Date   

Replacing Variable Vertical Attenuator Shaft

Dick
 

I broke one of the 1/8" shafts that goes from the Front Panel
to the Variable Attenuator Pot in one of the Vertical Amplifiers.

I removed the Outer Case and the cover on the Vertical Attenuator
and came to a grinding halt.

How does one get to that Pot so I can replace the shaft ?

Thanks for the help,

Dick, W1KSZ


Re: Very Inexpensive 7623A, but Problems

Harvey White
 

Tektronix had any number of supply strategies.  This is a linear supply, not switching.  So in the days before integrated circuit regulators, you had to roll your own.

A linear regulator is essentially a controllable voltage divider.  Bulk supply feeds the top, a pass transistor acts as a variable resistor, and the circuit load acts as the bottom of the divider.

In all cases for a linear regulator, the output voltage is compared against a reference voltage (however it may be derived), the difference between the two is used to adjust the power transistor to keep the load voltage stable.

You can limit the current from the supply when dealing with short circuits.  One good way is to put a low value series resistor in the supply line.  Put a transistor base-emitter junction across that resistor, and size the resistor so that when the desired maximum current flows through the resistor, the voltage drop across that resistor is 0.6 volts.  Lesser currents can't turn on that transistor, greater currents than desired turn it on.  The typical connections are to use an NPN transistor (just think positive supplies), and steal base current from it, which turns off the transistor a little.  Get the ratios right, and the voltage at the output drops to maintain that maximum current. Instant current limited supply.  (the old UA732 did this, and is a decent circuit to look at).

In the this power supply, the reference for the -50 volt supply is a zener diode.  The -50 volt supply is used to supply one end of a voltage divider as a reference for all the other supplies, so if it's not correct, then nothing is likely to be.  Since the other supplies are all controlled by resistor ratios, fixed at manufacturing time, you only have the one adjustment.

Essentially, any regulated supply works something like this. Take the output voltage, compare it against a reference, then do something to adjust the output voltage.  How that adjustment is done, well, another story.

Harvey

On 3/4/2021 10:33 AM, Jeff Dutky wrote:
Harvey,

Thanks for that tip, that really helped me validate the connections to and from the power supply. Between the indicator triangles and my check-in photos I was able to verify that all the cables appear to be connected correctly.

I am studying the theory of operation now, partly because my notes are hopelessly confused about the power rails (my confusion about the -15 rail is testimony to that), and partly because I am a bit at sea about where and how the CRT gets its sweep signals from.

-- Jeff Dutky





Re: 547 HV Transformer: Bill Schell rewind failed

Dave Wise
 

?Update.


This morning it ran for an hour maintaining normal brightness. I think it's healed. I guess it absorbed moisture over the four years it sat, and yesterday I baked it out.

I can't explain why it didn't become lossy during other years-long idle periods between 2003 and 2017.


Carry on.


Dave Wise

________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Roy Thistle via groups.io <roy.thistle=mail.utoronto.ca@groups.io>
Sent: Wednesday, March 03, 2021 2:58 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 547 HV Transformer: Bill Schell rewind failed

On Wed, Mar 3, 2021 at 01:19 PM, snapdiode wrote:


my 547 was working fine yesterday, but it didn't run for more than 30 minutes.
It didn't run for more than 30 minutes, and then failed ... or you didn't run it for more than 30 minutes? .... and then you turned it off. (In which case the working state is unknown.)


Re: Very Inexpensive 7623A, but Problems

Dave Peterson
 

Jeff,

I found this invaluable in sorting out the sweep logic for the 465 I'm working on:

https://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf


The sweep flow diagrams later in the book are great.

Dave

On Thursday, March 4, 2021, 07:34:04 AM PST, Jeff Dutky <jeff.dutky@gmail.com> wrote:

Harvey,

Thanks for that tip, that really helped me validate the connections to and from the power supply. Between the indicator triangles and my check-in photos I was able to verify that all the cables appear to be connected correctly.

I am studying the theory of operation now, partly because my notes are hopelessly confused about the power rails (my confusion about the -15 rail is testimony to that), and partly because I am a bit at sea about where and how the CRT gets its sweep signals from.

-- Jeff Dutky


Re: Very Inexpensive 7623A, but Problems

 

Harvey,

Thanks for that tip, that really helped me validate the connections to and from the power supply. Between the indicator triangles and my check-in photos I was able to verify that all the cables appear to be connected correctly.

I am studying the theory of operation now, partly because my notes are hopelessly confused about the power rails (my confusion about the -15 rail is testimony to that), and partly because I am a bit at sea about where and how the CRT gets its sweep signals from.

-- Jeff Dutky


Re: 3T77 tunnel diodes (again)

Albert Otten
 

I exchanged my waveform pictures in the 3S2 album by one more relevant picture. The important part of the S-2 output occurs within 0.5 us or so and was not well visible in the earlier pictures.
Compare with Fig. 6-9 in the 3S2 manual.


