Date   

Re: Epoxy HV Transformer Question

ykochcal
 

Morris

Can you enlighten us a bit on how you went about the rewind. Details or
information on Winder/wire/form/insulation/number of attempts to get one
working?

I have been working towards rewinding a 647a.

John



I have a 556 too and hate to have to tell you, but it had the problem. It
showed up on the lower beam transformer as that's the one that supplies the
PDA and has a higher power load, but I had them both rewound. If you're
going to do major surgery like that you might as well do them both at the
same time. The HVPSs are sandwiched in difficult positions at the back of
the scope on either side and require a prolonged effort and much profanity
before the job is done. The transformer rewinds were a new experience for me
and my transformer winding mate, and in order to avoid madness and repeated
assembly and disassembly for testing it was necessary to build up a test
jig with a copy oscillator circuit and loads. It works nicely now but as
Stan says in his book, is probably more scopeage than most people need.

Lots of fun!

Good luck,

Morris

I'm the proud new owner of a 556, which as I understand also has the
epoxy transformers. And not one, but two! As of now, it doesn't have the
"disease." I hope it never gets it.


Re: Epoxy HV Transformer Question

Morris Odell
 

I have a 556 too and hate to have to tell you, but it had the problem. It showed up on the lower beam transformer as that's the one that supplies the PDA and has a higher power load, but I had them both rewound. If you're going to do major surgery like that you might as well do them both at the same time. The HVPSs are sandwiched in difficult positions at the back of the scope on either side and require a prolonged effort and much profanity before the job is done. The transformer rewinds were a new experience for me and my transformer winding mate, and in order to avoid madness and repeated assembly and disassembly for testing it was necessary to build up a test jig with a copy oscillator circuit and loads. It works nicely now but as Stan says in his book, is probably more scopeage than most people need.

Lots of fun!

Good luck,

Morris

--------------------------
Posted by: "Cliff White" cn.white@sunbelt-plb.com kf5iyl
Date: Mon Feb 17, 2014 5:33 pm ((PST))

I'm the proud new owner of a 556, which as I understand also has the
epoxy transformers. And not one, but two! As of now, it doesn't have the
"disease." I hope it never gets it.


Re: OT: newly introduced ant species crawls into electronics to die

Dave Seiter
 

But neither are healthy for electronics.  I don't know how many times I've been poking around inside a piece of gear and a large, fat black spider runs out.  No ants yet...

-Dave


From: Don Black
To: TekScopes@...
Sent: Monday, February 17, 2014 10:14 PM
Subject: Re: [TekScopes] OT: newly introduced ant species crawls into electronics to die

 
I believe Arachnids are spiders, not ants (insects).
Don Black.

On 16-Feb-14 12:44 PM, dukeluca86@... wrote:
 
Wow... sounds like aracnattack or other b movies... never heard of this before... where i live (Italy) there's no problem with ants, they are in the ground, we over it... what's this things comin out from my keyboard ?

Seriously, i only had one case once upon a time with aracnid nest in an old tube radio, but very old and comin from eastern europe contry, they nested in the variable capacitor, blocking it.




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Re: Epoxy HV Transformer Question

Andy
 

I had good results removing the epoxy from the HV transformer of a 647.  It was a delicate operation, but it immediately reduced the power consumption of the HV circuit, and eliminated HV problem. 

Andy


Re: OT: newly introduced ant species crawls into electronics to die

Don Black <donald_black@...>
 

I believe Arachnids are spiders, not ants (insects).
Don Black.

On 16-Feb-14 12:44 PM, dukeluca86@... wrote:
 

Wow... sounds like aracnattack or other b movies... never heard of this before... where i live (Italy) there's no problem with ants, they are in the ground, we over it... what's this things comin out from my keyboard ?

Seriously, i only had one case once upon a time with aracnid nest in an old tube radio, but very old and comin from eastern europe contry, they nested in the variable capacitor, blocking it.





This email is free from viruses and malware because avast! Antivirus protection is active.



Re: S-6 sampling head

Eino Väänänen
 

Thanks Mike!
 
Do you mean this manual on TekWIKI site?
It is only manual I have.
 
Eino
 

Sent: Tuesday, February 18, 2014 2:06 AM
Subject: [TekScopes] RE: S-6 sampling head
 
 

Eino-
Look at the S-2 service manual, page 5-13, item 7. Your S-2 is likely misadjusted. 
Mike


Re: Epoxy HV Transformer Question

Chuck Harris <cfharris@...>
 

At some point in the early 1970s, Tek modified the
warranty agreements, and announced that they considered
any scope older than 5 years, I think, was past its
end of life... thus ending its "lifetime guarantee".

In my opinion, that was when the bean counters achieved
critical mass in the company, and the end had already
begun.

