Date   

Re: TM506

Harvey White
 

Interleaved:

On 7/22/2020 1:28 PM, Stephen wrote:
On Wed, Jul 22, 2020 at 04:21 AM, Harvey White wrote:

The NPN and PNP transistors for each slot are completely independent of
anything.  They're nothing but transistors connected to socket pins.
I'd suggest the following:

1) using one of the adaptors you bought, make a plugin to bring out the
wiring for each slot.  You're interested in the power supply voltages,
and the BEC junctions of the transistors.  Using a transistor tester
(the cheap ones built with a PIC or MEGA ought to be fine), test each
transistor. The advantage here is that the tester identifies which lead
is which.
Yes, but these adaptors will arrive late August or mid-September. I’m not gonna wait that long.
Ok, then see if you can find one of the Tektronix breadboard systems.  They were boxes with a substantial blank area and a power supply module.  I think you could also find one that's simply a frame and a plugin with a breakout.  Worst (not that it is) case is to find an old plugin card with the appropriate number of pins.  You might also consider buying a known bad, parts only, TM500 module, and instead of fixing it, make it into a test fixture.



2) Check the power supply voltages.  The bulk DC supplies are fused.
The AC windings are not fused,

3) Make a supply tester, that at least breaks out the voltages to banana
jacks or something like that.  You want to check each slot.  For now,
the current available may not be a factor, but you want to make sure
that all the voltages are where they should be.
Since I removed the bottom land top of the 506, I can easily check each slot individually with my DMM.
Same goes for debugging the plugins. Of course it’s not ideal, but that’ll have to do for now, I guess.
That'll do for inadvertent grounding.


4) that you have transistor failures suggests that at least one plugin
has a supply problem, and that you may have put in the transistors
wrongly.
Indeed. That much I understand. Now which one or ones...? I yet have to figure that out.
What I understand, it’s a never ending story. You make the 506 work on it’s own, than as soon as you plug in a module, if it’s bad, things will go sideways all over again. If I had produced codes or network designs with flaws like that, and no failsafe, I would’ve been out of a job very fast. But maybe I’m wrong and don’t yet grasp the whole concept.
Nope, cascade failure, shorts killing things.  First modules I'd test out would be the ones that don't use the external transistors, if there are any.  Next, I'd look at ones that don't use the AC voltage, not that there was a problem with those.  Then go to the other ones.  There's no really easy way other than a smart extender that allows you to monitor current, or put in a fuse (if possible).

However, without the plugin in the frame, if it does use an external frame transistor, the output part of the supply will be isolated and the input will be.  It's somewhat as if you removed the regulator tube from a tube supply.  You could test the bulk supply to the tube, then test the load, and in either case, see if there are any shorts.

If you had a variac, you could monitor voltages as you bring up the power slowly.  All the supplies are linear supplies, so there's not as much possibility of damage as there would be in a switching supply.




An ohmmeter cannot really tell the difference between the BE
and BC junctions, a beta test or transistor tester can.  If you have the
C and E leads reversed, you generally get a transistor with very low
beta, but it'll be a transistor.
I have a transistor tester on my DMM.
I'd be looking at that, then.


5) note that you have discovered that using plugins as test loads is not
the best idea.  A dedicated tester rig makes a lot of sense.
Tell me about it...! 😂
I admit though, that was stupid.
Everybody makes that kind of error every now and then.

Harvey




6) that tek-wiki article on the test module for the TM500 series frames
makes a lot of sense.


Harvey


Re: TM506

Stephen
 

On Wed, Jul 22, 2020 at 02:38 AM, Stephen wrote:


On Wed, Jul 22, 2020 at 02:34 AM, Michael W. Lynch wrote:


On Wed, Jul 22, 2020 at 07:42 AM, Stephen wrote:


