Date   

Re: Back feet for 335 scope

 

My 335 has ONE good, complete foot that I would loan out in the hope it might lead to the production of four new replacement feet.


Back feet for 335 scope

Phillip Potter
 

Hello all,

The feet on the rear of my 335 are crumbling apart, literally!

I talked to Walter at Sphere and he has nothing even close, and searches on the net reveal nothing... so, I am coming to the group to see if there might happen to be someone who has any extra rear feet (Tek PN 348-0425-00) or even just one, that could be spared (or loaned?) to me as an example of a complete foot?  I don't know if they could be 3-D printed or cast, but I don't have even one that is complete... mine are all crumbled.

Here is a picture of what it looks like (borrowed from the internet):

https://groups.io/g/TekScopes/photo/33014/1?p=Name,,,20,1,0,0

Thanks for any suggestion or help you can provide.

Phil


Re: Tek 2465a grid bias and brightness problems

Siggi
 

On Thu, 1 Mar 2018 at 02:00 Francesco <madowax@...> wrote:

Ok I have checked the Voltage at Q1980 collector, with r1878 full CW (max
grid bias) = 60V, with r1878 full CCW (min grid bias) = 120V, so there is
the correct range but shifted of 13V more or less. Q1980 test good out of
circuit.
Well, this shifting does seem to be your problem - especially if you're
measuring this at power-on, as the slow start should increase the nominal
voltages by ~10V initially. So if you're measuring this in the "cold"
state, you're more like 20V low.

I don't know where this is coming from, but there aren't very many
candidates.
If R1994 has drifted low, that'd do it.
If R1881 or R1992 have drifted high, that'd do it.
If R1878, the grid bias pot had high contact resistance or resistance to
ground, that'd do it.
If C1991 was leaky, that'd do it.

I think you'd best trace this by the currents to and from the Q1980 base
node. By measuring the values of R1881, R1992 and R1994, then measuring the
voltage drop over them, you should be able to to suss this out.

Good luck,
Siggi


Re: Tektronix 577/177 need some pictures

Velik Kazakov
 


Re: Tektronix 577/177 need some pictures

Velik Kazakov
 

Use this picture to make the scale. Think new scale looks good and will work. Make 3 different types to try the illumination under the scale.
I think the better one will be with the foil on bottom of the scale , but will try all.
Now will try to find a time to make new metal knob and to install all.
Thanks to all!


Re: Tek 2465a grid bias and brightness problems

Francesco
 

Measurements are taken at power on.


Re: Tek 2465a grid bias and brightness problems

Francesco
 

Ok I have checked the Voltage at Q1980 collector, with r1878 full CW (max grid bias) = 60V, with r1878 full CCW (min grid bias) = 120V, so there is the correct range but shifted of 13V more or less. Q1980 test good out of circuit.


Re: one last 7633 question (for now)

 

Also some plug-ins like the ubiquitous 7B53A used chiefly in 76xx
mainframes have no built in illumination anyway so adding the lamp
power modification to the mainframe makes no difference for them.

On Wed, 28 Feb 2018 16:43:38 -0000, you wrote:

While I intend to do this mod to my 7623A, it is worth bearing in mind a couple of things. If you check the app note/mod sheet (040-0686-01) you will see that some things should be down-rated afterwards - this might be significant to your needs. Also, those mainframes that had this power-supply for the push-switches as standard often had a switch where the light intensity could be turned down or completely off. It may be worth your while to include something like this, unless you like replacing the lamps in the switches on the plug-ins. Just a thought...

Colin.


Re: 7603 working .... then blank

tinkera123
 

Thankyou Roger and Menahem for your recommendations ... my Scope has run trouble free for quite few hours now ... and I am discovering its functionality is more complex than my el cheapo scope .... :)

Cheers,
Ian


Re: TM500 Series Extender Cable Keeps falling out

hpxref
 

Using the TM500 PSU / back plane as a standalone card tester :
I did the same as Edward some years ago before I made up my own (TM503 )
plug in metal frame extenders, (turned out to be a fiddly job) which fully supports the cable and card plug
But one thing to watch out for when just using the PSU/card cage is that, without
the TM500 case, the card alignment plastic slot(s) are not there to hold the card in, and it can easily
fall out of the socket, especially when you re position the PSU to get at a test connection, so you
might be back to square one. When I could, I used thin plastic tubing to tie/hold the cable plug in at that time
Rgds
John


Re: TekWiki Helper Idea. Brainstorm or Washout?