-Chuck Harris

Cliff White wrote:

Good. That's what I wanted to hear. :)

I'm the proud new owner of a 556, which as I understand also has the epoxy
transformers. And not one, but two! As of now, it doesn't have the "disease." I hope
it never gets it.

Has anyone here actually tried to contact Tek and make good on that "transformers are
warrantied for the life of the instrument"?

Respectfully,
Cliff White, W5CNW


Re: Epoxy HV Transformer Question

Leon Robinson
 

Tek cancelled that a LONG time ago.
 
Leon Robinson    K5JLR

Political Correctness is a Political Disease.


From: Cliff White
To: TekScopes@...
Sent: Monday, February 17, 2014 7:33 PM
Subject: Re: [TekScopes] Epoxy HV Transformer Question

 
Good. That's what I wanted to hear. :)

I'm the proud new owner of a 556, which as I understand also has the epoxy transformers. And not one, but two! As of now, it doesn't have the "disease." I hope it never gets it.

Has anyone here actually tried to contact Tek and make good on that "transformers are warrantied for the life of the instrument"?

Respectfully,
Cliff White, W5CNW
w5cnw@...
On 02/17/2014 10:43 AM, Chuck Harris wrote:
 
From my anecdotal experience, it would appear that
they are more likely to fail when they are left
unused.

Before I started rewinding 547 transformers, I was
given a 547 that had the transformer disease. It
manifested itself as normal operation for the first
15 minutes, and then the image started to grow in
size (bloom). When that happened, I would turn the
scope off. The next day I would turn it back on,
and then it took 20 minutes before the image bloomed.

This went on for several weeks as I played with the
scope, each time the on time increased somewhat until
it just didn't seem to fail anymore.

So, thinking I had solved the problem, I went on to
other things. At the end of the summer I tried the
scope again, thinking I would calibrate it, and it
worked for only 15 minutes before blooming... Rats!

The pattern repeated. The important thing to note is,
the scope probably went 10 years before the first time
it had an HV failure, and now it was down to a month
or so of disuse before failure. Clearly something had
degraded.

Others have tried baking the transformers for many
months and have achieved limited success... only to
have the transformer again fail after a short while
of sitting unused.

Long before I ever had a 547, I was talking to Deane
Kidd about this and that, and he brought up the transformer
problem... back then Bill Schell was rewinding. He
told me that Tek started to see failures in 547's and
545B's right around the end of their warranty period.
So, Tek took back the scopes, and replaced their transformers
with new old stock transformers... and found they were just
as bad as the transformers they replaced. The went through
their entire stock of transformers and found that virtually
all were bad, causing them to have to do a new run of
transformers just before the warranty was over for 547's.

Naturally, they just followed the exact same recipe
that they had years before, so they are likely doomed
to fail too... but by then the "lifetime" warranty
would be over...

-Chuck Harris

Cliff White wrote:
> Are epoxy transformers (such as in the 547) more or less likely to fail if the scope
> is used regularly versus rarely? Or does it matter?
>




Re: Epoxy HV Transformer Question

Cliff White
 

Good. That's what I wanted to hear. :)

I'm the proud new owner of a 556, which as I understand also has the epoxy transformers. And not one, but two! As of now, it doesn't have the "disease." I hope it never gets it.

Has anyone here actually tried to contact Tek and make good on that "transformers are warrantied for the life of the instrument"?

Respectfully,
Cliff White, W5CNW
w5cnw@...

On 02/17/2014 10:43 AM, Chuck Harris wrote:
 

From my anecdotal experience, it would appear that
they are more likely to fail when they are left
unused.

Before I started rewinding 547 transformers, I was
given a 547 that had the transformer disease. It
manifested itself as normal operation for the first
15 minutes, and then the image started to grow in
size (bloom). When that happened, I would turn the
scope off. The next day I would turn it back on,
and then it took 20 minutes before the image bloomed.

This went on for several weeks as I played with the
scope, each time the on time increased somewhat until
it just didn't seem to fail anymore.

So, thinking I had solved the problem, I went on to
other things. At the end of the summer I tried the
scope again, thinking I would calibrate it, and it
worked for only 15 minutes before blooming... Rats!

The pattern repeated. The important thing to note is,
the scope probably went 10 years before the first time
it had an HV failure, and now it was down to a month
or so of disuse before failure. Clearly something had
degraded.

Others have tried baking the transformers for many
months and have achieved limited success... only to
have the transformer again fail after a short while
of sitting unused.

Long before I ever had a 547, I was talking to Deane
Kidd about this and that, and he brought up the transformer
problem... back then Bill Schell was rewinding. He
told me that Tek started to see failures in 547's and
545B's right around the end of their warranty period.
So, Tek took back the scopes, and replaced their transformers
with new old stock transformers... and found they were just
as bad as the transformers they replaced. The went through
their entire stock of transformers and found that virtually
all were bad, causing them to have to do a new run of
transformers just before the warranty was over for 547's.

