Hi Brook,

I know it's a pricey box, but I got mine cheap (<$100) at an MIT Flea Market.

If I wanted a cheapo leakage tester, I'd build one with a simple, variable
voltage inverter, maybe a Cockroft-Walton stage or so, and a couple of $20
DMMs.

-John

=============

Yes, except the schematics suck. Dave H at ArtekMedia helped mo out with
that.

You could also get the manual from Sencor directly for something like $20

• $50, I forget exactly.

The LC 102 has been replaced with the LC 103, last seen.

-John

=================

All,

Speaking of replacing electrolytic capacitors, which I am now doing on a
Fluke 845A, I found a carbon comp resistor way out of spec. It is a 150
ohm, 1/4 watt current limiter, for a 10 Vdc zener. I noticed that it had
looked to have been hot (or gave off excessive heat), and had made a shiny
place on the PC board above it, though the resistor doesn't show any burnt
color. When I measured it, it was reading around 1 to 2 ohms. The zener was
still good, luckily, as was the bridge rectifiers, and filter cap (though
bulged), and this is the supply voltage for the switching transistors,
which run the chopper transformer.

My question is, have any of you seen a 150 ohm carbon comp resistor change
that much in value? I wouldn't think they could, but evidently, this one
did, and if so, I wonder about the others in the meter.

Thanks,

Will

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On 6/24/2011 at 11:22 AM Brooke Clarke wrote:

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Sencore 102 or 103's. If your lucky you can find one for less < $200.

If you don't mind the age. At the bottom of the pile are ones like the
Eico 950-B and many that are close. The 950-B is about the best
in the lower shelf.  Stick with the B, newer if anything and remember
Eico's also came as a kit. If you not in a rush, wait till you find a ....

Sprague Tel-Ohmike's The 5 and 6's being the last of the series
and the only ones to really consider. Just my call, others like some of the
older ones. Depending on condtion and phase of the moon you can get
a TO-6A for around $50, most go for about $100.

Next shelf up I would say the Clough-Brengle 712 and its military cousin
the ZM-11/U. I find it harder to use only in that everything is jammed so
close. And my 712 died a couple years ago and havn't got around to
looking inside. Price $50 to $100

Non of these prices reflect Ham-fests, Aunt Milli's thrift store etc.

All the above will or should be gone over, the usual stuff caps, resistors,
etc.

The one I use the most is the Tel-Ohmike 6A. Some say the 5 is better
and the 6's did dropped the transformer ration feature, but I only the thing
i use it for is caps.

Moving into the modern era, the Sencore's 75, 102 and 103.

Again at the top Sencore 102 and 103's, but you really have to be lucky
to get one under $100 or so. I've not been so lucky.

On Fri, Jun 24, 2011 at 11:22 AM, Brooke Clarke brooke@pacific.net wrote:

Yes, that's the one...  As Alan mentions there are several other articles, and I see the same website has them - just lop off the file name at the end of the URL to see the rest.  Here's the one specifically on electrolytics:

http://techdoc.kvindesland.no/radio/passivecomp/20061223155301644.pdf

• Chad.

On Jun 24, 2011, at 11:32, "Alan Melia" alan.melia@btinternet.com wrote:

Hi Will,

Is it possible that someone replaced the original resistor with the wrong one ?
I am suggesting that they were either color blind or were not paying attention to
what they were doing.

You must be talking about the version that does not have the battery option.  You
will notice that the battery version does not have a zener diode.  This is
because the battery is slightly trickle charged via the 150 Ohm resistor and
loads the transformer output enough that the voltage to the switching circuit
never gets high enough to be a problem (assuming no failures).

With the battery load missing in the AC only model, there is a need to help limit
the voltage out of the bridge rectifier.  The transformer and bridge output are
such that the voltage is barely above the zener value.  Very little current flows
through the zener.  The transformer winding resistance also comes into play as it
can barely deliver the required current and just maintain the needed voltage.  In
other words the winding resistance is such, along with the switching circuit
load, as to limit the amount of current the zener sees.

Bill....WB6BNQ

Will Matney wrote:

On Fri, 24 Jun 2011 11:11:34 -0700, GMail / AnalogAficionado
analogaficionado@gmail.com wrote:

.
This site has links to many of Cyril Bateman's articles, including the
EW series on capacitors.

http://www.proaudiodesignforum.com/forum/php/viewtopic.php?f=6&t=153&start=2

-- kc0ukk at msosborn dot com

If I recall, didn't B&K make a capacitor analyzer that did ESR measurements
too? I think it was a hybrid, part solid-state, and part tube, but folks
swore by them.

Best,

Will

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On 6/24/2011 at 2:34 PM Pete Lancashire wrote:

the

resistors,

thing

wrote:

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Hi:

Be careful, the web URL is Pro Audio Design Forum.  There are other cap
articles by the same author where he's measuring the distortion at 1 kHz
down to -140 dB.

Have Fun,

Brooke Clarke
http://www.PRC68.com

Matt Osborn wrote:

Bill,

Yes, this is the 845A, not the AB I have. Well, I first thought that about
the resistor, but sure enough, the color bands are brown, green, and brown,
or 150 ohms, as on the schematic. I wonder if the resistor was mis-painted
at the factory with the wrong color bands? I just couldn't see a carbon
comp resistor moving from that value to almost a short, but this one sure
shows it, and is why, I figure, it put off enough heat to leave a bright
spot on the board above it. The zener would have to sink a bunch more
current over it too, and on the side of the 400 uF cap beside it, was a
slight white discolored area that was given by the zener being warm.
Unhooking the zener showed it still good, and even though the 400 uF caps
end has a small bulge, it doesn't show a short. I didn't disconnect the
resistor from the circuit while reading it, as one side goes to the power
switch, and takes it out of circuit from the transformer.

Another thing I noticed was the GA2817 switching transistors show
conduction one way across the collector and emitter on both, but it isn't a
short. I figure they have built in snubber diodes in them, but I can't
cross the number to anything, as I think they were a custom or OEM for
Fluke from TI. I unplugged them so I could test the filter cap and bridge
rectifiers correctly. Does anyone know anything about these transistors?

Thanks,

Will

*********** REPLY SEPARATOR  ***********

On 6/24/2011 at 2:44 PM WB6BNQ wrote:

one ?

attention to

option.  You

and

circuit

help limit

output are

current flows

play as it

voltage.  In

circuit

shiny

burnt

was

(though

change

how

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