EJP
 

The easy way for people to add to a database is right here in the group. Create a Database here.


Re: MG Chemical Responds --> Re: Problems with MG Chemicals Super Contact Clearer

EricJ
 

I was going to say yesterday, they should have just sent you a new nozzle and tube. At least they finally wised up. And yup, I meant both ends of the tube, you got me! =)
--Eric
Sent from my Samsung Galaxy S8.

-------- Original message --------From: brasscat <brasscat@...> Date: 2/28/18 11:59 AM (GMT-06:00) To: TekScopes@groups.io Subject: [TekScopes] MG Chemical Responds --> Re: Problems with MG Chemicals Super Contact Clearer
They are being proactive.
---------------------------------------------------------------------------------
Hello Stan,

I have forwarded your concern to production team.  They have tried several tubes and nozzle
and seems to work fine. Also I tried myself as show this picture and I didn’t experience any
difficulty. I didn’t have to tilt or do anything special, it just fitted right in. This product is batch
code # 17193. I would like to resolve this issue and I would like to send you nozzle that has
tube fitted. All you have to do is to take the old one out and replace with new one.

(Photo of joined nozzle and tube )

Please provide me with your shipping information.
Again I do apologize for inconvenience this has caused.

Regards, Titus
---------------------------------------------------------------------------------
I responded with my address.


Re: one last 7633 question (for now)

Brendan
 

One thing that kinda threw me was no trigger light. Well just now looked inside my 7b53a and the previous owner had plugged in the pin header backwards. So the trigger light is now working. Jeesh


Re: Tek 2465a grid bias and brightness problems

Siggi
 

On Wed, 28 Feb 2018 at 12:22 Francesco <madowax@...> wrote:

On Q1980 collector with grid Bias at min I see 120 V and I have already
replaced C1991 and R1994 even if they tested good out of circuit (R1994 was
indeed a bit low: 1% out of tolerance on the low side)
If you have no control range to speak of on the bias pot, then I'd guess
Q1980 has gone bad.

Looking at the schematic, what the service manual states makes sense.
Discounting Q1980s base current, its collector voltage will be 42.7V +
150kOhm * (I_R1881 + I_R1992). The two control currents are then in the
range of I_R1881=~0-~440uA and I_R1992=~180-~120uA.

In simulation, I see the collector voltage range the service manual
describes, but when I disconnect Q1980s collector, I see the control
voltage rising from ~30V through to ~125V as C1990 charges, pretty much
irrespective the setting of the bias pot.


Re: one last 7633 question (for now)

Brendan
 

Details,details,details. Thanks for helping me not go crazy. I literally looked at that schematic for hours yesterday and today. Finally got to the "well i gotta ask" point. I told my wife I was too stupid to figure it out and to stubborn to give up. Glad I asked because it would have been another long day.


Re: one last 7633 question (for now)

cmjones01
 

On Wed, Feb 28, 2018 at 08:44 am, Colin Herbert wrote:

Also, those mainframes that had this power-supply
for the push-switches as standard often had a switch where the light intensity
could be turned down or completely off.
Note also that some plugins, notably the programmable ones (definitely 7A16P and 7B90P, probably 7A29P as well) use the 5V 'lights' supply to run their internal logic. They don't work at all in unmodified 76x3 mainframes, and neither do they work well in larger mainframes with the light intensity switched to 'dim'. I found that out the dumb way!

Chris


Re: Tek 475 attenuators faulty when two sections in series

Fabio Trevisan
 

Tom,
Thanks for the thumbs up and congrats that it's now doing it...
One of the atten. blocks showing flaky seems now much more sensible... What
wasn't making any sense before was that all combinations of all them
wouldn't work, but they would work well one-by-one...
The lenghty explanation... Well I'm not very good at summarizing my
thoughts... I keep thinking all is importante as I write.
I had myself to build my own normalizer too, and now that you mention I'm
not sure what kind of capacitor I have in parallel to the trimmer... I also
didnt get *perfect* results in all combinations and you maybe have got
it... On mine I think it was an NP0 cap (IIRC, CG0 and NP0 are
interchangeable terms for the same thing).

