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On Sat, Jan 2, 2021 at 09:07 PM, Michael W. Lynch wrote:

This may be the source of confusion for those of us not as well versed in
these issues. Regardless of your fine technical explanation, TEKTRONIX still
calls R1375 "GRID BIAS" on the schematics. That being said, who am I to argue
the point? If some EE or Designer at the place that made the instrument calls
it "GRID BIAS", then for continuity we poor and less educated souls in the
field tend to use that name. Right or wrong, that is the name that shows up on
the schematics. Another one of the many error and omissions we find in various
schematics.

Although English is not my mother tongue (Dutch is), I fail to see why using the term "Grid Bias Adjustment" for 'scope CRT's is wrong.

If I'm correct, two reasons are given to disparage the term:

1. Grid bias is not specified as a voltage with respect to "zero", "gnd" or the like (but against the cathode, which usually is at negative voltages exceeding - 2 kV)
2. Grid bias is not a steady state (DC) voltage

Ad 1. This to me seems an unnecessary bias towards a particular voltage point (namely, zero volts) in a circuit. Pun intended.
Ad 2. When adjusting "Grid Bias", that part (in time) of the voltage waveform necessary to achieve blanking of the beam (a negative-enough voltage with reference to the cathode) is adjusted. Class B (as an example) audio amplifiers contain a "bias current" setting to minimize cross-over distortion. The actual current through the circuits carrying the bias current at rest, when producing an audio signal, is an AC current many times larger at any sensible volume than that zero-signal DC-current.
In a 'scope, the Intensity adjustment pot sets the relatively positive amplitude excursions, where the grid is less negative in relation to the cathode, making the beam visible. So, Grid Bias is the most negative voltage of the grid, often 50 V to 80 V more negative than the cathode.

Raymond

On Sat, Jan 2, 2021 at 12:07 PM, Michael W. Lynch wrote:

This may be the source of confusion for those of us not as well versed in
these issues.

Jargon is always contextual, to the application, and the particular [engineering] culture. (Interpreting the parlance in the vernacular, can result in misunderstandings.)

Bias: In an electron tube, a steady DC voltage applied to the
control grid, to establish a reference level for its operation.
Also called grid bias.

Yet...

Bias voltage or current: the DC power
applied to a transistor allowing it to operate
as an active amplifying or signal generating
device. Typical voltage levels in GaAs FETs
used in receivers are 1 to 7 volts between the
drain and source terminals, and 0 to ?5 volts
on, or between, the gate and source terminals.

And yet...

Bias[ing]: the technique of applying a direct current voltage to a transistor or an active network to establish the desired operating point

David Campbell wrote:

With all due respect, theres a lot of wild and frustruating guessing going on. The answer is never 'lift components
and make measurments in good circuits" Circuit analysis is required.

In my defense, I was just following the diagnostic procedure in the service manual, and my circuit analysis skills are subpar.

Bad Z axis amp. WHich transistor?, theres 7 of them. If its not being driven in Z axis modulation, that circuit might not
be relevant. It doesnt take Z axis drive to put a spot on the screen.

five of the transistors and two diodes in the Z-axis amp were blown and had to be replaced. I don't think that the Z-axis amp is the culprit here, but it was my first suspect because a. it does play a role in controlling trace intensity, and b. I had just finished fixing it and was not completely confident in my fixes.

In tubes, the voltages on the elements between G1 and A can have a major effect on K-P current. Not as much, depending
on voltage, typically as the G1, since G1 is closest to K, but G2 can have a major effect. That CRT has FOUR GRIDS and
all 4 and the Cathode MUST have proper voltages

Yes, I can see this in the schematic of the CRT circuit. I will try to measure the other voltages (G2 and G4), but for G3

Low anode voltage can cause loss of brightness. That takes a HV probe.

I am waiting on the arrival of an HV probe.

Thank you for the clear and detailed explanation.

-- Jeff Dutky

I think this is the right datasheet for the original:



The bipolar transistors optimized for switching power applications tend to have low gain and strong SOA characteristics. There should be plenty of other transistor types that will do - just try to get similar specs and SOA ratings. I think the -0426- was Tek's go-to part for lots of secondary side (low voltage) DC-DC converter use in that era.

Ed

Hi everyone,

After a long time on the bench, finally my 2712 is alive and work 100%.
Using the suggestions that I received here, I start the service.
First I have made a visual inspection and look for some cable in wrong connector misplaced or lose but everything was ok.

Then I have checked all voltages and ripple on the power supply and all are OK.

