Date   

Re: Type 503 — power supply question

Brad Thompson
 

brian.kane@yale.edu wrote on 1/9/2021 12:36 PM:

<snip>
Regarding the issues with the filament voltage for the HV rectifier, I wouldn't mind doing whatever preventative measure I can do. So, just to make sure I'm understanding the issue, I'm going to restate it and you can tell me if I've got it correct. 1) The windings between tabs 6 and 7 on T601 is for the 6.3 V filament on the CRT. When the scope is going that winding gets elevated to -3000V. That can cause the T601 to fail since its a lot of stress on that winding. 2) And the solution is to get a separate transformer, one that drops the line voltage to 6.3V, and then move the wires to the CRT filament to that new transformer.
Hello--
Regarding the replacement filament transformer, I repaired a Tek RM503 several (20!) years ago.
The filament winding on T601 had failed open-circuit, and I decided to replace it with a
120 VAC to 6.3 VAC @ 60 Hz transformer. Unfortunately, the transformers in my collection
that were satisfactory rating-wise all were spec'ed for 2500 volt insulation.

Finding a replacement with 3000 volt insulation proved difficult, and IIRC I wound up
using a "medical-rated" 10 V @1.5 A transformer rated for 4000 volts and a series
dropping resistor on the secondary side to obtain 6.3 V for the filament.

Note that the transformer's  stray magnetic  field may affect the CRT, so
you may need to move the tranny through several orientations to
limit onscreen distortion. Finding a clear mounting spot in the RM503 was not a problem.

73--

Brad  AA1IP


Re: [dead tek 485] Can i fix it ? (newbie here)

 

Jose,

I've been going through the same process (bringing up a dead 475A and trying to calibrate without most of the cal equipment) and here are some more pointers:

I have been using a cheap signal generator (max 3 MHz, sine, triangle, sawtooth, square, and pulse waves, up to about 5V amplitude) as a stand in for the amplitude calibrator. There are two ways to do this, depending on what other equipment you have:

1. If you have another oscilloscope (I'm using a 60 MHz 2213, you just need to trust its amplitude readings) you can set the signal gen at a moderate frequency (e.g. 50 KHz), and adjust the amplitude using the scope for each specified signal from the service manual. I'm doing this with a BNC T connector so that I'm looking at the signal on the test scope while also feeding the same signal into the scope being calibrated. This will get you through much of the vertical system process.

2. If you DON'T have another scope, you can use a multimeter in AC mode. If you are generating a square wave then the meter will read half the amplitude. This is much slower, and probably less precise, than doing it with a scope, because the meter doesn't update very quickly and you have to adjust the signal gen very slowly.

I bought a fast pulse generator from Leo Bodnar (http://www.leobodnar.com/shop/index.php?main_page=product_info&cPath=124&products_id=295), originally to test the rise time of my scope, but it also works as a stand in for the time mark generator.

For the high bandwidth stuff I am waiting on delivery of a TinySA signal analyzer. Apparently it will also function as a high frequency signal generator. Mine hasn't arrived yet, so I can't say anything about what it's like to use it for the cal process.

My experience with the DIY calibration process so far is that it's pretty easy to follow the instructions in the manuals, especially if you download the manuals for the recommended calibration equipment so you can understand what kinds of signals they should be generating. The folks on this group are also very helpful. While you are doing the performance check and the calibration process it is pretty likely that you will have to repeat steps, and you are also likely to find other problems with the scope that need to be fixed. Both are normal; be patient; take your time.

Finally, you should understand that calibration is about making the instrument read within certain limits, not about some absolute precision. An analog scope is only so precise (because you're just eyeballing a trace of finite size against a graticule of finite precision). The real meat of the calibration process is making sure that both channels agree with each other, and that the different ranges on each channel agree as well.

-- Jeff Dutky


Re: 2465B all OPT, power supply reassembly: Cables?

Jean-Paul
 

Added photos album 2465B_ASSY


Re: Grid Bias Adjustment on 475A

John Griessen
 

On 1/8/21 10:15 PM, Jim Ford wrote:
Also Sprach Zarathustra (Thus Spoke Zarathustra) of course being the theme song of Stanley Kubrick's 1968 sci-fi claasic 2001: A Space Oddysey, for those who don't know.   I don't remember that scene, though, Tom.   It's been decades since I saw 2001, before the year 2001 itself, for sure.
I got to see 2001 at Radio City for its opening in NYC in '68 when I was ten. Had a big effect on me. I was already a rocket launch junkie though starting with the Gemini missions...