Brgrds,

Fabio


2018-02-28 15:03 GMT-03:00 Tom Gardner <tggzzz@...>:

Firstly, thank you for taking the time for a lengthy explanation.

Secondly, I didn't take any offence in any way. I'm only too aware that I
have a lot to learn, especially when I ask a question!

I've eventually managed to make progress, after real-life intervened. I
made my own normaliser and, while it significantly improved matters, the
result was still "sub-optimal". Eventually I noticed that the shape of
transitions depended on the level. I was, I thought, using a C0G capacitor
- but either I wasn't or they aren't as voltage insensitive as I believed.
Removing that and using only a trimcap solved that issue, and I made
progress.

Currently there is a good waveshape on both channels and at all
sensitivities, with a 50ohm terminator and a conventional *10 probe. The
notable exception is that one channel's /2 attenuator is very sensitive to
movement; the AC response varies significantly. I've ordered a replacement.

So, thank you very much indeed.



On 21/02/18 14:57, Fabio Trevisan wrote:

Hello Tom,
I own a 466 and, from your description, it seems your 475's vertical
attenuator works exactly as the one in mine (I`m not looking at the 475
manual right now).

Again, from your description, it seems that either you're getting the
frequency compensation adjustment / input capacitance adjustment procedure
wrong, or the input capacitance trimmer of *all* your attenuator modules
are bad or flaky.

Since it's unlikely that *all* them are bad, it seems more likely that
you're getting the procedure wrong (forgive me if I`m assuming too much
here).
It's easy to overlook the input capacitance and have them wrong if you're
always sourcing the signal through a low impedance generator (or low
impedance terminated cable), because whatever they're right or wrong,
these
tiny capacitances, won't trouble a 50 Ohm sourced signal...

Every attenuator module has a freq-compensation trimmer (which is in
series
with the signal, paralleled to the attenuator resistor in question), and
an
input capacitance trimmer, that's between the input of the attenuator and
ground.

The compensation capacitor (the one in series with the signal, paralleled
to the attenuator resistor) works against the input capacitance of the
scope *or* against the input capacitance trimmer of any other attenuator
module that is in series, down in the attenuation chain...so, it's
paramount that each attenuator module's input capacitance is adjusted to
*exactly* the same as the oscilloscope's bare front end capacitance.

So in order to get it right, first of all, you need an input capacitance
normalizer (or feed the signal through a x10 oscilloscope probe, but then
your generator needs to be able to generate some hefty 30Vpp for a 6 div
waveform).

Then you have to follow the sequence of adjustments...

1. Use the most sensitive setting of the scope (5mV/div, no atten.
inserted), source the signal through the input normalizer and adjust the
its trimmer to get a good square edge (or adjust your x10 probe
compensation).
This will assure that the normalizer's capacitance equals the input
capacitance of the oscilloscope front end's bare capacitance.
Adjust the frequency of the generator so that it's low enough for you to
see the square wave become round or pointy... don't set the frequency too
high, or it will only seem that the square wave is changing amplitude.

2. Double the output voltage of your generator, set the scope to 10mV/div
(x2 attenuator inserted), and then...

2.1. Source the signal to the scope through a 50Ohm pass-thru terminator,
and adjust the freq. compensation trimmer of the x2 attenuator module...
This will get the x2 freq. compensation right and will eventually change
by
some amount the input capacitance of the scope... which won't trouble your
50Ohm source.

2.2.Now, remove the 50Ohm pass-thru terminator, insert the input
normalizer
and adjust the input capacitance trimmer from the x2 attenuator module.
Since the input normalizer is adjusted to match the scope's bare input
capacitance (from step 1), when you now adjust the input capacitance
trimmer of the x2 module, you're
making the x2 input capacitance the same as the bare input, meaning that,
as from now, the x2 input capacitance is "normalized" and therefore, will
be seen by any preceding attenuator
that may be inserted in the chain, as having the same input capacitance as
the oscilloscope's bare front end.
Note:
This step is assuming that your connecting cable is short or that you're
hooking up your generator directly to the input of the
normalizer...(because the cable will be not properly terminated)
Anyway, at the frequency that you will be using, in the 10s of kHz, it
shouldn't be troubled too much by the cable's reflections.
If you're a purist, you can keep the 50Ohm pass through terminator before
the input normalizer, but then your square wave will be halved and it may
require you to double the output of the generator.
No big deal at this step, but it can be more difficult to get the
appropriate test level when you're setting the x100 attenuator.

