Date   
Re: Tek 7603 Followed Me Home

Chuck Harris
 

There is very little value in measuring the resistance
across these filter capacitors.

The ripple measurements tell the tale. If you had a scope
to use to look at the voltage across that capacitor, you
would see the unambiguous sign of a bad capacitor..

Replace the capacitor and move on.

-Chuck Harris

Robert Hay wrote:

Hmm, poor reporting on my part.

I measured the _Ohms_ across C808, which is on the (damn not -15) -50 volt
unregulated, and it measures about 7k Ohms. This was to correct my previous email
saying I had measured 0.0 Ohms.

Bob.

Re: 7S12 Extender.

Pete Lancashire
 

When you find out how about some pictures and measurements.

On Sun, Sep 9, 2018, 2:58 PM William Himbert via Groups.Io <wah_1003=
yahoo.com@groups.io> wrote:

I am in Eastern Pennsylvania. I can send my address off group.



Re: Tek 7603 Followed Me Home

Chuck Harris
 

One other thing:

Whenever I find a bad capacitor, I take a look at
all other examples of the same make and type.

I usually will replace them all as a matter of course.

When it comes to replacing the twist lock metal
can capacitors, I will often make an adapter board,
and mount a modern capacitor, or several if appropriate.

-Chuck Harris

Chuck Harris wrote:

There is very little value in measuring the resistance
across these filter capacitors.

The ripple measurements tell the tale. If you had a scope
to use to look at the voltage across that capacitor, you
would see the unambiguous sign of a bad capacitor..

Replace the capacitor and move on.

-Chuck Harris

Robert Hay wrote:
Hmm, poor reporting on my part.

I measured the _Ohms_ across C808, which is on the (damn not -15) -50 volt
unregulated, and it measures about 7k Ohms. This was to correct my previous email
saying I had measured 0.0 Ohms.

Bob.


Re: Tek 7603 Followed Me Home

bobh@joba.com
 

I was planning to buy some of those adapter boards on ebay.  I bought some small vector boards as well as a 1000 ufd 75 volt cap for testing today.  I may try making an adapter board.  Appreciate all the help and insights.

See https://groups.io/g/TekScopes/album?id=71341 !

Bob.

On 9/11/2018 10:15 AM, Chuck Harris wrote:
One other thing:

Whenever I find a bad capacitor, I take a look at
all other examples of the same make and type.

I usually will replace them all as a matter of course.

When it comes to replacing the twist lock metal
can capacitors, I will often make an adapter board,
and mount a modern capacitor, or several if appropriate.

-Chuck Harris

Chuck Harris wrote:
There is very little value in measuring the resistance
across these filter capacitors.

The ripple measurements tell the tale. If you had a scope
to use to look at the voltage across that capacitor, you
would see the unambiguous sign of a bad capacitor..

Replace the capacitor and move on.

-Chuck Harris

Robert Hay wrote:
Hmm, poor reporting on my part.

I measured the _Ohms_ across C808, which is on the (damn not -15) -50 volt
unregulated, and it measures about 7k Ohms. This was to correct my previous email
saying I had measured 0.0 Ohms.

Bob.

Re: Tek 7603 Followed Me Home

bobh@joba.com
 

BTW, if you are interested in other 7603 entries in the photo section of groups.io,  login on the web and go to the TekScopes photos section.  If you sort by title it should show albums with titles starting with numbers.  At the bottom of the screen you can jump to other pages of albums.  The 11th page, for me, was the start of the 7603 albums and there are quite a few.

Bob.

On 9/11/2018 11:53 AM, Robert Hay wrote:
I was planning to buy some of those adapter boards on ebay.  I bought some small vector boards as well as a 1000 ufd 75 volt cap for testing today.  I may try making an adapter board.  Appreciate all the help and insights.

See https://groups.io/g/TekScopes/album?id=71341 !

Bob.

On 9/11/2018 10:15 AM, Chuck Harris wrote:
One other thing:

Whenever I find a bad capacitor, I take a look at
all other examples of the same make and type.

I usually will replace them all as a matter of course.