Re: [HP-Agilent-Keysight-equipment] Two Simpson VOMs!

greenboxmaven
 

The Simpson 260 was almost a cult object among elevator and industrial control technicians for decades, and is still preferred by many even  today.  I was in the US Air Force 1969-73, and also started out as a ground radio tech, but managed to transition to navaids. The PSM-6 multimeter was the one  the younger people thought was The Ultimate, and by far the most common. There were some Simpson 260s  and Triplett 630s, but they were outnumbered ten times over by the the PSM-6.   Most of the scopes we had were Tektronix 524s, with a few LaVoie clones. If you could fenagle a 545,  you had the best.  A 555?  Not in this life!

      Bruce Gentry, KA2IVY

On 3/4/21 2:16, Richard R. Pope wrote:
Hello all,
    I was thinking about this and this why these Simpsons are important to me. When I joined the AF I became a Ground Radio Serviceman. One the instruments that I learned on was a Simpson 260. I hope everyone can understand why it is important to me that these two instruments end up in the hands of a collector. I cherish them and I want to see them preserved.
GOD Bless and Thanks,
rich





Re: TDS3064B "ripple" on calibrator signal

benj3867
 

Let me add that the max value changes for me between 5.36 and 5.44, which is more than it changes for you. However, this is due to the noise.


Re: TDS3064B "ripple" on calibrator signal

benj3867
 

Just checked a TDS3014B. The trace of the calibrator signal shows no such ripple whatsoever.
There is the usual noise making the trace a bit thick, (this obviously disappears when one turns on averaging), but it is flat as a ruler.


Re: WSTRO, WSTROU, WSTRM WaveStar Software for Scopes & Meters

 

On Wed, Mar 3, 2021 at 07:19 PM, Dennis Tillman W7pF wrote:


Sometime ago I bought a sealed copy of this Tek software:
Wavestar fo Scopes is now free and has been so for many years.
It's last version (3.0) can be downloaded fom Tek's website but
I can't see Wavestar for meters there. It was used to control
TX1 & TX3 DMM's (and others ?) and that's what the optical interface
cable is for. With an added software module the TX DMM's could be
calibrated and adjusted using a Wavetek 9100 or Fluke 5500A calibrator.

/Håkan


Re: Tektronix 606A that resists being repaired

Ozan
 

Q714 is currently a Tektronix transistor marked 151-0606-00 referenced as
Motorola SJE375 but I can't find any info on this device. The transistor that
used to be there (broken) has no identification at all. I tried several MJE800
https://w140.com/tek_common_design_parts_catalog_transistors_diodes_and_misc_may_1988.pdf
shows TIP142 for an equivalent (please double check). Digikey has them.

at startup. Can I add a small power resistor at the collector of Q714 to
prevent this? Under normal operation, the current through Q714 seems to be
about 1Amp (see below) so the MJE800 should work (4Amp rating)
TIP142 is a 10A transistor, stronger than MJE800, should work without modification unless there is still a lingering bug.

You say "The output will be shifted up if there is 1-ohm". I assume you are
referring to U740 pin 6. Even at a limited cathode voltage of -5000V, the
voltage here starts at 2V (with 1 Ohm R715).
You had a concern about higher output voltage than marked on the schematic at pin 6, and were planning to debug the error amp. I recommend delaying the debug to after placing the right power transistor, and putting back 0.5-ohm. And the new DC restorer diodes. After those changes voltage might end up at the expected value.

Ozan


Re: [HP-Agilent-Keysight-equipment] Two Simpson VOMs!

Richard R. Pope
 

Hello all,
I was thinking about this and this why these Simpsons are important to me. When I joined the AF I became a Ground Radio Serviceman. One the instruments that I learned on was a Simpson 260. I hope everyone can understand why it is important to me that these two instruments end up in the hands of a collector. I cherish them and I want to see them preserved.
GOD Bless and Thanks,
rich!

On 3/3/2021 11:31 PM, Richard R. Pope wrote:
Dave,
I agree but I am passed the collecting stage. The Simpsons are all
that I have left of my electronics stuff except for one DMM that I am
keeping. I would just like to find someone or someones that would make
me a reasonable offer before I die so that they don't end up in the
trash.
GOD Bless and Thanks,
rich!

On 3/3/2021 11:27 PM, Dave McGuire wrote:
On 3/3/21 8:23 PM, saipan59 (Pete) wrote:
I have a couple of 260's (one old, one newer), and a 360 (7-segment
LED display, but the case is almost the same as the 260).
Also have a 650 transistor tester accessory (clamps onto the bottom
of a 260).

Just braggin' !
Neat! I've seen these 360s around and I've long been curious about
them, but I know nothing about them. I should dig up the schematic.

Some time ago a friend gave me another
clamps-to-the-bottom-of-a-260 option, the Model 657 milliohmmeter
adapter. I've not tried it out yet, but it seems like an interesting
option.

