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JOHN E FAST

 

All,

Please excuse me if this is not the right place for this but there appear to be no discussion groups for the CD survey meters.

Does anyone know if the John E Fast capacitors are susceptible to moisture and should be replaced?
They appear in both the CD V-715 and CD V-717 survey meters.

Thanks,
Clint
 

If you are worried about it, pull one leg off the PCB and throw it on a cap tester and look for leakage at half voltage rating, then at full. I personally have not replaced this type before and always got a meter up by replacing the electrolytics.

-Stephen N.


On Mon, Jan 30, 2023 at 7:03 PM Clint <clintb@...> wrote:
Example



--
Stephen Nelson
KD6VEX
 

Generally speaking, we feel there's only one way to trust the CDV- 7xx ion chambers detectors. That is to buy one fully calibrated from KI4U.??

The amateur is just not equipped, nor could he be legally to even test them for function much less calibration.

It's hard to trust an instrument that "passes ckt check" even with the sensor completely? removed!

Just my personal opinion of course.

Geo

On Jan 30, 2023 9:02 PM, Clint <clintb@...> wrote:
Example
 

Clint:?
In my experience with vintage( 1950's 1960's) equipment, I have not come across a non-electrolytic cap that has gone bad due to age. Of course there are exceptions.
Electrolytic caps dry out and loose value and their ESR increases. Old carbon composition resistors seem to drift off, think that was due to moisture +/-20%
Is there a particular reason why you suspect a bad cap ?
Peter
 

Yes. ?I ruled out the second and third things shown below leaving possible moisture contamination. ?I tried desiccant but it didn't completely fix the problem. ?I would like to have more confidence that it will pass calibration before sending it in. ?I have a couple of meters that pass the circuit check and have a steady needle on all ranges, but that doesn't guarantee they can be calibrated. ?Maybe I'm mistaken but I doubt a meter with a drifting or erratic needle will pass.?



Looking at the John E Fast cap it appears to have a porous ceramic casing, so I was curious if anyone was aware of a problem with those capacitors before swapping them out.



Clint
 

Clint:
Is your issue just in the self check or zero settings or when the unit is switched to X0.1 range ?
I had a CDV-717 which had a oscillating needle on the X0.1 range. Did you look at sec 8.3 of the CDV-717manual ?

calibration adjustment by adding or removing a solder bridge on the pwb.
P
 

On my 720 and 717, drifting appears to be contamination on the high ohm resistors next to the triode under the cover. I looked at the procedure to clearn those and I feel I better leave that alone. When you add desiccant, and it behaves a little better, that tells me there is moisture reacting with stuff on those resistors causing leakage currents.

Team: Does KI4U also fix units that have issues or only provide calibration?

-Stephen N.

On Mon, Jan 30, 2023 at 9:02 PM Clint <clintb@...> wrote:
Yes.? I ruled out the second and third things shown below leaving possible moisture contamination.? I tried desiccant but it didn't completely fix the problem.? I would like to have more confidence that it will pass calibration before sending it in.? I have a couple of meters that pass the circuit check and have a steady needle on all ranges, but that doesn't guarantee they can be calibrated.? Maybe I'm mistaken but I doubt a meter with a drifting or erratic needle will pass.?



Looking at the John E Fast cap it appears to have a porous ceramic casing, so I was curious if anyone was aware of a problem with those capacitors before swapping them out.



Clint



--
Stephen Nelson
KD6VEX

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