Date   

Re: Repair of a 7S14

 

On Thu, Sep 23, 2021 at 12:22 AM, Jeff Dutky wrote:


Finding a +15 V connection point is no problem, but I'm befuddled about where
to connect to ground.
If you look at the image of my led-modded board in the 7S14 TekWiki article, you can clearly see where I made the GND connection: It's with the leftmost led connection of the left led-pair. The thin red wire to the right is connected to the +15 V.

Raymond


Re: Repair of a 7S14

 

With the replacement of the Schottky diodes out of the way I have been working on the LED assembly to replace the mercury cells. I've got an assembly that looks like it will work (produces 1.4-1.5 V at 2.5 mA when fed 15 V input to the illuminator LEDs), but I'm having trouble finding points to connect the illuminators.

Finding a +15 V connection point is no problem, but I'm befuddled about where to connect to ground. Is that pair of U-shaped traces (see photo https://groups.io/g/TekScopes/photo/267375/3305755) a ground plane? I'm a little wary of touching those: they look like they were made that way for A Reason [TM] that is beyond this mortal's ken. Is it safe to connect to the shell on J20 (or J10)? Again, I'm wary of tapping off a point so close to the input signal.

I have not gone into the sample board and to poke around with a multimeter, yet (getting that cover off is a pain); I have just been looking at my photos and the diagrams/schematics in the manual.

To reiterate the questions:

1. Is it safe to tap my ground connection from the shell of J10 or J20?
2. is it safe to tap my ground connection from the pair of U-shaped traces?
3. what is the purpose/function of the pair of U-shaped traces?

-- Jeff Dutky


Re: Tek 547 B intensified by A

Dave Wise
 

Now beef up the speedup capacitor and you’ll be like new. 220pF added should do.

Dave Wise

From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jayadamski728 via groups.io
Sent: Wednesday, September 22, 2021 1:31 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Tek 547 B intensified by A

Hi there thanks for your help, Q373 was the cause , a 2n2207 had turned into two diodes according to my tester, probably a whisker inside. I replaced it with a BC556 and it worked


Re: Tek 547 B intensified by A

Jayadamski728@...
 

Hi there thanks for your help, Q373 was the cause , a 2n2207 had turned into two diodes according to my tester, probably a whisker inside. I replaced it with a BC556 and it worked


Re: Tek 7603 missing readout but present when beam finder pressed

Roy Kalawsky
 

Roger, adjusting R2291 now brings the readout onto the crt screen. However, I had to set R2291 to an end stop. I guess I should check out possible out of spec resistors etc. It is possible that the previous owner may have tweaked gain controls etc so I reckon I should go through the calibration sequence. The plug-ins still have unbroken calibration seals.

Thank you again for your help - very much appreciated. Roy (proudness owner of a RollsRoyce oscilloscope.


Re: 7704A Vertical Amplifier Issues

n4buq
 

Yes, I plan to include that when I rebuild the circuit.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Albert Otten" <aodiversen@concepts.nl>
To: TekScopes@groups.io
Sent: Wednesday, September 22, 2021 11:11:31 AM
Subject: Re: [TekScopes] 7704A Vertical Amplifier Issues

On Wed, Sep 22, 2021 at 04:53 PM, Mark Vincent wrote:
If either/both output transistors in the IC short from C to B, that will
cause
the 33 ohm resistor to burn.
Perhaps the later on added R4426 2k between Q4420 collector and GND is
intended to prevent this.
Albert






Re: 7704A Vertical Amplifier Issues

Albert Otten
 

On Wed, Sep 22, 2021 at 04:53 PM, Mark Vincent wrote:
If either/both output transistors in the IC short from C to B, that will cause
the 33 ohm resistor to burn.
Perhaps the later on added R4426 2k between Q4420 collector and GND is intended to prevent this.
Albert


Re: Recreating an old board for the 7854

Zentronics42@...
 

I have confirmed that Tek still sells these and they are in production. They are $14.95 Each board will need 5x.

Part number is 131-1003-00

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of David C. Partridge
Sent: Wednesday, September 22, 2021 3:56 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Recreating an old board for the 7854

Tektronix sell the Peltola connectors.

David

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Zentronics42@gmail.com
Sent: 21 September 2021 20:57
To: TekScopes@groups.io
Subject: Re: [TekScopes] Recreating an old board for the 7854

As the board is moving in to real world resting there are 2 issues, I need to make people aware of.
I do not have a price per board yet but these boards are NOT small so I am expecting them to be on the high side.
Also there is a Tek specific connector that is used. They are called penotla connectors and the board needs 5 each. I have a source for the pins but I need the outer barrels to complete the connectors. I can get some of the supplies I need if any one has any junk boards laying around that I can pull them off of. Parts scopes in the 4xx 5xxx and 7xxx are all useful for this case.
This will ultimately be the limiting factor of how may boards I can make. I currently only have enough parts to make 8 complete connectors. I have a TON of pins. Not may barrels.

