[R-390] Carrier Level Meter Issues

Wed Mar 9 03:31:37 EST 2022

Thanks Jim.  You are right.  I should  have elaborated.

So Gary, If I were using my 50 ua vom (which is the largest scale I'd use
for measuring leakage), I'd use a 4 Meg Ohm resistor in series with the 200
vdc source, cap and meter to limit the current to 50 ua.  The res will skew
the reading a little, but that is not important.

Regards, Larry

On Tue, Mar 8, 2022 at 11:24 PM Jim Whartenby via R-390 <
r-390 at mailman.qth.net> wrote:

> When doing any kind of leakage testing, you have to think about unintended
> consequences.
> If you plan to measure current by putting the VOM or VTVM in series with
> the DUT (Device Under Test) plus the power supply then if the DUT fails in
> a short, the power supply will force the maximum current that it is capable
> of supplying through the meter.  That will do wonders to the pointer of the
> analog meter movement or the circuitry of a DMM.  Not to mention heating up
> the DUT.
> You should limit the maximum current so as not to overstress either the
> DUT, the power supply or the test equipment.  If you have a power supply
> that you can set current independently of voltage then with the voltage set
> to near zero, short the power supply leads together and adjust the current
> setting pot to set a maximum current of perhaps 25 mA.  Then if the DUI
> fails, the power supply voltage will fold back to whatever voltage is
> required to supply that set current.
> Don't have a fancy power supply?  You can select a resistor to provide a
> reasonable current at the test voltage you plan to use.    Measure the
> voltage drop across the resistor.  Each volt dropped across the resistor
> divided by the resistor's value is the total leakage current.
> By selecting a current limiting resistor of 1, 10, 100, 1k, 10k and so on
> ohms, one volt measured across that resistor is equal to one amp, 100 mA,
> 10mA, 1mA, 100 uA and so on.  You get the idea.
> Now you can run the leakage test without having to closely monitor what is
> happening.  If the DUT shorts, then the power supply, meter and DUT are
> protected form overstressing and this will help keep that magic smoke
> inside the power supply, meter and DUT.
> This same sort of setup can also be used to reform electrolytic capacitors
> that have been setting around for ages before you install it into the
> equipment you are repairing.
> JimLogic: Method used to arrive at the wrong conclusion, with confidence.
> Murphy
>
> -----Original Message-----
> From: Larry H <larry41gm at gmail.com>
> To: Gary I. Biasini <gary.biasini at shaw.ca>
> Cc: R-390 Forum <r-390 at mailman.qth.net>
> Sent: Tue, Mar 8, 2022 11:42 pm
> Subject: Re: [R-390] Carrier Level Meter Issues
>
> Hi Gary,  I'd start with a vom or vtvm.  If nothing there, apply about 200
> vdc (because of the circuit it is in) from can to one cap end and then
> the other one.
>
> Regards, Larry
>
> On Tue, Mar 8, 2022 at 9:13 PM <gary.biasini at shaw.ca> wrote:
>
> > Larry,
> >
> > How would you check cap to can leakage?  With an ohmmeter or at a higher
> > voltage?
> >
> > Thanks.
> >
> > Gary
> >
> > -----Original Message-----
> > From: r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> On
> > Behalf Of Larry H
> > Sent: March 6, 2022 8:30 PM
> > To: R-390 Forum <r-390 at mailman.qth.net>
> > Subject: Re: [R-390] Carrier Level Meter Issues
> >
> > Hi all,  There is a second type of leakage in this style of cap (cap in a
> > can), from cap to can (which is grounded).  This is just a damaging to
> the
> > agc circuit as the other normal type of leakage.  Both types of leakage
