Date   

Re: Little ceramic trimmer caps that always break... A fix.

Michael W. Lynch
 

On Wed, Aug 19, 2020 at 07:58 AM, Chuck Harris wrote:


I am getting older. I can't see as well as I once did, I cant type
as well as I once did... And I don't like it.
Chuck,

You always have a way to make me laugh, learn, or in this case; to feel better. I'm glad to hear that I am not alone.

--
Michael Lynch
Dardanelle, AR


Re: Little ceramic trimmer caps that always break... A fix.

Dave Wise
 

We're all aging, one day per day. I swap keystrokes and beat the shift all the time.

Five years from now someone will search for "FG504" and if not for pedantry, they would miss your helpful note.

Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Chuck Harris via groups.io <cfharris=erols.com@groups.io>
Sent: Wednesday, August 19, 2020 6:21 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix.

I am mid sixties as well, but to further my stress
is a little dementia thing that runs down my mother's
side of the family...

I have always edited myself, but lately there is way
too (just typed as "oot") much red on the page.

Anyway, I wanted this to be a little helpful note for
folks suffering from the trimmer capacitor plague.

I apologize for turning it into an exposition on my
degrading capabilities...

-Chuck Harris

n4buq wrote:
Mid-sixties here and having some of the same issues. I work with a lot of various systems and am constantly crossing up numbers and letters (or conflating one system's numbers with another, etc.). Very annoying. I have had to resort to carefully rereading what I've typed to pick out the nits (just like I did for this one). It is indeed frustrating if not downright embarrasing at times.

Thanks,
Barry - N4BUQ
<snip>


Re: A possibly sick 7904A

 

On Wed, Aug 19, 2020 at 12:12 PM, Roger Evans wrote:


I tried putting a fast rise square wave into my 7904 at 1kHz and qualitatively
I see what you see. I have to turn up the brightness a lot to see the trace at
1ns/div and it does defocus compared with the readout. I can improve the focus
slightly and that worsens the focus of the readout significantly.

Maybe if we get some more comments we can decide who is unrealistic and who is
easily satisfied. I have no idea what the factory specifications were.
I remember my disappointment when I started collecting 'scopes in 2012/13: I fed the < 1ns rise time signal from a PG506 into my newly acquired 7904A at a fast time base setting, expecting to clearly see the wave shape. The brightness was very disappointing, even at 1 MHz repetition rate. It turned out that the CRT had seen better days and had grown a bit tired. At normal repetition rates, as encountered by the ham that had sold me this instrument, all was fine.
The 7904's and 7904A that I acquired later were much better but the limitations in writing rate were obvious.
In the analog 'scope realm, apart from the 7104 or the 2467 with their MCP CRT's, nothing beats a 7834 or 7934 analog storage 'scope in this respect: Even single-shot 1ns edge speeds can be seen clearly.

Raymond


Re: Little ceramic trimmer caps that always break... A fix.

Paul Amaranth
 

I could type 40 wpm on a manual typewriter all day with very few mistakes.
I suppose that dates me.

Now I can't type a line without a couple of typos. My theory is that as
the cost of a mistake decreases we just get lazy. Making a typo in
an editing program has essentially zero cost (other than finding and
fixing it). Add in spell check and you don't even have to remember
spelling (I'll ignore auto-correct).

Age has nothing to do with it. That's my take and I'm sticking with it :-)

Thanks for your service notes Chuck. Whenever I see one I file it away.
They're always full of useful information.

Paul

On Wed, Aug 19, 2020 at 09:09:42AM -0400, n4buq wrote:
Mid-sixties here and having some of the same issues. I work with a lot of various systems and am constantly crossing up numbers and letters (or conflating one system's numbers with another, etc.). Very annoying. I have had to resort to carefully rereading what I've typed to pick out the nits (just like I did for this one). It is indeed frustrating if not downright embarrasing at times.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Chuck Harris" <cfharris@erols.com>
To: TekScopes@groups.io
Sent: Wednesday, August 19, 2020 7:58:25 AM
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix.

It is becoming a touchy subject for me. All my life I have
been a very fast touch typist. I spent a lot of time writing
programs, and later writing documentation, and could always
type quickly and effortlessly...

