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Tek 571 curve tracer

Bill Higdon
 


PS503A Mod FF Photos?

Jared Cabot
 

Hi,
Does anyone have a PS503A Dual Power Supply module with the Mod FF (adjustable 5v output) installed?
I'm just looking for some photos to determine the difficulty of retrofitting this mod to my unit.


Thanks!
Jared


Re: 7A26 CH2 Readout

Stephen
 

On Thu, Aug 20, 2020 at 12:29 PM, Raymond Domp Frank wrote:

Interleaved.

Yes, as a description of the actual situation, It seems to make sense.
However, the BNC Identfy ring (which was shorted to gnd) and the Identify
button are switched in parallel, see dwg 3 (if I'm looking at the right
schematic version).
I’m sure you are.

That means, if *either* is connected to gnd, the other
doesn't matter and has no further influence, unless... the ring-short wasn't
low-impedance enough. That would explain the slight movement when pressing
Identify.
I suppose it was very low imperfections. It was just, I think, what seemed to be, some kind metal part, less than a 1/10 of a mm long. I was very hard to tell, even with the magnifying glass I used.

The trace jump doesn't need and doesn't work in parallel with the readout
showing either IDENTIFY or voltage scale. That's the darlington circuit's
area.
That’s what I figured, without understanding how it actually works.

The trace jump circuit is completely on dwg 3.
Okay.

Again, I advise setting up and doing the live measurements. Being able to look
at CH2 and where necessary comparing CH1 and CH2 physically and logically next
to each other should really make this a lot easier.
I will definitely do that, or try to, next time I run into an issue. And since I bought quite a few things recently that need restoring or minor adjustments, it shouldn’t be long before I do.

Do have a look at the junction of CR621, R620, R621 and C621 in CH2 and
compare with CH1.
This is such a simple circuit that finding the fault shouldn't be that
difficult. This remark is in no way meant to criticize you; there's no reason,
looking at what you've achieved with this group recently.
Thank you. I’m doing my best, in my spare time, to educate myself and try to understand all this, little by little.
Since I had the readout board unscrewed to take those measurements, I figured I’d put back the original Q620.
And guess what. Everything is now back to normal, and working properly. I haven’t tried, but I must have mixed E and C on the equivalent I used. Could that reverse the order of things like I experienced?

Just make life a bit
easier, especially if you don't understand the circuit completely, as you
wrote earlier.
That is correct, I don’t.

Just one bit of information that you may not be aware of: The whole circuit of
Q620 and what is drawn to its right in dwg 5 is meant to set currents that the
analog readout control uses for generating its information to be displayed:
Resistors are switched in and out and Q620 is just one of the devices that
with its series resistor R622, controls a current, like the other mechanical
switches to the right of it with their series resistors like R630, R631, R647,
R648, etc. Read the interesting description of how the readout works here:
https://w140.com/tekwiki/wiki/7000_series_readout_system
or in one of the 7000-series mainframe manuals. Many (not all) go into great
detail on this. It's a brilliant circuit, devised by a Brit called Barrie
Gilbert.
Will definitely read it. Thank you 😊

Don't forget (in general): It's not completely unthinkable that a previous
owner modified the circuit...
Yes, nobody knows what previous owners did. But in this particular case, the original issue Was just the shorted BNC/Identifying Ring like Eric had experienced.

One last question: Are the voltage scale indications (V/div) correct?
Yes. Even when the order of operation was reversed, this was correct.


Re: 7A26 CH2 Readout

 

On Fri, Aug 21, 2020 at 12:36 AM, Stephen wrote:


Then I checked what Eric suggested, and sure enough, the ring was shorted to
ground, the same way his was.
When I removed the short, the trace was moving about 1 division BUT,
« IDENTIFY » was the default readout, and the voltage range was showing
when the button was pushed. In other words, it’s behaving as it should,
meaning the button does have an effect on the readout and the trace, but
backwards. Am I making sense?

