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Re: High Voltage Curve Tracer project

Ed Breya
 

There seems to have been some questions about what this is for. This info first appeared in message #164397, in a different discussion. Here is a copy, replicated here, that describes its function:

With all this talk about HV stuff, I think it's a good time to introduce my HV curve-tracer/test box thing. I have been wrapping up the final design and features recently, and it's looking real good, with high utility for all sorts of HV device testing. It's basically a low power, variable HV engine, using a 5 kV RMS "static-neutralizing" transformer, with various operating modes. A built in HV probe circuit, and special receivers for DUT return current and DC leakage, provide output signals to a scope and a DVM.

The HV engine has these main functions, selected by a SP8T HV switch:
FLOAT
-DC
-DC/sweep
AC/sweep
+DC/sweep
+DC
FLOAT
DISCHARGE

The AC is variable from ~0 to +/- 7500 V peak
The DC ones are variable from ~0 to 15 kV peak
The maximum steady-state current from any output is around 2 mA (shorted).

The HV probe drives a 1 meg scope input, with 1000:1 ratio, so 1V/kV.

The DUT return receiver absorbs the cold-end current, and drives another 1 meg scope input, with various ranges:
1V/mA, 2 kohm burden
1V/uA, 1 megohm parallel 200 pF burden
LOG (bipolar compression), about 4 mA/400 mV reference level, 1 kohm plus diode parallel 1.5 meg burden

The DC leakage receiver drives a DVM, and has internally selected termination Rs to accommodate DVMs with input R of 1 meg, 10 meg, or 1E9 and up.
It is especially useful for capacitor leakage testing, with low-pass filtering to reduce ripple current and interference. The ranges are:
1 V/mA, tau 1 sec, 2 kohm burden
1 V/uA, tau 1 sec, 1.1 meg burden
1V/uA, tau 11 sec, 1.1 meg burden

The receivers and other ports are protected from faults with spark gaps and other items. No equipment output signal can exceed 30 V.

My test setup with a 5 digit DVM, can resolve to 10 pA - but only after tens of minutes to allow settling of the dielectric absorption, and with maximum filtering, and with line voltage fairly stable (the HV is not regulated). This was on a .01 uf 5 kV ceramic cap - the rectangular type often found in old scopes - stressed at about 6500 V. I'm finding these caps are quite remarkable in performance, despite their age and being used. This particular unit settled at less than 100 pA with 6500 V, so well above E13 ohms, which I'd expect just from a good insulator, without any capacitance included. Of course, this is only at room temperature, with no other stresses applied, but it was quite surprising. I'll be reporting on the caps and other items separately - it's been a lot of fun checking things out, with interesting results.

There are also some other items and functions, jumper-selected on the working deck. These include 4600 pF of HV filter capacitance, clamp circuits to make +/- 2 kV and +/- 200 V, and a high R (160 meg) for DC leakage feed and other very low current uses. The 2 kV clamp makes a 4 kV pp trapezoidal wave, for amplitude calibration of the HV probe/scope combo, and the 200 V one makes a 400 V pp - at one-tenth the risetime - "square" wave, to adjust the probe and cable compensation.

Anyway, it is moving along and working nicely, so I'll soon be able to put out some info on it. I'll report more as I finalize and draft up documents from my notes. I think some will find the system and design concepts interesting and useful.

Now, this whole deal may be considered OT here, since it isn't about Tek scopes per se, but I think the principles are very useful for checking out many of the problematic HV type components used in our scopes. So Dennis, if you don't want this here, please speak up ASAP, and I will refrain from further discussion.

end of #164397

I'll have lots more to say as I go along.

Ed

Re: High Voltage Curve Tracer project

Ed Breya
 

I have just posted the schematic of the HV section of the HV engine, in the same pix folder as before.

https://groups.io/g/TekScopes/photo/241896/0?p=Created,,,20,2,0,0

This is the HV fun part. The rest is more mundane, about driving, control, and measurement. It will come later as I organize my stuff.

Ed

Re: Tektronix 2467B Auto Measure Faulty?