When it comes to replacing the twist lock metal
can capacitors, I will often make an adapter board,
and mount a modern capacitor, or several if appropriate.

-Chuck Harris

Chuck Harris wrote:
There is very little value in measuring the resistance
across these filter capacitors.

The ripple measurements tell the tale.  If you had a scope
to use to look at the voltage across that capacitor, you
would see the unambiguous sign of a bad capacitor..

Replace the capacitor and move on.

-Chuck Harris

Robert Hay wrote:
Hmm, poor reporting on my part.

  I measured the _Ohms_ across C808, which is on the (damn not -15) -50 volt
unregulated, and it measures about 7k Ohms.  This was to correct my previous email
saying I had measured 0.0 Ohms.

Bob.



Re: 7S12 Extender.

 

Hi William,

The 7S12 outputs an amplitude signal to the vertical channel and a sweep signal to the horizontal channel so two extenders will be necessary. I would think two 7000 Series Flexible Extenders will work. Much less desirable would be two 7000 Rigid Extenders. The 7S12 service manual will specify exactly what you should use.

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Pete
Lancashire
Sent: Tuesday, September 11, 2018 10:11 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7S12 Extender.

When you find out how about some pictures and measurements.

On Sun, Sep 9, 2018, 2:58 PM William Himbert via Groups.Io <wah_1003=
yahoo.com@groups.io> wrote:

I am in Eastern Pennsylvania. I can send my address off group.


--
Dennis Tillman W7PF
TekScopes Moderator

7704A system repair

Peter
 

Hello Everyone,

About ten years ago, among others, I was given a 7704A mainframe and two horizontal units, a 7B70 and a 7B71, condition unknown.
(A friend moved out to the west to live in a sailing boat and dumped all his unneeded test equipment he could not / wanted not to sell.)

Fast forward nine years, I bought three vertical units at a ham-fest, a 7A26, 7A24, and a 7A22.
Finally, a couple of days ago, I plugged in two vertical and two horizontal units into the mainframe and turned the scope on.
Only a very bright dot at the middle of the screen, and the intensity control did not do anything, I turned off the scope quickly.
Finally, with the focus control, I could make the spot into a smallish vertical line that (hopefully) does not damage the screen (still, only had the scope on for very short periods of time).
I could hear snaps coming from the scope, and opening up the side of the scope, the HV unit is arching over behind that black rectifying block.

I guess there is no other way than to dig into the manual, starting with the main frame.
First order of business would be to find out why that intensity control does not work.
Also checking if the PS voltages are in spec.

Any words of wisdom, best approach, to bring that beast back to life?

Thanks, Peter

Re: 310A scope : serial number oddity ? Ideas ?

Vincent Trouilliez
 

On Mon, Sep 10, 2018 at 10:12 PM, David DiGiacomo wrote:
There's no mystery. The serial numbers were not coordinated between the manufacturing sites.
Your scope was the 1239th 310A made on Guernsey, but there could have been a million units made in Beaverton before that.
Yes that makes sense and that's what I therefore thought at first.... but this then poses another problem : in the service manual, in the parts list, when they make a modification to whatever component, when they specify the change point, the S/N they give are 6 digits only, they do not specify the manufacturing plant... so this can only work if there a common numbering system/sequence for all plants.

Or maybe this could be explained because, just a theory : the service manual I downloaded from TekWiki, is most likely, obviously, the US version of the manual. And since the 310A was introduced (correct me if I am wrong) a bit BEFORE the Guernsey plant was built/operational, then maybe the Manual available on Tekwiki was published at the time were Beaverton was the one and only plant in the world, hence they didn't feel the need to explicit the ' B ' prefix all the time in the parts list.
In other words... the parts list present in this particular manual, simply does not apply to non-US 310A scopes... well at least regarding to component changes/modifications.

In my 2232 service manual, a much later scope then, I see that they do specify the 'B' prefix when they modify something...


Vincent Trouilliez

Re: 310A scope : serial number oddity ? Ideas ?

