Date   

Re: Rail Probes?

John Gord
 

In addition to good connection methods (very short grounds, etc.), a valuable technique for these measurements is to loop the probe cable a few times through a large ferrite core (split cores are easiest). This minimizes the added high frequency noise from ground currents between the DUT and measuring scope. I learned this from a designer of multi-kilowatt power converters.
--John Gord

On Thu, Apr 23, 2020 at 02:43 PM, Ed Breya wrote:


I had never heard of these, but from the data I'd say their usefulness is
mostly in the form of convenience. The exact same kind of measurements have
been done before, by many, for decades - I've done it. You measure the DC and
low frequency content with a regular scope input, and the high frequency
content with an AC-coupled 50 ohm wide BW input. These "power rail" probes
just combine the measurements into one channel, and add DC offsetting - look
at the 7A13 for an earlier example.

They are intended for low impedance sources, like power supply outputs, to
look at interference, ripple, and noise. There is a generalized term for all
of this, called PARD. If you want to see really high frequency content, you
use 50 ohm wide BW gear - a scope for time domain, or an SA for frequency. The
important thing is to isolate the DCV of the supply by AC-coupling, and most
importantly, to protect the equipment from surges that occur during
connect/disconnect, power up/down, and PS or load faults, etc.

In the block diagram, it may be shown simply as AC-coupling, but in the
details you would find that the HF signal path is all RF, 50 ohm environment,
including the RF coupling cap, with sufficient voltage rating.(not just any
old cap), and various protection circuitry on the 50 ohm output side going to
the equipment.

So, if you can live with the inconvenience of using a regular scope input or a
7A13 for DC and LF, and having to rig up a fairly simple AC-coupling and
protection circuit (the fanciness and complexity depend mostly on the required
BW) for HF, you can save the 4 grand or so.

Also note that the key to HF performance and CMRR is to carry the signals
directly in coax, with minimal impedance connections. You can get some ideas
looking at the optional accessories and how they attach to the DUT - that's
the part that really makes it work.

Ed




Re: 577 curve tracer 177 test fixture current per division troubleshoot

teamlarryohio
 

I just fired mine up on 25V with the front porch unplugged. No yellow
light.
-ls-


Re: Troubleshooting and repairing a 7704A instrument

 

I am pleased of having "discovered" the data sheets of most of the integrated circuits of the 7000s in tekwiki. Most of you have probably benefited from these data sheets already.

These are the schematics and some logic diagrams of the parts 155-0009, 155-0010, 155-0012, 155-0013, 155-0022, 155-0067. Not included is the 155-0078, the big hybrid at the output of the vertical amplifier. This one may be still withheld as a trade secret? I also see that these integrated circuits are still available, something reassuring if one ever needs one. Fortunately, the ones on my 7K seem to work well.

The advantage of these data sheets is that one can at last understand the logic of the circuit diagrams in the mainframe and plugins, for example the vertical channel in the 7A26, without having to guess from the "circuit description".

On another issue, I have found a solution for the 50 Mhz parasitic oscillation in the horizontal amplifier of my 7704A. The solution is to keep connected a X10 probe to one of the outputs stages, a 15 pF capacitance?,ha ha.
I don't have an electronic lab at home, but I do everything in my office. And I had to start populating it with components since I started to play again with electronics a few month ago. Now I have to wait for an order of small pF caps! In the meantime, the probe is connected there, and I don't mind it, having enough probes. I could even find space in the 7704 display unit to leave it there permanently... (I'm kidding)
I had dismounted the horizontal amplifier to change its two decoupling capacitors of the +- 15V to little ceramics. In doing so I discovered that one of these had a broken lead, so the scope had worked without it for undefined time. When I did the exchange and tried again, the problem of oscillations persisted, confirming my idea that these caps are there mainly for "good practice".

What I find is that two transistors in the differential output drive, U4356 and U4366, get very hot, even after having squelched the 50 Mhz oscillation. I question if this is normal? Time will tell.

Ernesto


Re: Rail Probes?