But in my 60's, I am noticing coordination problems in my typing,
I "slur" my shift control, and swap adjacent letters.

FG504 can become FG540, Chuck can become CHuck...

I even do a little weird thing where small common words, like
"the" come out backwards "eht", and other words always gain an
extra letter, such as "ratio" always getting typed "ration".

I always find it amusing when I type a long treatise on some subject
or other, and the only comments that get made are about a misplaced
comma, or a typo.

I am getting older. I can't see as well as I once did, I cant type
as well as I once did... And I don't like it.

I am working through a couple of FG504's. If I can help, just ask.

-Chuck Harris


Colin Herbert via groups.io wrote:
No, the typo doesn't matter in so far as that is what it was. I was just
curious because I am trying to get a FG504 working correctly and not doing
too well at the moment. I didn't mean to insult you or anything like that;
please forgive me if that's what it came over as.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck
Harris
Sent: 19 August 2020 13:22
To: TekScopes@groups.io
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A
fix.

Honestly, does it really matter that I mistyped FG504?

I am talking about ceramic trimmers that exist in
hundreds of Tektronix instrument models.

-Chuck Harris

Colin Herbert via groups.io wrote:
Do you mean an FG504? I can't find any FG540 on TekWiki.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck
Harris
Sent: 19 August 2020 05:15
To: TekScopes
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break...
A fix.

Just to clear up some confusion:

This note is about subminiature ceramic disk type
trimmer capacitors. Tektronix equipment from the
1980's onward is littered with these little timebombs.

It is a "modernization" of the old style ceramic
trimmers that had a silver plated half circle on
the lid that was soldered to the adjusting screw.

In this case, the silver plating is inside of the
trimmer, and the ceramic disk is held on by very
temperamental magic. The moving ceramic disk sticks
to its ceramic base, and the magic disappears.

-Chuck Harris

Chuck Harris wrote:
Hi All,

Just a note. As happens to all of us, one of those
little ceramic trimmers in an FG540 was broken. The
screw turned and turned, but the ceramic disk on top
didn't. It was frozen solid.

Bother...

I didn't have a spare, so I removed the trimmer, and
found the ceramic disk frozen solid to the ceramic
base... no trimming going on here!

First, I put the capacitor into some IPA to soak for
a bit. There was more than enough stinky flux on
the cap, so I think the flux was gluing the cap stuck.

After it soaked for a while, I was able to turn the
disk with my fingers... don't use tools, it will break!

I put it in for some more soaking, and twisting, until
it was good and clean.

Next, I took a small dot of cyanoacrylate glue, and
spread it around the screw. A small dot, not a flood.
[If you can't control your glue bottle, put some CA glue
on a piece of plastic, and use a toothpick to bring a dot
to your trimmer.]

Then finally, I gave a rag a squirt of "Kicker", a CA
glue accelerator, and put the rag near the trimmer... The
kicker's fumes are enough to harden the glue almost
instantly. If you don't have any kicker, just let it set
a while, it will harden from the moisture in the air.

I gave the screw a twist, and all was back to normal.

-Chuck Harris




















!DSPAM:5f3d24a4225522099113515!
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group of Michigan, LLC | Security, Systems & Software
paul@AuroraGrp.Com | Unix/Linux - We don't do windows


Re: Little ceramic trimmer caps that always break... A fix.

Chuck Harris
 

I am mid sixties as well, but to further my stress
is a little dementia thing that runs down my mother's
side of the family...

I have always edited myself, but lately there is way
too (just typed as "oot") much red on the page.

Anyway, I wanted this to be a little helpful note for
folks suffering from the trimmer capacitor plague.

I apologize for turning it into an exposition on my
degrading capabilities...

-Chuck Harris

n4buq wrote:

Mid-sixties here and having some of the same issues. I work with a lot of various systems and am constantly crossing up numbers and letters (or conflating one system's numbers with another, etc.). Very annoying. I have had to resort to carefully rereading what I've typed to pick out the nits (just like I did for this one). It is indeed frustrating if not downright embarrasing at times.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Chuck Harris" <cfharris@erols.com>
To: TekScopes@groups.io
Sent: Wednesday, August 19, 2020 7:58:25 AM
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix.