Yes, as a description of the actual situation, It seems to make sense.
However, the BNC Identfy ring (which was shorted to gnd) and the Identify button are switched in parallel, see dwg 3 (if I'm looking at the right schematic version). That means, if *either* is connected to gnd, the other doesn't matter and has no further influence, unless... the ring-short wasn't low-impedance enough. That would explain the slight movement when pressing Identify.
The trace jump doesn't need and doesn't work in parallel with the readout showing either IDENTIFY or voltage scale. That's the darlington circuit's area. The trace jump circuit is completely on dwg 3.

Again, I advise setting up and doing the live measurements. Being able to look at CH2 and where necessary comparing CH1 and CH2 physically and logically next to each other should really make this a lot easier.

Do have a look at the junction of CR621, R620, R621 and C621 in CH2 and compare with CH1.
This is such a simple circuit that finding the fault shouldn't be that difficult. This remark is in no way meant to criticize you; there's no reason, looking at what you've achieved with this group recently. Just make life a bit easier, especially if you don't understand the circuit completely, as you wrote earlier.

Just one bit of information that you may not be aware of: The whole circuit of Q620 and what is drawn to its right in dwg 5 is meant to set currents that the analog readout control uses for generating its information to be displayed: Resistors are switched in and out and Q620 is just one of the devices that with its series resistor R622, controls a current, like the other mechanical switches to the right of it with their series resistors like R630, R631, R647, R648, etc. Read the interesting description of how the readout works here:
https://w140.com/tekwiki/wiki/7000_series_readout_system
or in one of the 7000-series mainframe manuals. Many (not all) go into great detail on this. It's a brilliant circuit, devised by a Brit called Barrie Gilbert.

Don't forget (in general): It's not completely unthinkable that a previous owner modified the circuit...

One last question: Are the voltage scale indications (V/div) correct?

Raymond


Re: 7A26 CH2 Readout

Stephen
 

On Thu, Aug 20, 2020 at 11:27 AM, Raymond Domp Frank wrote:


On Fri, Aug 21, 2020 at 12:25 AM, Raymond Domp Frank wrote:


between the Identify ring, right?
...between the Identify ring and ground, right?

Raymond

Yes


Re: 7A26 CH2 Readout

Stephen
 

On Thu, Aug 20, 2020 at 11:25 AM, Raymond Domp Frank wrote:


On Fri, Aug 21, 2020 at 12:20 AM, Stephen wrote:


It seems « incompatible » because you’re mixing excerpts from
different
time lines. As I mentioned, things have happened in between.
I thought as much but couldn't match it. Actual situation is you have a
reversed operation of Identify after replacing Q620 and removing a short
between the Identify ring, right?

Raymond
Correct. I replaced Q620 with an equivalent that has a different pinout. I think I did put it the right way.
Now, after I did this, I didn’t have « IDENTIFY » showing up all the time, but the trace was still not moving upwards the way it should. And instead of « IDENTIFY », I had the voltage range displayed. Which is the normal behavior.

Then I checked what Eric suggested, and sure enough, the ring was shorted to ground, the same way his was.
When I removed the short, the trace was moving about 1 division BUT, « IDENTIFY » was the default readout, and the voltage range was showing when the button was pushed. In other words, it’s behaving as it should, meaning the button does have an effect on the readout and the trace, but backwards. Am I making sense?


Re: 7A26 CH2 Readout

 

On Fri, Aug 21, 2020 at 12:25 AM, Raymond Domp Frank wrote:


between the Identify ring, right?
...between the Identify ring and ground, right?

Raymond


Re: 7A26 CH2 Readout

 

On Fri, Aug 21, 2020 at 12:20 AM, Stephen wrote:


It seems « incompatible » because you’re mixing excerpts from different
time lines. As I mentioned, things have happened in between.
I thought as much but couldn't match it. Actual situation is you have a reversed operation of Identify after replacing Q620 and removing a short between the Identify ring, right?