Zen

-----Origin


Re: 7704A Vertical Amplifier Issues

Mark Vincent
 

Barry,

CR4419 is a clamp. Voltage at the emitter and one end of the 33 and 5600 ohm resistors can go lower than 15,6-15,7V, not higher. It also sets the common base voltage and current limit for the output stages. The voltage divider on the base of Q4420 sets that voltage at the base and emitter. If either/both output transistors in the IC short from C to B, that will cause the 33 ohm resistor to burn. Testing those two junctions will determine if the output transistors are good or bad between those two junctions. One thing that can cause the output to go bad is someone turning the bias control too high, R4415 at too low resistance making the voltage higher than 10,1V at one end of R4416. If that pot was not touched, it should be at the proper voltage. Once you get it working, check that voltage and adjust as necessary. If you want, you can turn the pot a little so the voltage will be bit low at first then increase. Starting at a lower current will not hurt. You reduce the chance of any damage with lower current. When set right, the vertical will be correct. The centering control may need adjusting. That is done with no vertical plug-ins installed. Any other controls for things may need to be touched up slightly with another IC installed. See if the controls need adjustment after it is working and a known type of signal is applied. If the trace is the way it should be, leave the other controls alone. The manual will say how to calibrate.

Mark


Re: 7704A Vertical Amplifier Issues

n4buq
 

Okay, Mark. Will do.

BTW, can you explain the function of CR4419? I don't find the part of the circuit surrounding Q4420 outlined in the Circuit Description section of the manual for the Vertical Amplifier.

Thanks again,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@gmail.com>
To: TekScopes@groups.io
Sent: Wednesday, September 22, 2021 8:46:02 AM
Subject: Re: [TekScopes] 7704A Vertical Amplifier Issues

Barry,

I was wrong about the 2N2222A being a sub. The original is a PNP. My mistake.

The voltages would be best checked with the transistor and resistors
replaced. Testing the output IC from the base to collectors can be done now.
One end of the meter to where the 33 ohm connects and the other end of the
meter to each plate. That will tell if that part of the output transistors
will be good. That is not a conclusive test for the output IC. Replace the
parts. See if the 33 ohm resistor gets warm. If it gets hot/burns again, the
IC is the problem.

Mark






Re: 7704A Vertical Amplifier Issues

Mark Vincent
 

Barry,

I was wrong about the 2N2222A being a sub. The original is a PNP. My mistake.

The voltages would be best checked with the transistor and resistors replaced. Testing the output IC from the base to collectors can be done now. One end of the meter to where the 33 ohm connects and the other end of the meter to each plate. That will tell if that part of the output transistors will be good. That is not a conclusive test for the output IC. Replace the parts. See if the 33 ohm resistor gets warm. If it gets hot/burns again, the IC is the problem.

Mark


Re: 7904A compress sweep

 

On Wed, Sep 22, 2021 at 02:53 PM, Tom Phillips wrote:


I had some of the round two fin tophat style sinks and after filing flats on a
side of each can fit pairs
onto the outputs.
Neat!

I also was concerned about possible capacitive coupling
effects. So far have not
observed a problem doing casual checking with pulse generator at high sweep
rates...
Well, if it's not visible, it won't do any harm. I'd guess most is hidden in the trace blanking time anyway.


Really need to find a good time mark generator since I have several 7000
series and plugins that need
to be checked out.
Try and find a TG501 and don't forget to terminate into 50 Ohm or you'll think it malfunctions. The TG501 nicely matches Tek's adjustment procedures.

Raymond


Re: 7904A compress sweep

Tom Phillips
 

Hi Raymond,

I had some of the round two fin tophat style sinks and after filing flats on a side of each can fit pairs
onto the outputs. I also was concerned about possible capacitive coupling effects. So far have not
observed a problem doing casual checking with pulse generator at high sweep rates...

Really need to find a good time mark generator since I have several 7000 series and plugins that need
to be checked out.

-Tom Phillips


Re: 7704A Vertical Amplifier Issues

n4buq
 

Hi Mark,

Okay on the parts. Apparently I was searching for a 2N4152 for CR4419 instead of a 1N4152 (which is readily available).

Is it acceptable to check the voltages at the IC without Q4420 connected? It would be good if I could go ahead check that now and get something ordered if necessary.

You mentioned a 2N2222A as a sub for Q4420. Isn't Q4420 an NPN? I have some 2N3906s on order (thought I had a few in my parts bin but apparently not).