Leandro Lindemann
 

Looking at the diagram, I realize that this point is the output to the BNC connector labeled B Gate. So, I believe it is correct to only have a signal at this point when Sweep B is used.

Thanks.

Re: Tektronix 2467B Auto Measure Faulty?

Leandro Lindemann
 

I took the measurements at the test points suggested by Mr. Chuck.

At test point 42 I only have the indicated waveform when using the Sweep B function. In Swep A I have no waveform. Should there be a signal at this point when Sweep A is selected?

I used my other Scope for measurements.

Thanks in advance.

Re: 547 scope HV transformer problem. One practical solution.

Jim Ford
 

Hi, Steve.I think most, if not all, the people in this group understand that having a portable scope that connects to modern PCs and such is very handy, preferring though we may to use those glorious old analog beasts.We have the TDS3032, 3052, and 3054 models at work, and they are certainly quick and easy to grab off the shelf and carry over to a bench or to another lab or wherever.  Quick and easy enough to trigger on whatever signal and "stop time", my favorite feature of a DSO vs analog scopes.  Yes, I know somebody will bring up storage scopes, but I don't even want to go there.   Another rabbit hole I don't have time for (Got enough already with my Tek scope and HP microwave gear obsessions)I am glad to get home to my 7904, 7603, and 5103N D10 analog scopes (and HP 54504A DSO) at the end of the day, though.  The bright sharp traces, simple and repairable electronics, the versatility with all the plug-ins, and just the feel of such high-quality products can't be matched by the mass-produced, dumbed-down, bean-counter-designed junk of today.<Rant off>Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: stevenhorii <sonodocsch@...> Date: 2/22/20 1:24 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] 547 scope HV transformer problem. One practical solution. I once ran into a former Tek employee at a hamfest where I was looking overone of the 500-series scopes. He said that in the day when Tek servicedthem, they washed them with water and then warm-air dried them. I will haveto look for that publication to verify what he said. I don’t doubt it wouldwork with the tube-type scopes but I’d have some concerns about doing thatwith the solid state ones. Some of the switches in the plug-ins don’t lookwaterproof but also look like they would be difficult to dry out with air.I’m new to this group, but not to using Tek scopes. My first was a purchasefrom DoD Surplus Sales (back before they privatized it). It was a 545A andwas DOA. I found the problem quickly - a bad resistor in the power supply.I replaced that, and the scope powered right up. I had several of the500-series after that (a 585, 547, and a 556 - should have kept that one. Idonated the scopes to the lab I was working in when I left. By that time, Istarted getting the 7000-series scopes and still have most of those (a7704A, 7904A, 7104, R7844, 7854). I also had an oddball 7000-series that Ithink was a short-lived precursor of the 7854. It had a section in betweenthe plug-ins and the display that, like the 7854, had a number of waveformcomputing functions. I don’t recall the number and I no longer have it - Isold it at a hamfest. Also, I don’t see it on TekWiki. I still use theR7844 on occasion, but have mostly turned to the TDS3054C digital. I knowthe analog folks have likely instantly put me on their “oust from thegroup” list, but it’s a matter of practicality - portability and I’m notworried about aliasing for the applications I have. I have found the Tekscopes over the years to be reliable and with all the plug-ins, veryversatile.SteveOn Sat, Feb 22, 2020 at 15:35 Randy Newman <randy.n.at.home@...>wrote:> Hi Ernesto.> As a happy 555 owner (beautiful sharp blue trace (p13 phosphor?). Re> washing, check the BAMA (Boat Anchor ....) and look in the tek section for> tektronix magazines....or maybe I am thinking of the w140.com site.> Yes...the latter...see the 111wiki, then section 38 manuals, catalogs, and> other publications...then "Tektronix magazines" Tekscope vol 8 no. 4> 1976..has tek's scope washing procedure. This is a 2-parter..don't have the> other issue...might be vol 9 no. 1. Plus there is a wealth of information> on tube and xsistor scopes. I also have a 7834, 7633, and 7623. But I> really like the 555, even with its external supply(!!). Nice garage> heater....some day I will have a real shop area.> Hope this helps!>> On Thu, Feb 20, 2020, 9:27 AM Ernesto <ebordon@...> wrote:>> > Hi John,  thank you for pointing me to the world of oscilloscope washing,> > cleaning.> >> > I read about the experiences of others and the industry washing> > oscilloscopes with water.  The hairs on my head used to stand up at the> > idea,  but now I recognize that it is relatively safe,  although it> > requires WORK.> > I compare it with my long experience of "don't fix what is not broken",> > and the good luck I have with my old scope that had a 40 years leave of> > absence.> >> > I perfectly cleaned the exterior of my 547, and it is shiny.  The inside> > is different,  with plenty of dust deposited on the tubes and surfaces.> I> > like to preserve it like that for its dramatic effect.  The instrument> will> > be perfect for my grandchildren to play with it when they are a little> > bigger,  and it may awaken their interest in electronics.  I plan to show> > them the inside of the scope to be impressed with its age,  but after> that> > the inside will be off limits to them.> >> > But...  if I experience any failures,  I feel competent enough to trace> > them to the failed component,  or particles of dust,  and I will remove> > just those offending particles.> >> > NOTE: I have a different standard for washing myself, staying clean> inside> > and changing my underwear,  ha ha ha.> >> > Cheers,> > Ernesto> >> >> >> >>> >>

