Topics

TM500 Module Construction Details


 

I recently picked up a 5A21N scope plug-in as a parts unit from which to build Jared Cabot's updated TM500 mainframe tester. I noticed this type lacks the back-plate or lower guide-pins found in some modules. I'm not sure if the pin-less/back-plate-less construction is normal for scope modules, but I seem to recall some TM500 modules lacked back-plates, but had pins. Is there an underlying configuration rule guiding this? Possibly air-flow for heat removal was a consideration.

Since the back-plate is about 0.085-inch thick, possibly longer pins were used in te absence of a back-plate.

Any thoughts?

Bruce, KG6OJI


Jared Cabot
 

I have noticed that the pins are the same with or without the back plate, with tubular washers used when there is no back plate to keep the pins at the same length. Some modules lack pins entirely.
I'm not sure what the ideas behind having a back plate or not are, except the usual airflow/EMI shielding assumptions.

Here's a photo of the pins with and without a back panel:
https://i.imgur.com/omQwaDF.jpg


Mlynch001
 

I think I remember Dennis saying that these features were a victim of the ruthless cost cutting that went on as TEK came under more and more economic pressures in the 80’s and later. I have some modules that do not have guide pins or the reinforcement frames.

--
Michael Lynch
Dardanelle, AR


Larry McDavid
 

What purpose do these pins serve?

The module card edge connector engages before the pins could; the mainframes I've looked at don't have corresponding tight-fit holes for the pins, only rectangular openings with clearance all around the pins.

Yet, all the modules I've looked at have at least one pin. These pins must not be for aligning the module and card-edge connector.

Would these pins prevent plugging a TM500 module into a 5000 scope?

Like in Jared's photo, all my modules without a back plate have the short bushing to space the pins out to compensate for the missing back plate thickness.

Larry

On 1/17/2021 9:21 AM, Jared Cabot via groups.io wrote:
I have noticed that the pins are the same with or without the back plate, with tubular washers used when there is no back plate to keep the pins at the same length. Some modules lack pins entirely.
I'm not sure what the ideas behind having a back plate or not are, except the usual airflow/EMI shielding assumptions.
Here's a photo of the pins with and without a back panel:
https://i.imgur.com/omQwaDF.jpg
--
Best wishes,

Larry McDavid W6FUB
Anaheim, California (SE of Los Angeles, near Disneyland)


Roy Thistle
 

On Sun, Jan 17, 2021 at 08:41 AM, ebrucehunter wrote:


I recently picked up a 5A21N scope plug-in as a parts unit from which to build
Jared Cabot's updated TM500 mainframe tester.

Any thoughts?
Well if a thought can be a question... I have a question... It's not directed at Bruce.
I don't know why, on a forum, that is dedicated to helping people keep/restore classic Tektronix, we are discussing a project that could contribute to helping people destroy them.


Glenn Little
 

If the part is beyond repair due to parts not being available and redesign being too costly, the repurpose of the item to aid in the repair of other equipment that can be repaired should be encouraged.
In many cases the alternative is e-waste.

This is my opinion, and mine alone.

Glenn

On 1/17/2021 4:22 PM, Roy Thistle wrote:
On Sun, Jan 17, 2021 at 08:41 AM, ebrucehunter wrote:


I recently picked up a 5A21N scope plug-in as a parts unit from which to build
Jared Cabot's updated TM500 mainframe tester.

Any thoughts?
Well if a thought can be a question... I have a question... It's not directed at Bruce.
I don't know why, on a forum, that is dedicated to helping people keep/restore classic Tektronix, we are discussing a project that could contribute to helping people destroy them.
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@arrl.net AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI, FRA, NRA-LM ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"


Jim Ford
 

Well, I for one agree with you 100%, Glenn.   Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: Glenn Little <glennmaillist@bellsouth.net> Date: 1/17/21 1:27 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] TM500 Module Construction Details If the part is beyond repair due to parts not being available and redesign being too costly, the repurpose of the item to aid in the repair of other equipment that can be repaired should be encouraged.In many cases the alternative is e-waste.This is my opinion, and mine alone.GlennOn 1/17/2021 4:22 PM, Roy Thistle wrote:> On Sun, Jan 17, 2021 at 08:41 AM, ebrucehunter wrote:> >>>> I recently picked up a 5A21N scope plug-in as a parts unit from which to build>> Jared Cabot's updated TM500 mainframe tester.>>>> Any thoughts?>>> Well if a thought can be a question... I have a question... It's not directed at Bruce.> I don't know why, on a forum, that is dedicated to helping people keep/restore classic Tektronix, we are discussing a project that could contribute to helping people destroy them.> > > > > -- -----------------------------------------------------------------------Glenn Little                ARRL Technical Specialist   QCWA  LM 28417Amateur Callsign:  WB4UIV            wb4uiv@arrl.net    AMSAT LM 2178QTH:  Goose Creek, SC USA (EM92xx)  USSVI, FRA, NRA-LM    ARRL TAPR"It is not the class of license that the Amateur holds but the classof the Amateur that holds the license"