3. Walk you way up through the next attenuation levels, x4, x10 and x100,
repeating the same procedure of step 2, 2.1 and 2.2, as you increase the
output of the generator.

At the end, all input attenuator blocks will present the same input
capacitance to the input BNC of your scope, or to any precedent attenuator
block, as the scope's front end bare capacitance.

Hope I guessed it right, because other than that, to me it simply doesn't
make sense (in considering the way how the blocks are interconnected and
how they're performing correctly when each one is inserted alone).

rgrds,

Fabio




2018-02-21 6:16 GMT-03:00 Tom Gardner <tggzzz@...>:

I'm having a problem setting up the attenuators in my 475. It appears that
each section is working individually, but not when there are two sections
in series.


The background...

The 475 was very cheap because the timebase was unreliable. It was a
little mucky on the outside, but there's no visible problem inside.
There
are signs that a previous owner had been inside before. The power
supplies
are all good, and so far the only components I've replaced has been the
motor controller quad transistors (with ZTX630s that just happened to be
available).

I've got the timebase working by a combination of using:
- IPA to clean the pin in the timebase knob that prods the A/B
microswitch
- IPA on smooth paper to clean the timing board finger contacts
- since that wasn't completely successful, using a jeweller's screwdriver
to add a tiny drop of Caig DeOxit to each switch contact
I'd have preferred not to use DeOxit since it might attract crap over
time, but it wasn't good enough without it. Conclusion: those switch
contacts were imperfect.


The problem...

So now I've moved onto the input channels. I've used a multimeter to
check
the continuity of the topside attenuator finger contacts, and they are
all
fine (<<1ohm). I've reseated all the attenuators and "sel"
resistors/jumpers in the attenuator and added a tiny drop of DeOxit,
without effect.

But I'm getting ambiguous behaviour when 2 attenuator sections are in
series:

1) on 5mV/div the displayed waveform is perfect from DC to 1.8ns
risetime.
I interpret this to everything after the attenuator is working well, and
finger contacts underneath the attenuator board are working.

2) on 10mV/div, I tweaked the *2 attenuator capacitors to get a perfect
display. Therefore that attenuator and those contacts are working.

3) on 20mV/div, ditto with *4 attenuator

4) on 50mV/div, ditto with *10 attenuator

5) on 100mV/div, the displayed waveform shows pronounced HF compensation
error. An attenuator can be re-tweaked to get a good display, but it is
very sensitive to position. Of course that invalidates steps 2 or 4

6) ditto 200mV/div, and invalidating steps 3 or 4

Summary: it appears the *2, *4, *10 attenuator/switch are working
individually, but not in combination.


Future...

So, what's my next step?
I could use IPA and/or DeOxit on the finger contacts. But that might
attract crap, and if a film bridged the gaps it might subtly affect HF
performance.
I believe that sometimes it helps to resolder the contacts inside the
attenuator. But that feels like kill-or-cure, particularly since I don't
know the temperature and the plastic looks like it might melt easily.

Are there any other diagnostics I can do?
What's the best course of action?
What iron temperature and re-soldering techniques should I use?
Would 465 attenuator sections be substitutes for some of the 475's
attenuator?

Thanks








Amazing 453A, nicest old scope I have ever seen

 

I recently got a 453A off ebay because it was shown working with a bright CRT, and all the BNC connectors were still clean and shiny. It turned out to be amazing in real life, everything worked, (one slightly noisy intensity pot, slightly noisy vertical attenuators from not being switched in heaven knows how many years), the CRT is like new, and everything on it sparkles as if it has been sealed in a plastic bag for 40 years. needless to say, it had bad rear feet (I retrofitted our helimec feet in about 10 minutes), and some paint scuffs on the case, so I will re-paint later.

this 453A looks slightly different than normal, it is s/n B071809 (late), and has MOD 221T, does anyone have details on it? incredibly, the cal sticker said Tektronix, 1985, and the cal was still bang on. that is IMPRESSIVE, 33 years later, and still ticking like new. I am curious to learn more about this unit, as it is clearly a keeper, so any more info on MOD 221T is appreciated.

