Date   

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
-


Tek 492BP age and does it have surface mount parts sn B0303xx

Edward Prest
 

S/N B0303xx 492BP
The production date seems to be around 1989 or so, can someone confirm that?

I am looking to buy one but it would be nice to know if there were no surface mount caps in it.


Re: Tektronix 5A20N differential amplifier plug-in repair

Harvey White
 

I have an audio rack I constructed from a picture that the manufacturer very kindly provided.  It's two rack units with a bridge between them.  They're slightly angled and between them is a work surface.  The bridge section could hold a scope or so should I wish.

You can get bits and pieces of rack hardware without too much problem.  You can find black formica to coat the bridge sections and the inside of the rack sections.  The rack sections themselves are stained plywood.  You can also buy a press-in edge molding. The workbench itself is a green marbled kitchen top counter (without backstop).

Right now, it's got the audio editing setup on it, as well as one of the LCD TVs.

Harvey

On 9/21/2021 11:59 PM, Dave Peterson via groups.io wrote:
When I picked up a 5111A to drive the 5CT1N I got in a fried 5440, it was in a rack mount. Andy W. here was kind enough to send me a bench-top case to convert it.

I've since repaired the 5440, and also picked up a 5103N (wrapped around a 5L4N). I now have 3 5000 series scopes! How did that happen!?

In any case, why have I never thought of building a wood rack? I love it!

I'm in serious need of rebuilding my bench to accommodate the equipment I've collected. Rack mounting the 5000 scopes along with a hefty HP 141T is the solution I've needed. A bit of cabinetry is right up my alley. Just another thing to do, eh?

Another nice piece of work Magnus. Thanks for sharing.

Dave





Re: Tektronix 5A20N differential amplifier plug-in repair

Dave Peterson
 

When I picked up a 5111A to drive the 5CT1N I got in a fried 5440, it was in a rack mount. Andy W. here was kind enough to send me a bench-top case to convert it.

I've since repaired the 5440, and also picked up a 5103N (wrapped around a 5L4N). I now have 3 5000 series scopes! How did that happen!?

In any case, why have I never thought of building a wood rack? I love it!

I'm in serious need of rebuilding my bench to accommodate the equipment I've collected. Rack mounting the 5000 scopes along with a hefty HP 141T is the solution I've needed. A bit of cabinetry is right up my alley. Just another thing to do, eh?

Another nice piece of work Magnus. Thanks for sharing.

Dave


Re: Wanted: 5000 series extender(s)

Dave Peterson
 

Magnus, thank you for your comments.

Your craftsmanship is quite nice. I like how you've created a built-in tester with the extender. A much more robust and safe build. I think I prefer your extender over Tektronix's!

Perhaps a future project for me to undertake.

Dave


Re: 7704A Vertical Amplifier Issues

Mark Vincent
 

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


Re: Recreating an old board for the 7854

Harvey White
 

That's a very large board.  Had you considered a smaller board with some 3D printed rails?, or two boards with an IDC jumper? I've used that approach.

Harvey

On 9/21/2021 11:19 PM, Zentronics42@gmail.com wrote:
Assembly is not to complicated now that I am prototyping in the real world not just digital I need to check the physical dimensions make sure everything lines up. I used a mix of THT and SMD everything is in current production that Is needed so it should not be too hard to source parts. All SMD parts are 1206 to aid in a stress free assembly. I will have to outsource the board as I am not able to may anything at home Larger thank 8 1/2 X 11 that board is around 15 inches long so it is rather large.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of demianm_1 via groups.io
Sent: Tuesday, September 21, 2021 9:07 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Recreating an old board for the 7854

I have 3 7854's so a valid interest. How involved is the assembly?











Re: Recreating an old board for the 7854

Zentronics42@...
 

Assembly is not to complicated now that I am prototyping in the real world not just digital I need to check the physical dimensions make sure everything lines up. I used a mix of THT and SMD everything is in current production that Is needed so it should not be too hard to source parts. All SMD parts are 1206 to aid in a stress free assembly. I will have to outsource the board as I am not able to may anything at home Larger thank 8 1/2 X 11 that board is around 15 inches long so it is rather large.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of demianm_1 via groups.io
Sent: Tuesday, September 21, 2021 9:07 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Recreating an old board for the 7854

I have 3 7854's so a valid interest. How involved is the assembly?