Re: 2215A repair and restoration

satbeginner
 

Correction: it was not the Var Hold Off potmeter that was broken, but the B-Trigger potmeter, I wish it would have been the Var Hold Off, that one is easy to replace.....

To be continued,

Un saludo,

Leo

2215A repair and restoration

satbeginner
 

Hi all,

I recently got a (very?) sick 2215A from the well known ePay site.
It came to me perfectly packed from Germany (Thank you for that!) , and was as described and as it was shown in the pictures:

A few scratches on the outside, it powered on, showing a about 6mm trace on the right side of the middle of the screen.
Vertical positioning is working as it should, horizontal position does nothing.
The little piece of trace does follow the timebase settings.
Furthermore there were like 5 knob-caps missing, and the Var Hold Off potmeter axle was broken, and the two front legs are missing.

Using another scope ( a Tek ofcourse!! ) I found that none of the signals around U760 (the horizontal (Pre-) amplifier were correct.
Also, X-Y mode was not working, vertical OK, Horizontal nothing.
To narrow it down further, I removed plug P9705 from the A4 Timing Board where U760 is located, and carefully temporarily bend aside pins 2 and 3 to isolate the Timing board signals from the Main board.
These two pins are the (left of centre and right of centre) signals into the horizontal HV (100V) deflection amplifiers on the main board, now I powered the scope back on:

Right, now I got a perfectly aligned spot exactly in the middle of the screen :-) which I consider good.

To further eliminate possible causes of the problem, I now fed a low (0 - 5V) DC voltage with a 10kOhm series resistor into the two horizontal HV amplifiers (one at the time),
and yes, the dot would move to right and left, according to the input I used and the voltage I applied, and vertical position was working too.
My conclusion so far: the deflection HV amplifiers and the CRT are all OK.

Did I already mentioned the inside of this scope is like new, but I mean, no dust or dirt at all, everything is just spotless.

Anyway, back to the repair.

With the outputs of the U760 still disconnected, I checked the inputs of U760, and they were all still wrong, so I suspect this IC is dead.... (155-0124-00)

I managed to find this IC at Qservice in Greece, not the IC alone, but I found this IC (155-0124-00) is also used in a 455, a SC503, SC504, 2336 and a 2337.
The individual IC was not available at their site, so I ordered a SC503 timing board from them that is sold as tested OK, and has this IC in a socket :-)
In preparation I removed my A4 Timing board, removed the IC U760 and put a socket in myself, so when it arrives, it should be a fairly easy placement.

I also removed the broken Var Hold Off potmeter, and here is were I was a bit disappointed about how Tek put this scope together: removing the front panel from this scope is an utter horrible task!!

