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On Sun, Jan 3, 2021 at 10:08 AM, Greg Muir wrote:

If you want to kill your liver, soak your hands in MEK. Acetone and lacquer
thinner are just as bad. All can be very destructive on components.

MEK is not MEKP... and MEK is not known to be toxic to the liver. Acetone is not as "bad" (whatever that means) as MEK... and acetone is present in the human body, and disposed by it, during normal metabolic processes.
Respect chemicals; but running in a panic for the hazmat suit, at the mention of the word "chemical" isn't necessary.
On the other hand... worrying about being bored to death, by studying too much chemistry... doesn't seem to be much of a problem.

I have also thought about a TM500 tester that included:

- Presence/absence (but not correctness or ripple) of each of the supply
voltages
- Brought out all supplies to banana jacks for metering and load testing
- Indicated correct/incorrect phasing of the AC supplies
- Pass/fail indication for the pass transistors

The Tek fixture demonstrates how to indicate the correct phasing.

After looking into those cheap component testers, they all seem to be AVR
based, the code and principles of operation are openly available, and I was
thinking that it should be possible to bludgeon the code into submission to
expect an NPN transistor on one set of pins, and a PNP on another, measure
the hFE and provide red/amber/green indication for each transistor (amber
being low hFE (< 20.)

At first, I was thinking of making a board that fitted into a module, but
bringing all the supplies out to jacks/binding posts, and the indications
just seemed like a headache given the front panel real-estate - plus the
PCB would be large, but mostly empty, therefore not very cost effective.

I am coming round to the idea of an external box plus a butchered Jamma
cable, thoughts ?

On Sun, Jan 3, 2021 at 9:35 AM Colin Herbert via groups.io <colingherbert=
[email protected]> wrote:

Some time ago I had similar thoughts on accessing the connections to the
pass transistors, as well as accessing the 25 VAC connections. I had a
problem on one of my TM50X mainframes with one of these windings wired up
incorrectly, so that a plug-in module worked fine in one mainframe, but not
in another. After some fiddling about, I purchased a JAMMA male connector
which would mate with the backplane of the TM50X and modified it slightly
to make it compatible. I also soldered bare copper wires to the appropriate
connections for 25 VAC and the EBC of both pass-transistors. With the use
of an extender, I was able to check the pass-transistors with one of those
cheap Chinese testers and to bring out all three 25VAC points to a scope.
Triggering off the 17.5 VAC winding, I was able to see if the 25 VAC
windings were in phase or not.

After showing the proof of concept, I thought that I might make a very
simple custom plug-in module to bring the interesting connections out to
the front panel in order to be able to do the job more easily. This project
is still in my imagination, but it shouldn't take too long to put together
when I get "a round tuit".

I have already made some posts on these ideas on this Forum a while ago.

Keep Safe, Colin.

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Michael W. Lynch via groups.io
Sent: 02 January 2021 04:44
To: [email protected]
Subject: Re: [TekScopes] I built a TM500 mainframe tester, and updated the
design. Someone might find this useful?

Jared,

Is there a way to easily bring the EBC of each pass transistor to the
front panel? These transistors are items that often fail and need to be
tested, especially on these old frames. Not trying to throw a wrench into
the works, but those pass transistors are a major point of failure and they
can cause all sorts of damage to the plug ins when they are bad. Even if
you could add some pads near the appropriate connections at the rear to
allow those of us who wanted to add such functionality at our option?

--
Michael Lynch
Dardanelle, AR

I need to dissolve the black HV potting compound of a 12VDC powered
Helium-Neon laser inverter power supply I have that stopped working. I would
appreciate any suggestions on what works to do this. I’m guessing it may be
epoxy. I stuck the tip of a hot soldering iron in it for a few seconds
without much effect.

When it was working it turned out to be perfect for powering gas filled
Spectrum Tubes. These spectrum tubes (smaller versions of neon signs) filled
with a variety of gasses are an excellent source of spectral lines for the
7J20 / J20 Rapid Scan (Optical) Spectrometer to measure.

Spectrum tubes require an initial high voltage (1,000V to 1,500V for
example) to break down the gas and start it conducting. Once the gas in the
spectrum tube conducts the voltage across the gas drops (250V to 450V for
example) and unless you limit the current (to a few mA) it will destroy the
tube. Can anyone can point me to a source of information on how to determine
the proper voltage and current I need to power these spectrum tubes? Is
there a web site or group devoted to Spectrum Tubes?

Something happened to the inverter and it stopped working. The input is now
open. The inverter is a black potted brick 3” x 1?” x 1”. The ballast
resistor has continuity so that is not the problem. The original label on
the inverter is partially destroyed so I can’t tell what its initial high
voltage output was or what it current limits at. All I do know is that it
was made by
Laser Drive Inc.
5465 Wm. Flynn Hwy. Gibsonia, PA 15044
Model: 1150-6330, S/N: 610574
The input was +12VDC at 0.35A.

I wrote to the company that took over the company that took over Laser Drive
Inc. asking if they could tell me the output voltage and limiting current
but I didn’t receive a reply.

At this point I am hoping if I can remove the potting compound I can figure
out what went wrong with it.

