Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
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.
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-----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
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Re: A question from the unwashed relative to: I built a TM500 mainframe tester...
Yep, the mainframe tester tests for short/leakage and beta, along with the DC and AC voltages, and phasing of the two floating AC windings.
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
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.
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-----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.
-- Best wishes, Larry McDavid W6FUB Anaheim, California (SE of Los Angeles, near Disneyland)
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Re: A question from the unwashed relative to: I built a TM500 mainframe tester...
On Sun, Jan 3, 2021 at 08:29 AM, Jared Cabot wrote:
The Mainframe tester will allow for a full functional test without risking
damage to a potentially expensive module.
Yes, These will cause a cascade of failures with certain modules. I always try to at least diode check those pass transistors before inserting any module or powering up. So your Mainframe tester module does utilize or test the Pass transistors of the individual slot in some form or fashion? -- Michael Lynch Dardanelle, AR
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Re: A question from the unwashed relative to: I built a TM500 mainframe tester...
The trick is a bad pass transistor can quickly kill a module, which can then go on to kill another slot in the mainframe, etc etc.
Using a module (that isn't the purpose built tester) to test the mainframe also won't allow you to test voltages, ripple, transistor beta, transistor leakage etc.
The Mainframe tester will allow for a full functional test without risking damage to a potentially expensive module.
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
I just used a prototype board and brought the pins out. I am sure that the traces on a dead plug in could be isolated and used as well.
I find that many of the transistors read lower gain than expected and end up replacing those with new parts.
This may not be a problem for most plug ins as the load is usually under an amp.
ed
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Hi all
Quite a lot of years ago there was a topic posted here that went on for some time but never reached any conclusion as to the cause of the problem...unfortunately the exact problem I think I'm having right now. I wonder if any of you have encountered this and with fresh insight perhaps shine light on the cause? I've done a fair bit of investigation so far but I'm loathe to really get stuck in and start pulling the thing to bits without at least a better likelihood of being sure where the problem probably lies. Some basics - in NON storage everything is perfect and ALL diagnostics pass OK. In this respect there is zero problem. I re-calibrated it all about 18 months ago and have loved this scope for many years. PROBLEM - In STORAGE mode everything seems a bit mixed up. Channel 1 displays a trace but the amplitude is half or less of the real value. Channel 2 is similar but probably a quarter of the real value. Switching to BOTH it looks like there is only one trace but actually they are both overlaid on top of each other and it is not possible to separate them at all. Putting a sine into 1 and a square into 2 then the resulting waveform is an odd hybrid of both but not in the way 'add' would do that. Similar strange things happen with the amplitude also and all the other issues are a combination of this general characteristic. With the 4 wire connector going to channel 2 on the storage board removed and grounded appropriately leaving only channel plug connected watching a sine trace in store mode as I write it is just 20% of the real value but but does keep expanding to around 50% every now and then. The post from years ago seemed to point to U2101 on the storage board that both channels go to first but I'm not sure. Someone actually said it was that chip mixing up the signals but never gave evidence as to why that was so. Those chips just do not exist anymore so if it is then it's game over. I de-soldered mine and put it in a socket so I could take it out easily if I needed to. Is it an issue with the vector board perhaps? That's a pain to get to so I'd like a good idea the issue might be there before I go that route. Finally, time measurements are NOT affected. So, if you've got this far reading I thank you and if anyone has any thoughts please do share, I'd be very grateful. Cheers.
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It is a cute little scope, but very low bandwidth,
something like 10MHz. Its HV transformer suffers
from the epoxy disease that affects 547 scopes.
They are quiet, not having a fan, and the plugins
contain all the deflection circuitry (as I recall).
I used to like them quite a lot back in the day, for
audio work.
The storage functions are finicky.
-Chuck Harris
Stephen wrote:
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Hi all, and Happy New Year 2021,
Is a 564B a good grab, is it desirable at all?
It¡¯s not considered a 500 series, right?
56x family I suppose...
Thanks ?
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Re: Slightly OT: How can I dissolve Potting Compound?
Dennis the 26 cm Spectral tubes are the most popular, used in physics labs
These use 5 kV open ckt current limited transformers and run at 5 - 20 mA.
The optical spectrum is dependent on gas mix, and temperature and not on tube current or voltage.
The best lamps are "hollow cathode"
Jon
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Re: Grid Bias Adjustment on 475A
The mesh is an electrostatic lens that magnifies the
limited vertical and horizontal deflection to fill the
viewing screen area.
