Date   

Re: TDS420a - Known weak spots/typical failures?

John Hudak
 

Thank you all for your comments. Much appreciated.
John


Re: Using a 7CT1N

n4buq
 

Yes, I was just testing it with a 7B50 and that works. I was foolishly trying this with a time-base without a source input and using the cable inserted into the trigger input. That will produce a set of traces but they're nothing like what they're supposed to be. It then occurred to me why I was getting such odd results...

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "NigelP" <nigel-pritchard@...>
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, May 16, 2022 10:42:53 AM
Subject: Re: [TekScopes] Using a 7CT1N
I use a 7B50 for this; it has a BNC external input socket exactly suitable for
this mode and interfaces with the waggley connector coming out of the front of
the 7CT1N.

Regards

Nigel



Re: Using a 7CT1N

n4buq
 

Okay, that makes sense. Essentially, it's an X-Y type of operation.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Harvey White" <madyn@...>
To: "tekscopes" <TekScopes@groups.io>
Sent: Monday, May 16, 2022 10:40:42 AM
Subject: Re: [TekScopes] Using a 7CT1N
Interleaved:

On 5/16/2022 11:30 AM, n4buq wrote:
I purchased a 7514 which came with, among other plugins, a 7CT1N. After
cleaning some of the dirty switches (still need to clean the leaf switches),
I'm able to get a set of traces for a 2N3904 and/or 2N3906; however, I'm
unclear on exactly how this is to be used in a vertical slot and an associated
time-base.
7CT1N's are quite nice.

If I understand correctly, when using it in a vertical slot, it's necessary to
use a time-base that has an amplifier function, ensure the time-base is
actually in amplifier mode, and adjust the amplifier gain to get the desired
traces. Is that correct?
Yes, correct.  You could also put a vertical plugin in a horizontal slot
and use it.

If in a horizontal slot, you use a vertical plugin.  You do need to
change the setting to reflect which kind of slot the plugin is in.


I ask because I don't exactly find that in the manual. It lists some of the
time-bases that are suitable for this but I don't see where it goes into detail
on exactly how to configure the time-base. I presume using the time-base in
amplifier mode is correct because I get a set of traces that are somewhat
comparable to the ones I get when using the tracer in a vertical slot and
plugging the cable into an amplifier's input.
All you're doing is using the plugin as a feedthrough to the horizontal
channels.  A vertical plugin (however simple, if it has the right
attenuation) will work.


Harvey


Thanks,
Barry - N4BUQ







Re: Using a 7CT1N

NigelP
 

I use a 7B50 for this; it has a BNC external input socket exactly suitable for this mode and interfaces with the waggley connector coming out of the front of the 7CT1N.

Regards

Nigel


Re: Using a 7CT1N

Harvey White
 

Interleaved:

On 5/16/2022 11:30 AM, n4buq wrote:
I purchased a 7514 which came with, among other plugins, a 7CT1N. After cleaning some of the dirty switches (still need to clean the leaf switches), I'm able to get a set of traces for a 2N3904 and/or 2N3906; however, I'm unclear on exactly how this is to be used in a vertical slot and an associated time-base.
7CT1N's are quite nice.

If I understand correctly, when using it in a vertical slot, it's necessary to use a time-base that has an amplifier function, ensure the time-base is actually in amplifier mode, and adjust the amplifier gain to get the desired traces. Is that correct?
Yes, correct.  You could also put a vertical plugin in a horizontal slot and use it.

If in a horizontal slot, you use a vertical plugin.  You do need to change the setting to reflect which kind of slot the plugin is in.


I ask because I don't exactly find that in the manual. It lists some of the time-bases that are suitable for this but I don't see where it goes into detail on exactly how to configure the time-base. I presume using the time-base in amplifier mode is correct because I get a set of traces that are somewhat comparable to the ones I get when using the tracer in a vertical slot and plugging the cable into an amplifier's input.
All you're doing is using the plugin as a feedthrough to the horizontal channels.  A vertical plugin (however simple, if it has the right attenuation) will work.