I wasn't aware of the Model 650 transistor tester option. That
sounds like it might be very handy!

-Dave





Re: 547 HV Transformer: Bill Schell rewind failed

Roger M
 

Just another flashlight probing the darkness...

Back in December I received some mis Tek goodies from a kind member of the "Old Tek Scopes"
Facebook group,.. some obviously appearing to be HV transformer rewinds. One has the hand written
notation on the tape holding the core halves: "0308 6-6-94 W.A.S." (could be W.R.S.) on one side,
"Either 547 or 454 Good" on the other This specimen has what appears (by fingernail test and sight)
to be a beeswax coating. Defiantly not epoxy. The wind job also looks to be a professional universal,
and hasn't been put to use since re-manufacture.

-Roger


Re: TEK465 Horizontal trace

Dave Peterson
 

Looks like I found the problem!

I'll have to add Q1038 and Q1098 to my horizontal amp simulation.

Clearly both of these transistors need to be in place and working for the correct DC level on Q1224base.

I swapped Q1226/Q1236 (2N3906s) into Q1038/Q1098 and the sweep sawtooth into Q1224 is now correct and their collectors are now correct too. Of course there's no second stage loading the first, and who knows what else is going on with this scope. I'm supposed to get my collection of various transistors from Amazon tomorrow and I'll find out if I can get a display back on this old bird.

I suspect that it's only Q1098 that's bad, and the lack of it's pull up contribution to the Q1224base node is what's causing the negative bias. A simulation will help clarify that. I need a proper transistor tester. A DMM shows it good. Clearly it's not.

So that's been satisfying. Just learned more about the sweep circuits than I ever would have just staring at schematics.

Dave


Re: 155-0001-00 repair or replacement?

 

Turns out my request was #3 in line... but the #2 person thoughtfully yielded his place to me, so I could buy one. Thank you, anonymous Tekkie :) Despite the post office's best efforts to flatten it into foil (separate post), it apparently survived.

The most likely cause of the S-4 with offscreen trace is a bad hybrid. It's not hard to blow those microscopic diodes. Rather than spend time on troubleshooting, I just changed the hybrid. Surprisingly easy, especially since I read the instructions first...

Sure enough, it's now pretty close to balanced even without tweaking the bridge adjustments, and it displays the same waveform as the S-1 and S-2 with a little overshoot/ring visible on each rising and falling edge. At least with real-time sampling (and the relatively limited speed of my 114 pulse generator) since I haven't resumed my battle with the 3T77A.


Re: Sampling head extender missing coax connectors

 

Me either.
I finally ended up drilling a small hole in the PC board and mounting a sturdy solder lug, to which I fastened the coax connector and then soldered.. It took quite a bit of fiddling to get it properly lined up with the hole in the casting in all three axes, too. At least nobody can see the hack job inside the case ;)

But it is now a useable extender. I'm still not sure how well the trigger pickoff will work at really high frequencies (due to the rigged junctions at the connectors), but I doubt I'll ever work with anything that fast, or on the extender. I really just wanted it for repairing sampling heads.


Re: Very Inexpensive 7623A, but Problems

 

A correction: where I wrote that the -15 V rail now measures as -21 V, I should have written that the -18 V rail now measures as -21 V. I appear to have mis-transcribed the spec value for that power rail as -15 V instead of the proper value of -18 V. In any case, that the rail now reads -21 V means that it is much closer to it's spec (at -18 V) than it was before I replaced the big filter cap (C811).

I am tempted to remove the transistors in the -18 V regulator again and duplicate my measurements from before the cap replacement, but I'm not sure that will tell me anything new. I did check the two dual NPN transistors (after building an adapter for my component tester) and they look good (as in they are not shorted, or open, or measure as a resistor or capacitor).

Otherwise I can see what measurements the service manual specifies for the horizontal and vertical boards and do those. There are a couple test points there, and I feel as if that is likely to be the next avenue of investigation.

I did notice that the horizontal and vertical deflection wires are clearly visible just in front of the horizontal and vertical boards. They appear to be properly connected, but that doesn't mean that they're getting good signals, or that the CRT is responding to them.

-- Jeff Dutky


Re: O.T. Digital scopes versus Tek analogue.

Michael
 

I figured that I would not even try to repair it when it fails. I would just replace it. I am 78 years old. I am not particularly worried about whether these Siglent scopes are running in 40 or 50 years. :-)


Re: Very Inexpensive 7623A, but Problems

 

I have added 19 photos to the "Sick 7623A" album showing the current symptoms and the "check-in" photos I took before doing any work on the instrument.

https://groups.io/g/TekScopes/album?id=260677


Re: 547 HV Transformer: Bill Schell rewind failed

snapdiode
 

I powered the 547 for 30 minutes and everything was normal for that time. Then I turned it off.

4981 - 5000 of 184529