No voltage at pin 1 on any of the slots. Schematic shows 24.8V RMS.
Are you checking this voltage between 1A and 1B of the back plane connector?
It appears to me that the 24.8VAC source at each slot is supplied by
independent winding in the Main XFMR, It seem unimaginable that every one
of
these windings in the main XFMR would have shorted out. However, I am
certainly no expert on the TM506, I suppose it is possible? You can check
the individual windings at each slot by connecting an ohmeter between 1A and
1B and looking for continuity of about 1.6 ~1.8 Ohms and then between each
contact and the chassis for no continuity. I just did this test on my
TM506,
so you should see something similar on yours.
--
Michael Lynch
Dardanelle, AR
Will do when I get back. At the store at the moment.
This is very strange. I even thought for a minute that I had wired everything
backwards. I checked, and rechecked, and re-double checked against the
schematic and the pinouts, and I don’t see any problems...
So unless my unit is, for some obscure reason, wired differently, all should
be ok. But it’s not...
I’ve fixe the transistor to ground issue by inserting plastic sheets between the screws and the baseplate. No more collector shorts to ground. Although I bought a few extras, I left the same transistors for now. I only replaced 3/10.
I checked the voltages on all slot between 1A-1B and I have around 26.2VAC in all of them. But my unit is set for 220V, and I have 232VAC from the wall.... that could explain the higher voltages. I saw the jumpers to switch the input voltages, but nowhere did I see in the manual how to set it up.


Re: Cleaning the screen of a TDS744A ?

David Slipper
 

Thanks, I used a few drops of baby shampoo in warm water (very very dilute) and applied it with a barely damp lint free pad then dried with a clean microfiber cloth. Worked a treat.
Dave

On 21/07/2020 17:10, Roy Thistle wrote:
On Tue, Jul 21, 2020 at 01:35 AM, David Slipper wrote:

What is the best way to get greasy finger prints off the plastic sheet that is
in front of the CRT

From page 6-5 in Zenith's scan of the "TDS 684A & TDS 744 Service Manual" on Tekwiki at
http://w140.com/tekwiki/images/d/d6/070-8992-02.pdf

"Clean the light filter protecting the monitor screen with a lint-free cloth dampened with either isopropyl alcohol or, preferably, a gentle, general purpose detergent-and-water solution."


It appears... looking at the mechanical parts drawing... the "light-filter" is not a separate numbered component (not listed as such, in the "Mechanical Parts List") but is part of/comes with the front panel assembly? or with the display frame? So how do you remove it? So what's the "plastic filter's" material? could be acrylic or polycarbonate? ... and it's hard to tell the difference between between acrylic and polycarbonate, just by looking.

For the nervous, who want to do de-fingerprinting service... I'd start with the lint-free (supposed to be really lint free, and anti-static is better too... like Kimwipes)... I'd start with the general purpose detergent (a.k.a., mild dish detergent) and lint-free cloth... and then move up to the alcohol...if detergent doesn't work.
For fingerprint "grease" (fingerprint "grease" isn't just grease)... a detergent, and water, solution works better than the alcohol, in my opinion... in the following way. If you can remove the plastic filter?, clean it with the detergent solution, and then flush the soapy filter with distilled water... preferably, from a squeeze bottle... so you get a pressurized stream... this flushes the hopefully emulsified, and dissolved, fingerprints from the plastic filter.
Other solvents are a big no-no... they are probably going to damage the plastic... so no acetone, naptha, et. al.



.


Re: TM506

Stephen
 

On Wed, Jul 22, 2020 at 04:21 AM, Harvey White wrote:


The NPN and PNP transistors for each slot are completely independent of
anything.  They're nothing but transistors connected to socket pins.
I'd suggest the following:

1) using one of the adaptors you bought, make a plugin to bring out the
wiring for each slot.  You're interested in the power supply voltages,
and the BEC junctions of the transistors.  Using a transistor tester
(the cheap ones built with a PIC or MEGA ought to be fine), test each
transistor. The advantage here is that the tester identifies which lead
is which.
Yes, but these adaptors will arrive late August or mid-September. I’m not gonna wait that long.

2) Check the power supply voltages.  The bulk DC supplies are fused. 
The AC windings are not fused,

3) Make a supply tester, that at least breaks out the voltages to banana
jacks or something like that.  You want to check each slot.  For now,
the current available may not be a factor, but you want to make sure
that all the voltages are where they should be.
Since I removed the bottom land top of the 506, I can easily check each slot individually with my DMM.
Same goes for debugging the plugins. Of course it’s not ideal, but that’ll have to do for now, I guess.