7704A Vertical Amplifier Issues

n4buq
 

A few weeks ago, I posted a message regarding something that overheated from in/around the Vertical Amplifier board in my 7704A. Night before last, I was trying to determine what might be causing the traces to occupy only about 1/10 of the vertical space on the CRT and the vertical position has very little effect. I thought that the two connections to the vertical plates might be touching something between the vertical amplifier board and where they plug in to the pins on the CRT neck. When I powered it back on, I noticed smoke again and observed that R4419 was the culprit.

In my previous post, I noted that there appeared to be a "flying wire" mod on the vertical amplifier board but after noticing which component was overheating, I investigated the schematic and found R4419 is part of what appears to be a factory upgrade to include Q4420 and its supporting components. I also discovered that Q4420 is fully open so I plan to rebuild that entire circuit as the one I have isn't done as neatly as I've seen other examples.

One of the components is CR4419 which was originally a 2N4152 and I'm not finding much in the way of cross-references for that. I think the original part is still good but has fairly short leads and I would like to have a diode with longer leads to work with. Does anyone know of a good sub? I have 1N400x and 1N5819. Would either of those be suitable? I prefer the 1N5819 due to the slightly smaller package but should be able to work with either one.

Also, from what I've seen, the problem with my vertical amplifier may be U4413. I'm holding out hope it isn't that but I have a bad feeling that it is.

Thanks,
Barry - N4BUQ


Re: Recreating an old board for the 7854

demianm_1
 

I have 3 7854's so a valid interest. How involved is the assembly?


Re: 2445B tick mode issue -- fixed (inverter and regulator board recap and repair)

Keith
 

Thanks Marcel!

I appreciate the video and the BOM file. I have a 2445b that is working fine, but I dread the day that the SMPS ever goes dead, as I know so little about them. Now, having your video and BOM provides me with a measure of peace of mind. Thanks again for your extra work to do these postings.

Keith
CoolBlueGlow


Re: Recreating an old board for the 7854

Zentronics42@...
 

Yep those sorry about the typo. The board only needs 1 cable. But it needs 5 connectors. It allows for some signal termination to cables that exist in the scope already. I have some of the micro coax lines from some scopes that had terminal issues. The pre-trigger signal gets a cable it is BNC input micro coax out to 7854. J610 is the pretrigger out. J805, J900, J1600, J1500 are the terminators for the lines already in the scope. J805 and J900 are actually mounted on the back of the board.

Zen

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of redarlington
Sent: Tuesday, September 21, 2021 4:03 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Recreating an old board for the 7854

https://w140.com/tekwiki/images/thumb/6/6b/Peltola-connector-socket.jpg/640px-Peltola-connector-socket.jpg

Those guys? Peltola?

Can you tell us how these are used with the board? Are you planning on
providing cable assemblies along with them? or just need the socket on the
board to use with existing cables in the 7854? Am I completely wrong
with this connector and it really is a Penolta?

Thanks,
Bob - N3XKB

On Tue, Sep 21, 2021 at 1:56 PM <Zentronics42@gmail.com> wrote:

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


Tektronix 5A20N differential amplifier plug-in repair

magnustoelle
 

Good Day to the group,

I have just completed a simple repair of a type 5A20N differential amplifier plug-in for the 5000/5400 series of Tektronix oscilloscopes. There is not much to "write home about" this, but I thought I share my joy with you...

*Problem containment:* The input signal present at either the positive or negative input was not displayed properly. The trace was heavily distorted and shifted grossly over the whole screen when rotating the VOLTS/DIV deflection factor settings.
*Troubleshooting and repair:* Using my DIY-made extender, all supplies and the push-pull output stage composed of Q163/Q263 were measured with a DMM and found nominal. Injection of an external small signal into Q129A/B of the input stage resulted in a reasonable display. Both input protection fuses were found open and were replaced. A dual N-channel JFET Q120A/B (Tektronix part # 151-1049-00) in the input stage was found "toast".
As several other group member have already discussed, this is a hard-to-obtain transistor pair. So, I have used my 5CT1N curve tracer to match two standard "dirt cheap" Fairchild BF245A JFETs from my local stock. I have sanded the flat side of the package and super-glued the two units together. I was pleased to find that with this replacement the plug-in was fully restored.
*Conclusion:* A massive electrical over-load event has taken the N-channel JFET and both fuses at the input stage out.

A full calibration was completed after the repair.

I have uploaded a few pictures to https://groups.io/g/TekScopes/album?id=268328

Cheers,

Magnus


3 photos uploaded #photo-notice

TekScopes@groups.io Notification <noreply@...>
 

The following photos have been uploaded to the Tektronix 5A20N repair and calibration album of the TekScopes@groups.io group.

By: magnustoelle <magnustoelle@...>

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