Jim Ford
 

PARD being an acronym for Periodic And Random Disturbance, for those who haven't seen the term before. Jim Ford Sent from my Verizon, Samsung Galaxy smartphone

-------- Original message --------From: "Ed Breya via groups.io" <edbreya=yahoo.com@groups.io> Date: 4/23/20 2:43 PM (GMT-08:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Rail Probes? I had never heard of these, but from the data I'd say their usefulness is mostly in the form of convenience. The exact same kind of measurements have been done before, by many, for decades - I've done it. You measure the DC and low frequency content with a regular scope input, and the high frequency content with an AC-coupled 50 ohm wide BW input. These "power rail" probes just combine the measurements into one channel, and add DC offsetting - look at the 7A13 for an earlier example.They are intended for low impedance sources, like power supply outputs, to look at interference, ripple, and noise. There is a generalized term for all of this, called PARD. If you want to see really high frequency content, you use 50 ohm wide BW gear - a scope for time domain, or an SA for frequency. The important thing is to isolate the DCV of the supply by AC-coupling, and most importantly, to protect the equipment from surges that occur during connect/disconnect, power up/down, and PS or load faults, etc. In the block diagram, it may be shown simply as AC-coupling, but in the details you would find that the HF signal path is all RF, 50 ohm environment, including the RF coupling cap, with sufficient voltage rating.(not just any old cap), and various protection circuitry on the 50 ohm output side going to the equipment.So, if you can live with the inconvenience of using a regular scope input or a 7A13 for DC and LF, and having to rig up a fairly simple AC-coupling and protection circuit (the fanciness and complexity depend mostly on the required BW) for HF, you can save the 4 grand or so.Also note that the key to HF performance and CMRR is to carry the signals directly in coax, with minimal impedance connections. You can get some ideas looking at the optional accessories and how they attach to the DUT - that's the part that really makes it work.Ed


Re: 577 curve tracer 177 test fixture current per division troubleshoot

DW
 

I started to look at taking the switch out of the 177 fixture of the donor and so far this is appearing the be a nightmare of a task.

It looks like everything is built on top of other things, in order to get to the switch most of the fixture has to be completely disassembled. I wonder if anyone else has undertaken the task of working on a 177 test fixture?

On the manual it states to just simply remove the knob which is easy enough, and then the hex bolts which one side is not so hard to get at but other is way back in there. Finally desolder the leads from the switch however the front plate of the fixture is in the way for some of the leads.

I notice there is a plate over top of the fixture, it would be nice if I could just remove the front plate and remove the nuts for the switch. Wish I could just take out a few screws and out the board comes and then I can enjoy the working current division ranges along with my sanity


Re: Rail Probes?

Ed Breya
 

I had never heard of these, but from the data I'd say their usefulness is mostly in the form of convenience. The exact same kind of measurements have been done before, by many, for decades - I've done it. You measure the DC and low frequency content with a regular scope input, and the high frequency content with an AC-coupled 50 ohm wide BW input. These "power rail" probes just combine the measurements into one channel, and add DC offsetting - look at the 7A13 for an earlier example.

They are intended for low impedance sources, like power supply outputs, to look at interference, ripple, and noise. There is a generalized term for all of this, called PARD. If you want to see really high frequency content, you use 50 ohm wide BW gear - a scope for time domain, or an SA for frequency. The important thing is to isolate the DCV of the supply by AC-coupling, and most importantly, to protect the equipment from surges that occur during connect/disconnect, power up/down, and PS or load faults, etc.

In the block diagram, it may be shown simply as AC-coupling, but in the details you would find that the HF signal path is all RF, 50 ohm environment, including the RF coupling cap, with sufficient voltage rating.(not just any old cap), and various protection circuitry on the 50 ohm output side going to the equipment.

So, if you can live with the inconvenience of using a regular scope input or a 7A13 for DC and LF, and having to rig up a fairly simple AC-coupling and protection circuit (the fanciness and complexity depend mostly on the required BW) for HF, you can save the 4 grand or so.

Also note that the key to HF performance and CMRR is to carry the signals directly in coax, with minimal impedance connections. You can get some ideas looking at the optional accessories and how they attach to the DUT - that's the part that really makes it work.

