Date   

Re: CRT question

Craig Sawyers <c.sawyers@...>
 

My guess is, just like analog meters, linearity between 1/3 and
2/3 is best.
The numbers are probably more generous for CRT, but there is something
there.
I think that there is a bandwidth issue too. The 545A is the same vintage
as the 575 curve tracer. The 545A has a 10ns rise time for the mainframe
(35MHz) and has 4cm deflection. The 575 has 8cm. Now the CRT for the 575
also went in the 525 TV waveform processing 'scope, with a maximum bandwidth
of 5MHz.

So I suspect that in the 50's, there was a problem is getting high
deflection and bandwidth. It was also probably limited by the available
drive from wide band deflection amps at the time (the famous Tek distributed
amp).

Craig


Inendiary discs, was Tek 465 repair hints, svc manual? (fix story)

Craig Sawyers <c.sawyers@...>
 

Like a 3 volt p-p signal riding on 6 volts of DC
with a .01
50 volt disc. Where did my signal go? Took the cap out and measures 4
ohms. No stress there but the cap failed. So it dont suprise me either,
but its not the first thing I go looking for either.
One evening, listening to the Television sound through a stereo amp (50W)
and speakers the amp died - smoke and flames. Took the lid off, and all
that had happened was a 0.1uF disc ceramic decoupler had gone short and
crowbarred the power supply. There was enough energy in the smoothing caps
to incinerate it after the fuse had blown (around 20J).

Craig


Re: Differential probe

Craig Sawyers <c.sawyers@...>
 

could you please give me the schematic of a differential probe?
Er - there's all sorts of differential probes. There are active FET probes,
and passive ones too. The active ones are seriously difficult to get right.
Commercial active designs have to fulfill several criteria:

(a) They need to be compact
(b) They need to have a high bandwidth (>100MHz)
(c) They need to have excellent common-mode rejection over the bandwidth

Meeting these requirments leads to a complicated design, with many
adjustments to tweak the common mode. The Tek P6046 has a CMRR of 20,000:1
up to 60kHz, reducing to 2000:1 at 50MHz. The probe head has 13 miniature
transistors in it and around a dozen adjustments. The associated amplifier
has a further 12 transistors and a further 6 adjsutments. Oh - and there's
a stabilized power supply with 9 transistors.

So buying one from eBay is something of a bargain, really. I got a good
deal - I bought a brand new one (everyting still packed in the baggies, and
the Tek tag on the lead) for around $100.

Alternatively there are wide bandwidth passive differential probes, which
are a good deal easier to hand craft. These don't have the high input
impedance of the FET probes, but have very low input capacitance, which is
more important at hundreds of megahertz. Have a look at
http://emcesd.com/pdf/cd94scr.pdf. This is from a site containing lots of
interesting information on high frequency measurement techniques at
http://www.emcesd.com/.

Craig


Re: Tek 465 repair hints, svc manual? (fix story)

Miroslav Pokorni
 

The mylars are supposed to be self-healing type, if there is enough energy
in the circuit to burn the foil, otherwise short remains. Mylar insulation
exhibits high resistance, so ESD, probably repeated, might have a part in
initial failure. In old times, ESD was not taken seriously; I believe even
explosives people did not take notice of ESD until around mid 80s.

As for ceramics, a physical crack opens all sorts of ways to build up a
short, primarily through whisker growth (metal used for plates is the
culprit). And again, if there is not enough energy in circuit to clear up
initial short or clearing does not happen while short is still nascent, the
whiskers can build up over time to successfully short even a power supply.
The crack forms primarily through physical or thermal abuse of cap. Those
are micro-cracks, certainly not visible to a naked eye and quite possibly
not visible under a microscope, either. You would have use a penetrant to
detect them.

Back in early 80s, when high capacity ceramic caps, at the time that was
0.010 and 0.050 microFarads, there was a series consideration that such caps
could not be reliable because of high failure rate. I do not think that
silver ink was used at that time, because that was just around time of Hunt
brother's silver gig, so silver was still expensive. Over time, cap industry
fixed the problem, but if you want to retain the fait in quality of caps,
never, ever take a tour of a cap factory. To paraphrase worn out saying:
'about sausages, laws and ceramic caps it is best not to know how they are
made'.