> > need to be checked.
> >
> > Regards, Larry
> >
> > On Sun, Mar 6, 2022 at 9:27 AM <gary.biasini at shaw.ca> wrote:
> >
> > > Renee,
> > >
> > >
> > >
> > > Thanks for your thoughts.  What do you use to heat the C551 can to
> > > disassemble it?
> > >
> > >
> > >
> > > Thanks again.
> > >
> > > Gary
> > >
> > >
> > >
> > > From: Renee K6FSB <k6fsb.1 at gmail.com>
> > > Sent: March 6, 2022 10:16 AM
> > > To: Jordan Arndt <Outposter30 at shaw.ca>; gary.biasini at shaw.ca; R390A
> > > List < R-390 at mailman.qth.net>
> > > Cc: 'R-390 Forum' <R-390 at mailman.qth.net>
> > > Subject: Re: [R-390] Carrier Level Meter Issues
> > >
> > >
> > >
> > > Hi All-
> > > I replace C551 on sight....on 16 (IIRC) IF decks I have never found
> > > one that does not have leakage current ( maybe just my bad luck,
> > > tested on Sencor LC102)...oil/paper....i went with mylar anywhere
> > > between 1.5uf or
> > > 1.8 uf ( I liked these best) to 2.2uf.
> > > I machined small rectangular aluminum cans (with teflon feed thru for
> > > the
> > > leads) for them to fit in the original space. and as Jordan suggests
> > > the 1.5uf will fit in the original can......I drill a small hole
> > > before heating to disassemble the can. I do not like hot oil
> > everywhere......
> > > some of the postage stamp Micas are starting to have shorting issues
> > > due to impurities, moisture intrusion and what is called silver
> > > migration...so do not rule them out because they are mica.
> > > Renée, K6FSB
> > >
> > >
> > > On 3/6/22 4:25 AM, Jordan Arndt wrote:
> > >
> > > Hi again group...
> > >
> > > Any leakage of C551 will dramatically alter the AGC characteristics,
> > > with the results of leakage being seen as a longer to much longer AGC
> > > recovery time and a lower and "softer" AGC voltage.
> > >
> > > I rebuilt C551 in my three 390As using non-polarized 1.5uF @ 450Vdc
> > > film caps which just fit inside the original square can. The result is
> > > a "stiffer" AGC voltage, and a noticeably quicker return to receive
> > > than with a 2uF cap.
> > >
> > > I use a restored Sprague TO-6 to detect leakage, and these film caps
> > > show no measurable leakage at all, where all of the original C551 caps
> > > clearly showed varying degrees of leakage. I'd expect that most, if
> > > not all, of the original C551 caps are leaky by now and should be
> > replaced/rebuilt...
> > >
> > > 73...Jordan VE6ZT
> > >
> > > ----- Original Message ----- From:  <mailto:gary.biasini at shaw.ca> <
> > > gary.biasini at shaw.ca>
> > > To: "'Larry H'"  <mailto:larry41gm at gmail.com> <larry41gm at gmail.com>
> > > Cc: "'R-390 Forum'"  <mailto:R-390 at mailman.qth.net>
> > > <R-390 at mailman.qth.net>
> > >
> > > Sent: Saturday, March 05, 2022 10:13 PM
> > > Subject: Re: [R-390] Carrier Level Meter Issues
> > >
> > >
> > >
> > >
> > >
> > > Larry,
> > >
> > >
> > >
> > > Thanks. In fact, I started on one tonight which will be the subject of
> > > a separate post once I do a bit more work.
> > >
> > >
> > >
> > > I checked the manual for the IT-11 and in fact, when properly
> > > calibrated, on the setting for “Paper, Mica, etc.” capacitors – i.e.
> > > anything other than Electrolytic or Mini-Electrolytic capacitors, the
> > > eye will not open if the leakage is more than 2 ua so, the C551 that I
> > > tested leaks less than 2ua.
> > >
> > >
> > >
> > > By the way, the threshold for Mini-‘lytics is 15ua and the threshold
> > > for Electrolytics is the 2ma.
> > >
> > >
> > >
> > > Thanks again for your response.
> > >
> > >
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