Naturally, they just followed the exact same recipe
that they had years before, so they are likely doomed
to fail too... but by then the "lifetime" warranty
would be over...

-Chuck Harris

Cliff White wrote:
> Are epoxy transformers (such as in the 547) more or less likely to fail if the scope
> is used regularly versus rarely? Or does it matter?
>



Re: S-6 sampling head

Mike
 

Eino-
Look at the S-2 service manual, page 5-13, item 7. Your S-2 is likely misadjusted. 
Mike


Re: Model 555 in Detroit area --- free to a "good" home.

Paul Amaranth
 

If anybody is interested in this, I can serve as an intermediary. I have no
interest (or room) for this one myself.

Paul

On Mon, Feb 17, 2014 at 01:44:02PM -0500, Mark Kahrs wrote:
From another list, reposting with permission:

Subject: [rescue] Old oscilloscope free to a good home (detroit metro area)
I picked up an old tektronix 555 a while ago and I haven't had the desire
to fix it up that I thought I would. It supposedly has bad power caps, but
the diagnosis will have to continue after they are replaced if they're not
the only problem. It's a huge 'scope and really quite good looking to me,
but I want the space and would feel bad about scrapping it for parts. I
have a few plug-in modules for it, and they can go with it. It's hitting
the scrapper in a week if I can't get someone to take it by then.

Evan Allen

abzman2000 at google's email service if you know what I mean...
--
Paul Amaranth, GCIH | Rochester MI, USA
Aurora Group, Inc. | Security, Systems & Software
paul@AuroraGrp.Com | Unix & Windows


Model 555 in Detroit area --- free to a "good" home.

Mark Kahrs
 

From another list, reposting with permission:

Subject: [rescue] Old oscilloscope free to a good home (detroit metro area)
I picked up an old tektronix 555 a while ago and I haven't had the desire
to fix it up that I thought I would.  It supposedly has bad power caps, but
the diagnosis will have to continue after they are replaced if they're not
the only problem.  It's a huge 'scope and really quite good looking to me,
but I want the space and would feel bad about scrapping it for parts.  I
have a few plug-in modules for it, and they can go with it.  It's hitting
the scrapper in a week if I can't get someone to take it by then.

Evan Allen

abzman2000 at google's email service if you know what I mean...



Re: Problem after recaping LV power supply on 2445A

amit s
 

Thanks tom for getting that info.I am sorry david but the measurements you asked will be over my capability.It would be great if someone can perform those tests.Sorry for my ignorance.


Re: Epoxy HV Transformer Question

Chuck Harris <cfharris@...>
 

From my anecdotal experience, it would appear that
they are more likely to fail when they are left
unused.

Before I started rewinding 547 transformers, I was
given a 547 that had the transformer disease. It
manifested itself as normal operation for the first
15 minutes, and then the image started to grow in
size (bloom). When that happened, I would turn the
scope off. The next day I would turn it back on,
and then it took 20 minutes before the image bloomed.

This went on for several weeks as I played with the
scope, each time the on time increased somewhat until
it just didn't seem to fail anymore.

So, thinking I had solved the problem, I went on to
other things. At the end of the summer I tried the
scope again, thinking I would calibrate it, and it
worked for only 15 minutes before blooming... Rats!

The pattern repeated. The important thing to note is,
the scope probably went 10 years before the first time
it had an HV failure, and now it was down to a month
or so of disuse before failure. Clearly something had
degraded.

Others have tried baking the transformers for many
months and have achieved limited success... only to
have the transformer again fail after a short while
of sitting unused.

Long before I ever had a 547, I was talking to Deane
Kidd about this and that, and he brought up the transformer
problem... back then Bill Schell was rewinding. He
told me that Tek started to see failures in 547's and
545B's right around the end of their warranty period.
So, Tek took back the scopes, and replaced their transformers
with new old stock transformers... and found they were just
as bad as the transformers they replaced. The went through
their entire stock of transformers and found that virtually
all were bad, causing them to have to do a new run of
transformers just before the warranty was over for 547's.

Naturally, they just followed the exact same recipe
that they had years before, so they are likely doomed
to fail too... but by then the "lifetime" warranty
would be over...

-Chuck Harris

Cliff White wrote:

Are epoxy transformers (such as in the 547) more or less likely to fail if the scope
is used regularly versus rarely? Or does it matter?


Epoxy HV Transformer Question

Cliff White
 

Are epoxy transformers (such as in the 547) more or less likely to fail if the scope is used regularly versus rarely? Or does it matter?   

--
Respectfully,
Cliff White, W5CNW
w5cnw@...


Re: Tektronix 2710 Spectrum Analyzer Unable to Coun t (VCO,IF)

cmbath
 

After a very looooooong delay.........