Regards

Miroslav Pokorni

----- Original Message -----
From: "Mark Anton" <heightstv@hotmail.com>
To: <TekScopes@yahoogroups.com>
Sent: Monday, February 17, 2003 11:13 PM
Subject: Re: [TekScopes] Re: Tek 465 repair hints, svc manual? (fix story)








In many types of equipment, I have found shorted disc and mylar caps just
often enough to be aware that it happens. Not really frequent at all, but
often enough to know that they never go bad.
Actually have found shorted discs where the voltage should not have been a
problem at all. Like a 3 volt p-p signal riding on 6 volts of DC with a
.01
50 volt disc. Where did my signal go? Took the cap out and measures 4
ohms. No stress there but the cap failed. So it dont suprise me either,
but its not the first thing I go looking for either.

Mark.
----Original Message Follows----
From: E K <dataclue@yahoo.com>
To: TekScopes@yahoogroups.com
CC: E K <dataclue@yahoo.com>
Subject: [TekScopes] Re: Tek 465 repair hints, svc manual? (fix story)
Date: Mon, 17 Feb 2003 18:58:13

-- the Z axis circuitry is coupled to the horizontal amp via R1475, so it
was the latter after all.
Turns out the supply does not come back even with all the transistors
removed!
7. There are very few possible paths between +110 and ground with the
output
transistors out of circuit, found a drop of several volts across R1283 (a
47Ohm resistor). Aha! It's connected to ground via C1283, a 0.01 uF 150V
ceramic cap enough, removing it restores the supply. Once it's removed, I
of
course notice a small charred spot next to one of the leads, 8. Replacing
the 0.01 uF cap brings back the supply and the horizontal sweep. You may
have heard about the tantalum caps in these scopes, I know I did. But the
ceramic caps must have also come from a bad batch or weren't really rated
150V.
.
E K <





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Re: CRT question

Miroslav Pokorni
 

My guess is, just like analog meters, linearity between 1/3 and 2/3 is best.
The numbers are probably more generous for CRT, but there is something
there.

Regards

Miroslav Pokorni

----- Original Message -----
From: "Mark Anton" <heightstv@hotmail.com>
To: <TekScopes@yahoogroups.com>
Sent: Monday, February 17, 2003 11:50 PM
Subject: [TekScopes] CRT question


I was wondering why on so many of these old scopes, that you are only able
to use so little of the screen, Like 4 or 6 divisions. Why not the whole
face of the tube?

Thanks Mark Anton.





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Re: CRT question

Jose V. Gavila <eb5agv@...>
 

I guess it is a matter of geometry. I have seen older scopes which used all
the display and, well, what you saw at the edges was just an approximation ;-)

Regards,

JOSE

At 01:50 18/02/2003 -0600, Mark Anton wrote:
I was wondering why on so many of these old scopes, that you are only able
to use so little of the screen, Like 4 or 6 divisions. Why not the whole
face of the tube?

Thanks Mark Anton
----------------------------------------------------------------------
73 EB5AGV / EC5AAU - JOSE V. GAVILA
La Canyada - Valencia (SPAIN)

Vintage Radio: http://jvgavila.com
Vintage Test Equipment: http://jvgavila.com/testeq.htm
European Boatanchors List: http://groups.yahoo.com/group/euro_ba_swap


CRT question

Mark Anton
 

I was wondering why on so many of these old scopes, that you are only able to use so little of the screen, Like 4 or 6 divisions. Why not the whole face of the tube?

Thanks Mark Anton.





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515 mystery "solved"

Mark Anton
 

I ran into something interesting. I was given a 515 scope a long time ago, did some troubleshooting on it about 5 yrs ago. The trace looked really funny and seemed to be intermittant. It was really strange. Well anyway, I put it aside. Well, as time went on I sort of started robbing parts, sold the side panels to someone else, and the thing was in nasty condition anyway. Well, anyway, I decided to part it out. That is when I found the cause of my problem. The deflection plates in the CRT had broken away from their mounts and were just hanging there.
Dont know if that was a common problem for that scope or what, or if it got dropped really hard.