492 specurum analyzer -50dB loss

vk2bea
 

I'm repairing a 492 spectrum analyzer.
I fixed a faulty -15V supply (shorted tantalum) but now see that the signal is shown -50dB down from what it should be. (the 100MHz cal signal (and external signals)).
I've injected the signal directly into the first mixer to eliminate the attenuator, limiter and front end relays from contention.
Does anyone have a good suggestion as to what I should look at next or what is likely to be at fault?
I'm stymied a bit since I don't have another spectrum analyzer or power meter I can use. (I have a network analyzer but it is only low frequency (<1300MHz))


Re: Type 503 — power supply question

brian.kane@...
 

Dan,

Thank you for this. I'm never restored an oscilloscope before, so I'm learning as I go.

I'm delighted that T620 is good. Whew! I was worried that I fried it and that it would be nearly impossible to find a replacement. I wrote down all the DC resistances of T620 on the power supply schematic in the manual, so I won't lose them if I have to get back into the power supply and fuss with it.

Regarding the issues with the filament voltage for the HV rectifier, I wouldn't mind doing whatever preventative measure I can do. So, just to make sure I'm understanding the issue, I'm going to restate it and you can tell me if I've got it correct. 1) The windings between tabs 6 and 7 on T601 is for the 6.3 V filament on the CRT. When the scope is going that winding gets elevated to -3000V. That can cause the T601 to fail since its a lot of stress on that winding. 2) And the solution is to get a separate transformer, one that drops the line voltage to 6.3V, and then move the wires to the CRT filament to that new transformer.

Is that right? (Sorry, noob here...)

I love the X-Y display on this scope and the differential inputs. I don't think I'll be using it in day to day work, but I thought it would be good for aligning FM detectors, and some other audio work. The x-y on my other scope just isn't as quick and sharp as on the 503.

Thanks in advance. This is a great forum...so helpful!

All best,
Brian


Re: A resurrected 465 parts scope.

 

Thanks again Dave for taking time to provide the detailed listing of 465 replacement caps and adapter boards. I have ordered a set of the boards and will keep your parts list on hand for that inevidable day when the screen goes dark.

I clearly remember my first encounter with the 465. In about 1970, my workplace was in the process of ordering a Sony-Tektronix portable when the Tek rep whispered that we should hold tight for a couple of weeks for a revolutionary new product. The 465 was announced and we quickly bought one. Of course it was years later before I acquired one for home use, but by then it was a familiar old friend.

Bruce, KG6OJI


Re: Update on Domestic US Book Delivery Dates

Scott Walters
 

Received mine this morning
Niagara Falls ,NY
Thank you very much

On Jan 8, 2021, at 6:03 PM, Michael W. Lynch via groups.io <mlynch003=yahoo.com@groups.io> wrote:

Mine arrived in the wilds of Arkansas today.

--
Michael Lynch
Dardanelle, AR





Re: Grid Bias Adjustment on 475A

 

Jeff,

Well done in tracing problem to R1303.

On Sat, Jan 9, 2021 at 01:21 AM, Jeff Dutky wrote:
I replaced R1303 in my 475A (using the donor part), soldered all the
connections back as they should be, checked R1303A's value in-circuit (still
reads as 13 M ohms, even though it reads as 24.8 M ohms out-of-circuit),
It is very hard to accurately measure high value resistors in circuit. I see your DMM916 measures resistances up to 40Mohm, so 40.0001Mohm would measure over-range on your meter. The value of 40Mohm in parallel with 25Mohm is around 15Mohm (1/Rt=1/R1+1/R2 for two resistors in parallel) which is not far off your measurement of 13Mohm.

Regards,
John


Re: 7B53A not working as delayed tb

Richard Steedman
 

The symptoms you describe are entirely consistent with the microswitch (S252) not switching properly. There is a small metal rod that pushes against the white plastic cylinder when the grey time/div knob is pushed in. (Rotate the time/div to 0.1ms to see it when the right side screen of the plugin is removed.) This rod can jam in the 'pushing' position when the grey knob is pulled out such that the white plastic cylinder does not move and the microswitch does not switch. If it is jammed, it should just need a disassembly and clean to fix, perhaps adding a tiny blob of silicone grease.


Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?

-
 

Larry,

I'm interested in at least one set of boards and the front panel. Can
you tell me what the estimated costs is including shipping to 32765? Do
you want to take these type of questions off-lists? If so do you have or
can you set up an alternate e-mail address?