It is becoming a touchy subject for me. All my life I have
been a very fast touch typist. I spent a lot of time writing
programs, and later writing documentation, and could always
type quickly and effortlessly...

But in my 60's, I am noticing coordination problems in my typing,
I "slur" my shift control, and swap adjacent letters.

FG504 can become FG540, Chuck can become CHuck...

I even do a little weird thing where small common words, like
"the" come out backwards "eht", and other words always gain an
extra letter, such as "ratio" always getting typed "ration".

I always find it amusing when I type a long treatise on some subject
or other, and the only comments that get made are about a misplaced
comma, or a typo.

I am getting older. I can't see as well as I once did, I cant type
as well as I once did... And I don't like it.

I am working through a couple of FG504's. If I can help, just ask.

-Chuck Harris


Colin Herbert via groups.io wrote:
No, the typo doesn't matter in so far as that is what it was. I was just
curious because I am trying to get a FG504 working correctly and not doing
too well at the moment. I didn't mean to insult you or anything like that;
please forgive me if that's what it came over as.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck
Harris
Sent: 19 August 2020 13:22
To: TekScopes@groups.io
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A
fix.

Honestly, does it really matter that I mistyped FG504?

I am talking about ceramic trimmers that exist in
hundreds of Tektronix instrument models.

-Chuck Harris

Colin Herbert via groups.io wrote:
Do you mean an FG504? I can't find any FG540 on TekWiki.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck
Harris
Sent: 19 August 2020 05:15
To: TekScopes
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break...
A fix.

Just to clear up some confusion:

This note is about subminiature ceramic disk type
trimmer capacitors. Tektronix equipment from the
1980's onward is littered with these little timebombs.

It is a "modernization" of the old style ceramic
trimmers that had a silver plated half circle on
the lid that was soldered to the adjusting screw.

In this case, the silver plating is inside of the
trimmer, and the ceramic disk is held on by very
temperamental magic. The moving ceramic disk sticks
to its ceramic base, and the magic disappears.

-Chuck Harris

Chuck Harris wrote:
Hi All,

Just a note. As happens to all of us, one of those
little ceramic trimmers in an FG540 was broken. The
screw turned and turned, but the ceramic disk on top
didn't. It was frozen solid.

Bother...

I didn't have a spare, so I removed the trimmer, and
found the ceramic disk frozen solid to the ceramic
base... no trimming going on here!

First, I put the capacitor into some IPA to soak for
a bit. There was more than enough stinky flux on
the cap, so I think the flux was gluing the cap stuck.

After it soaked for a while, I was able to turn the
disk with my fingers... don't use tools, it will break!

I put it in for some more soaking, and twisting, until
it was good and clean.

Next, I took a small dot of cyanoacrylate glue, and
spread it around the screw. A small dot, not a flood.
[If you can't control your glue bottle, put some CA glue
on a piece of plastic, and use a toothpick to bring a dot
to your trimmer.]

Then finally, I gave a rag a squirt of "Kicker", a CA
glue accelerator, and put the rag near the trimmer... The
kicker's fumes are enough to harden the glue almost
instantly. If you don't have any kicker, just let it set
a while, it will harden from the moisture in the air.

I gave the screw a twist, and all was back to normal.

-Chuck Harris




















Re: SC502 With Display Issues

tekscopegroup@...
 

On Tue, Aug 18, 2020 at 11:02 AM, Dave Wise wrote:

Am I missing something?
2N3565 is available at Mouser: 1,683 Can Ship Immediately, $5.30 each.
https://www.mouser.com/ProductDetail/Central-Semiconductor/2N3565-PBFREE?qs=%2Fha2pyFaduixFoFz41ximubJVln7aNMI0hWYPb32rxc%3D
Not available where I live. And 3904’s seem to do the job perfectly in that
application.
And my local store said they were obsolete parts.
Just out of curiosity, Mouser.com in the US does not ship to Paris? I know there is a Mouser.eu, but it should be easy to get around that limitation if need be.


