to this model, I noticed that when pressing any front panel switch, all the other indicators seem to very briefly flash in unison before the requested change is executed. Is this normal? Also, under certain conditions, specially when using the x10 horizontal magnifier and on the lower vertical v/div ranges (10mV and bellow), the traces seem somewhat blurry. But without changing the v/div range they clear up nicely and look very sharp when I engage the 20MHz BW limit, tough. Would this possibly mean HF power supply noise or power line ripple creeping into the circuits? (aging filter caps that need to be replaced?). I have not yet gotten to checking all the power rails at J119, will do so when the Mouser parts order arrives and the cover needs to come off again.

The other issue I've seen is that the automatic frequency measurement (press the measure button and then select 1 for frequency) is off usually by at least 10% or so, sometimes even more. Accuracy of the internal 10MHz reference oscillator not really being that accurate? If so wish there was a way to retrofit an external 10MHz ref input, which I understand is one of the standard options. I read somewhere that it is fairly easy to do it, but found no detailed information. As a comparison, my 2247A will always read the frequency very accurately, and its off by just 71Hz tested against a freshly calibrated rubidium oscillator.

Lastly, I figure you're probably the best person to ask this. On the installed options sticker on the back, the only field marked (punched out) is 46 (between the 22 and 1E fields) on this rear aluminum sticker. So far I have not been able to find any reference at all for an Option 46 on these scopes, and nobody that I asked so far seems to know. Are you by any chance familiarized with what this option 46 entails?

Thanks much.
-Alex



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