The next step was to change the two batteries, an I would like to tell an interesting thing that happened when changing the battery that is on the GPIB board that powers the RTC.
I have the habit of always measuring the current drain of the batteries when I replace for a fresh one.
For my surprise, the meter shows 4mA.!! I thought it could be some capacitor leaking on the battery line or even some bad ICs.
Based on some previous experiences, I put the card back in the equipment and turned it on. As expected, the current drained from the battery was zero.
So I turned off the equipment and continued to look the current meter. It shows near zero for several hours.
This led me to conclude that when some ICs stay without power for a long time, when they are powered for the first time, they need to be initialized in some form to work properly and not drain this high current.
I removed the current meter and everything is OK with the RTC and battery for a few days.

Well, the 2712 still not work… So next I kept checking the 100MHz oscillator, as suggested by Paul / WB6GHK.

BINGO!!

There was no 100MHz. signal on any of the three output connectors and also on the output intended for the calibrator (with it ON of course).
So I removed the 100MHz PCB from the 2712 and removed the shields, which was a very boring job to do.
in the smaller shielded, I observed the existence of a kind of sponge in the position where the crystal is soldered, and that sponge was deteriorated, looking like a bubble gum and with the feeling of being damp.

As a result of this sponge being in contact with the crystal terminals, they oxidized a lot, and broke close to the crystal. Luckily I had a 100MHz crystal to put it there. It does not have the same type of packaging, but it fit perfectly inside the thermal chamber. So with everything still open I gave power on to see if the oscillator was working, and it was !! I checked all the outputs and found the correct levels according to the service manual.

As I can see, this oscillator has no adjustment, and I limited myself to measuring the frequency that was very close to the ideal.
After 15 minutes os warmup the oscillator was on 99,999.988 what I thought was reasonable and I set out to reassemble the shields and install the card in the 2712 to see the result.

After everything was in place, I crossed my fingers and gave power on the 2712 …

Fantastic! It is working!!

I followed the menu to proceed with the normalization, and everything was OK.
So to finish, I proceeded with the normalization of the TG which was also ok.

Now I have this fantastic instrument on my bench.

I would like to thank the friends who gave me advice to make the repair, and say that I am very happy to belong to this group. I hope that someday I can help someone too.
Happy New Year for everyone!

Marcus - PP5MS

Michael Lynch wrote:

Can you measure the voltage drop across the diode? That is partially how I discovered the "bad" VR1374 on my 475.
You should measure 82V across the diode

Yes, I measure 81.78 V across VR1374, which sounds like it's in spec (sadly, that would have been an easy replacement).

All of this is making me think that the problem must further along the way to the CRT. I think that the grid being biased is pin 3 on the CRT, which is the acceleration grid immediately in front of the cathode. There are several components between the grid bias adjustment circuit and the grid in the CRT: C1371, CR1371, R1372, CR1377, CR1378, and R1379. Maybe I can get a better idea of what I should be seeing by reading the theory of operation section again.

-- Jeff Dutky

I am sure you in the US are aware and may have experienced this with
mailing packages and letters for the holidays, but US mail has been
considerably delayed, though it has gotten somewhat better in the last
week. I had a media mail package shipped by an eBay seller and it took
three weeks to get here.

I would not be overly concerned if the US shipments seem to be
taking longer than expected.

Steve Horii

On Sat, Jan 2, 2021 at 15:20 Dennis Tillman W7pF <dennis@...>
wrote:

This morning I mailed 76 of Peter Keller's books. These went to 72 people
in
the USA who ordered Peter's book.

At the request of our currently shorthanded post office staff I have been
asked to wait until Thursday to mail the 25 International orders when there
will be enough people on duty to process them. It takes time to verify the
address, determine the postage, and process the customs forms for each
international order.

Here is the list of domestic orders I mailed today. Because these were send
Media Mail Rate the clerk only has to enter the zip code and print out a
label for each box. It took about 1 1/2 hours to process 72 domestic
orders.
There are no tracking numbers for Media Mail packages.