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Mark Vincent" <orangeglowaudio@gmail.com>
To: TekScopes@groups.io
Sent: Tuesday, September 21, 2021 10:34:55 PM
Subject: Re: [TekScopes] 7704A Vertical Amplifier Issues

Barry,

You can test from the two bases of the outputs to the collectors. That may
indicate the output IC is bad. Q4420 is a 2N3906 and CR4419 is a 1N4152. A
2N2222A and 1N4148 or 1N4937 will work as subs for these two. At the emitter
of Q4420 should be 15,6V. The 33 and 5600 ohm resistors should be 1W. The
bias voltage at R4416 should be 10,1V. The output pins should be 36V and 37V
when working. Since the 33 ohm resistor burned, it is likely the IC is bad.
If the 50V supply went too high, that will short the output IC. There is a
seller on "that site" that has some known working boards from this model.
Ask if he has the vertical output board. There is a NOS IC on there also.
See if the voltages at the pins are correct. These can be done at ends of
resistors. The four 200 ohm resistors should have 9,3V at the IC. Voltages
that are way off, will also mean the IC is bad. It looks like the parts you
ordered made the power supply work.

Mark






Tek 6R1 used in the real world

snapdiode <snapdiode@...>
 

In this video I saw a quick glimpse of a 567 with a 6R1 built right into a PDP-4 computer.

https://youtu.be/sPU8-fkaRWc?t=530

That's pretty cool.


Re: 3 photos uploaded #photo-notice

Lawrance A. Schneider
 

Would it not be more informative to say: 3 photos uploaded relative to a tek 5A20N ?

Thanks larry


Re: P6065 probe

Edward Prest
 

I bought Chinese ones when I restored my scope. They compensate fine. It seems there is only one big manufacturer and a million people selling the same thing. At the price they ask you can buy 2 or 3 sets for the price of used tek and have spares.


Re: Tektronix 5A20N differential amplifier plug-in repair

magnustoelle
 

Hello Ron,

thank you for your kind words.

I have curve-traced the JFETs for their standard output characteristics, i.e. Id vs. Vds, and best similarity of the ohmic, say the linear region and best matching characteristics of all displayed curves.
The two JFETs I have picked as a replacement for the defect dual JFET were matching so closely that I could hardly see any trace shift on the CRT, probably a fraction of a millimeter when switching between them with my adapter. Some samples showed curves shifted by more than half of a screen division or so...

With the 5CT1N one can easily test for the DUT's behaviour under various conditions and check for other parameters, but I kept it easy for this repair.

I am also a big fan of the "test it in the application"-principle. So, with the two "matched" JFETs (glued together) inserted into the 5A20N, I have tested the positive and the negative input of the plugin for how well they are matching with various input signals. Considering the opposite polarity, of course. And they matched nicely across the whole VOLTS/DIV settings range.
For the fun of it, I have used my heat gun and heated the PCB/circuitry up to almost "too hot to touch" temperature. The 5A20N's data sheet specs say its operating range is from 0 to +50°C. And I was pleased to see only a minimum amount of trace drift when the temp. went from room temp. say 22°C up to about 50°C. The trace shifted barely at all, worst case by half a trace, or approx. 1/5th of a subdivision on the screen.

Touching or moving the side panel cover definitely had a much greater influence at the low VOLTS/DIV settings, so I have re-tested the unit without the adapter. I have found that's good enough by my standards and then carried on with the calibration :-)

Cheers,

Magnus

On 22/09/2021 05:12, Ron wrote:


Magnus,

Great work, thanks for sharing. Which parameters were used to
match the JFETs? How close were the parameter readings to get an OK
match?

Regards, Ron
-






Re: Recreating an old board for the 7854

 

Tektronix sell the Peltola connectors.

David

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Zentronics42@gmail.com
Sent: 21 September 2021 20:57
To: TekScopes@groups.io
Subject: Re: [TekScopes] Recreating an old board for the 7854

As the board is moving in to real world resting there are 2 issues, I need to make people aware of.
I do not have a price per board yet but these boards are NOT small so I am expecting them to be on the high side.
Also there is a Tek specific connector that is used. They are called penotla connectors and the board needs 5 each. I have a source for the pins but I need the outer barrels to complete the connectors. I can get some of the supplies I need if any one has any junk boards laying around that I can pull them off of. Parts scopes in the 4xx 5xxx and 7xxx are all useful for this case.
This will ultimately be the limiting factor of how may boards I can make. I currently only have enough parts to make 8 complete connectors. I have a TON of pins. Not may barrels.

Zen

-----Origin


Re: Tektronix 5A20N differential amplifier plug-in repair

Ron
 

Magnus,

Great work, thanks for sharing. Which parameters were used to match the JFETs? How close were the parameter readings to get an OK match?

Regards, Ron
-

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