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Re: Tek 465 repair hints, svc manual? (fix story)

Mark Anton
 

In many types of equipment, I have found shorted disc and mylar caps just often enough to be aware that it happens. Not really frequent at all, but often enough to know that they never go bad.
Actually have found shorted discs where the voltage should not have been a problem at all. Like a 3 volt p-p signal riding on 6 volts of DC with a .01 50 volt disc. Where did my signal go? Took the cap out and measures 4 ohms. No stress there but the cap failed. So it dont suprise me either, but its not the first thing I go looking for either.

Mark.
----Original Message Follows----
From: E K <dataclue@yahoo.com>
To: TekScopes@yahoogroups.com
CC: E K <dataclue@yahoo.com>
Subject: [TekScopes] Re: Tek 465 repair hints, svc manual? (fix story)
Date: Mon, 17 Feb 2003 18:58:13

-- the Z axis circuitry is coupled to the horizontal amp via R1475, so it was the latter after all.
Turns out the supply does not come back even with all the transistors removed!
7. There are very few possible paths between +110 and ground with the output transistors out of circuit, found a drop of several volts across R1283 (a 47Ohm resistor). Aha! It's connected to ground via C1283, a 0.01 uF 150V ceramic cap enough, removing it restores the supply. Once it's removed, I of course notice a small charred spot next to one of the leads, 8. Replacing the 0.01 uF cap brings back the supply and the horizontal sweep. You may have heard about the tantalum caps in these scopes, I know I did. But the ceramic caps must have also come from a bad batch or weren't really rated 150V.
.
E K <





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Re: Tek 465 repair hints, svc manual? (fix story)

E K
 

Got the 465 horizontal sweep fixed a couple of weeks ago, thanks to David DiGiacomo for a service manual. This didn't take very long, but had some interesting twists and turns.
1. Quickly verified that the over-current protection of the +110V power supply was kicking in (easily done by checking whether the smaller transistor is on).
2. Found the power supply isolation procedure thoughtfully included in the manual and disconnected the horizontal amplifier by desoldering four components (two feed resistors into the final output stage, a resistor for the X10 MAG neon light (!), and a 6.7V zener also connected to the output stage.
3. The power supply went up somewhat, to ~50V. Followed the second half of the isolation procedure, disconnecting the Z axis amplifier / CRT circuit. The supply cheerfully returned to 110V. Ok, it's not the horizontal amplifier after all!
4. Spent a some time chasing around the intensity amplifier, checking caps, removing some of the transistors, and trying to find the presumed short. This didn't lead anywhere.
5. Decided to reconnect the horizontal amplifier (with Z axis amp still disconnected) and the power supply dropped back down to below half of nominal. After a little bit of confusion, noticed the mistake -- the Z axis circuitry is coupled to the horizontal amp via R1475, so it was the latter after all.
6. Checking the various semiconductors and capacitors yields nothing, somewhat surprisingly. No obviously shorted caps, no shorted transistors or diodes. Turns out the supply does not come back even with all the transistors removed!
7. There are very few possible paths between +110 and ground with the output transistors out of circuit, found a drop of several volts across R1283 (a 47Ohm resistor). Aha! It's connected to ground via C1283, a 0.01 uF 150V ceramic cap that previously escaped suspicion. Sure enough, removing it restores the supply. Once it's removed, I of course notice a small charred spot next to one of the leads, and feel like an idiot -- should've noticed it a long time ago. Try to make myself feel better saying that the charring probably appeared over time as I was debugging. ;-)
8. Replacing the 0.01 uF cap and putting everything back together brings back the supply and the horizontal sweep. An astigmatism adjustment and the scope is ready for use, the only remaining problem being a flaky CH1 vertical position pot, to be fixed some other time.
9. You may have heard about the tantalum caps in these scopes, I know I did. But the ceramic caps must have also come from a bad batch or weren't really rated 150V.
All told, an investment in a service manual, a one cent capacitor and 8 total hours or so of fun yield a working 465 scope.
E K <dataclue@yahoo.com> wrote:
Working on a Tek 465 with a horizontal deflection problem. Namely, no horizontal deflection under normal operation and no response to horizontal position adjustment. Limited horizontal deflection if "beam find" pressed, however. It seems that there is a sweep signal being generated, so expecting the problem to be further down the line. This is somewhat buttressed by the fact that a +110 testpoint reads about 40V, other easily checked voltages are normal (e.g., +15, -8).