Ed


Re: Vacuum forming 7K interface "covers"

Eric
 

I could be wrong but I believe the part number is shared across the entire 7K line. Handling with care is needed as depending on the age of the scope could be 50 + years of thermally cycled plastic.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of David C. Partridge
Sent: Thursday, April 23, 2020 4:11 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Vacuum forming 7K interface "covers"

Yes, same part on 7603 etc. 'scopes.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Michael W. Lynch via groups.io
Sent: 23 April 2020 19:42
To: TekScopes@groups.io
Subject: Re: [TekScopes] Vacuum forming 7K interface "covers"

If I had one of these as a sample, I would gladly attempt to design and 3D print one of suitable quality.

Would this be a part that would be found in the 76xx series Scopes? If so, is this easy to access without totally destroying the scope? I have two of these scopes, so I might obtain a sample from one of these scopes.

Looking at the document that Håkan posted, they do not appear that complex. I would need to see the actual part to determine if it was possible to produce a 3D print of the item.

Sincerely,

--
Michael Lynch
Dardanelle, Arkansas


Re: 577 curve tracer 177 test fixture current per division troubleshoot

Eric
 

I can run the measurement I have an (as far as I know) good 577 though my 177 is in need of a looking cap before I can use it.

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of DW
Sent: Thursday, April 23, 2020 3:12 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 577 curve tracer 177 test fixture current per division troubleshoot

I would say to have someone independently run a test on their 577 is still desired, though if they are willing and at their own convenience.

I am in the process where I am thinking about transplanting the current per division switch from a donor 177 but their serial numbers are different

The donor 177 is B052747
The 177 that will get the replacement part is B020417

I have looked at both switches and they appear to look the same with the same connections and similar resistors with similar placements. Looking at the table above the values are only slightly different. I would then conclude that replacement should be fine.


Re: Vacuum forming 7K interface "covers"

 

Yes, same part on 7603 etc. 'scopes.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Michael W. Lynch via groups.io
Sent: 23 April 2020 19:42
To: TekScopes@groups.io
Subject: Re: [TekScopes] Vacuum forming 7K interface "covers"

If I had one of these as a sample, I would gladly attempt to design and 3D print one of suitable quality.

Would this be a part that would be found in the 76xx series Scopes? If so, is this easy to access without totally destroying the scope? I have two of these scopes, so I might obtain a sample from one of these scopes.

Looking at the document that Håkan posted, they do not appear that complex. I would need to see the actual part to determine if it was possible to produce a 3D print of the item.

Sincerely,

--
Michael Lynch
Dardanelle, Arkansas


Re: 577 curve tracer 177 test fixture current per division troubleshoot

Dave Casey
 

Well of course their serial numbers are different.
If you're worried about it, the manual should tell you the serial number
effectivity for any component changes.

Dave Casey

On Thu, Apr 23, 2020 at 2:12 PM DW <wilson2115@...> wrote:

I would say to have someone independently run a test on their 577 is still
desired, though if they are willing and at their own convenience.

I am in the process where I am thinking about transplanting the current
per division switch from a donor 177 but their serial numbers are different

The donor 177 is B052747
The 177 that will get the replacement part is B020417

I have looked at both switches and they appear to look the same with the
same connections and similar resistors with similar placements. Looking at
the table above the values are only slightly different. I would then
conclude that replacement should be fine.





Re: 577 curve tracer 177 test fixture current per division troubleshoot

DW
 

I would say to have someone independently run a test on their 577 is still desired, though if they are willing and at their own convenience.

I am in the process where I am thinking about transplanting the current per division switch from a donor 177 but their serial numbers are different

The donor 177 is B052747
The 177 that will get the replacement part is B020417

I have looked at both switches and they appear to look the same with the same connections and similar resistors with similar placements. Looking at the table above the values are only slightly different. I would then conclude that replacement should be fine.


Re: Rail Probes?

dnmeeks
 

Thanks, yeah I see the data sheet. I was hoping to know exactly how it's made. What's inside. The real scooby.


Re: Vacuum forming 7K interface "covers"

Michael W. Lynch
 

If I had one of these as a sample, I would gladly attempt to design and 3D print one of suitable quality.

Would this be a part that would be found in the 76xx series Scopes? If so, is this easy to access without totally destroying the scope? I have two of these scopes, so I might obtain a sample from one of these scopes.

Looking at the document that Håkan posted, they do not appear that complex. I would need to see the actual part to determine if it was possible to produce a 3D print of the item.