Jim Ford
 

Another point on the curve, Bruce; my two 5A15Ns and 5B10N have neither backplates nor alignment pins, and my (TM50X) PS-501-1 has the pins but no backplate.  Interestingly, the pins go into what look like banana jacks.  Maybe they ground the module to the TM50X mainframe?  (TM 515 in my case).  And plastic back-assemblies (not really plates) on the dozen or so 7000 series plug-ins I own.  HTH   Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: "ebrucehunter via groups.io" <Brucekareen=aol.com@groups.io> Date: 1/17/21 8:41 AM (GMT-08:00) To: TekScopes@groups.io Subject: [TekScopes] TM500 Module Construction Details I recently picked up a 5A21N scope plug-in as a parts unit from which to build Jared Cabot's updated TM500 mainframe tester.  I noticed this type lacks the back-plate or lower guide-pins found in some modules.  I'm not sure if the pin-less/back-plate-less construction is normal for scope modules, but I seem to recall some TM500 modules lacked back-plates, but had pins.  Is there an underlying configuration rule guiding this?  Possibly air-flow for heat removal was a consideration.Since the back-plate is about 0.085-inch thick, possibly longer pins were used in te absence of a back-plate.Any thoughts?Bruce, KG6OJI


Mlynch001
 

Glenn,

Agree 100%. I am all for doing this in order to create a much more useful tool.

I, personally have seriously damaged a PG506 due to faults within a TM506, faults that this tester would have located. In hindsight, I would have gladly sacrificed any number of more ubiquitous plug ins for necessary parts to construct this tool in order so save a more valuable device, such as the PG506.

Of course, that is just my opinion.

--
Michael Lynch
Dardanelle, AR


Harvey White
 

The plastic pieces on the backs of the 7000 series scopes are guides for the connector, and were originally intended to align the fiber optics intended for the readouts (they left the 4 holes).

I've seen the variety of back treatments as well.  I'd suggest that things like meters and signal generators may have metallic backplates for shielding, and things such as power supplies and breadboards may not.

On the guide pin, it may well have been a victim of the cost cutting extravaganza.  I don't remember the connector having very much freedom of movement, so when inserting a plugin, I suspect that things have to align rather well to avoid damage.  That guide pin may have been for that.   I don't remember ever seeing any literature indicating that the guide pin was used to prevent certain modules from being used in a frame.  The connector keying was to do that, I think.

There is another (and unrelated) pin on the high power compartments, which triggers a switch in a power module to indicate to the module that it's plugged into a high power compartment.  There's often a matching blank hole in the plugin that doesn't use this, thus avoiding breaking off pins.

Harvey

On 1/17/2021 5:40 PM, Jim Ford wrote:
Another point on the curve, Bruce; my two 5A15Ns and 5B10N have neither backplates nor alignment pins, and my (TM50X) PS-501-1 has the pins but no backplate.  Interestingly, the pins go into what look like banana jacks.  Maybe they ground the module to the TM50X mainframe?  (TM 515 in my case).  And plastic back-assemblies (not really plates) on the dozen or so 7000 series plug-ins I own.  HTH   Jim Ford Sent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: "ebrucehunter via groups.io" <Brucekareen=aol.com@groups.io> Date: 1/17/21 8:41 AM (GMT-08:00) To: TekScopes@groups.io Subject: [TekScopes] TM500 Module Construction Details I recently picked up a 5A21N scope plug-in as a parts unit from which to build Jared Cabot's updated TM500 mainframe tester.  I noticed this type lacks the back-plate or lower guide-pins found in some modules.  I'm not sure if the pin-less/back-plate-less construction is normal for scope modules, but I seem to recall some TM500 modules lacked back-plates, but had pins.  Is there an underlying configuration rule guiding this?  Possibly air-flow for heat removal was a consideration.Since the back-plate is about 0.085-inch thick, possibly longer pins were used in te absence of a back-plate.Any thoughts?Bruce, KG6OJI



