frank.stellmach | 25 Mar 12:38 2015
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Junior Member Lost Shirt on 720a KVM Purchase

Hi Stan,
 
The Deck A switch is a 3 layer, 1 to 12 type.
 
I assume that one of the (ceramic?) layers is broken.
 
You may desolder and disassemble the switch, to find out.
 
Maybe it's repairable ( i doubt that).
 
So you may get a spare part from Fluke, as I think, they still manufacture these instruments.
 
Or you may get such a switch from IET Labs, as they also actually produce a clone of this.
 
You may also order a custom made replacement from ELMA.
They offer a modular precision switch, gold plated contacts, Type 04
The isolation resistance is high enough, only the contact resistance is not so well specified, and may
degrade the performance of the 720A.
 
http://www.elma.com/en-eu/products/rotary-switches/rotary-switching-products/product-pages/type-04-detail/
 
Frank
 
 

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Stan Katz | 25 Mar 03:32 2015
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Junior Member Lost Shirt on 720a KVM Purchase

I purchased a 720a KVM off Ebay, and let it sit until I had gotten my
HP419A Null Meter working.  I now have the null meter working, but it
appears that the 720a sealed switch S1 ("A" divider ) is bad. At least
that's what I think. The "A" divider dial has no effect at any dial
position (constant open "A" divider), and only the B - G switches work.
Rotation of the entire instrument to a vertical position causes the "A"
switch to lock up between positions 4 and 6. Thus, my guess is something
broke off inside the switch and just happens to settle into a
non-interference location when the instrument is righted.  The switch was
manufactured for Fluke by Tech Laboratories of Palisades Park, NJ and bears
the stamps 720A-801 Rev2---2012-1512-3. That firm seems to have gone out of
business sometime in the 1970s. I did a proforma check of solder joints to
see if I could spot any cold, or open ones. They all looked good to me.

Does anyone have any advise as to my next action with the instrument other
than resell this one on Ebay for "Parts not Working" and taking a chance
with another Ebay purchase?

Stan
Richard Moore | 21 Mar 21:02 2015
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Fluke 731B

Hi all — realisitcally, what sort of stability can be expected from a fully functional 731B regarding
variation in ambient temp a few degrees C around 23, and for long-term drift? 

Fluke’s specs are very conservative, and I think the 731 is far better than the specs would lead you to
believe, but I have no practical experience with these units.
Cowham, Chuck | 19 Mar 18:45 2015

HP 3456A Input Impedance Check

Recently, I was curious about the HP 3456A input impedance.  The manual
states >1E10 ohms.  But, what is my 40+ year-old meter today?  Using a 10 V
source and a switchable 1x/10x scope probe I did a quick check.  When the
scope probe is switched to 10x a 9 meg series resistor is inserted between
the probe tip and the meter input.  Input impedance can be checked by
comparing 1x and 10x readings.

With autozero on, readings were 1x:  9.99995 V and 10x:  9.99990 to 9.99993.
Worst case, there was a 50 uV drop across the 9 meg resistor, which puts
input impedance at 1.8E12 ohms.  Quite amazing.

Then, wondering if the autozero was injecting charge into the input and
causing the readings to change with the probe at 10x, I checked again with
autozero off.  Now the readings for x1 and x10 are the same or at most one
digit (10 uV) different.  One digit difference equals 9E12 ohms.

I'm sure the dry winter air is helpful for this measurement.  I'll check
again in steamy August.

-- Chuck

gavin_pro | 12 Mar 09:49 2015

回复: volt-nuts Digest, Vol 67, Issue 2

Thanks !

Gavin 

-------- 原始邮件 --------
发件人: volt-nuts-request@... 
日期:03-11-2015  00:00  (GMT+08:00) 
收件人: volt-nuts@... 
主题: volt-nuts Digest, Vol 67, Issue 2 

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To subscribe or unsubscribe via the World Wide Web, visit
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When replying, please edit your Subject line so it is more specific
than "Re: Contents of volt-nuts digest..."

Today's Topics:

   1. Datron 1271 (Михаил)
   2. Re: Datron 1271 (Didier Juges)

----------------------------------------------------------------------
(Continue reading)

cfo | 11 Mar 22:26 2015
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Seeking Racal 9480 manuals

Gents

I just got a Racal 9480 w. OCXO and 40x10MHz outputs
I can't find any user or service manuals for this unit.

Can anyone help out here ?

I don't even know if the OCXO labeled "Frequency Standard 11-7038" 
is an Opt 04A or 04F.

TIA
CFO - Denmark

--

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frank.stellmach | 11 Mar 15:49 2015
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Datron 1271

Hello Mickle,
 
many thanks for these documents!
 
Do you know, whether Datron 1271, 1281 are identical in hardware, and Fluke 8508A very similar to the Datron
instruments, concerning the main PCB?
Maybe differences between 8508 and 1281, only concerning volt references and user inetrface?
 