Sincerely,

--
Michael Lynch
Dardanelle, Arkansas


Re: 577 curve tracer 177 test fixture current per division troubleshoot

David Berlind
 

should I assume, based on this last note, that having someone else
independently run the 25V collector test on their 577 is no longer needed?
I have a 577 in storage that I've earmarked for Dennis T's Eico 667 mod. I
haven't even turned it on since acquiring it.

On Thu, Apr 23, 2020 at 12:07 PM DW <wilson2115@...> wrote:

I used a LCR meter set to Z with a voltage level set to 0.3 volts. With
the test fixture taken apart I connected one probe to TP617 which is next
to the plug interface of the fixture with Q626 printed right next to it and
a disk capacitor, I put the other probe on S640 where the thick blue and
white wire connects to it. In the 177 schematic it looks like probing
between these locations can get an idea of the resistance behavior as I
move S630 Current per division around. I have another 177 test fixture
which is broken which I compared to to, here are my results

177 A is a broken test fixture I have to test against
177 B is the test fixture I am using but when current per division 0.5A
0.2A and 0.1A selections not working

If you look at the tests results below you will find a clear difference
between the measurements of 177A and 177B at 0.5A 0.2A 0.1A, A measures
0.25 ohms while B is measuring in mega ohms, something is definitely going
open on the switch! No wonder my read out disappears when selecting between
05A to 0.1A. I am wondering how difficult it is to transplant the switch
from the broken 177 test fixture to the working one, would this disturb the
calibration I wonder causing issues with accurate readings?

Selection Reading from 177 A Reading from 177 B
======= ================ =============
2A 0.154 ohm 0.230 ohm
1A 0.161 ohm 0.222
.5A 0.258 ohm *2.74 m ohm*
.2A 0.247 ohm *2.74 m ohm*
.1A 0.251 ohm *2.73 m ohm*
50mA 1.146 ohm 1.245 ohm
20mA 1.144 ohm 1.240 ohm
10mA 1.142 ohm 1.244 ohm
5mA 10.197 ohm 10.22 ohm
2mA 10.189 ohm 10.22 ohm
1mA 10.192 ohm 10.22 ohm
.5mA 199.65 ohm 200.4 ohm
.2mA 199.64 ohm 200.4 ohm
.1mA 199.64 ohm 200.4 ohm
50uA 1.9961 k 2.011 k ohm
20uA 1.9961 k 2.011 k ohm
10uA 1.9961 k 2.011 k ohm
5uA 19.971 k 20.04 k ohm
2uA 19.970 k 20.04 k ohm
1uA 19.971 k 20.04 k ohm
.5uA 196.80 k 196.3 k ohm
.2uA 196.80 k 196.3 k ohm
.1uA 196.80 k 196.3 k ohm
50nA 991k 955 k ohm
20nA 991k 955 k ohm
10nA 991k 955 k ohm
5nA 1.15m 1.1 m ohm
2nA 1.15m 1.1 m ohm




Re: Vacuum forming 7K interface "covers"

Ed Breya
 

I popped one of the covers from a 7904 main interface board that I mentioned earlier, that looked different from the batch I looked at. They appeared to have angled ends versus square. On close inspection of all eight in situ, I found that the ends were still just cut, but more sloppily, and at various angles - no two were identical at the ends. They were basically finished the same way as the others. On the one I popped, sure enough, there are eight gate (or maybe ejector) marks on the inner (concave) surface, as Chuck described previously.

So, I'm guessing this kind were likely injection-molded in long strips, then cut to make multiple covers, versus the extruded type that were likewise cut up. The end result is the same part shape, more or less. I don't know which is newer or better, and neither looks like the "old" ones that were failing according to the document recently posted:

http://www.hakanh.com/dl/docs/hardtofind/200-0950-00.pdf

I don't recall ever seeing one of these very old types with the "notched" end features.

So anyway, the exact processes and materials used are still somewhat a mystery, but at least we know the shape. I think it would be great if someone can come up with a newer yet and improved version using 3D printing, that may not have to be an exact replica, but can incorporate the necessary features, and be sturdier, and still fit within all the mechanical constraints.

