Date   

Re: 465B strange ripple

Chuck Harris <cfharris@...>
 

Hi Michael,

Generally, you won't see the anomalies for most signals,
but when you are trying to get a handle on the low mv
ripples in the power supply, the back feed of current
between the test scope's chassis, and the measuring scope's
chassis is bigger than the signal being measured.

Because the scope probe's shield is very small, the
IR voltage induced in the probe shield cable is on the
order of the same as the ripple you are trying to measure.

The bonding wire in the scope's power cord is too long,
and just isn't heavy enough to link the chassis together.

So, I use a 2-3 foot long #14ga banana jumper between the
two scope's front panels, and the ripple suddenly comes
into spec.

-Chuck Harris



Michael W. Lynch via groups.io wrote:

On Sun, Feb 14, 2021 at 12:12 AM, Chuck Harris wrote:


One tiny note:

When doing ripple tests, it is important that you make a
cable connection between the ground on the scope making the
test, and the scope being tested.
Chuck,

Would you say that it would be good general practice to connect the Test scope chassis and DUT chassis when making other measurements as well, in addition to these for power supply ripple?


(Solved) Re: 7854 - No RO in SCOPE + WF modulates RO in STORED

Ram
 

I managed to understand the working and schematics of the 7854's digital section since I last reported this issue, and fixed the problem. For posterity and for the benefit of anyone who is trying to troubleshoot problems with the 7854 I thought I'd document what I understood. Hope it turns out useful to someone!
- There are several test points of the 7854 accessible from the top side where the digital board get plugged in. These are exceedingly useful. Some waveforms described in the manual are, however, not accessible from these test points. An easy way to create access is to pull out the respective board and solder a header pin to the point in question. Then you can simply plug in a receptacle pin onto the header whenever you need to make an observation. (You need to bend the header pin so it points upwards.)
- The scope display alternates between XY mode (not to be confused with the X vs Y displays for obtaining Lissajous figures) and YT mode. YT mainly handles real-time waveforms and XY mainly handles digitized data and readouts. The two kinds of signals meet at the Vertical Amplifier (and Horizontal Amplifier for horiz signals). One of them is suppressed by the XYINH signal (which is not TTL).
- In this particular case since both signals were getting mixed up, the investigation quickly narrowed down to a few signals including the XYINH signal. This signal is generated in schematic 34 in the Display D/A and Amplifier section, using !DSYOFF, by a few transistors including Q1830 (CA3046). Turned out that one of the transistors in the CA3046 had gone bad and so the XYINH was not able to go positive. Replacing the chip has solved this problem - my scope which was apparently not able to store any waveforms earlier now does so!
It still stops acquisition with an error beep because it is not able to store the readout information (which is missing in the SCOPE mode) and I believe that is due to a bad XY signal. If and when I get round to solving that I'll post my findings here.
Best - Ram


Re: Very Inexpensive 7623A, but Problems

Harvey White
 

Judging from what I've seen of transistor installations, in this case, you want thermal coupling between the two so that their temperatures track.

One way is to have single transistors and have the both fit side by side into a heatsink.

Another would be to have the two transistors mounted in the same package, with or without a heatsink as needed.

That may well explain the different configurations.

I seem to remember seeing both in the same equipment but in different generations.

Harvey

On 2/14/2021 9:37 PM, Jeff Dutky wrote:
Thanks for the explanation. That's kind of what I was expecting for the NS7348s, that they were matched and thermally coupled. My real problem is that I can't seem to find any information on NS7348, and what I've found in the Common Design Parts Catalog (for Tek part # 151-0232-00) has only confused me further.

The service manual calls the part out as

151-0232-00 TRANSISTOR,SILICON,NPN,DUAL NS7348

but the CDPC (1982) lists 151-0232-00 as a 2N2484, and gives some specs, but does not indicate a saturation voltage (see pages 6-10 and 6-14).