On Sat, Jan 9, 2021 at 1:03 AM Larry McDavid <lmcdavid@lmceng.com> wrote:

This is just a brief update on the status of the group buy of board sets
for the TM500 tester. If you don't remember what this is about, view the
YouTube link shown below.

I've researched flat envelopes and packaging materials and now have a
plan for both domestic and international shipping. I expect to be close
to needing 50 sets of the four boards to fulfill the requests.

If anyone else is considering adding to the requests, this is a good
time to speak up... I don't have final pricing but I expect it to be
close to the previous estimates for domestic delivery. Unfortunately,
international shipping of even rigid flat envelopes is astonishingly
expensive.

Larry


On 12/31/2020 11:27 AM, Jared Cabot via groups.io wrote:
Hi all,

I have been accumulating TM500 modules and mainframes for a little
while, so I recently finished building an 067-1201-99 TM500 mainframe
tester from the Tek construction notes floating around.
I updated the design somewhat and designed it for simplified
construction (Not a single wire to strip and solder!) and I thought someone
here might be interested in taking a look or even building one themselves.
Here's a link to the youtube video:
https://www.youtube.com/watch?v=Afwqtc6Fxd4...
--
Best wishes,

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






Re: [dead tek 485] Can i fix it ? (newbie here)

Roger Evans
 

Jose,

The description in the manual of the various calibration procedures is only valid if you have all the calibration equipment listed in the manual. Most of us don't have all the equipment listed and we get by as best we can, and are still very happy to enjoy our hobby and to keep learning.

The Tektronix time mark generator displays a set of vertical spikes equally spaced in time. I am guessing you don't have this but you may have other equipment in which case please tell us what you do have. Even if you have no test equipment you can check many things just using the 485 calibration generator, this provides a square wave output with a frequency switchable between 1kHz and 1MHz. Nominally the duration of the high level and the low level of the square wave are equal but this is not guaranteed. The voltage output is nominally 5V into the 1Mohm input impedance and 0.5V into 50ohm input imedance.

So if you connect the calibrator to Channel 1 and set the vertical sensitivity to 1V/div and the sweep speed to 1msec/div and the calibrator to 1kHz you should see a vertical signal of about five divisions and close to one cycle of the square wave every horizontal division. The cycles should be equally spaced even if they are not precisely one division. If you set the sweep speed to 2msec/div you should about two cycles per horizontal division and at 5msec/div five cycles per division. You can then switch the calibrator frequency to 1MHz and use sweep speeds of 1usec/div, 2usec/div and 5usec/div. Previously you implied that the sweep was not linear, but if you try the above sequence you can give us more information to try and find the source of any error.

For the vertical calibration you can check the accuracy of the calibrator to some extent by using ordinary batteries. With the scope input grounded position the trace vertically so that it is at the bottom of the screen, exactly on the lowest graticule line. Set the vertical deflection to 1V/div, input coupling to DC, and connect something like a mobile phone battery that gives 4 - 5 volts output. Measure as precisely as you can the vertical position of the trace and then measure the battery voltage with your digital multimeter. Divide the battery voltage by the measured vertical deflection to get the actual value of Volts/div. Repeat for Channel 2.

That should give you some confidence that the scope is working ok or it will unearth some more issues to be worked through.

Greater accuracy for the time calibration requires additional equipment, if you have some programming skills it is possible to make an adequate time standard with some frequency synthesiser modules available very cheaply.

Regards,

Roger


Re: A resurrected 465 parts scope.

Harvey White
 

Good Heavens, man, think of your diet!

You should use low fat margarine instead.

Harvey

On 1/9/2021 11:21 AM, Raymond Domp Frank wrote:
On Sat, Jan 9, 2021 at 04:48 PM, Dave Peterson wrote:

Butter!? "It's a desert toping AND a floor polish!" Sorry, couldn't help
myself. :^)
Yep,
It's as ridiculous and risky as washing old (tube) Tek 'scopes using water, as Tek itself did.
It was safe if done correctly and did the job well.

Raymond





Re: [dead tek 485] Can i fix it ? (newbie here)

Harvey White
 

Two traces is good (Ch1 and Ch2), you should be able to turn them on and off by turning on/off the individual channels.

What signal sources do you have?  Tektronix always assumed you had a bench full of their own equipment and wrote the manuals accordingly.