4) that you have transistor failures suggests that at least one plugin
has a supply problem, and that you may have put in the transistors
wrongly.
Indeed. That much I understand. Now which one or ones...? I yet have to figure that out.
What I understand, it’s a never ending story. You make the 506 work on it’s own, than as soon as you plug in a module, if it’s bad, things will go sideways all over again. If I had produced codes or network designs with flaws like that, and no failsafe, I would’ve been out of a job very fast. But maybe I’m wrong and don’t yet grasp the whole concept.

An ohmmeter cannot really tell the difference between the BE
and BC junctions, a beta test or transistor tester can.  If you have the
C and E leads reversed, you generally get a transistor with very low
beta, but it'll be a transistor.
I have a transistor tester on my DMM.

5) note that you have discovered that using plugins as test loads is not
the best idea.  A dedicated tester rig makes a lot of sense.
Tell me about it...! 😂
I admit though, that was stupid.


6) that tek-wiki article on the test module for the TM500 series frames
makes a lot of sense.


Harvey


Re: "Selected" components

snapdiode
 

Well we have the list of checked tubes, I wonder if we have other lists?

Tubes are here

http://w140.com/tekwiki/images/1/14/157-_checked_and_tested_tubes_specs_and_procedure.pdf


Re: TM506

Stephen
 

On Wed, Jul 22, 2020 at 04:21 AM, Harvey White wrote:


The NPN and PNP transistors for each slot are completely independent of
anything.  They're nothing but transistors connected to socket pins.

1) if any transistor is mounted and any lead goes to ground/frame, bad
things happen.
Yep, that was the case, and bad things did happen. I hope I didn’t damage the 506... And that the plugins are still salvageable.
I bought new resistors. The schematic calls for 0.27R 10%. All I could find were 0.33R 5%.


Re: TM506

Stephen
 

I think I’ve identified my mistake. I sure didn’t see that coming. I should’ve been more careful.

The collectors of both the original transistors in this pair are connected to the back of the case. But because of the case design which adds a molded plastic ring around the mounting screw, they are isolated from the chassis. On the other hand, the new TIP55C & 56C also have the collector connected to the back of the case plate. But the plate extends beyond the top of the transistor, and does not provide isolation from the screw.
In other words, you guessed it, both collectors were grounded.
Now, i don’t know yet if this is the whole issue, but it’s a start...

See pict here: https://groups.io/g/TekScopes/photo/250733/0?p=Created,,,100,2,0,0


Re: 485 Cordwrap Feet

Jeff Davis
 

Hi Chuck,

I like your reasoning - the scopes do look very similar to a 485. But the foot the customer sent me was not a 453 or 454 foot. It looks like it's an earlier vintage than that. I've uploaded some photos of the foot the customer sent me, hoping that someone on the list will recognize it. https://groups.io/g/TekScopes/album?id=250966

I've also asked him for some photos of the scope, front and back, but have not heard back.

Jeff

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Chuck Harris <cfharris@...>
Sent: Wednesday, July 22, 2020 8:26 AM
To: TekScopes@groups.io <TekScopes@groups.io>
Subject: Re: [TekScopes] 485 Cordwrap Feet

Jeff,

I think if you explore this further with your customer,
you will find he doesn't have a 485 at all, but rather
has one of the similar looking scopes, the 453, or 454.

-Chuck Harris

Michael W. Lynch via groups.io wrote:
Jeff,

I don’t see any way that a 485 could use cordwrap feet like a 465/475. The area where these mount to the scope is very narrow. Too narrow for the footprint of the 465/475 type of foot. It would take a hybrid design, sort of a melding of the 465 foot with the 485 foot.

I would ask the customer for a picture of the back and front of the scope.

I would be very interested to see what they have.

Thanks

Michael W. Lynch
11993 Wildcat Hollow Road
Dardanelle, AR
72834


Re: "Selected" components

SCMenasian
 

Perhaps the resistor wasn't selected for value but for temperature coefficient. This might make some sense since it is a precision resistor with provisions made for fine adjustment during calibration. I haven't analyzed the circuit but there could be other selection criteria, as well (for example, noise or voltage coefficient, which might be critical in some circuits)


Re: "Selected" components

Harvey White
 

Looking at any design with component tolerances, they can average out, or pile up one way or the other.  The idea behind the 500 ohm pot is to give a certain range of adjustment, say, ideally with the desired adjustment about halfway.  Selecting the value of the series resistor compensates for component tolerances in this build, and can center that range.