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Looking for probes

Tracy Nelson <tnelson158@attbi.com> <tnelson158@...>
 

I've got a couple of 310As and a 647. I'm trying to teach myself
something about electronics. Problem is, I've got a motley collection
of random probes, and I don't think any of them are impedence-matched
for my scopes. Two are so old and worn there isn't any manufacturers
information on them, and one says "RCA WG-400A". I'm not getting what
I think are proper readings from it, though, so I don't think it's one
I can use.

Is there a source for probes for instruments this old, and if so what
kind should I be looking for? Right now all I need is a
general-purpose probe, and maybe one for high-voltage work (one of my
310As isn't working on AC, so I thought I'd try to fix it once I know
enough).

Thanks!
-- Tracy Nelson


Differential probe

Marcello Pellerano
 

Hello all,
could you please give me the schematic of a differential probe?
I've seen some of them in various catalogues, but it seems to me that the price required is not so cheap, so I'd like to build one of these.
Thanks
Marcello


Re: 485 Repair Question

Jose V. Gavila <eb5agv@...>
 

Hi Dick,

I picked up a nice clean Tek 485 at Marlboro Saturday. I know it has
problems and thought it would make a good winter project (between
shoveling snow !).
Mine was also got as a winter project and ended as a nice working unit :-)!

First though, what is the procedure for removing the case ?
I am trying to locate a Service Manual, but want to look inside
without breaking anything in the process.
Remove the four screws inside the back plastic supports. I think there is
another screw on the bottom of the scope. Then slide carefully the green
cover and get the unit out of its case.

I have the service manual for it in case you need any detailed information.
As you probably know, usual troubles include the switching supply which is
not easy to work on (but not impossible :-)! )

Good luck!

Regards,

JOSE
----------------------------------------------------------------------
73 EB5AGV / EC5AAU - JOSE V. GAVILA
La Canyada - Valencia (SPAIN)

Vintage Radio: http://jvgavila.com
Vintage Test Equipment: http://jvgavila.com/testeq.htm
European Boatanchors List: http://groups.yahoo.com/group/euro_ba_swap


485 Repair Question

w1ksz <w1ksz@tiac.net> <w1ksz@...>
 

I picked up a nice clean Tek 485 at Marlboro Saturday. I know it has
problems and thought it would make a good winter project (between
shoveling snow !).
First though, what is the procedure for removing the case ?
I am trying to locate a Service Manual, but want to look inside
without breaking anything in the process.

Thanks, Dick, W1KSZ


Re: Tektronix 7M11 Delay Line plug-in

david@...
 

Anyone know what kind of coax cable is used in this delay line
unit... is it flexible or semi-rigid... or what?
It is flexible. Interestingly, it's not insulated - I guess otherwise
they wouldn't have been able to cram it all in.


485 part needed

Sam Reaves
 

I need a vertical attenuator switch assembly modules (with the PCB)
fpr a Tek 485. Someone used freon based or some other cleaned and
disolved and damaged the PCB.

Thanks

Sam


How to use YahooGroups.com?

John Herbster <herb-sci1@...>
 

I am writing this post to find out how to use yahoogroups. I want to review messages in the TekScopes group, but cannot "get there". Yahoo keeps saying my profile (what ever that is supposed to be) is invalid and will not accept any new profile that I enter. So I cannot see anything that is posted.

Does anyone know what could be wrong or can you refer me (by e-mail) to an explanation? --JohnH


Tektronix 7M11 Delay Line plug-in

konnylagarde2002
 

Anyone know what kind of coax cable is used in this delay line
unit... is it flexible or semi-rigid... or what?

THANKS for your help!!!

Konny


561s/766h

arthurok_2000 <arthurok_2000@yahoo.com> <arthurok_2000@...>
 

ibm service used alot of 561s scopes and it was concidered
much better then a fairchild dumont 766h
They were both replaced by 453 and 454 scopes


Anyone have a spare CRT?

vollumscope <perls@ime.net>
 

Howdy all--

I'm looking for a CRT for my TEK 549--

154-0498-00

Easy to identify:

5" round,
10cm X 6cm screen window in aluminized front for tube.

Any help appreciated.

Thanks!

Regards

Robert

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