Harvey


Thanks,
Barry - N4BUQ





Using a 7CT1N

n4buq
 

I purchased a 7514 which came with, among other plugins, a 7CT1N. After cleaning some of the dirty switches (still need to clean the leaf switches), I'm able to get a set of traces for a 2N3904 and/or 2N3906; however, I'm unclear on exactly how this is to be used in a vertical slot and an associated time-base.

If I understand correctly, when using it in a vertical slot, it's necessary to use a time-base that has an amplifier function, ensure the time-base is actually in amplifier mode, and adjust the amplifier gain to get the desired traces. Is that correct?

I ask because I don't exactly find that in the manual. It lists some of the time-bases that are suitable for this but I don't see where it goes into detail on exactly how to configure the time-base. I presume using the time-base in amplifier mode is correct because I get a set of traces that are somewhat comparable to the ones I get when using the tracer in a vertical slot and plugging the cable into an amplifier's input.

Thanks,
Barry - N4BUQ


Re: No Nameplate/Badge, No Problem #photo-notice

David Slipper
 

Looks very good to me :-)

Dave

On 16/05/2022 15:13, jimbert4 via groups.io wrote:
Here are some pictures of my completed 2465 restoration. I didn't have a real nameplate for it, so I grabbed a picture of a 2465 that I found here and cut the nameplate from it. I did a little editing (I know, a bit crude) to improve the image and glued it to the 'scope with some Scotch Glue Stick. Here's a link to the pictures and the nameplate. I won't feed bad if someone wants to improve on the nameplate. I did the best I could with the image I grabbed and MS Paint.

https://groups.io/g/TekScopes/album?id=275143




Re: Tek 2465A Frequency readout

 

Nick,

If you have option 06 (Counter/Timer/Trigger) then your scope can show you the frequency of a triggering input signal. If I am reading the manual correctly it looks like Option 06 is only good up to about 150 MHz. This coincides with my own experience using the counter/timer function on my 2465 DMS (Options 01, 06, 09, and 10: DMM, Counter/Timer, Word Recognizer, and GPIB) which seems to top out around 150 MHz.

If your scope's counter/timer function is topping out at only 10 MHz then either something is very wrong, or maybe you have the BW limit switch engaged? (that's a 20 MHz limit, but it's close enough to what you're seeing to be worth checking)

-- Jeff Dutky


Re: Tek 2465A Frequency readout

Siggi
 

Hey Nick,

It's my understanding that the auto measurement functionality was
introduced with the 2465/2467B. Your 2465A and my 2467 should have all the
same features, aside from options (mine has opt 09, CTT - counter timer).
I think it might help if you describe the feature you're using to do this
measurement in more detail.
On my scope I can get a frequency reading with cursor measurements, with
single or dual delay, with or without B-trigger. These scopes pack a wallop
in features, so it helps to be specific.

Siggi

On Sun, May 15, 2022 at 4:26 PM <njkenworthy@...> wrote:

Hi
I fixed my 2465 over a number of years, replacing the ROMs etc and
fighting my way through the CAL process despite not having the best kit.
My question relates to the frequency measurement readout. While I can get
reasonably accurate 1/dt frequency readings with the cursors, the auto
measurement function tops out around 10Mhz.
I cant find any useful info in the manual on what its capabilities are ,
so don't know for sure if its faulty and I've only ever had access to my
own scope.
Should the frequency measurement work for the full bandwidth of the scope?
If so, is this likely to be connected to the final parts of the CAL which
rely on the PG506, which I have never had access to, and which I had to
"fudge " as best as I could with what I had.

If not, any tips on where to focus to clear up the problem.

Nick






No Nameplate/Badge, No Problem #photo-notice

jimbert4@...
 

Here are some pictures of my completed 2465 restoration. I didn't have a real nameplate for it, so I grabbed a picture of a 2465 that I found here and cut the nameplate from it. I did a little editing (I know, a bit crude) to improve the image and glued it to the 'scope with some Scotch Glue Stick. Here's a link to the pictures and the nameplate. I won't feed bad if someone wants to improve on the nameplate. I did the best I could with the image I grabbed and MS Paint.

https://groups.io/g/TekScopes/album?id=275143


Re: Help with diagnosis of Tek 2465 Power Supply Problem

jimbert4@...
 