A time mark generator just simply puts out a series of pulses at a known frequency.  So for a 1 ms/division sweep, when calibrated, a 1 Khz square wave (or series of pulses) should appear every grid mark.  You put in the right signal, then align the firs pulse to the first grid mark, then see if the 9th pulse lines up with the right grid line.

These are rough checks for performance.

Ditto with the vertical attenuator checks, you want to get close.  If you had a good DMM and a nicely adjustable power supply, you could use DC, but it's nicer to use AC for calibration.

The Tektronix equipment was built in a way to provide all of the signals you need an at the right voltages and times.

Some of this stuff you can make depending on whether or not you want to go make stuff.  For instance, a 10 Mhz crystal, divided down by 74LS192 chips, gives you 1 Mhz, 100 Khz, and so on.  Take each signal and divide it by either 2 (500 Khz = 2 us/cycle) or 5, (200 Khz = 5 us/cycle) to get the other timings.  If this makes sense and you want to do it, fine, if not, a halfway decent signal generator will do the job, within the accuracy of how well you can set the generator's accuracy.  You could even do the job with an arduino, more or less.

All you're trying to do is see that the thing works, and depending on the equipment you have, you'll just get close. That'll be good enough.

Harvey

On 1/9/2021 11:01 AM, marcosjl31@gmail.com wrote:
I need to be more accurate on the measures.

It's going to be a long journey... ;o)

Now the issue "Unit not powering on after power off" is gone.

I've got 2 traces on screen : think it's a good point to start from...

What should I do next ? I'm afraid I lack the necessary test equipment (as listed in manual) to thoroughly follow "Performance check" section (5.4) nor undestand perfectly how to perform the test.

As en example of non undestanding : in Step 4 - Check B sweep timing accuracy, "Position one time mark to 1 and read error to 9" makes just no sense to me (told you guys : I'm newbie, but definetely willing to learn !)

Jose





2465B all OPT, power supply reassembly: Cables?

Jean-Paul
 

Bonjour a tous: A fine 2465B sn B060 with OPT CTT/HPIB/WR is ready for reassembly after teardown and a PSU repair.

The placement of the many cables and harmonica connectors to PCBs pins is a problem
It was received with the cables all pulled, so no photos of original config.

In service manuals, placement of the cables and harmonica connectors is a problem, especially for the options.

I shall appreciate any details, photos, diagrams of the cables/connectors for any /all of these options, especially the polarization pin 1 positions and the cable locations and attachement on the option board.

Many thanks
Bon Journee,

Jon


Re: 4 photos uploaded #photo-notice

 

Are those Spectrol Potentiometers?
Takes me back nearly 50 years, to when I was just starting out as a green technician!


Re: Grid Bias Adjustment on 475A

 

On Sat, Jan 9, 2021 at 04:49 PM, Siggi wrote:


I had a precision resistor in my 485 that measured spot-on, but then beat
Ohms law by some 10% under actual operating conditions. Seems it came to
identify as a VDR.
It probably aspired at becoming something better and who are we to blame it?

Raymond


Re: A resurrected 465 parts scope.

 

On Sat, Jan 9, 2021 at 04:48 PM, Dave Peterson wrote:


Butter!? "It's a desert toping AND a floor polish!" Sorry, couldn't help
myself. :^)
Yep,
It's as ridiculous and risky as washing old (tube) Tek 'scopes using water, as Tek itself did.
It was safe if done correctly and did the job well.

Raymond


Re: [dead tek 485] Can i fix it ? (newbie here)

marcosjl31@...
 

I need to be more accurate on the measures.

It's going to be a long journey... ;o)

Now the issue "Unit not powering on after power off" is gone.

I've got 2 traces on screen : think it's a good point to start from...

What should I do next ? I'm afraid I lack the necessary test equipment (as listed in manual) to thoroughly follow "Performance check" section (5.4) nor undestand perfectly how to perform the test.

As en example of non undestanding : in Step 4 - Check B sweep timing accuracy, "Position one time mark to 1 and read error to 9" makes just no sense to me (told you guys : I'm newbie, but definetely willing to learn !)

Jose


Re: Grid Bias Adjustment on 475A

Siggi
 

On Fri, Jan 8, 2021 at 8:40 PM Harvey White <madyn@dragonworks.info> wrote:

It seems that R1303 was behaving badly, perhaps at high voltages
(difficult to test).
I had a precision resistor in my 485 that measured spot-on, but then beat
Ohms law by some 10% under actual operating conditions. Seems it came to
identify as a VDR.

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