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


Re: Tek 475 attenuators faulty when two sections in series

Tom Gardner
 

Firstly, thank you for taking the time for a lengthy explanation.

Secondly, I didn't take any offence in any way. I'm only too aware that I have a lot to learn, especially when I ask a question!

I've eventually managed to make progress, after real-life intervened. I made my own normaliser and, while it significantly improved matters, the result was still "sub-optimal". Eventually I noticed that the shape of transitions depended on the level. I was, I thought, using a C0G capacitor - but either I wasn't or they aren't as voltage insensitive as I believed. Removing that and using only a trimcap solved that issue, and I made progress.

Currently there is a good waveshape on both channels and at all sensitivities, with a 50ohm terminator and a conventional *10 probe. The notable exception is that one channel's /2 attenuator is very sensitive to movement; the AC response varies significantly. I've ordered a replacement.

So, thank you very much indeed.

On 21/02/18 14:57, Fabio Trevisan wrote:
Hello Tom,
I own a 466 and, from your description, it seems your 475's vertical
attenuator works exactly as the one in mine (I`m not looking at the 475
manual right now).

Again, from your description, it seems that either you're getting the
frequency compensation adjustment / input capacitance adjustment procedure
wrong, or the input capacitance trimmer of *all* your attenuator modules
are bad or flaky.

Since it's unlikely that *all* them are bad, it seems more likely that
you're getting the procedure wrong (forgive me if I`m assuming too much
here).
It's easy to overlook the input capacitance and have them wrong if you're
always sourcing the signal through a low impedance generator (or low
impedance terminated cable), because whatever they're right or wrong, these
tiny capacitances, won't trouble a 50 Ohm sourced signal...

Every attenuator module has a freq-compensation trimmer (which is in series
with the signal, paralleled to the attenuator resistor in question), and an
input capacitance trimmer, that's between the input of the attenuator and
ground.

The compensation capacitor (the one in series with the signal, paralleled
to the attenuator resistor) works against the input capacitance of the
scope *or* against the input capacitance trimmer of any other attenuator
module that is in series, down in the attenuation chain...so, it's
paramount that each attenuator module's input capacitance is adjusted to
*exactly* the same as the oscilloscope's bare front end capacitance.

So in order to get it right, first of all, you need an input capacitance
normalizer (or feed the signal through a x10 oscilloscope probe, but then
your generator needs to be able to generate some hefty 30Vpp for a 6 div
waveform).

Then you have to follow the sequence of adjustments...

1. Use the most sensitive setting of the scope (5mV/div, no atten.
inserted), source the signal through the input normalizer and adjust the
its trimmer to get a good square edge (or adjust your x10 probe
compensation).
This will assure that the normalizer's capacitance equals the input
capacitance of the oscilloscope front end's bare capacitance.
Adjust the frequency of the generator so that it's low enough for you to
see the square wave become round or pointy... don't set the frequency too
high, or it will only seem that the square wave is changing amplitude.

2. Double the output voltage of your generator, set the scope to 10mV/div
(x2 attenuator inserted), and then...

2.1. Source the signal to the scope through a 50Ohm pass-thru terminator,
and adjust the freq. compensation trimmer of the x2 attenuator module...
This will get the x2 freq. compensation right and will eventually change by
some amount the input capacitance of the scope... which won't trouble your
50Ohm source.

2.2.Now, remove the 50Ohm pass-thru terminator, insert the input normalizer
and adjust the input capacitance trimmer from the x2 attenuator module.
Since the input normalizer is adjusted to match the scope's bare input
capacitance (from step 1), when you now adjust the input capacitance
trimmer of the x2 module, you're
making the x2 input capacitance the same as the bare input, meaning that,
as from now, the x2 input capacitance is "normalized" and therefore, will
be seen by any preceding attenuator
that may be inserted in the chain, as having the same input capacitance as
the oscilloscope's bare front end.
Note:
This step is assuming that your connecting cable is short or that you're
hooking up your generator directly to the input of the
normalizer...(because the cable will be not properly terminated)
Anyway, at the frequency that you will be using, in the 10s of kHz, it
shouldn't be troubled too much by the cable's reflections.
If you're a purist, you can keep the 50Ohm pass through terminator before
the input normalizer, but then your square wave will be halved and it may
require you to double the output of the generator.
No big deal at this step, but it can be more difficult to get the
appropriate test level when you're setting the x100 attenuator.