On Sun, May 15, 2022 at 08:23 PM, Luca wrote:


I checked the addresses from A0 to A15. They decrease in frequency by half
each time. I didn't check the timing of them relative to each other, only one
line at a time. The frequencies seem correct.
Yes, the halving of the frequency at each next most significant address line is what I see as well. Did you also check that the decodes are being triggered? All of them should "fire" at their proper decode. You can even check that they fire at the proper address(es) by triggering on the decode output and looking to see what each address line is at that time.


Re: 2445A CH1 attenuator

Roger Evans
 

Looking at the construction of my spare attenuator module (removed from a 2440 part 119-2342-10), you should be able to remove the black plastic cover that holds the four latching relays, carefully remove the plugin relays (they have very thin connecting wires) and then you have access to clean the relay armatures and the area where they contact the ceramic substrate. Overshoot is very commonly due to poor connections giving an effective parallel RC circuit in the signal path.

You will almost certainly need to remove the attenuator from the main board to do this.

Regards,

Roger


2445A CH1 attenuator

Fred Schumacher
 

Hi All,
I got a 2445A Tek scope with a CH 1 problem. Applying a square wave to the input of this channel gives me a square wave on my display with an overshoot on the trailing edge, which isn’t present on all other channels.
Switching from 1 mV/div. To 50 mV presents a perfect square wave but switching to a higher attenuation the mentioned problem is present.
Connecting the CN1 attenuator output to the input of the CH2 pre amplifier and connecting the CH2 attenuator output to the CH 1 pre amplifier input gives me the mentioned problem on my CH2 display.
Also I interchanged the connecting rc network between the attenuator and pre amplifier. Checking the internal resistors of both attenuators showed no difference between them. The attenuator showed correct attenuation.
This mean the problem is in the CH 1 attenuator.
So my question is, is it possible to repair this unit or do I have to replace it as a unit.
Part number of this attenuator is 119-2342-01.
Thanks for your advice.


Re: 7A16A high frequency compensation.

unclebanjoman
 

On Mon, May 16, 2022 at 09:12 AM, Ozan wrote:


On Sun, May 15, 2022 at 11:49 PM, unclebanjoman wrote:

Do you put the attenuator at source side or at the plugin side?
Yeah, I always use this signal path: PG506 -> 80 cm coax -> x10 50 ohm attenuator -> 50 ohm feed-thru termination -> BNC of 7A16A

Does removing Q150 still clean up the waveforms? If you keep Q150 in place and
remove U350 does it change anything? This experiment is in case somehow
amplifier stage is loading Q150 output and it is not able to function as
source follower. I think you swapped U350 but there could be a fault in the
components around U350. The problem with this theory is final settled
amplitude is correct.
O.K. I will try with mooore calm this evening.

Otherwise cam switches of the attenuator (e.g. if one of the attenuator
sections is not completely isolated) and attenuator ground connections are
possible suspects. However, it doesn't explain behavior with Q150 removed.
I'm thinking the same. One test at a time and I will report to you ASAP.

Max


Re: 7A16A high frequency compensation.

Ozan
 

On Sun, May 15, 2022 at 11:49 PM, unclebanjoman wrote:


Thinking of, you should note that the input signal is clean with no
aberrations when the input selector is in the GND position. In this case the
input signal is grounded via the series combination R102/R104 (1 Mohm + 56
ohm) and all things are fine.
Positioning the selector in the DC (or AC, has the same effect) things changes
completely. Seems that some strange thing happens inside the input stage...
while theoretically should see always 1 Mohm.... or not?
Because of C132 high frequencies (or faster edges) will see a lower impedance. However, it should still be relatively higher impedance than the 50-ohm source.

Do you put the attenuator at source side or at the plugin side?

Does removing Q150 still clean up the waveforms? If you keep Q150 in place and remove U350 does it change anything? This experiment is in case somehow amplifier stage is loading Q150 output and it is not able to function as source follower. I think you swapped U350 but there could be a fault in the components around U350. The problem with this theory is final settled amplitude is correct.