If I look up the 2N2484 online, it is NOT a TO-78 package and does not appear to be a dual NPN transistor (it only has three leads).

Further down (in the Transistor Cross Reference Index, on page 9-11, there are several iterations of part 151-0232:

-01 = 2N2919
-02 = 2N2919
-03 = 2N2918
-04 = ITS1276

If I look up 2N2919 online I find what do appear to be dual NPN transistors in a TO-78 package, just like the transistors I have in hand. Same for the 2N2918. My searches for ITS1276 have been essentially fruitless.

Is the 2N2919 a substitute for the NS7348?

I'm surprised that I can't seem to find any information on the NS7348, not online, not in Tek's reference books, and not even in Nat Semi's Transistors Databook (1982). It doesn't help that the parts themselves only have the tektronix part number on them, so I am left wondering if there ever existed such a part as the NS7348.

I know too well that you should always work your way forward from the wall socket when diagnosing problems, but the temptation to start in the middle is often overwhelming, especially when starting from the wall socket requires more effort (I didn't realize until after I had blown a transistor that removing the power supply was easier than it appears). I'd say "live and learn" but I'm in my 50s and I just seem to be getting better at making the same mistakes.

-- Jeff Dutky





Re: Very Inexpensive 7623A, but Problems

Dave Hills
 

It is common for a design engineer to write a part specification for a catalog part with tighter limits than normal
to insure it will work in their circuit. For example he/she may spec beta limits of 150-250, whereas the catalog
spec may be Beta 50-300. The semi house supplying it may then specify some non-JEDC part number and create their
own drawing as well. The data for that part would only exist at the semi house and never see the light of day outside,
explaining why you can't find it. I've written a lot of those myself. You prefer to use the commodity part, but when your
application requirements push the limits of available components, you sometimes have no other choice.

I would not worry about saturation voltage, as this is not a saturated switch application. I have never had any affiliation
with TEK other than purchasing and using their equipment, so I can't comment about their parts lists or cross references.

Those parts probably are sourced from 2N2918 or 2N2919, but it would be nice to know the selection criteria, (usually
Beta or leakage current, I would guess Beta in this application)

Well, I'm in my seventies (barely), and I guess I've finally recognized (let a lot of smoke out) that haste does indeed make waste.

Dave

On Sun, Feb 14, 2021 at 06:37 PM, Jeff Dutky wrote:


Thanks for the explanation. That's kind of what I was expecting for the
NS7348s, that they were matched and thermally coupled. My real problem is that
I can't seem to find any information on NS7348, and what I've found in the
Common Design Parts Catalog (for Tek part # 151-0232-00) has only confused me
further.

The service manual calls the part out as

151-0232-00 TRANSISTOR,SILICON,NPN,DUAL NS7348

but the CDPC (1982) lists 151-0232-00 as a 2N2484, and gives some specs, but
does not indicate a saturation voltage (see pages 6-10 and 6-14).

If I look up the 2N2484 online, it is NOT a TO-78 package and does not appear
to be a dual NPN transistor (it only has three leads).

Further down (in the Transistor Cross Reference Index, on page 9-11, there are
several iterations of part 151-0232:

-01 = 2N2919
-02 = 2N2919
-03 = 2N2918
-04 = ITS1276

If I look up 2N2919 online I find what do appear to be dual NPN transistors in
a TO-78 package, just like the transistors I have in hand. Same for the
2N2918. My searches for ITS1276 have been essentially fruitless.

Is the 2N2919 a substitute for the NS7348?

I'm surprised that I can't seem to find any information on the NS7348, not
online, not in Tek's reference books, and not even in Nat Semi's Transistors
Databook (1982). It doesn't help that the parts themselves only have the
tektronix part number on them, so I am left wondering if there ever existed
such a part as the NS7348.

I know too well that you should always work your way forward from the wall
socket when diagnosing problems, but the temptation to start in the middle is
often overwhelming, especially when starting from the wall socket requires
more effort (I didn't realize until after I had blown a transistor that
removing the power supply was easier than it appears). I'd say "live and
learn" but I'm in my 50s and I just seem to be getting better at making the
same mistakes.