Re: Little ceramic trimmer caps that always break... A fix.

n4buq
 

Mid-sixties here and having some of the same issues. I work with a lot of various systems and am constantly crossing up numbers and letters (or conflating one system's numbers with another, etc.). Very annoying. I have had to resort to carefully rereading what I've typed to pick out the nits (just like I did for this one). It is indeed frustrating if not downright embarrasing at times.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Chuck Harris" <cfharris@erols.com>
To: TekScopes@groups.io
Sent: Wednesday, August 19, 2020 7:58:25 AM
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix.

It is becoming a touchy subject for me. All my life I have
been a very fast touch typist. I spent a lot of time writing
programs, and later writing documentation, and could always
type quickly and effortlessly...

But in my 60's, I am noticing coordination problems in my typing,
I "slur" my shift control, and swap adjacent letters.

FG504 can become FG540, Chuck can become CHuck...

I even do a little weird thing where small common words, like
"the" come out backwards "eht", and other words always gain an
extra letter, such as "ratio" always getting typed "ration".

I always find it amusing when I type a long treatise on some subject
or other, and the only comments that get made are about a misplaced
comma, or a typo.

I am getting older. I can't see as well as I once did, I cant type
as well as I once did... And I don't like it.

I am working through a couple of FG504's. If I can help, just ask.

-Chuck Harris


Colin Herbert via groups.io wrote:
No, the typo doesn't matter in so far as that is what it was. I was just
curious because I am trying to get a FG504 working correctly and not doing
too well at the moment. I didn't mean to insult you or anything like that;
please forgive me if that's what it came over as.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck
Harris
Sent: 19 August 2020 13:22
To: TekScopes@groups.io
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A
fix.

Honestly, does it really matter that I mistyped FG504?

I am talking about ceramic trimmers that exist in
hundreds of Tektronix instrument models.

-Chuck Harris

Colin Herbert via groups.io wrote:
Do you mean an FG504? I can't find any FG540 on TekWiki.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck
Harris
Sent: 19 August 2020 05:15
To: TekScopes
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break...
A fix.

Just to clear up some confusion:

This note is about subminiature ceramic disk type
trimmer capacitors. Tektronix equipment from the
1980's onward is littered with these little timebombs.

It is a "modernization" of the old style ceramic
trimmers that had a silver plated half circle on
the lid that was soldered to the adjusting screw.

In this case, the silver plating is inside of the
trimmer, and the ceramic disk is held on by very
temperamental magic. The moving ceramic disk sticks
to its ceramic base, and the magic disappears.

-Chuck Harris

Chuck Harris wrote:
Hi All,

Just a note. As happens to all of us, one of those
little ceramic trimmers in an FG540 was broken. The
screw turned and turned, but the ceramic disk on top
didn't. It was frozen solid.

Bother...

I didn't have a spare, so I removed the trimmer, and
found the ceramic disk frozen solid to the ceramic
base... no trimming going on here!

First, I put the capacitor into some IPA to soak for
a bit. There was more than enough stinky flux on
the cap, so I think the flux was gluing the cap stuck.

After it soaked for a while, I was able to turn the
disk with my fingers... don't use tools, it will break!

I put it in for some more soaking, and twisting, until
it was good and clean.

Next, I took a small dot of cyanoacrylate glue, and
spread it around the screw. A small dot, not a flood.
[If you can't control your glue bottle, put some CA glue
on a piece of plastic, and use a toothpick to bring a dot
to your trimmer.]

Then finally, I gave a rag a squirt of "Kicker", a CA
glue accelerator, and put the rag near the trimmer... The
kicker's fumes are enough to harden the glue almost
instantly. If you don't have any kicker, just let it set
a while, it will harden from the moisture in the air.

I gave the screw a twist, and all was back to normal.

-Chuck Harris


















Re: 7854 display set up procedure without the calculator keyboard

Martin Whybrow
 

On Tue, Aug 18, 2020 at 08:40 PM, redarlington wrote:


Tektronix 7854 Calculator
All in the USA unfortunately, but bit the bullet and bought one. Cheers guys.