If you want to know if I mailed your book(s) today scan down this zip code
sorted list for your initials.
------ --- -------
01460, HV, 1 Book
01510, PE, 1 Book
01742, SB, 1 Book
02090, JY, 1 Book
04605, LS, 1 Book
06057, EO, 1 Book
06851, LK, 1 Book
07023, MD, 1 Book
10034, PC, 1 Book
11507, LL, 1 Book
13211, BG, 1 Book
13635, BL, 1 Book
14094, SW, 1 Book
14131, CD, 1 Book
15068, DM, 1 Book
17044, DK, 1 Book
18944, CA, 1 Book
19010, SH, 1 Book
19808, RD, 1 Book
20169, CL, 1 Book
20613, TK, 1 Book
20872, CH, 2 Books
20901, JD, 1 Book
22406, FD, 1 Book
23236, MV, 1 Book
27932, RB, 1 Book
28411, VS, 1 Book
29445, GL, 1 Book
30064, MM, 1 Book
30341, HO, 1 Book
32707, SB, 1 Book
32754, DD, 1 Book
32765, JR, 2 Books
45014, ES, 1 Book
45066, LS, 1 Book
45801, TL, 1 Book
48206, CW, 1 Book
48371, VV, 1 Book
48843, JR, 1 Book
56549, EN, 1 Book
59405, GM, 1 Book
66062, JF, 1 Book
67212, CC, 1 Book
72834, ML, 1 Book
78746, MA, 1 Book
80015, CD, 1 Book
80023, PB, 1 Book
80234, JM, 1 Book
80907, KP, 1 Book
87107, JG, 1 Book
87124, CM, 1 Book
87544, BD, 1 Book
89511, MM, 1 Book
91602, BH, 1 Book
92109, SP, 1 Book
92806, LM, 1 Book
94301, BC, 1 Book
94550, JR, 1 Book
94602, RD, 1 Book
94941, BH, 1 Book
94947, JP, 1 Book
95320, TN, 3 Books
95693, KS, 1 Book
97338, JG, 1 Book
97424, TP, 1 Book
98008, DM, 1 Book
98030, BL, 1 Book
98115, MH, 1 Book
98166, CN, 1 Book
98275, SJ, 1 Book
98501, DG, 1 Book
Anonymous, 1 Book

Dennis Tillman W7pF

A few things are missing from the descriptions.
1. There was a blank module available2. The modules could be user keyed for certain slots3. They could be interconnected unseen in the rear.4. There is/was a high power compartment (mentioned)5. Every module had their own separate power supply6. Uncommitted pass transistors were available for use.
It was a very nice system.? A one bay TM500 module could house a scope current probe for instance.
You could design your own test instrument with the various modules.

We made a laser scanner that mapped the output of a solar cell by position using two function generators, a power supply module, a multimeter and a glue module.? This drove a storage medical display scope from tek and mirror galvanometers.

The glue module selected x and Y modulation, it set the blanking level and x or xy scanning.? Anyway, the modules electronics were minimal.? All of the interconnections were behind the scenes.

Later, we were able to capture the data with a PDP-11 and A/D converters.? The display was then a VT100 with a board and CRT to turn it into a TEK display terminal.
The main purpose was to scan for defects and up the power of a laser to remove the defects.

The 5000 series added IEEE-488 to the mix.?

take a look here:

I am also interested in a set of boards.
Bruce, KG6OJI

FAN to you, too, Giovanni!

I agree with Thomas that something rather generic, like the TIP31C that he mentioned, would probably work just fine. Even though it's an obsolete transistor, it still seems to be quite available.

I'm assuming you are in Italy (or at least somewhere in the EU), but if you are in the US, I could easily send you one.

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

I would also like a set of boards. Thank you for the great project, for the time you spent, and for the clever mechanical and electrical engineering.

Let’s see….

Dennis’s time of xxx hours times a $50.00 hourly rate to do all of this equals $xxxx.xx.

Although it is only one book for me you have put in a monumental effort to get all of this done. What is your next feat? Walking a tightrope between two high rise buildings, putting on a jet pack and flying through the Grand Canyon from one end to the other or traveling across the country in a lawn chair attached to helium filled balloons???

Greg

On Fri, Jan 1, 2021 at 11:02 PM, EJP wrote:

I have an FG504 and such a TM504 that I had to correct the phasing on.

If you might indulge a few inquiries...
Did incorrect phasing damage the FG504?
Is that something you did to the TM504?... or was it miswired at the factory... or during a "repair, someone else?"
Do you know... was the TM504... and early manufacture... or a later one?

On Fri, Jan 1, 2021 at 08:47 PM, demianm_1 wrote:

I'm working on an interface board to enable powering and getting the signal
out of a Tek 7000 plugin

This had been done, many times... and there is much ink spilled about it, on this forum... and on the Web... that is... if you are mentioning about something (a cable, or board) that plugs into the connector at the back of a bay, in a 7000 frame, and then allows one to attach (and "run/test") a 7000 plug-in.
To see... search this forum on "extender."

Dennis, you're a saint! Sorry that no good deed goes unpunished!

Happy New Year,
Tom

Sent from my iThing, so please forgive the terseness and typos.

Chuck,

Thanks for that as I did not feel qualified to make such a statement, based on my very limited knowledge of the subject. Appreciate that you have confirmed that I am not totally without a clue.