3. Walk you way up through the next attenuation levels, x4, x10 and x100,
repeating the same procedure of step 2, 2.1 and 2.2, as you increase the
output of the generator.

At the end, all input attenuator blocks will present the same input
capacitance to the input BNC of your scope, or to any precedent attenuator
block, as the scope's front end bare capacitance.

Hope I guessed it right, because other than that, to me it simply doesn't
make sense (in considering the way how the blocks are interconnected and
how they're performing correctly when each one is inserted alone).

rgrds,

Fabio




2018-02-21 6:16 GMT-03:00 Tom Gardner <tggzzz@...>:

I'm having a problem setting up the attenuators in my 475. It appears that
each section is working individually, but not when there are two sections
in series.


The background...

The 475 was very cheap because the timebase was unreliable. It was a
little mucky on the outside, but there's no visible problem inside. There
are signs that a previous owner had been inside before. The power supplies
are all good, and so far the only components I've replaced has been the
motor controller quad transistors (with ZTX630s that just happened to be
available).

I've got the timebase working by a combination of using:
- IPA to clean the pin in the timebase knob that prods the A/B microswitch
- IPA on smooth paper to clean the timing board finger contacts
- since that wasn't completely successful, using a jeweller's screwdriver
to add a tiny drop of Caig DeOxit to each switch contact
I'd have preferred not to use DeOxit since it might attract crap over
time, but it wasn't good enough without it. Conclusion: those switch
contacts were imperfect.


The problem...

So now I've moved onto the input channels. I've used a multimeter to check
the continuity of the topside attenuator finger contacts, and they are all
fine (<<1ohm). I've reseated all the attenuators and "sel"
resistors/jumpers in the attenuator and added a tiny drop of DeOxit,
without effect.

But I'm getting ambiguous behaviour when 2 attenuator sections are in
series:

1) on 5mV/div the displayed waveform is perfect from DC to 1.8ns risetime.
I interpret this to everything after the attenuator is working well, and
finger contacts underneath the attenuator board are working.

2) on 10mV/div, I tweaked the *2 attenuator capacitors to get a perfect
display. Therefore that attenuator and those contacts are working.

3) on 20mV/div, ditto with *4 attenuator

4) on 50mV/div, ditto with *10 attenuator

5) on 100mV/div, the displayed waveform shows pronounced HF compensation
error. An attenuator can be re-tweaked to get a good display, but it is
very sensitive to position. Of course that invalidates steps 2 or 4

6) ditto 200mV/div, and invalidating steps 3 or 4

Summary: it appears the *2, *4, *10 attenuator/switch are working
individually, but not in combination.


Future...

So, what's my next step?
I could use IPA and/or DeOxit on the finger contacts. But that might
attract crap, and if a film bridged the gaps it might subtly affect HF
performance.
I believe that sometimes it helps to resolder the contacts inside the
attenuator. But that feels like kill-or-cure, particularly since I don't
know the temperature and the plastic looks like it might melt easily.

Are there any other diagnostics I can do?
What's the best course of action?
What iron temperature and re-soldering techniques should I use?
Would 465 attenuator sections be substitutes for some of the 475's
attenuator?

Thanks





MG Chemical Responds --> Re: Problems with MG Chemicals Super Contact Clearer

brasscat
 

They are being proactive.
---------------------------------------------------------------------------------
Hello Stan,

I have forwarded your concern to production team. They have tried several tubes and nozzle
and seems to work fine. Also I tried myself as show this picture and I didn’t experience any
difficulty. I didn’t have to tilt or do anything special, it just fitted right in. This product is batch
code # 17193. I would like to resolve this issue and I would like to send you nozzle that has
tube fitted. All you have to do is to take the old one out and replace with new one.

(Photo of joined nozzle and tube )

Please provide me with your shipping information.
Again I do apologize for inconvenience this has caused.

Regards, Titus
---------------------------------------------------------------------------------
I responded with my address.