I have a different, bigger Laser Drive Inc. potted inverter which is powered
by 115VAC. It puts out 2350VDC at 6.5mA. This causes the Spectrum Tubes to
flicker. They do not run continuously. I am guessing that this because 6.5mA
is more current than the tube can conduct. The amount of current the tube
draws increases in proportion to the inside diameter of the tube but I don’t
know much about this matching the power supply to the tube. All I do know is
the one that went bad seems to be an ideal match for the spectrum tubes I
have.

Battery operated (DC input) inverters are much more desirable than AC input
inverters for this application because the AC rectification and poor
filtering shows up on the output DC as significant ripple causing the
amplitude of each spectral line to be blurred.

Dennis Tillman W7pF

Greetings Attilio - I did some research on the 502, and the xtal that tek used.
It is a SC cut 3d overtone series resonant crystal in a TO-5 transistor package.
Bliley Crystal in the US still might offer this cut.
The parts I have are AT cut 3 OT 7pF shunt resonant. My experience with them
is that they have a sharp resonance range. In the 502, the crystal Fc is stretched in
a VCXO circuit to effect the tracking of the SA. An AT cut crystal will move a bit
in frequency then just quit oscillating. It will also not fit in the available space. -J-
-----Original Message-----
From: "Attilio" <a.alovisetti@...>
Sent: Sunday, January 3, 2021 12:48pm
To: [email protected]
Subject: Re: [TekScopes] Spectrum analyzer Tektronix 7L13 on mainframe Tektronix 7603



Jim Mcvein,
do you have any news for me in relation to 52.5 MHz crystal?
I am in Italy, if you give me your bank details and the amount I have to pay for the crystal and the shipping costs, I will make you an international bank transfer
Alternatively I can pay with PayPal..

Thanks

-- Cheers
Attilio

I have a nice looking Tek 2247A scope here that has been sitting on the shelf for a while, due to a bad Channel i input. the signal is a horribly attenuated and differentiated replica of the actual input. Everything else is perfect. In a moment of covid-induced boredom, I felt I had to get to the bottom of this. I had a hunch that this was the input resistor being broken or damaged (there is always a flying resistor from the input BNC to the vertical input on 2200 series scopes). It was the only thing I could think of that could give this result.

It takes some effort to de-can the scope, and remove the complex shield over the vertical inputs, but sure enough, when opened, the barely visible input resistor (62 ohm carbon film) was BURNED. I replaced it, and ta-da, everything is working. What the heck?

Here's what I just can't figure out, this scope has no 50 ohm input function, so no low impedance path exists to help burn this resistor due to over-driving, SO HOW DID it get burned and leave the scope undamaged?

I am totally mystified by this, and keen to hear any opinions. I just can't see how this fault happened without vaporizing the vertical input channel.

all the best for the new year,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.

Larry is there a chance that there might be a purchase of the Rotary switch as a group purchase from DigiKey or all parts sourced up to the individuals.
Craig...

Hi Larry,
I might well be interested in a board set, so long as the cost and shipping to London, UK aren't too crazy. I have been intending to build one of these testers for a while and have a few of the components necessary, plus a main board that would certainly do the job, but Jared's looks like it could make the job fairly straightforward. I especially like the front panel - very nice-looking!
Colin.
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Larry McDavid
Sent: 31 December 2020 23:13
To: [email protected]
Subject: Re: [TekScopes] I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
Anyone interested in buying sets of boards to share?
Larry
On 12/31/2020 11:27 AM, Jared Cabot via groups.io wrote:

Hi all,

I have been accumulating TM500 modules and mainframes for a little while, so I recently finished building an 067-1201-99 TM500 mainframe tester from the Tek construction notes floating around.
I updated the design somewhat and designed it for simplified construction (Not a single wire to strip and solder!) and I thought someone here might be interested in taking a look or even building one themselves.
Here's a link to the youtube video:


And here's a link to the google drive with all the gerbers and schematics and stuff. I went so far as to rewrite the manual with the alterations and corrections included.


Direct link to the new manual:


Let me know what you think, and let me know if you see any errors that need correcting. :)

Regards
Jared.

I have a nice looking Tek 2247A scope here that has been sitting on the shelf
for a while, due to a bad Channel i input. the signal is a horribly attenuated
and differentiated replica of the actual input. Everything else is perfect. In
a moment of covid-induced boredom, I felt I had to get to the bottom of this.
I had a hunch that this was the input resistor being broken or damaged (there
is always a flying resistor from the input BNC to the vertical input on 2200
series scopes). It was the only thing I could think of that could give this
result.

It takes some effort to de-can the scope, and remove the complex shield over
the vertical inputs, but sure enough, when opened, the barely visible input
resistor (62 ohm carbon film) was BURNED. I replaced it, and ta-da, everything
is working. What the heck?

Here's what I just can't figure out, this scope has no 50 ohm input function,
so no low impedance path exists to help burn this resistor due to
over-driving, SO HOW DID it get burned and leave the scope undamaged?

I am totally mystified by this, and keen to hear any opinions. I just can't
see how this fault happened without vaporizing the vertical input channel.

all the best for the new year,
walter (walter2 -at- sphere.bc.ca)
sphere research corp.