The potmeter is a 311-2147-00 (5kOhm, through hole 3mm, half flat axle) Qservice also had one of these so I ordered it with it them too.
Wait and see how this will fit, because the one from the 2215A is a full plastic potmeter, and the one shown in the picture is metal and has thread to mount it, but it looks the same, it also has the very same partnumber.

With respect to the missing knobs: I still have a few of these snap-on knobs (also used on my favorite 24xx scopes) but I ordered some with them too, you just never know, and to get the free shipping ofcourse ;-)

To be continued,

un saludo,

Leo

Re: 7L5 dot frequency reset bug - any clues or a fix?

Dan G
 

I also experience this failure-to-reset problem on my 7L5 (B09xxxx) when installed in the
7854 mainframe. However, the problem never appears when the 7L5 is installed in the
7603 or the R7603.

And now for something interesting: if I turn off the 7854, and then turn it back on
four seconds later, the 7L5 resets itself properly. But if I wait 8 seconds instead of 4,
the reset bug appears again. This is quite reproducible with my hardware.
I wonder if it is related to the R621/C621 RC constant...


dan

AC Gnd DC input coupling switch on 466

Edward Prest
 

The ch 2 lever moves but stays in dc mode. There is no detent snap but some drag going through gnd position.

Am I correct assuming this is a loose grub screw?

Re: 555 Attributes, facets, benefits and General Discussion

 

Hi fiftythreebuick,

Your thread is quite informative about the 555, and the great satisfaction to own and use it..

My single-beam 547 has an adjustment for trace rotation. in the dual-beam tube, unless it is very precisely machined, how is it possible to independently rotate the traces to bring them together in alignment?

Ernesto

Re: Tektronix 2467B Auto Measure Faulty?

Leandro Lindemann
 

I'm not in my workshop now. Tomorrow, I will check the suggested test points.

I am going to buy the U500 from an American seller that I once bought a 2465B, which I ended up selling to buy this 2467B that I like so much, it is a confiable supplier.

When I receive the U500, which should take at least 40 days, I will update this topic.

Chuck, I have no words to thank you.

You are a kind-hearted person.

Thank you very much.

Strong hug.

Leandro Lindemann.

Re: 555 Attributes, facets, benefits and General Discussion

Morris Odell
 

It sounds like a 502, which was my first Tek and I still have it stored away. It is a double beam with one timebase common to both beams. It's a little bit smaller than a 545. The vertical amps are built in and use very high quality low noise tubes that audiophooles would kill for. It was intended for biomedical use and the VAs are very sensitive, down to 100 uV/div and the bandwidth varies from 500 KHz down to 100 KHz at maximum sensitivity. I appreciated it at the time when I was working on audio stuff and RTTY modems etc but it's not really practical for other things.

Morris
--------------------------------
Roy wrote:

Some decades ago (2 or 3) I had a different dual trace scope but am unsure of the model number. It was the size of the 545 with no separate power unit. It had two vertical channels and time base without any plug-ins as I remember. The bandwidth was modest, meant for medical/physiology use.

It must have been the 502. Maybe I will discover it buried in my long-neglected storage unit.

Re: Tektronix 2467B Auto Measure Faulty?

Chuck Harris
 

Not really. U500 is a pretty high failure item. I suggested the
measurements around CHN5B, and CHN5A pins because they are the way
it is driven for automatic tests. The transistor that drives CHN5B
sometimes fails... but not as often as U500.

The transistors around U500, and U975 are just GP NPN and PNP transistors
like 2N3904 and 2N3906.. They are very reliable... and you should be
able to find them in your TV repair store.

-Chuck Harris

Leandro Lindemann via Groups.Io wrote:

Chuck, I'll take this and ask one more question:

In addition to the U500, any other suspicious ICs that you can buy to take advantage of the shipment from the USA to Brazil?

Thanks



Re: Tektronix 2467B Auto Measure Faulty?

Chuck Harris
 

Generally, I go right from the AUTO voltage measurement failure
to cleaning U500, to replacing U500.... but then, I have spare
scopes that I keep to verify failed hybrids..