Vincent Trouilliez
 

I would not dissolve the cadmium yellow, just find something to pint it with
to bind it in place. Like acrylic clear paint
applied with a brush in a thin mix. Dissolving it will not yield results
since there is a thick layer of shiny white metal
underneath it ready to turn into cadmium yellow as soon as exposed to the air.
--
John Griessen

Hi John,

Wow, that's extreme ! :-O
I can't see keeping the cadmium, an acceptable solution :-/ Be it for health purposes, or from a restoration point of view.
Some shafts are seized so it will have to go anyway, locally at least.

From what you say, I don't see an acceptable solution then... will keep the scope anyway but not going to restore the thing if I have to leave all that ugly cadmium all over the place :-/



Vince

Re: Bringing up a Tek 555 dual-beam scope

Kurt Rosenfeld
 

I definitely agree about the high-ohm resistors in the CRT circuit. Whether or not they get replaced before first power-up, they should be on the suspect list.

Also, the 0.001uF cap in parallel with the primary of the HV transformer is an often-overlooked source of trouble. The symptoms of that capacitor failing are similar to the symptoms of the transformer failing, i.e., regulator running full-throttle but little or oscillation and no CRT cathode voltage being produced. Obviously it's great news when the problem is just the cap. I've seen this failure more frequently than failure of HV diodes or caps on the secondary side.

On the subject of black beauties, failure is often not an intrinsic state of the capacitor, but really a combination of the capacitor and the circuit where it is used. Circuits where the capacitor has high voltage across its terminals but operates in a high impedance environment are the places I most frequently see black beauties fail. One such place is in the feedback path of the low-voltage power supply. On positive supplies, e.g., +225V in the 555, if C682 has significant DC leakage (e.g., more than 10uA), the equilibrium output voltage will be less than +225V, assuming everything else in the circuit is normal. So even if you choose not to replace the black beauties, it's helpful to keep them on the suspect list. And Tek was nice enough to give us R682 to use as a current sense resistor, so in-circuit measurement with a high-impedance voltmeter is all you need to confirm/refute the leaky cap hypothesis in those circuits. I used to immediately suspect the error amplifier tube, e.g., the 12AX7 V684 in the 555. I don't think that ever turned out to be the problem in any piece of Tek equipment I've worked on.

Re: 7S12 Extender.

William Himbert
 

Hi Dennis: I have a set of the flexible mainframe extenders, I purchased kits for these from John Griessen. I am just looking for the internal card extender right now (the one that can be used to extend the horiz / vert card upward so it can be accessed). The only thing I find challenging with the kit mainframe extenders is being able to hold them from being pulled-out of the mainframe slots while testing. The Tek originals have a frame that locks them in, whereas the kit ones are just cards that easily fall out. I am thinking up some ways to secure them.

Re: 7S12 Extender.

William Himbert
 

Hi Pete: I will. Originally I thought that there was noting in common between horizontal and vertical, but now that I have done some looking there is in fact one derived power supply rail (-12.5 V) that is delivered to both the pulse generator and the sampler. I will check that first.

Re: Tek 7603 Followed Me Home

bobh@joba.com
 

Kevin,

Your recollection is right on.  The disassembly to the point where I can actually get a capacitor can out is extensive.  I have a plastic bin with about twenty screws and 3 or 4 plugin connectors hanging in midair.  It's like a Pandora's box.  Hope it is not cursed or that I get zapped along the way and that I can get it back together without left over parts.

I am thinking I will just replace the one bad cap although I now appreciate the comments about you really don't want to got back in there.  My plan is to use a small vector board to make the negative connections between the four pads on the power supply board.  This just makes the connections more consistent with the other caps, and so there are no undocumented jumpers on the power supply board.

Bob.

On 9/11/2018 7:15 AM, Kevin Wood wrote:
If it helps, I had a 7603 fault due to one of those reservoir caps failing
and, when I got round to checking them, most of the caps on that rectifier
board were on their way out, so I changed them all.

That doesn't mean yours will be, of course, and I'm not generally an
advocate of "re-capping" devices en-masse, but my recollection is that it
was not that easy to get to the board and change the caps either, so it
might be a false economy to change just one or two.