Raymond


Re: 7A26 CH2 Readout

Stephen
 

On Thu, Aug 20, 2020 at 11:08 AM, Raymond Domp Frank wrote:


On Thu, Aug 20, 2020 at 10:01 PM, Stephen wrote:


I replaced Q620, and now it displays the voltage range, but not
« IDENTIFY » anymore when the button is pressed. But the trace moves a
tiny bit, like it was before.
That seems incompatible with this:

On Thu, Aug 20, 2020 at 10:01 PM, Stephen wrote:

Also, the push button has no effect on what is displayed, and only move the
trace up just very little
compared to the other channels
and this:

On Thu, Aug 20, 2020 at 11:48 PM, Stephen wrote:


You were right. The ring was shorted to ground.

It’s always on « IDENTIFY », and when I press the button, the trace
moves exactly as it should, and
the display shows the voltage range... Backwards....

Hmmm.. What did I do wrong? Did I put the new Darlington equivalent (Q620)
backwards?
That wouldn’t do that, would it?
So that's different behavior from what I understood earlier.
It looks like the darlington isn't functioning as it should.

The simplest thing to do probably is putting the 7A26 in the rightmost slot as
I described earlier and do live (comparative) voltage measurements.
Creating a convenient working environment often makes up 50% of the job.

Raymond
It seems « incompatible » because you’re mixing excerpts from different time lines. As I mentioned, things have happened in between.


Re: 7A26 CH2 Readout

 

Your latest message arrived just after I sent mine. Please take that into account when reading it.

Raymond


Re: 7A26 CH2 Readout

 

On Thu, Aug 20, 2020 at 10:01 PM, Stephen wrote:


I replaced Q620, and now it displays the voltage range, but not
« IDENTIFY » anymore when the button is pressed. But the trace moves a
tiny bit, like it was before.
That seems incompatible with this:

On Thu, Aug 20, 2020 at 10:01 PM, Stephen wrote:

Also, the push button has no effect on what is displayed, and only move the trace up just very little
compared to the other channels
and this:

On Thu, Aug 20, 2020 at 11:48 PM, Stephen wrote:


You were right. The ring was shorted to ground.

It’s always on « IDENTIFY », and when I press the button, the trace moves exactly as it should, and
the display shows the voltage range... Backwards....

Hmmm.. What did I do wrong? Did I put the new Darlington equivalent (Q620) backwards?
That wouldn’t do that, would it?
So that's different behavior from what I understood earlier.
It looks like the darlington isn't functioning as it should.

The simplest thing to do probably is putting the 7A26 in the rightmost slot as I described earlier and do live (comparative) voltage measurements.
Creating a convenient working environment often makes up 50% of the job.

Raymond


Re: 7A26 CH2 Readout

Stephen
 

On Thu, Aug 20, 2020 at 10:04 AM, Raymond Domp Frank wrote:

Interleaved.


- Pushing Identify should move the trace up at least one minor division. Not
sure if that happens, since you're writing "a tiny bit".
What I meant was about a 1/10 of a division.... virtually nothing. Barely visible.

- If you don't have an extender, you may consider putting the 7A26 without its
right side panel into the rightmost slot (yes, that's a "horizontal" slot but
this a 7000 system, use the orthogonal architecture to your advantage), remove
the right side panel of the 'scope and measure voltages on the readout boards
live.

I guess you already checked the following:
No, I don’t have an extender. And I haven’t checked the voltages yet, precisely because of that.
I didn’t know you could do that to check voltages. But I guess that makes sens. Thanks for the tip, it may come in handy.

- Without depressing the Identify button, the voltage at the Identify ring
around the BNC input connector should be at about -15V. Depressing it should
change that to about 0V. See Dwg 3.
- The connection between CR621 (anode), R620 and R621 should behave about the
same (voltages and level shift). If it doesn't, something 's probably (still)
wrong with / around Q620.

- Did you measure voltages around the darlington on the CH1 readout board and
compare? You may consider swapping the darlington from CH1 in.
I haven’t checked any voltage, because of the lack of an extender (previous answer)

Thank You Raymond.


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

 

On Thu, Aug 20, 2020 at 11:46 PM, Raymond Domp Frank wrote:


Then I use that hand for applying outward force along the axis of the tube.
Still further clarification: "tube" indicating the small hollow tube on the pin, *not* the CRT......