Mlynch001
 

Further perusal of various parts manuals, shows that the “support pins” and “washers” as TEK calls them, were removed from most instruments after certain serial numbers. I looked at mechanical parts lists for TG501, 502, SG503 and others. Most follow this same pattern.
--
Michael Lynch
Dardanelle, AR


Roy Thistle
 

On Sun, Jan 17, 2021 at 01:27 PM, Glenn Little wrote:


If the part is beyond repair due to parts not being available and redesign
being too costly, the repurpose of the item to aid in the repair of other
equipment that can be repaired should be encouraged.
In many cases the alternative is e-waste.
Yes. I would agree with that.


Roy Thistle
 

On Sun, Jan 17, 2021 at 02:58 PM, Mlynch001 wrote:


I, personally have seriously damaged a PG506 due to faults within a TM506,
faults that this tester would have located.
Okay, that gets at the crux of it.
I have these things too.
And personally, I've never run across a frame that had phasing problems, or known that improper phasing in a frame, can cause damage. (How does improper phasing damage a PG506?)
This appears to have been an internal project within Tektronix, for testing on production units... and never actually manufactured for sale to the public... and why not? (Tektronix certainly made a huge variety of TM500 plug-ins.)
I don't think it does anything, one can't do with a multimeter, and a scope... and ought to do before using an unknown frame... especially when plugging in an expensive unit.
Now I won't say there are not junk plug-ins... or that many people on the list won't know junk from good... clearly there are... and clearly they will... but for the reasons given above... it appears to me... it is my opinion... that the project is antithetical to what the TekScopes forum is trying to promote. I might be wrong.
Perhaps if this post is generative of further discussion, we ought to move it to it's own thread.


Jared Cabot
 

It looks to me like Tek made the testing modules available for purchase.

https://w140.com/tekwiki/wiki/067-1201-99

I figured building a module to plug in and flick a few switches was easier in the long term for me than opening enclosures trying to probe card edge connectors without slipping and shorting the contacts, while applying loads as needed here and there.
I have 10 mainframes of various sizes here at the moment, and I regularly buy (and less regularly sell) these things so it made sense to me to have some fun and build the tester. It seems at least 70 other people agreed.

That's not to say one way is better than the other, both methods of testing are perfectly valid if they get the required results. I like to build stuff and it makes the actual testing process easier so I made the tester. :)

On Mon, Jan 18, 2021 at 09:36 AM, Roy Thistle wrote:


On Sun, Jan 17, 2021 at 02:58 PM, Mlynch001 wrote:


I, personally have seriously damaged a PG506 due to faults within a TM506,
faults that this tester would have located.
Okay, that gets at the crux of it.
I have these things too.
And personally, I've never run across a frame that had phasing problems, or
known that improper phasing in a frame, can cause damage. (How does improper
phasing damage a PG506?)
This appears to have been an internal project within Tektronix, for testing on
production units... and never actually manufactured for sale to the public...
and why not? (Tektronix certainly made a huge variety of TM500 plug-ins.)
I don't think it does anything, one can't do with a multimeter, and a scope...
and ought to do before using an unknown frame... especially when plugging in
an expensive unit.
Now I won't say there are not junk plug-ins... or that many people on the list
won't know junk from good... clearly there are... and clearly they will... but
for the reasons given above... it appears to me... it is my opinion... that
the project is antithetical to what the TekScopes forum is trying to promote.
I might be wrong.
Perhaps if this post is generative of further discussion, we ought to move it
to it's own thread.


Harvey White
 

replies interleaved.....

On 1/17/2021 7:36 PM, Roy Thistle wrote:
On Sun, Jan 17, 2021 at 02:58 PM, Mlynch001 wrote:

I, personally have seriously damaged a PG506 due to faults within a TM506,
faults that this tester would have located.
Okay, that gets at the crux of it.
I have these things too.
And personally, I've never run across a frame that had phasing problems, or known that improper phasing in a frame, can cause damage. (How does improper phasing damage a PG506?)
Nor have I, but evidence says that it's possible to have, and checking is not a major item.

This appears to have been an internal project within Tektronix, for testing on production units... and never actually manufactured for sale to the public... and why not? (Tektronix certainly made a huge variety of TM500 plug-ins.)
Tektronix likely assumed that if it got out of the factory, it was working fine.  How many 7000 series scope power supply plugins have you seen?  5000 series?  even the 2600 series.....