Beware that several of those caps have multiple can connections to the
board and, on some, I think they are used as "jumpers" to connect traces
across the board. If replacing with caps of a different form factor, which
will probably be almost inevitable, you might need to insert jumpers
across some of the can connections. Apologies if I'm delivering lessons in
"egg-sucking"!

Kevin
G7BCS

Chuck,

C808 on the -50 v unregulated is the only cap that tests at 0.0 Ohms and
is the only one that doesn't charge up to some value using the cap test
position on my Tek DMM916.

I ordered some replacement caps although I am not sure whether to
ultimately replace all the cans in the back section.  I may use two
1000ufd 100v caps to replace the 1800 ufd 75 volt C808 on the -50
unreg.  In this case the can is connected to the -50 unregulated rather
than ground so I need to tie all those loose ends together.

I'll hit up the local electronic surplus tomorrow to see if I can find a
replacement cap for testing while waiting for the ones I ordered.

Bob.


Re: 067-0587-01 Calibrator Fixture

Tomas Alori
 
Edited

Thanks Fabio for taking your time!

I actually tried the leveled sine wave test mode and the amplitude of the wave definitely changes with frequency. I made sure the CW indicator was lit as long as I could through the procedure. I used a very cheap freq generator (at 1V) that goes only up to 24Mhz. I set the generator at 24Mhz 1V, adjusted calibrator amplitude until the signal was about 4 divisions (CW on) and went downwards in frequency. There is a weird spot between 1Mhz and 24Mhz where the signal gets an offset of about 0.2 div but amplitude remains constant. At 1Mhz signal is still 4 div. At 100Khz the signal is 4.2 div. 10KHz is 6.2 div. That is as low as I can go since anything below that the signal becomes too strong and the CW indicator turns off. I didn't know if my generator has horrible frequency response, or if its my calibrator, or the mainframe. I tried the same procedure with a 7A26 and didnt see that increase at low frequencies. I am not sure what to make of it to be honest. EDIT: I've since realized that 7A26 test was invalid because I was using a compensated 10x probe which will always show a constant amplitude.

On an unrelated note: I read your profile and it seems we are neighbors! I am from Montevideo, Uruguay. Didn't know we had these kind of scopes in south america. I bought my 7704A from an old couple who didn't seem to know anything about it. It's my first and only scope and I got it for 150 dollars which is quite a steal considering how rare these things are around here. I wouldn't be surprised if it was the only one of it's kind in this country. It's funny how cheap these scopes are in the US. My particular scope seems to have been shipped from the US sometime around late 90s judging from calibration dates (done in the US). The mainframe has "16680 W CLEVELAND AVE" carved on it.

I am an electric engineering student so I am probably much younger (and less knowledgeable) than the average user. I'd probably make my life easier getting a digital scope. However there is something about having a piece of such quality and history that makes me want to bring it back to perfect condition and preserve it forever. It will probably be a never ending battle, but it sure is fun and I'll probably learn a thing or two in the process. The mainframe came with a 7A26, 7A18N, 7A13 (dead) and a 7B50. I've since bought another 7A26, a 7A22, 7B92A, 7D15 and now this calibrator (all from US ebay). In the same vein as your 464 pretty much all plugins have their problems (this is why I'd probably be better off with a digital scope). The 7B92A sometimes has problems triggering (uses the dreaded tunnel diodes) and the non-intensified trace in alt mode is missing. The 7A22 works pretty much perfectly but lost a trimmer cap during shipping. The FREQ mode in 7D15 sometimes stops counting. Both 7A26 have non-functioning top channels. The trace in the mainframe has a modulating Z-Axis which shows up as a horzontal running pattern. The CRT tube makes some crackling noises and there is a point in the intensity knob where the CRT goes down in brightness. Not too sure if this is a case of double peaking or if its the limiter doing its job. At peak intensity the CRT is very bright and otherwise healthy. I hope I can get these things fixed faster than they get broken!

Anyway, good to know that there are other 7000 series owners nearby!

Re: Tek 7603 Followed Me Home

Kevin Wood G7BCS
 

Hi Bob,

Sounds like you're on the right track. Of course, it might make sense just
to replace the one cap until you know the condition of the rest of the
scope. I knew mine was good apart from the power supply ripple so knew the
investment in all those caps would be worthwhile.