Raymond


Re: 7A26 CH2 Readout

Stephen
 

On Thu, Aug 20, 2020 at 09:33 AM, Eric wrote:


I had one that was doing the same thing on channel 2 it ended up being a
bad BNC connector on the front panel. There is a low Ohms resister from
the BNC scene ring to the push button switch if you lift the resister
and it drops out of identify check the resistance to ground from the pin
on the jack on a healthy jack it should show open mine was 39K Ohms.

Eric
You were right. The ring was shorted to ground. Removed the little shield at the back of the BNC, desoldered the 100R resistor from the ring, and the ceramic cap from the ground, inspected the BNC from the back. I couldn’t really see anything except for maybe a tiny « something » stuck in between the ring and the shield. I’m not very sure what it was. I started twisting very slightly the BNC from the front, less then 1/4 of a turn, and sure enough continuity from the ring to ground disappeared. Now all is working perfectly......
Except.... BACKWARDS. 🤷‍♂️

It’s always on « IDENTIFY », and when I press the button, the trace moves exactly as it should, and the display shows the voltage range... Backwards....

Hmmm.. What did I do wrong? Did I put the new Darlington equivalent (Q620) backwards? That wouldn’t do that, would it?


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

 

On Thu, Aug 20, 2020 at 11:39 PM, Raymond Domp Frank wrote:


I usually grab them with the tip of long pliers, applied at 90 degrees and
push the end of the pliers away from the CRT, using the 'scope's chassis as
support for my hand.
Further clarification: I hold the pliers steady in one hand and apply force by putting a few fingers of my other hand near the tip of the pliers. Then I use that hand for applying outward force along the axis of the tube.

Raymond


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

 

On Thu, Aug 20, 2020 at 11:39 PM, Raymond Domp Frank wrote:


I usually grab them with the tip of long pliers,
Make sure to apply the pliers near the soldering end of the tube to avoid pinching the CRT's pin, making removal much more difficult.

Raymond


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

 

On Thu, Aug 20, 2020 at 10:53 PM, <Greenpitu@gmail.com> wrote:


Trying to figure out how to repair this one! I tried pulling the pin, hoping
it is pluggable itself, but no luck (I didn't try too hard just in case). Does
anyone know how I should proceed to fix this one?
The soldered pieces are actually clamping hollow tubes that are just pushed onto the CRT's pins. Pulling strictly lengthwise should get them off. I usually grab them with the tip of long pliers, applied at 90 degrees and push the end of the pliers away from the CRT, using the 'scope's chassis as support for my hand. Hope that makes sense. It feels very controlled.

Raymond


Re: 2246A Power supply failure turning on / off

JorgeTop
 

On Thu, Aug 20, 2020 at 08:00 AM, <tekscopegroup@miwww.com> wrote:


N400x series diodes as a replacement for these application, they are way too
slow and will not work in this case that requires fast switching. MUR-160 or
any 1Amp and 200-600PIV equivalent fast switching diode will work just fine.
Thank you for the information, I will search for the diodes tomorrow.


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

SCMenasian
 

I don't have this 'scope or the tube; but, i I suspect that the pin connects to a deflection plate, which is rather high impedance. A silver bearing epoxy would probably do the job without degrading bandwidth significantly.


Re: 7A26 CH2 Readout

 

- Pushing Identify should move the trace up at least one minor division. Not sure if that happens, since you're writing "a tiny bit".

- If you don't have an extender, you may consider putting the 7A26 without its right side panel into the rightmost slot (yes, that's a "horizontal" slot but this a 7000 system, use the orthogonal architecture to your advantage), remove the right side panel of the 'scope and measure voltages on the readout boards live.

I guess you already checked the following:
- Without depressing the Identify button, the voltage at the Identify ring around the BNC input connector should be at about -15V. Depressing it should change that to about 0V. See Dwg 3.
- The connection between CR621 (anode), R620 and R621 should behave about the same (voltages and level shift). If it doesn't, something 's probably (still) wrong with / around Q620.

- Did you measure voltages around the darlington on the CH1 readout board and compare? You may consider swapping the darlington from CH1 in.

Raymond

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