I have managed to borrow I reference oscillator board from a 2712 which seems to be the same part number as the one installed in my machine. It seems that the 100MHz output to the CFC board is working from this board (I guess one can only assume that there must be an issue with the reference oscillator board) however the signal is very very low from the borrowed reference oscillator – about 2mV.

The new board has given new life to the SA and with the calibrator on I can see the 100Mhz signal + harmonics on the display. The “cannot count (VCO,IF)” error surprisingly still remains. The signal from the CFC board to the counter on the microprocessor now seems to have a triangular waveform on it but it is very noisy.

I am wondering what is now wrong. The output signal level from the reference oscillator board seems to be too low. Should it only be producing a signal of about 2mV?

I can see the display “surging” as the wide span at 180Mhz/div is swept which seems to be related to the current varying to the YIG oscillator and the power supply not being able to cope with this. One thing for sure is that it would have never done this when it was new so something has gone wrong.

Sorry about the long pause in replying to those who replied to the original message.

Chris


Re: Tektronix 2710 Spectrum Analyzer Unable to Coun t (VCO,IF)

cmbath
 

After a very looooooong delay..........

I have managed to borrow I reference oscillator board from a 2712 which seems to be the same part number as the one installed in my machine. It seems that the 100MHz output to the CFC board is working from this board (I guess one can only assume that there must be an issue with the  original reference oscillator board) however the signal is very very low from the borrowed reference oscillator – about 2mV.

The new board has given new life to the SA and with the calibrator on I can see the 100Mhz signal + harmonics on the display. The “cannot count (VCO,IF)” error surprisingly still remains. The signal from the CFC board to the counter on the microprocessor now seems to have a triangular waveform on it but it is very noisy.

I am wondering what is now wrong. The output signal level from the reference oscillator board seems to be too low. Should it only be producing a signal of about 2mV?

I can see the display “surging” as the wide span at 180Mhz/div is swept which seems to be related to the current varying to the YIG oscillator and the power supply not being able to cope with this. One thing for sure is that it would have never done this when it was new so something has gone wrong.

 

Sorry about the long pause in replying to those who replied to the original message.

Chris


Re: S-6 sampling head

Eino Väänänen
 

Yes, that is right. Type 284 is working right. I get soon an other 7S11 and S-4 head. Maybe they work better and square wave pulse like it should look.
 
Eino
 

Sent: Monday, February 17, 2014 1:49 AM
Subject: RE: [TekScopes] S-6 sampling head
 
 

I’m still not sure what you are doing here.

The fast pulse rise you show is clearly with the 284 mode switch set to pulse output and your cable to the left hand socket – and that is a fixed repetition rate of 50kHz.  But you also show a 1MHz square wave to show a strange droop – presumably with the mode switch changed to “square wave or sine wave output” and your connection swapped across to the right hand socket.

Is that right?

And have you checked that the square wave output of your 284 is working right?

Craig


Re: S-6 sampling head

jvanderwall1941
 

If you use a sampling head extender make sure it's the short one (3 feet). The longer cable has some peculiar effects which I never bothered to chase down back in the seventies. I merely shortened the cable.

Regards,

Jonathan


Re: Problem after recaping LV power supply on 2445A

 

I think the inductor is there to mitigate cross conduction of the power MOSFETs
which do not have non-overlapping drive. When the current rises during cross
conduction, the inductor allows the source voltage to rise which lowers the gate
to source voltage so the conductance of the MOSFETs goes down limiting the
current. The resistor lowers the Q of the inductor like you say and limits the
source voltage excursion to prevent excessive gate to source voltage. It is a
current snubber instead of a voltage snubber although there is one of those also
made up of the network built around C1065 which handles the leakage inductance
of T1060.

I think they added this more for noise suppression than to protect the power
MOSFETs although it should also lower their power dissipation.

It would be interesting to measure both the current and voltage waveforms with
and without the inductor. I usually tune these kinds of circuits with trial and
error since correct operation should be verified by measurement anyway.

On Sun, 16 Feb 2014 23:48:06 -0500, you wrote:

Ok, I was looking at the wrong coil. LR1060 is a 1/2 watt 75 ohm 20 % carbon comp resistor with a single layer of AWG 34 winding almost the full length. The manual calls it a 2.5 uH choke. The one I measured was 89 ohms so I don't think its exact value is that important. I am sure it is just there to de-Q the coil.

HTH,
Tom

----- Original Message -----
From: Tom Miller
To: TekScopes@yahoogroups.com
Sent: Sunday, February 16, 2014 2:44 PM
Subject: Re: [TekScopes] Re: Problem after recaping LV power supply on 2445A

I looked at a good one. It is a 1 watt resistor with a single layer of winding covered by heat shrink tubing. Later today, I will lift it off the board and unsolder one end of the winding to see the details.

Tom

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