Harvey

On 7/22/2020 9:47 AM, Colin Herbert via groups.io wrote:
Does anyone know what criteria were used by Tektronix to "select" components? This may be a far-ranging question, but the specific instance that I am looking at is in an FG504 function generator. In the triangle wave generator circuit and connecting to U375, resistor R358 is described on the schematic as "selected", and in the electrical parts list it is described as "RES., FXD, FILM: 3.74K OHM, 1%, 0.125W (NOMINAL VALUE, SELECTED)". Since this resistor is in series with a preset variable resistor of 500 Ohm, what would be the purpose of selection and what would the criteria be? Maybe ensuring that the preset adjusts to the middle of its adjustment, more-or-less? I can see that 500 Ohms is close to 1/9th of the total resistance of the series pair.

These series resistances connect pin #8 of U375 to the -15V rail and the preset adjusts the "DC level" (it isn't achieving that function very well at the moment; all waves are offset and distorted). There is also a 316 Ohm resistor connecting pin #8 to ground. Similarly, on pin #1 of U375 there is another 316 Ohm resistor (R352) going to ground and a 3.83 Ohm resistor (not marked as selected) connecting to the +15V rail.

It would be nice to solve this dilemma, because on my FG504 someone has substituted what seems to be a 3K Ohms preset for R358 which is adjusted to ~610 Ohms. That all seems a bit too low.

TIA, Colin.



Re: 485 Cordwrap Feet

Chuck Harris
 

Jeff,

I think if you explore this further with your customer,
you will find he doesn't have a 485 at all, but rather
has one of the similar looking scopes, the 453, or 454.

-Chuck Harris

Michael W. Lynch via groups.io wrote:

Jeff,

I don’t see any way that a 485 could use cordwrap feet like a 465/475. The area where these mount to the scope is very narrow. Too narrow for the footprint of the 465/475 type of foot. It would take a hybrid design, sort of a melding of the 465 foot with the 485 foot.

I would ask the customer for a picture of the back and front of the scope.

I would be very interested to see what they have.

Thanks

Michael W. Lynch
11993 Wildcat Hollow Road
Dardanelle, AR
72834


Re: "Selected" components

Tony G4NGV <tonyvirago2@...>
 

I have seen the same. A specific oddball value R, in series with a pot!

On Wed, 22 Jul 2020, 14:48 Colin Herbert via groups.io, <colingherbert=
blueyonder.co.uk@groups.io> wrote:

Does anyone know what criteria were used by Tektronix to "select"
components? This may be a far-ranging question, but the specific instance
that I am looking at is in an FG504 function generator. In the triangle
wave generator circuit and connecting to U375, resistor R358 is described
on the schematic as "selected", and in the electrical parts list it is
described as "RES., FXD, FILM: 3.74K OHM, 1%, 0.125W (NOMINAL VALUE,
SELECTED)". Since this resistor is in series with a preset variable
resistor of 500 Ohm, what would be the purpose of selection and what would
the criteria be? Maybe ensuring that the preset adjusts to the middle of
its adjustment, more-or-less? I can see that 500 Ohms is close to 1/9th of
the total resistance of the series pair.

These series resistances connect pin #8 of U375 to the -15V rail and the
preset adjusts the "DC level" (it isn't achieving that function very well
at the moment; all waves are offset and distorted). There is also a 316 Ohm
resistor connecting pin #8 to ground. Similarly, on pin #1 of U375 there is
another 316 Ohm resistor (R352) going to ground and a 3.83 Ohm resistor
(not marked as selected) connecting to the +15V rail.

It would be nice to solve this dilemma, because on my FG504 someone has
substituted what seems to be a 3K Ohms preset for R358 which is adjusted to
~610 Ohms. That all seems a bit too low.

TIA, Colin.




Re: TM506

Harvey White
 

The NPN and PNP transistors for each slot are completely independent of anything.  They're nothing but transistors connected to socket pins.

1) if any transistor is mounted and any lead goes to ground/frame, bad things happen.

2) if you reverse the base and collector, or base and emitter, that's not going to help.  The worst case is that you get the BE junction connected where the EC junction ought to be, and you get a series diode, therefore, bulk voltage goes to the regulated output.