Sincerely,

--
Michael Lynch
Dardanelle, AR

Dennis,

THANK YOU. I know that we do not say this enough for all that you do to keep this group running smooth. You are GREATLY appreciated!

Sincerely,

--
Michael Lynch
Dardanelle, AR

That and perhaps what he asserts is nonsense?

The grid is most assuredly biased relative to the cathode
on this, and probably any, CRT.

-Chuck Harris

Michael W. Lynch via groups.io wrote:

Hello

Many moons ago I saw a topic on here regarding the 2230 and a storage display problem and as far as I could tell it never reached a conclusion. Unfortunately it is the problem I have now...or very similar. Therefore, I wonder if anyone has a recollection of the problem and what the solution is or was? Briefly, in storage mode BOTH traces are displayed on top of each other when 'both' are selected so it just looks like one trace. Using only channel 1, inputting a 2Vpp signal gives a perfect image BUT half the actual voltage, 1Vpp.Inputing a square wave into channel 2 same amplitude it's 25% of the voltage. Select both and the waveforms are summed giving a display that's a little of each, straight sides and rounded tops. If a 2Vpp sine is input to BOTH channels and only channel one is activated and displayed in storage then you get a 2Vpp sine wave which is what it should be. In short, it seems like there is some mixing going on of the waveform content and amplitude. Normal mode is perfect in all respects. As I recall there was a suspicion U2101 was the culprit but it was never confirmed. At the moment I have the 4 wire connection plug that goes to channel 2 on the storage board removed and the 2 signal wires earthed with jumpers. I can still use channel 1 storage and multiply the amplitude by 2 as a rough guide although it's far from accurate. Anyone remember something like this and what the cause was? Many thanks in advance.

This morning I mailed 76 of Peter Keller's books. These went to 72 people in
the USA who ordered Peter's book.

At the request of our currently shorthanded post office staff I have been
asked to wait until Thursday to mail the 25 International orders when there
will be enough people on duty to process them. It takes time to verify the
address, determine the postage, and process the customs forms for each
international order.

Here is the list of domestic orders I mailed today. Because these were send
Media Mail Rate the clerk only has to enter the zip code and print out a
label for each box. It took about 1 1/2 hours to process 72 domestic orders.
There are no tracking numbers for Media Mail packages.

If you want to know if I mailed your book(s) today scan down this zip code
sorted list for your initials.
------ --- -------
01460, HV, 1 Book
01510, PE, 1 Book
01742, SB, 1 Book
02090, JY, 1 Book
04605, LS, 1 Book
06057, EO, 1 Book
06851, LK, 1 Book
07023, MD, 1 Book
10034, PC, 1 Book
11507, LL, 1 Book
13211, BG, 1 Book
13635, BL, 1 Book
14094, SW, 1 Book
14131, CD, 1 Book
15068, DM, 1 Book
17044, DK, 1 Book
18944, CA, 1 Book
19010, SH, 1 Book
19808, RD, 1 Book
20169, CL, 1 Book
20613, TK, 1 Book
20872, CH, 2 Books
20901, JD, 1 Book
22406, FD, 1 Book
23236, MV, 1 Book
27932, RB, 1 Book
28411, VS, 1 Book
29445, GL, 1 Book
30064, MM, 1 Book
30341, HO, 1 Book
32707, SB, 1 Book
32754, DD, 1 Book
32765, JR, 2 Books
45014, ES, 1 Book
45066, LS, 1 Book
45801, TL, 1 Book
48206, CW, 1 Book
48371, VV, 1 Book
48843, JR, 1 Book
56549, EN, 1 Book
59405, GM, 1 Book
66062, JF, 1 Book
67212, CC, 1 Book
72834, ML, 1 Book
78746, MA, 1 Book
80015, CD, 1 Book
80023, PB, 1 Book
80234, JM, 1 Book
80907, KP, 1 Book
87107, JG, 1 Book
87124, CM, 1 Book
87544, BD, 1 Book
89511, MM, 1 Book
91602, BH, 1 Book
92109, SP, 1 Book
92806, LM, 1 Book
94301, BC, 1 Book
94550, JR, 1 Book
94602, RD, 1 Book
94941, BH, 1 Book
94947, JP, 1 Book
95320, TN, 3 Books
95693, KS, 1 Book
97338, JG, 1 Book
97424, TP, 1 Book
98008, DM, 1 Book
98030, BL, 1 Book
98115, MH, 1 Book
98166, CN, 1 Book
98275, SJ, 1 Book
98501, DG, 1 Book
Anonymous, 1 Book

Dennis Tillman W7pF