Otherwise cam switches of the attenuator (e.g. if one of the attenuator sections is not completely isolated) and attenuator ground connections are possible suspects. However, it doesn't explain behavior with Q150 removed.


Ozan


Re: 7A16A high frequency compensation.

unclebanjoman
 

Thinking of, you should note that the input signal is clean with no aberrations when the input selector is in the GND position. In this case the input signal is grounded via the series combination R102/R104 (1 Mohm + 56 ohm) and all things are fine.
Positioning the selector in the DC (or AC, has the same effect) things changes completely. Seems that some strange thing happens inside the input stage... while theoretically should see always 1 Mohm.... or not?

Max


Re: 7A16A high frequency compensation.

unclebanjoman
 

I use the same cables and terminations with my 7A16 and 7A19 with no problems. I've checked and tried different feed-thru terminations and cables, with no difference.
The same cable and termination (they are labeled and distinguishable) I used to calbrate this 7A16 about one year ago.

The problem had probably been dormant for some time. I realized it a cople of weeks ago while I was making measurements on an RF oscillator output using the offending 7A16A.
As the frequency changed between 100MHz and 200 MHz, there was a point where the amplitude of the generated sinewave decreased and then rose again, something that did not happen to me with the 7A19.
Suspecting something anomalous in the bandwidth in the 7A16A, a quick check with the PG506 revealed (to my regret) the problem I am now trying to solve.

The slow start of PG506 is due to the fact that, when i took that photo, its output signal was very low. For very low signals my PG506 always has a slow start, that decresases with increasing amplitude. In fact I usually use a x10 attenuator to circumvent this idiosyncrasy when calibrating the 5/10 mV range. Which I didn't when I took the photos with the 3340.
I remember that it was talked about in other topics a long time ago.

Anyway, this evening I will try some other experiments.

Max


Re: Help with diagnosis of Tek 2465 Power Supply Problem

Luca
 

On Sun, May 15, 2022 at 07:40 AM, <jimbert4@...> wrote:


From the Service Manual, Pg 6-17: A good way to test the microprocessor
address lines (and address decode) is to move Jumper P503 (diagram 1) to the
Diagnostic position. This will disable the Data Bus Buffers and force the
micro into a NOP loop, continuously incrementing the address lines.
I checked the addresses from A0 to A15. They decrease in frequency by half each time. I didn't check the timing of them relative to each other, only one line at a time. The frequencies seem correct.

Luca


Re: Help with diagnosis of Tek 2465 Power Supply Problem

Luca
 

On Sun, May 15, 2022 at 07:23 PM, Ozan wrote:

In the error light pattern are Ch1-4 lights off?
Correct. All of Ch1-4 lights are off when the Kernel is trapped in error.

If you push delta-V/delta-T/slope buttons all at once you will enter the test
menu. Then if you push "Trigger coupling" up button scope should run a small
diagnostic. I don't think EPROM checksum is executed from that menu but it is
worth a try.
All the 5 Tests passed.

I can enter the Exercises 01-04 and Exercise 04 report the checksums, that is how I got the checksum values, which all looked correct.

I wonder if it is some kind of power problem. When the CPU starts running, the power on the ROM is not ready yet. But once after a few seconds, the power is stable, and all is fine. I will be looking for a way to RESET the machine after it is powered up. If the kernel check passes, then it should be power related problem.

Luca


Re: Help with diagnosis of Tek 2465 Power Supply Problem

Ozan
 

On Sun, May 15, 2022 at 04:40 PM, Luca wrote:

...
I recommend checking connectivity between each address pin of U2378 and one
of the working EPROMs.

I checked the connectivity. It is all connected (the corresponding addressing
pin of U2378 is connected to other EPROMs).
In the error light pattern are Ch1-4 lights off?

If you push delta-V/delta-T/slope buttons all at once you will enter the test menu. Then if you push "Trigger coupling" up button scope should run a small diagnostic. I don't think EPROM checksum is executed from that menu but it is worth a try.

Ozan

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