It also "followed me" - back from a radio rally, by the way! I'm glad it
did. The nice large, bright CRT makes it a nice 'scope to work with.

Best Regards


Kevin

Kevin,

Your recollection is right on.  The disassembly to the point where I can
actually get a capacitor can out is extensive.  I have a plastic bin
with about twenty screws and 3 or 4 plugin connectors hanging in
midair.  It's like a Pandora's box.  Hope it is not cursed or that I get
zapped along the way and that I can get it back together without left
over parts.

I am thinking I will just replace the one bad cap although I now
appreciate the comments about you really don't want to got back in
there.  My plan is to use a small vector board to make the negative
connections between the four pads on the power supply board.  This just
makes the connections more consistent with the other caps, and so there
are no undocumented jumpers on the power supply board.

Bob.

Re: 067-0587-01 Calibrator Fixture

Harvey White
 

On Tue, 11 Sep 2018 20:35:23 -0700, you wrote:

Thanks Fabio for taking your time!

I actually tried the leveled sine wave test mode and the amplitude of the wave definitely changes with frequency. I made sure the CW indicator was lit as long as I could through the procedure. I used a very cheap freq generator (at 1V) that goes only up to 24Mhz. I set the generator at 24Mhz 1V, adjusted calibrator amplitude until the signal was about 4 divisions (CW on) and went downwards in frequency. There is a weird spot between 1Mhz and 24Mhz where the signal gets an offset of about 0.2 div but amplitude remains constant. At 1Mhz signal is still 4 div. At 100Khz the signal is 4.2 div. 10KHz is 6.2 div. That is as low as I can go since anything below that the signal becomes too strong and the CW indicator turns off. I didn't know if my generator has horrible frequency response, or if its my calibrator, or the mainframe. I tried the same procedure with a 7A26 and didnt see that increase at low frequencies. I am not sure what to make of it to be honest.
Since you have only the one scope, then I'd suggest swapping the
vertical and horizontal plugins for right now, and seeing if the two
7A26's behave identically in this configuration. I'd also check the
other 7A26 to see if they both behave the same. They ought to behave
the same in all four slots.

The frame's frequency response ought to be identical.

I just spent some time with the plugin, and ran it with an SG502
(constant amplitude sinewave generator) and an FG502 (function
generator).

Feeding the SG502 into the aux input and picking the non-leveled
setting (not freq-response), gives no difference in the mainframe
response from about 10 Hz (all I did) on up to 20 Mhz or so (all I
did).

With the same setup, but picking freq-response (leveled mode in the
plugin), I do see a large low frequency "hump" in response. It's the
plugin doing this. Now, this is with the "CW leveled" light on. It's
both input amplitude and frequency dependent.

A quick check of the manual says "leveled from 3 Mhz to 500 Mhz
sinewave input".

I'll go out on a limb here and suggest that the "leveled" response you
see at frequencies below 3 Mhz should be disregarded. Not only the
manual but the SG502 suggest that.

I learned a bit today, so thanks.






On an unrelated note: it seems we are neighbors! I am from Montevideo, Uruguay. Didn't know we had these kind of scopes in south america. I bought my 7704A from an old couple who didn't seem to know anything about it. I got it for 150 dollars which is quite a steal considering how rare these things are around here. I wouldn't be surprised if it was the only one of it's kind in this country. It's funny how cheap these scopes are in the US. My particular scope seems to have been shipped from the US sometime around late 90s judging from calibration dates (done in the US). The mainframe has "16680 W CLEVELAND AVE" carved on it.
Well, they were made in the US, so no tariffs. The main "consumers"
were the aerospace industry, perhaps the military, and government
contractors. Since they were "obsoleted" somewhere no later than 2010
(a guess), they're (or did) show up on the surplus market.