It's an internal tool.

I don't think it does anything, one can't do with a multimeter, and a scope... and ought to do before using an unknown frame... especially when plugging in an expensive unit.
The problem is in bringing out the connections, doing the breadboard needed to make the tests (and just phasing is not sufficient), and then interpreting the results.

If you're doing this on a production basis, that's another matter.

Now I won't say there are not junk plug-ins... or that many people on the list won't know junk from good... clearly there are... and clearly they will... but for the reasons given above... it appears to me... it is my opinion... that the project is antithetical to what the TekScopes forum is trying to promote. I might be wrong.
IMHO, you are.  You're looking at several factors here:

1) I got a frame, is it good or not?  Let's plug in the PG506 and see...

2) I got a plugin, it ain't working.  Could the frame be the problem?  Let's plug in a module that doesn't need the same connections.   Maybe I don't have a working one of whatever it is I bought....

3) there are FAR more junked/scrapped/salvaged plugins in any of the tektronix line than you may know.  I personally know of a surplus dealer who said "I can't sell these, and it's not worth it to me to check them out.  I want them scrapped for value."  What happens then?

4) if we take your arguments to the limit (reducto ad absurdum), then NO tektronix plugin should EVER be scrapped regardless of the reason, availability of parts, and cost of repair.  Everyone makes an economic decision of what it's worth to them, and repairing/replacing/refurbishing  is done on the basis of time, energy, and available parts.  As a example, the 1502 TDR uses a tunnel diode that is impossible (or nearly) to replace.  If I have one where the entire assembly is missing, should I take the HV supply, the CRT and the horizontal amplifier out to repair a 1503 that is possible to repair?  Or is that somehow antithectial to the purposes of the list?

I have a 7104 where the CRT rattles.  anybody got a spare CRT for the 7104?  Oh wait, I already used it's horizontal hybrid to fix the one I use.


Perhaps if this post is generative of further discussion, we ought to move it to it's own thread.
Well, that's up to someone else.

Harvey





Harvey White
 

I think you have an excellent design, updated for today's (PC boards can be made more or less inexpensively) process.  What I think that Tek did is to release the design of an internal project to the public.  If you consider the construction techniques available then, the amount of hand wiring was just part of the job.  I don't know if Tek had any pick and place machines then, and they had entire assembly lines capable of wiring and hand assembling PC boards.

You could redesign the entire thing with surface mount parts (where possible), but then that requires people to be able to do surface mount assembly.  Not everybody can (or wants to).

Tek did this design to minimize production and testing time on the assembly line, as well as minimize mistakes and damage due to an improperly built test set rebuilt time after time on the production line (IMHO).

Considering these factors, as well as the 2 AM factor, it makes perfect sense for a project.

You did a very good job, and it shows.

Harvey

On 1/17/2021 7:57 PM, Jared Cabot via groups.io wrote:
It looks to me like Tek made the testing modules available for purchase.

https://w140.com/tekwiki/wiki/067-1201-99

I figured building a module to plug in and flick a few switches was easier in the long term for me than opening enclosures trying to probe card edge connectors without slipping and shorting the contacts, while applying loads as needed here and there.
I have 10 mainframes of various sizes here at the moment, and I regularly buy (and less regularly sell) these things so it made sense to me to have some fun and build the tester. It seems at least 70 other people agreed.

That's not to say one way is better than the other, both methods of testing are perfectly valid if they get the required results. I like to build stuff and it makes the actual testing process easier so I made the tester. :)


On Mon, Jan 18, 2021 at 09:36 AM, Roy Thistle wrote:

On Sun, Jan 17, 2021 at 02:58 PM, Mlynch001 wrote:

I, personally have seriously damaged a PG506 due to faults within a TM506,
faults that this tester would have located.
Okay, that gets at the crux of it.
I have these things too.
And personally, I've never run across a frame that had phasing problems, or
known that improper phasing in a frame, can cause damage. (How does improper
phasing damage a PG506?)
This appears to have been an internal project within Tektronix, for testing on
production units... and never actually manufactured for sale to the public...
and why not? (Tektronix certainly made a huge variety of TM500 plug-ins.)
I don't think it does anything, one can't do with a multimeter, and a scope...
and ought to do before using an unknown frame... especially when plugging in
an expensive unit.
Now I won't say there are not junk plug-ins... or that many people on the list
won't know junk from good... clearly there are... and clearly they will... but
for the reasons given above... it appears to me... it is my opinion... that
the project is antithetical to what the TekScopes forum is trying to promote.
I might be wrong.
Perhaps if this post is generative of further discussion, we ought to move it
to it's own thread.