Frank

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Stan Katz | 11 Mar 06:42 2015
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OCD About My HP419A Attenuator Switch Gold Plated Contacts

Now that I've restored my HP419A to running order for the meantime, I have
nagging questions regarding the continuous use of the attenuator switch.
The main board of the instrument, A4, was badly polluted with an invisible
layer of potassium hydroxide from the 30 years of being in the same box
with dead/mummified nicad batteries.

In accordance with
http://www.faa.gov/documentLibrary/media/Advisory_Circular/AC43-206part2.pdf I
prepared a 3% boric acid solution and flushed the affected circuit board
several times, while scrubbing with a soft nylon toothbrush. I then flushed
the board with hot water. After leaving the board on my furnace plenum for
a few days to thoroughly dry out, the board problem was sorted out. If the
KOH deposited an invisible layer on A4, then certainly, there must be a
layer of KOH on the attenuator switch's gold contacts, as well. I posted my
concern about the KOH on a premier chemistry forum. The administrator
himself answered my query. He indicated that the only way to remove the KOH
from the switch is to thoroughly flush with di water.  There's no place for
a flushing stream of water to exit the instrument safely.   I'm not about
to remove the switch! Now, I don't know the hardness of KOH,  but Potassium
has a very small .5 mohs of hardness. I presume, that KOH is similar. In
any event, I would tend to believe there will be some small abrasive wear
from the KOH. The attenuator on a null meter is heavily utilized, and even
a light abrasive can cause trouble eventually.  Proper gold plating, that's
kept clean, never suffers from abrasive wear. Improper plating, can suffer
from adhesive wear, but I have confidence that the HP of the 1960s-80s was
using the finest gold plating available.  I thought about applying one the
the Deoxit products. A careful reading of the Deoxit literature claims that
the D-series treatment is for "non-critical metal surfaces". I think that
the gold plating in the HP419A qualifies as "quite critical". The Deoxit G
series literature leads me to believe it may not have enough cleaning
(Continue reading)

Stan Katz | 1 Mar 07:53 2015
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HP419A Temporary Chopper Fix

For those of us who are in need of a temporary fix for our HP419A null
meters, with dead neons, here is some good news.

At http://dabbledoo.weebly.com/hp419a.html you will find an intriguing
circuit that overcomes the need for SOT neons with specific strike and
breakdown voltages.

I built this circuit, and ordered NE2U chopper capable neons from
bulbtown.com to replace the dead ones in my unit. They are cheap, and made
in Taiwan, which means there's a good chance they were manufactured in the
last 1 to 15 years. Beware of purchasing genuine US made 30 to 50 year old
NE2Us. The Krypton 85 in NE2U lamps only has a half life of about 10 years.
US made neons would have marginal dark effect compensation left in them.
Not only that, they go for over 100 times the cost of the Taiwanese ones at
bulbtown.

I aged the newly installed NE2Us for 2 weeks without the dabbledoo circuit
installed. During that time the unit continued to malfunction.  I then
connected the add-on circuit into the unit. Voila, my HP419A came back on
the air!  I inserted the circuit on a floating perf board using Bendix
connector female sockets (TE Connectivity P/N 66360-4 and male pins P/N
66361-4) thereby avoiding having to chop up any of the unit's wiring if
things didn't work out. The females were perfect, the pins just a shy too
big.

Caveats: This fix should be considered temporary. There's the possibility
that one, or both of the replacement NE2Us breakdown voltage could climb
beyond the capability of the 419's blocking oscillator, which is still the
source of firing voltage with the add-on circuit installed. Thus, you may
have to go through additional bulbs to find ones that fire. I give no
(Continue reading)

new | 23 Feb 18:14 2015

John Miles' GPIBKIT - how to get it? Re: volt-nuts Digest, Vol 66, Issue 15

I find no 'search' function on here... How do you get to
the GPIBKIT ?
Willy

On 2/20/2015 12:00 PM, volt-nuts-request@... wrote:
> Send volt-nuts mailing list submissions to
> 	volt-nuts@...
>
> To subscribe or unsubscribe via the World Wide Web, visit
> 	https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts
> or, via email, send a message with subject or body 'help' to
> 	volt-nuts-request@...
>
> You can reach the person managing the list at
> 	volt-nuts-owner@...
>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of volt-nuts digest..."
>
>
> Today's Topics:
>
>     1. Fluke 725 and 726 (pa4tim@...)
>     2. Re: 3458a BASIC commands for today??? (cfo)
>     3. What do the NIST numbers on a calibration sheet come from and
>        what do they mean? (John Phillips)
>
>
> ----------------------------------------------------------------------
>
(Continue reading)

John Phillips | 19 Feb 21:06 2015
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What do the NIST numbers on a calibration sheet come from and what do they mean?

--

-- 

*John Phillips*

Gmane