-- Jeff Dutky


Re: Very Inexpensive 7623A, but Problems

 

The manual seems to indicate that the power supply can be removed from the unit without disconnecting any cables, but when I try it appears that several cables (one ribbon cable attached to the backplane, and two cables that disappear behind the readout board) become taught when the power supply is only half way out. The manual shows literally three steps: 1. remove side panels, 2. remove six screws, 3. slide power unit out the rear until it can be set down on the work surface.

I must be missing something.

-- Jeff Dutky


Re: Sampling head extender missing coax connectors

snapdiode
 

PM me


Re: Very Inexpensive 7623A, but Problems

 

Thanks for the explanation. That's kind of what I was expecting for the NS7348s, that they were matched and thermally coupled. My real problem is that I can't seem to find any information on NS7348, and what I've found in the Common Design Parts Catalog (for Tek part # 151-0232-00) has only confused me further.

The service manual calls the part out as

151-0232-00 TRANSISTOR,SILICON,NPN,DUAL NS7348

but the CDPC (1982) lists 151-0232-00 as a 2N2484, and gives some specs, but does not indicate a saturation voltage (see pages 6-10 and 6-14).

If I look up the 2N2484 online, it is NOT a TO-78 package and does not appear to be a dual NPN transistor (it only has three leads).

Further down (in the Transistor Cross Reference Index, on page 9-11, there are several iterations of part 151-0232:

-01 = 2N2919
-02 = 2N2919
-03 = 2N2918
-04 = ITS1276

If I look up 2N2919 online I find what do appear to be dual NPN transistors in a TO-78 package, just like the transistors I have in hand. Same for the 2N2918. My searches for ITS1276 have been essentially fruitless.

Is the 2N2919 a substitute for the NS7348?

I'm surprised that I can't seem to find any information on the NS7348, not online, not in Tek's reference books, and not even in Nat Semi's Transistors Databook (1982). It doesn't help that the parts themselves only have the tektronix part number on them, so I am left wondering if there ever existed such a part as the NS7348.

I know too well that you should always work your way forward from the wall socket when diagnosing problems, but the temptation to start in the middle is often overwhelming, especially when starting from the wall socket requires more effort (I didn't realize until after I had blown a transistor that removing the power supply was easier than it appears). I'd say "live and learn" but I'm in my 50s and I just seem to be getting better at making the same mistakes.

-- Jeff Dutky


Re: Sampling head extender missing coax connectors

 

If you have a male and a female (since I need one for each end of the extender) ;) I'd happily pay postage.

D-sub coax contacts can be had, for example:
https://www.digikey.com/en/products/filter/d-sub-d-shaped-connectors-contacts/332?s=N4IgjCBcoLQdIDGUBmBDANgZwKYBoQB7KAbXDAFYQBdAgBwBcoQQBfVggJlJACUBxOAHYALAAJEhNAA8arIA

For almost $16 for just one pair. Plus postage!
I'm going to check my cable bin, maybe there are some coax contacts as mentioned...


Re: Sampling head extender missing coax connectors

snapdiode
 

Meh, I creatively destroyed my connectors to get the contacts inside. Why not, I don't even know how or why I have a 7W2 in my box of shiny things. If they fit, I can ship them to you for the price of postage.


Re: Sampling head extender missing coax connectors

-
 

"They could be dsub coaxial contacts, as used in 13W3 connectors. I'd have
to measure it.

...beats me."

If they are then those same contacts were used in some of the old Sun
and SGI monitors and you might be able to get one of the video cables and
rob the connectors out of it. HP also used the same contacts in various
extender and unit interconnect cables.