This is done to allow a lower deflection plate voltage on
a fairly short CRT.
The mesh lens is the magic sauce that allowed tektronix
to abandon vacuum tube deflection amplifiers for solid
state, and to break the about 50MHz bandwidth limitation
tube amplifiers imposed.
The downside is the mesh lens adds thickness to the trace
that would have been avoided with a longer CRT or a higher
deflection voltage. It also adds some spurious ghost
images on the screen at high intensities.
The mesh bias places the lens at a voltage where it won't
adversely affect the electron beam (attract it, deflect it,
reflect it, distort it...)
-Chuck Harris
Jeff Dutky wrote:
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So I've measured everything EXCEPT the high voltage levels (waiting on an HV probe).
R1396 and R1399 feed the second grid on pin #8, the schematic says they should see +50 V, and I measured +50 V
R1398 feeds the astigmatism grid, schematic says the range should be -8 V to +110 V, I see that range, the original setting was +40.82 V
R1330, R1329, VR1329, C1329, and CR1329 feed the mesh and all meet at a node on one of the ceramic terminals, according to the schematic that node is supposed to be -150 V, but I measure -110 V. The -150V level is supposed to have (if I am reading the schematic correctly) a sine wave superimposed with a range of 300 mV peak to peak, but what I see when I hook the scope up to the common node on the ceramic terminal (rather than the opposite side of CR1329, which I think is high voltage) is only 150 mV peak to peak, and not very sinusoidal.
So the mesh voltage is low (high?) and its AC signal looks wrong. Maybe one or more of the passive components is failed (which I can check pretty easily, with the power off, by lifting the legs attached to the ceramic terminal), but it might also be a problem with T1320, which I guess is on the opposite side of the board? I have an HV multimeter probe coming on Tuesday, so I'll feel better about checking the high voltage stuff then.
I don't really understand what the mesh is doing in this CRT. Is the mesh bias really a good candidate for the symptom I'm seeing?
-- Jeff Dutky
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Hi all, and Happy New Year 2021,
Is a 564B a good grab, is it desirable at all?
It¡¯s not considered a 500 series, right?
56x family I suppose...
Thanks ?
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Re: How to clean Helitrim potentiometers?
Hello perhaps you are confusing Helipot a multiturn precison 3,5,10,15 turn potentiometer with internal 1 turn pcb mounted trimpots or single turn controls?
If you can pr¨¦cis your questions with photos of the pots or reference to the schematic part number or function you can receive better answers.
In general every old instrument can benefit from exercising every switch and control, use of contact cleaner or renew
Sealed pots that are blue and square are Bournes ModPot, lubricant with syringe or spray tube down the shaft and on the edges of the sections.
Bon Chance
Jon
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Re: font/typeface for Tektronix binder spines - was Re: [TekScopes] Push button font
I'm sorry I arrive pretty late in the conversation. There are online tools to identify fonts, with easy yes/no questions. I used one once to find which font was used on Philips instruments (for a Python GUI I designed to control a PM5192 generator). Can't find the site any more though... There are sites where you can upload an image and they find what font is used but I haven't tried them, for example (from a Google search results) : Nicolas ________________________________ De : [email protected] < [email protected]> de la part de toby@... <toby@...> Envoy¨¦ : samedi 2 janvier 2021 17:59 ? : [email protected] < [email protected]> Objet : font/typeface for Tektronix binder spines - was Re: [TekScopes] Push button font On 2020-12-14 9:04 a.m., toby@... wrote: On 2020-12-14 12:17 a.m., Chuck Harris wrote:
I'm pretty sure it is something put together
by Tektronix's graphics department.
Yes, and I don't think it's consistent either; after all, it spanned
several decades. It would probably be possible to find a suitable free
bold, compressed font that resembles it.
Turns out I have considered something suitable for binder spines before: View/Reply Online (#146250): /g/TekScopes/message/146250I also took a shot of my own shelf with some sample setting: /g/TekScopes/album?id=258709Of course Fjalla isn't the _same_ font as any of the binders, but the binders aren't consistent either, so it might help someone get close to the original look. You could also try horizontal scaling as desired (I couldn't do that in GIMP?!) --Toby --Toby
-Chuck Harris
snapdiode via groups.io wrote:
Cough, cough... Can someone perhaps identify the font(s) used on the plastic CombBind spines of the manuals?