If you want to be doubly sure, go to the schematic page for the
A/B sweep, and trigger hybrid, and notice that there are hexagons
with numbers and pointers on the schematic. These are test points,
and there is an earlier page that shows the settings the scope
should be in, and what the waveform at the test point should look
like.

Look at the test points: 28, 46, 36, 29, 34 and 42.

-Chuck Harris

Leandro Lindemann via Groups.Io wrote:

Chuck.

I will order this IC on Ebay then.

Before ordering the CI, would you like me to do some other measure in the scope? I have another scope (hitachi) that I can use for this.

Thanks for your help.

Re: Tektronix 2467B Auto Measure Faulty?

Leandro Lindemann
 

Chuck, I'll take this and ask one more question:

In addition to the U500, any other suspicious ICs that you can buy to take advantage of the shipment from the USA to Brazil?

Thanks

Re: Tektronix 2467B Auto Measure Faulty?

Leandro Lindemann
 

Chuck.

I will order this IC on Ebay then.

Before ordering the CI, would you like me to do some other measure in the scope? I have another scope (hitachi) that I can use for this.

Thanks for your help.

Re: Tektronix 2467B Auto Measure Faulty?

Chuck Harris
 

My next step after cleaning U500 is to replace it with
a known working U500 from one of my test scopes.

They are a very common failure part.

-Chuck Harris

Leandro Lindemann via Groups.Io wrote:

Hello Chuck.

I removed the IC U500. I cleaned with Deoxit D5 its terminals and its socket.

Unfortunately it didn't. Problem persist.

Then I removed the IC PAL, cleaned his contacts and the problem persists.

I will leave the scope open, hoping that I have time to continue helping me.

Thank you.



Re: Tektronix 2467B Auto Measure Faulty?

Leandro Lindemann
 

Hello Chuck.

I removed the IC U500. I cleaned with Deoxit D5 its terminals and its socket.

Unfortunately it didn't. Problem persist.

Then I removed the IC PAL, cleaned his contacts and the problem persists.

I will leave the scope open, hoping that I have time to continue helping me.

Thank you.

Re: Tektronix 2467B Auto Measure Faulty?

Chuck Harris
 

Yes.

Leandro Lindemann via Groups.Io wrote:

I understood your explanations Chuck.

I will do this today, and I will return with the result.

With much hope of being something simple, like bad contact.

In this case, the hybrid is the U500, correct?

Thank you.

Leandro Lindemann.



Re: 547 scope HV transformer problem. One practical solution.

 

I have now ended the resuscitation from 40 years hibernation of my 547 scope. I could not be more pleased with it.

It has now inside an added little centrifugal blower fan that cools the HV supply. This has solved the classical HV transformer problem, that caused it to fail after 10 minutes.
This internal cooling was not easy, since the HV supply on the top left back corner is so removed and inaccessible to any air flow.
I removed the big metallic electrolytic cap. C802 so the hole left in its place is an opening to the metal enclosure, and replaced this cap with a small modern equivalent.
I cut a large opening into the front plastic box in front of the transformer to leave it exposed to incoming air.
I placed the blower in the space behind the vertical amplifier, and made an air conduit with plastic sheet, paper tubing, etc. around the CRT neck, then through the hole left by the capacitor, to the opening of plastic box in front of the transformer, a messy fix that I may improve some day when I am motivated. The plastic cover of the HV transformer, diodes, is now left off. Messy, but it works, and I am the only one aware of it.

In gratitude for working well again, I eased the strain on the supply by lowering the HV from 1850 to 1750 volt, a 5% change I don't notice on the screen, and I readjusted the gains of the horizontal and vertical amplifiers.
To further ease the work of the 6AU5 oscillator tube I lowered the supply voltage to the unit from the 325 unreg by 110 volt with a string of zener diodes.
Finally, to let the scope run cooler I changed the selector of line supply to the input transformer taps from MED to HI, since my home power is about 120 VAC.

If the HV transformer starts failing again after some decades in the future, I might not be around anymore to notice. In the meantime, the 547 is in my office on a cart, together with two TM504 supply boxes with miscellaneous plugins. I won't be able to resist powering up the instruments every day just to see the nice traces on the oscilloscope screen.