I'd suggest the following:

1) using one of the adaptors you bought, make a plugin to bring out the wiring for each slot.  You're interested in the power supply voltages, and the BEC junctions of the transistors.  Using a transistor tester (the cheap ones built with a PIC or MEGA ought to be fine), test each transistor. The advantage here is that the tester identifies which lead is which.

2) Check the power supply voltages.  The bulk DC supplies are fused.  The AC windings are not fused,

3) Make a supply tester, that at least breaks out the voltages to banana jacks or something like that.  You want to check each slot.  For now, the current available may not be a factor, but you want to make sure that all the voltages are where they should be.

4) that you have transistor failures suggests that at least one plugin has a supply problem, and that you may have put in the transistors wrongly.  An ohmmeter cannot really tell the difference between the BE and BC junctions, a beta test or transistor tester can.  If you have the C and E leads reversed, you generally get a transistor with very low beta, but it'll be a transistor.

5) note that you have discovered that using plugins as test loads is not the best idea.  A dedicated tester rig makes a lot of sense.

6) that tek-wiki article on the test module for the TM500 series frames makes a lot of sense.


Harvey

On 7/22/2020 9:38 AM, Stephen wrote:
On Wed, Jul 22, 2020 at 02:34 AM, Michael W. Lynch wrote:

On Wed, Jul 22, 2020 at 07:42 AM, Stephen wrote:

No voltage at pin 1 on any of the slots. Schematic shows 24.8V RMS.
Are you checking this voltage between 1A and 1B of the back plane connector?
It appears to me that the 24.8VAC source at each slot is supplied by
independent winding in the Main XFMR, It seem unimaginable that every one of
these windings in the main XFMR would have shorted out. However, I am
certainly no expert on the TM506, I suppose it is possible? You can check
the individual windings at each slot by connecting an ohmeter between 1A and
1B and looking for continuity of about 1.6 ~1.8 Ohms and then between each
contact and the chassis for no continuity. I just did this test on my TM506,
so you should see something similar on yours.
--
Michael Lynch
Dardanelle, AR
Will do when I get back. At the store at the moment.
This is very strange. I even thought for a minute that I had wired everything backwards. I checked, and rechecked, and re-double checked against the schematic and the pinouts, and I don’t see any problems...
So unless my unit is, for some obscure reason, wired differently, all should be ok. But it’s not...



Re: TDS540B switches during boot VGA output from color to monochrome

unclebanjoman
 

I'Hi,
see that topic:
https://groups.io/g/TekScopes/message/157826
I think you have the same problem...

Max


Re: "Selected" components

Ray
 

From experience outside of tek,It is common practice to through a battery of tests and sometimes decide a particular resistor with a decade box based on engineering criteria, then solder in a resistor with the value needed. We somtimes put in a higher value then soldered in a paralell resistor to get where we needed to be.  RaySent from my T-Mobile 4G LTE device------ Original message------From: Colin Herbert via groups.ioDate: Wed, Jul 22, 2020 08:48To: TekScopes@groups.io;Cc: Subject:[TekScopes] "Selected" componentsDoes anyone know what criteria were used by Tektronix to "select" components? This may be a far-ranging question, but the specific instance that I am looking at is in an FG504 function generator. In the triangle wave generator circuit and connecting to U375, resistor R358 is described on the schematic as "selected", and in the electrical parts list it is described as "RES., FXD, FILM: 3.74K OHM, 1%, 0.125W (NOMINAL VALUE, SELECTED)". Since this resistor is in series with a preset variable resistor of 500 Ohm, what would be the purpose of selection and what would the criteria be? Maybe ensuring that the preset adjusts to the middle of its adjustment, more-or-less? I can see that 500 Ohms is close to 1/9th of the total resistance of the series pair.

These series resistances connect pin #8 of U375 to the -15V rail and the preset adjusts the "DC level" (it isn't achieving that function very well at the moment; all waves are offset and distorted). There is also a 316 Ohm resistor connecting pin #8 to ground. Similarly, on pin #1 of U375 there is another 316 Ohm resistor (R352) going to ground and a 3.83 Ohm resistor (not marked as selected) connecting to the +15V rail.

It would be nice to solve this dilemma, because on my FG504 someone has substituted what seems to be a 3K Ohms preset for R358 which is adjusted to ~610 Ohms. That all seems a bit too low.