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Re: Slightly OT: How can I dissolve Potting Compound?
Dear Dennis: We worked on arc and gas lamp ballasts since 1970s.
Then designed and manufactured 12 kV HV modules, in 1980s..1990s.
The encapsulant is a very high solids epoxy, specially cured.
We used heat and mechanical picking to disassemble.
The components can be damaged by the depotting process, so it is a destructive diagnostic but you will not revive the PSU.
Especially susceptible is the transformer insulation, it will be contaminated in the process.
Better idea is to replace with a new one.
Finally the laser supply and spectral lamps have very different performance, eg lasers DC with HV ignition pulse, spectral can use current limited AC similar to a neon sign transformer.
If you have a small neon transformer, try that on a variac.
If you PM me the specs and exact model of tubes, I may have an off the shelf supply I could send to you.
Happy New Years,
Jon
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
HI
Please,Larry,add me to the list.I am located at Spain.
Regards.
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
I would also be interested in a set of the boards, please add my name to the list. I am in Dublin, Ireland so I am aware that shipping will be somewhat more than the nominal amount suggested. I am happy to provide payment up front via PayPal friends and family. My thanks to Jared for the detailed engineering that went in to this, and for being willing to share it with the community, and to Larry for making a group purchase possible.
kind regards,
Peter Mulvey.
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Thank you to everybody!
I have enough information to attempt a transplant.
I'll post here the outcome
Giovanni
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Re: Slightly OT: How can I dissolve Potting Compound?
Hi Dennis, On Sat, Jan 2, 2021 at 06:18 PM, Dennis Tillman W7pF wrote: 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 believe it's not worth the effort, I'd personally build a new one using instructions from Sam's Laser FAQ: You'll find wealth of information on this site, it's amazing (even I contributed with my unusual Argon laser specimen). 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. I have no experience with spectral tubes but from your description it appears they work in the same way as a HeNe laser tubes do. Therefore a matching HeNe power supply will work for sure, but to my recollection the values you stated are much lower than the usual for HeNe tubes. These start with approx. 5-15kV and work (steadily conduct) at approx. 1-2kV. So to use an off the shelf HeNe PSU I'd try under-powering it (in therms of voltage) and/or increasing the ballast resistor. 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. The PSU needs to be matched to the particular tube you're using, my experience with HeNe tubes is the following: - High voltage for initial start has ample tolerance, it just needs to be able to start the tube. It is universally implemented as a diode-capacitor ladder multiplier so you can add elements until you get it high enough. Capacitors are normally small as you don't need excessive energy to kick-start the tube (e.g. CRT HV power supply can deliver orders of magnitude more energy than HeNe HV starter). - Ballast resistor and working voltage need to be fairly matched. The flicker you experienced with the other PSU is exactly the symptom of a mismatch. The ballast resistor cannot counter the intrinsic negative impedance of the working gas tube and the resulting runaway results in tube shutting down. The flicker is due to HV start occurring in a random loop. You can safely try to increase the ballast resistor and see if that improves the situation. This helps with aged HeNe tubes when they start flickering at end of life, sometimes ballast needs to be increased as much as threefold. The ballast resistor needs to be low enough to supply enough current through the tube to maintain plasma, but also high enough to limit the current. - The working voltage of a traditional transformer based PSU can be adjusted using a variac. Since in your case you most likely need to go down with the voltage, I'd say variac approach will give you ample headroom to match the HeNe PSU to your tubes. HTH Best regards and Happy New Year, Nenad Filipovic
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Re: Slightly OT: How can I dissolve Potting Compound?
Supposedly a 50/50 mix of formic and acetic acids will do the trick but I've never tried it.
DaveB, NZ
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-----Original Message----- From: [email protected] [mailto: [email protected]] On Behalf Of Dave Daniel Sent: Sunday, January 03, 2021 21:59 To: [email protected]Subject: Re: [TekScopes] Slightly OT: How can I dissolve Potting Compound? My approach to this sort of problem (I¡¯ve done it twice in the past thirty or so years) has been to use an Xacto knife to cut the potting compound away. I never did find a solvent that seemed to work. DaveD On Jan 2, 2021, at 21:18, Dennis Tillman W7pF <dennis@...> wrote:
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
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Jared Cabot
Michael W. Lynch
Kevin
Jean-Paul
Peter Mulvey
Giovanni IZ5PQT