On Sun, Feb 14, 2021 at 7:27 PM snapdiode via groups.io <snapdiode=
yahoo.com@groups.io> wrote:

Whoever did that did a pretty despicable thing... This connector kind of
looks like a SMB but isn't. The manual seems to suggest it is built of
parts intended for other things.

The inner female conductor is a DM53740-5001 which still exists today

https://www.mouser.ca/ProductDetail/ITT-Cannon/DM53740-5001/?qs=qCxwlXJ4fnyo0PCCdeMbuA==

...which says it's meant for RG187 or RG188 coax, which leads to these
connectors

http://www.coax-connectors.com/products/cables/ab/rg187.aspx
http://www.coax-connectors.com/products/cables/ad/rg188.aspx

They could be dsub coaxial contacts, as used in 13W3 connectors. I'd have
to measure it.

...beats me.






Re: Sampling head extender missing coax connectors

 

I'll look for your album, thanks.

The NorComp contacts are proving elusive (DigiKey lists them as "obsolete" and no price. Of course).

However, it appears that other manufacturers also make similar coaxial contacts, for example:
https://www.mouser.com/datasheet/2/18/amphenol_d-sub_inserts-1157297.pdf

I might as well chase this mirage while I'm waiting on Schottky (and tunnel) diodes ;)


2 photos uploaded #photo-notice

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

The following photos have been uploaded to the D-sub coaxial connectors used in 012-0124-00 extender album of the TekScopes@groups.io group.

By: snapdiode <snapdiode@...>


Re: Sampling head extender missing coax connectors

snapdiode
 

I think that will be the bigger problem, naturally the connectors need to be mounted at the right distance to work... Check out my exciting photo album.


Added album D-sub coaxial connectors used in 012-0124-00 extender #photo-notice

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

snapdiode <snapdiode@...> added the album D-sub coaxial connectors used in 012-0124-00 extender: Looks like these fit


Re: Sampling head extender missing coax connectors

 

Those look good, but I wonder how the contacts were originally mounted in the extender cable. There is no mark where a nut or clip would have been, and no separate bracket. Perhaps it's a push-in lock (as it works in the D-sub connector body)?


Re: Sampling head extender missing coax connectors

snapdiode
 

Forgot to link

https://www.norcomp.net/series/682m-series-solder-cup

sort of looks right. Don't know.


Re: Sampling head extender missing coax connectors

 

Thanks! Please post if you find out more details or measurements :)
The extender is still partially useful to start debugging the S-1 once I get the Schottky diodes from Digikey, assuming that doesn't fix it right away.
Meanwhile I can just leave the sampling heads in the scope and run a GR-874 cable to whatever I'm playing with. I've got a bunch of those cables in various lengths/delays and a variety of 874 adapters too.


Re: Sampling head extender missing coax connectors

snapdiode
 

Whoever did that did a pretty despicable thing... This connector kind of looks like a SMB but isn't. The manual seems to suggest it is built of parts intended for other things.

The inner female conductor is a DM53740-5001 which still exists today https://www.mouser.ca/ProductDetail/ITT-Cannon/DM53740-5001/?qs=qCxwlXJ4fnyo0PCCdeMbuA==

...which says it's meant for RG187 or RG188 coax, which leads to these connectors

http://www.coax-connectors.com/products/cables/ab/rg187.aspx http://www.coax-connectors.com/products/cables/ad/rg188.aspx

They could be dsub coaxial contacts, as used in 13W3 connectors. I'd have to measure it.

...beats me.


Re: EIP 101B Spectrum Analyzer Plug-In - MPC "Panoramic Rx P/I"

Alain Mionnet
 

If it is a plug-in for Tek Scopes with Plug-in as 1Lxx you may create an album for the MPC.
I have tested the 101A. Video output seems not correct for the sensitivity.
I have the bandpass filter but the CF resolution is not enough fine with the potmeter definition.(because wire-wound)
I wrote many lines , must be read again.

Alain

France


Re: Sampling head extender missing coax connectors

 

After searching through the TekWiki connector page, I think it might be an SMB?

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