I am an electric engineering student so I am probably much younger (and less knowledgeable) than the average user. I'd probably make my life easier getting a digital scope. However there is something about having a piece of such quality and history that makes me want to bring it back to perfect condition and preserve it forever. It will probably be a never ending battle, but it sure is fun and I'll probably learn a thing or two in the process. The mainframe came with a 7A26, 7A18N, 7A13 (dead) and a 7B50. I've since bought another 7A26, a 7A22, 7B92A, 7D15 and now this calibrator (all from US ebay). Pretty much all plugins have their problems (this is why I'd probably be better off with a digital scope).
Not necessarily so. Please see some of my earlier comments on
replacing chips. As long as you have the parts, they are physically
replaceable so you can isolate down to the part and fix something
here.

One of the little "lunchbox" tek scopes, cute, 100 Mhz bandwidth,
almost fits in a briefcase.

Didn't work (wasn't mine).

Took it apart. Power supply board, CPU board, display, input and
processing board.

The only parts that could be easily removed were the power supply
capacitors (which didn't help this one), and the input jacks.

Literally, there were no chips that I could remove because they were
all BGA chips. I could get them out, but the replacements (!) would
have to be available, I'd have to try to make sure all the connections
were OK.

Nope, not having any.

Now I do, rather routinely, deal with 144 pin VQFP (Very Thin Quad
Flatpack) chips, with lead spacings of 0.5mm. So, IF I could get a
Tektronix chip of that variety, I could likely replace it (the 144
pins I can't do well in removal, the 100 pins I can handle; package
size).

Scope was not fixable at my level of equipment.

You've got good stuff there.


The 7B92A sometimes has problems triggering (uses the dreaded tunnel diodes) and the non-intensified trace in alt mode is missing. The 7A22 works pretty much perfectly but lost a trimmer cap during shipping. The 7D15 sometimes the loses the FREQ mode. Both 7A26 have non-functioning
top channels. Hope I can get these fixed faster than they get broken!
I may have parts for 7A26's, as do other people on the group. Feel
free to ask.




Anyway, good to know that there are other 7000 series owners nearby!
I'm in the US, so not nearby.

Harvey




Re: Tek 7603's to ship home

John Griessen
 

While we're noticing that 7603's have easy linear power supplies,
does anyone want some of my too many 7603's? I'm going to be moving a a year or so...
Some are old some more recent, not all have the large screen...
If there is interest in shipped scopes, I'll pull them down from the attic and
put through some paces. Else they will go to craigslist later on.
--
John

Re: Tek 7603's to ship home

Harvey White
 

On Wed, 12 Sep 2018 11:16:16 -0500, you wrote:

While we're noticing that 7603's have easy linear power supplies,
does anyone want some of my too many 7603's? I'm going to be moving a a year or so...
Some are old some more recent, not all have the large screen...
If there is interest in shipped scopes, I'll pull them down from the attic and
put through some paces. Else they will go to craigslist later on.
I could be interested, I rather wanted a 7603R, just because (I have
some rack equipment), but I'm in Florida, and shipping can be nasty
(as well as dangerous to the equipment). Large screen is nice....



Harvey

Re: Tek 7603's to ship home

John Brown
 

John:

Where (at least in general) are you located? I'm grumpy regards the value of shipping the old boat anchor scopes; but they're a good excuse for an interesting drive.

Thanks
John

OT: HV Power-supply manual needed.

Colin Herbert
 

I realise that this is not Tektronix, but it is electronics, at least. I bought a huge British-made, valve-based HV power supply some time ago and I would like to source a manual for it. The actual PSU is an AEI R1103A, but it was also marketed under the Siemens and Ediswan badges (with the same model number) and the Marconi TF1109A is similar, if not identical in the circuitry. I have searched the internet with no result so far. The valve line-up is 2 x 6F12, 1 x 85A2 and 2 x 12E1. It outputs 200-400 VDC in three ranges at up to 200 mA and also has 6.3 VAC at 2 A and 4 A.
I realise that it is a long shot that anyone on this Forum might be able to help, but stranger things have happened and there are so many knowledgeable people here.
To be clear, I am not looking for any discussion relating to the PSU, just a copy of the manual, paper or pdf, or at least a schematic.
Any information gratefully received.
TIA, Colin.