EJP
 

How does improper phasing damage a PG506?
Nobody said it was improper phasing.


Michael W. Lynch
 

On Sun, Jan 17, 2021 at 07:26 PM, EJP wrote:



How does improper phasing damage a PG506?
Nobody said it was improper phasing.
No, in fact, it was not improper phasing, and I never said it was. Come to find out later, It was a pair of shorted pass transistors in a compartment.

I don't know how or why, but the PG506 worked when plugged into one bay of the TM506, and when I moved it to another, it quit working. Moved it back to the original bay, where it had previously worked. and it would no longer work there. 3 of the 6 bays had "bad" pass transistors and the rest did not. This was long ago and early in my "journey" down this rabbit hole. This was also well before I learned some of the finer points regarding the relationship between various plug ins and the TM506. I do not have the luxury of decades of experience, so I paid a steep price for this lesson.

All anecdotal evidence, but I did find and replace the shorted pass transistors in three bays. Was the PG506 "on the edge of failure?" Did the shorted parts pushed it over the edge? I do not know, All I know now is that after the repair, a PG506 or any other plug in works just fine in any bay that I choose to insert it into.

I think that it is more important to find these "Bad" pass transistors before you insert a valuable and/or delicate plug in into any bay. These transistors are a known problem in these 30-40+ year old devices. Even though that was probably not the original purpose of this tool, it could have revealed a problem with the pass transistors.

Like I said, I have learned a lot from that error, so I will not make the same mistake again. I never insert a plug in in to the bay of an untested TM50X.

Thanks

--
Michael Lynch
Dardanelle, AR


tedbmoss@...
 

I am 77 years old (WA7VQR) and I think anyone can do what he wants when he is older than 50. Thanks for saving me some trouble . I just bought some 500 mainframes. Last week I did not know they even existed. I will test them before using them.I am learning how to fix 2246, 2230, TDS640, TDS754, etc. So far I haven't broken anything


 

Over the years, many people have noted the flimsy construction (especially at the rear ) of the TM500 plug ins and 5000 scope plug ins. the lack of guide pins and a rigid back surface to keep the case square seem to have been (at least anecdotally from Tek employees) related to cost issues. There certainly was NO profound design reason to make it that way, so I think low cost was in fact the issue.

The real mechanical purpose of the two rear pins is to take stress off the edge connectors and insure correct centered seating. this really has relevance for the TM515 especially where the unit can be tossed around (some humor there, it is heavy as hell), possibly damaging the backplane. If you look at how much play there is with no rear plate, this does make sense. I thought I recalled reading somewhere that adding the rear pins was specifically for the TM515, but I could be wrong.

The design of the internal cards makes any kind of back plate difficult, as the card goes almost to the top and bottom of the module, not allowing for much metal to help anchor the back together.  I do see plates on many later production modules, and it certainly improves the structural integrity of the modules, but it is not easy to do thanks to the tall card design.

As I mentioned in an earlier post, it IS possible to make very strong TM500 plug ins from scratch using square cross section 10" tapped aluminum stand-offs from RAF. I just got a quote from them to satisfy my curiosity, and found that the current price is US$14+ in small lots (way too costly as 6 are needed), dropping to an affordable $4.50 at 2500 pieces. I think that is not really worth pursuing, although it does make for a really great assembly.

I think to make Jared's current project, everybody will just have to scrounge up a scrap 5K scope plug in or a scrap TM500 unit. Unless of course, there's a big stock of the plug in top/bottom extrusion sitting somewhere. That's really the key piece to duplicating the plug in housing. Also, as mentioned earlier, DO NOT bother to add the pull tab for this test plug in, it just makes using the plug in so much harder, and serves no real purpose.

all the best,
walter

--
--
Walter Shawlee 2
Sphere Research Corp. 3394 Sunnyside Rd.
West Kelowna, BC, V1Z 2V4 CANADA
Phone: +1 (250-769-1834 -:- http://www.sphere.bc.ca
+We're all in one boat, no matter how it looks to you. (WS2)
+All you need is love. (John Lennon)
+But, that doesn't mean other things don't come in handy. (WS2)
+Nature is trying very hard to make us succeed, but nature does not depend on us.
We are not the only experiment. (R. Buckminster Fuller)