TIA, Colin.


Re: "Selected" components

Dave Wise
 

I agree with your assessment, Colin.

Dave Wise

This was an easy case. Other times it's hard to even come up with a hypothesis.
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Colin Herbert via groups.io <colingherbert=blueyonder.co.uk@groups.io>
Sent: Wednesday, July 22, 2020 6:47 AM
To: TekScopes@groups.io
Subject: [TekScopes] "Selected" components

Does anyone know what criteria were used by Tektronix to "select" components? This may be a far-ranging question, but the specific instance that I am looking at is in an FG504 function generator. In the triangle wave generator circuit and connecting to U375, resistor R358 is described on the schematic as "selected", and in the electrical parts list it is described as "RES., FXD, FILM: 3.74K OHM, 1%, 0.125W (NOMINAL VALUE, SELECTED)". Since this resistor is in series with a preset variable resistor of 500 Ohm, what would be the purpose of selection and what would the criteria be? Maybe ensuring that the preset adjusts to the middle of its adjustment, more-or-less? I can see that 500 Ohms is close to 1/9th of the total resistance of the series pair.

These series resistances connect pin #8 of U375 to the -15V rail and the preset adjusts the "DC level" (it isn't achieving that function very well at the moment; all waves are offset and distorted). There is also a 316 Ohm resistor connecting pin #8 to ground. Similarly, on pin #1 of U375 there is another 316 Ohm resistor (R352) going to ground and a 3.83 Ohm resistor (not marked as selected) connecting to the +15V rail.

It would be nice to solve this dilemma, because on my FG504 someone has substituted what seems to be a 3K Ohms preset for R358 which is adjusted to ~610 Ohms. That all seems a bit too low.

TIA, Colin.


Re: TDS794D with broken Hard drive

Reginald Beardsley
 

I mainly posted to the list as a heads up to anyone else who needs one.

Good luck,
Reg


"Selected" components

Colin Herbert
 

Does anyone know what criteria were used by Tektronix to "select" components? This may be a far-ranging question, but the specific instance that I am looking at is in an FG504 function generator. In the triangle wave generator circuit and connecting to U375, resistor R358 is described on the schematic as "selected", and in the electrical parts list it is described as "RES., FXD, FILM: 3.74K OHM, 1%, 0.125W (NOMINAL VALUE, SELECTED)". Since this resistor is in series with a preset variable resistor of 500 Ohm, what would be the purpose of selection and what would the criteria be? Maybe ensuring that the preset adjusts to the middle of its adjustment, more-or-less? I can see that 500 Ohms is close to 1/9th of the total resistance of the series pair.

These series resistances connect pin #8 of U375 to the -15V rail and the preset adjusts the "DC level" (it isn't achieving that function very well at the moment; all waves are offset and distorted). There is also a 316 Ohm resistor connecting pin #8 to ground. Similarly, on pin #1 of U375 there is another 316 Ohm resistor (R352) going to ground and a 3.83 Ohm resistor (not marked as selected) connecting to the +15V rail.

It would be nice to solve this dilemma, because on my FG504 someone has substituted what seems to be a 3K Ohms preset for R358 which is adjusted to ~610 Ohms. That all seems a bit too low.

TIA, Colin.


Re: 485 Cordwrap Feet

Jeff Davis
 

Hi Michael and Dave,

Thanks for your responses. Looking at Michael’s photo, I totally see his point about a 465 style foot not fitting. So the question is really, what kind of scope did the foot come from, as Michael suggests.

I’ve asked for photos and will advise when I hear more.

Jeff

On Jul 22, 2020, at 5:56 AM, Michael W. Lynch via groups.io <mlynch003=yahoo.com@groups.io> wrote:

On Tue, Jul 21, 2020 at 11:47 PM, Daveolla wrote:


If the fellow read the "6" in 465 as an "8" he would get 485.
That is the only explanation that I can imagine.

--
Michael Lynch
Dardanelle, AR



Re: TM506

Stephen
 

On Wed, Jul 22, 2020 at 02:37 AM, <scm@...> wrote:


Oops. My scanned manual is fuzzy. Try R655. It's connected to the -20V bus on
one end and the pin 10A on the backplane connector (also tje base of Q660)
That’s much better! 😂😂😂
Thank you