One thing that occurs to me is that the part number should have been listed in Tek's mechanical parts* catalog. I don't know if this catalog is among the ones recently (last couple years or so?) put up on tekwiki. If so, there may be more info available. *Or alternatively, maybe in the electro-mechanical one, as a sub-part to a listed connector?

Ed


Re: Rail Probes?

Bruce Atwood
 

Data sheet:
https://www.tek.com/datasheet/active-power-rail-probes

Interesting, but U$4300.00 for the cheap one. Accessories are extra.


Rail Probes?

dnmeeks
 

Hey team -
I changed roles at work and I ran into a new animal called a rail probe. I have never seen one of these things before, even though I have been doing analog and power for a few decades now.
Does anyone know what's inside one of these? I see the input impedance is relatively low, and it gets lower with frequency... and the attenuation is something like 1.2.
It would help me understand their usefulness if I could see the circuitry inside - compared to a good passive probe with proper shielding.
Thanks
dan


Any interest in Tek 360 scope plug ins?

kim.herron@sbcglobal.net
 

Hi Gang!

I have salvaged 5 of these plug ins from the scrap barrel. They are missing the CRT's. There was only one good one, and it's on E-Bay. If someone here is interested in it, I can kill the auction. There are several different configurations of these plugins and there is enough stuff here that if someone needs parts or whatever, I'd rather see it go to somebody here on the group.

Thanks for reading the mail.


Re: 577 curve tracer 177 test fixture current per division troubleshoot

DW
 

I used a LCR meter set to Z with a voltage level set to 0.3 volts. With the test fixture taken apart I connected one probe to TP617 which is next to the plug interface of the fixture with Q626 printed right next to it and a disk capacitor, I put the other probe on S640 where the thick blue and white wire connects to it. In the 177 schematic it looks like probing between these locations can get an idea of the resistance behavior as I move S630 Current per division around. I have another 177 test fixture which is broken which I compared to to, here are my results

177 A is a broken test fixture I have to test against
177 B is the test fixture I am using but when current per division 0.5A 0.2A and 0.1A selections not working

If you look at the tests results below you will find a clear difference between the measurements of 177A and 177B at 0.5A 0.2A 0.1A, A measures 0.25 ohms while B is measuring in mega ohms, something is definitely going open on the switch! No wonder my read out disappears when selecting between 05A to 0.1A. I am wondering how difficult it is to transplant the switch from the broken 177 test fixture to the working one, would this disturb the calibration I wonder causing issues with accurate readings?

Selection Reading from 177 A Reading from 177 B
======= ================ =============
2A 0.154 ohm 0.230 ohm
1A 0.161 ohm 0.222
.5A 0.258 ohm *2.74 m ohm*
.2A 0.247 ohm *2.74 m ohm*
.1A 0.251 ohm *2.73 m ohm*
50mA 1.146 ohm 1.245 ohm
20mA 1.144 ohm 1.240 ohm
10mA 1.142 ohm 1.244 ohm
5mA 10.197 ohm 10.22 ohm
2mA 10.189 ohm 10.22 ohm
1mA 10.192 ohm 10.22 ohm
.5mA 199.65 ohm 200.4 ohm
.2mA 199.64 ohm 200.4 ohm
.1mA 199.64 ohm 200.4 ohm
50uA 1.9961 k 2.011 k ohm
20uA 1.9961 k 2.011 k ohm
10uA 1.9961 k 2.011 k ohm
5uA 19.971 k 20.04 k ohm
2uA 19.970 k 20.04 k ohm
1uA 19.971 k 20.04 k ohm
.5uA 196.80 k 196.3 k ohm
.2uA 196.80 k 196.3 k ohm
.1uA 196.80 k 196.3 k ohm
50nA 991k 955 k ohm
20nA 991k 955 k ohm
10nA 991k 955 k ohm
5nA 1.15m 1.1 m ohm
2nA 1.15m 1.1 m ohm


Re: 7K Fiber Optic Readout Holes WAS Vacuum forming 7K interface "covers"

 

So that's why!

My 547 has a round opening on the left cover just in front of the vertical amplifier's connection to the vertical plates.
The opening is covered with a metal plate, of the same color of the cover.

So now I know what to do when I want to connect directly to the CRT plates!

Ernesto