Re: Little ceramic trimmer caps that always break... A fix.

Chuck Harris
 

It is becoming a touchy subject for me. All my life I have
been a very fast touch typist. I spent a lot of time writing
programs, and later writing documentation, and could always
type quickly and effortlessly...

But in my 60's, I am noticing coordination problems in my typing,
I "slur" my shift control, and swap adjacent letters.

FG504 can become FG540, Chuck can become CHuck...

I even do a little weird thing where small common words, like
"the" come out backwards "eht", and other words always gain an
extra letter, such as "ratio" always getting typed "ration".

I always find it amusing when I type a long treatise on some subject
or other, and the only comments that get made are about a misplaced
comma, or a typo.

I am getting older. I can't see as well as I once did, I cant type
as well as I once did... And I don't like it.

I am working through a couple of FG504's. If I can help, just ask.

-Chuck Harris


Colin Herbert via groups.io wrote:

No, the typo doesn't matter in so far as that is what it was. I was just curious because I am trying to get a FG504 working correctly and not doing too well at the moment. I didn't mean to insult you or anything like that; please forgive me if that's what it came over as.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: 19 August 2020 13:22
To: TekScopes@groups.io
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix.

Honestly, does it really matter that I mistyped FG504?

I am talking about ceramic trimmers that exist in
hundreds of Tektronix instrument models.

-Chuck Harris

Colin Herbert via groups.io wrote:
Do you mean an FG504? I can't find any FG540 on TekWiki.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: 19 August 2020 05:15
To: TekScopes
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix.

Just to clear up some confusion:

This note is about subminiature ceramic disk type
trimmer capacitors. Tektronix equipment from the
1980's onward is littered with these little timebombs.

It is a "modernization" of the old style ceramic
trimmers that had a silver plated half circle on
the lid that was soldered to the adjusting screw.

In this case, the silver plating is inside of the
trimmer, and the ceramic disk is held on by very
temperamental magic. The moving ceramic disk sticks
to its ceramic base, and the magic disappears.

-Chuck Harris

Chuck Harris wrote:
Hi All,

Just a note. As happens to all of us, one of those
little ceramic trimmers in an FG540 was broken. The
screw turned and turned, but the ceramic disk on top
didn't. It was frozen solid.

Bother...

I didn't have a spare, so I removed the trimmer, and
found the ceramic disk frozen solid to the ceramic
base... no trimming going on here!

First, I put the capacitor into some IPA to soak for
a bit. There was more than enough stinky flux on
the cap, so I think the flux was gluing the cap stuck.

After it soaked for a while, I was able to turn the
disk with my fingers... don't use tools, it will break!

I put it in for some more soaking, and twisting, until
it was good and clean.

Next, I took a small dot of cyanoacrylate glue, and
spread it around the screw. A small dot, not a flood.
[If you can't control your glue bottle, put some CA glue
on a piece of plastic, and use a toothpick to bring a dot
to your trimmer.]

Then finally, I gave a rag a squirt of "Kicker", a CA
glue accelerator, and put the rag near the trimmer... The
kicker's fumes are enough to harden the glue almost
instantly. If you don't have any kicker, just let it set
a while, it will harden from the moisture in the air.

I gave the screw a twist, and all was back to normal.

-Chuck Harris
















Re: A possibly sick 7904A

Chuck Harris
 

Your description is pretty accurate.

The more modern scopes have compensation circuitry
that changes the focus voltage with the instantaneous
intensity setting.... and changes the instantaneous
intensity settings for the different beam uses...

So, the intensity is separately controllable for the A
horizontal plugin, the B horizontal plugin, the readout,
and in some cases, the "intensified" horizontal A vs B
settings... but FOCUS, and ASTIGMATISM, each have only
one user control.

Each of these settings result in a different beam current,
which require a different focus/astigmatism voltage.

For the 7904A, which was one of the earlier adopters of
this enhancement, they have a circuit called Auto Focus,
and in the Performance check and Adjustment procedure,
page 5-12 of my manual, they explain how it gets adjusted.

The do the main focus adjustment with the beam very dim,
and then they adjust the Auto Focus circuit with the beam
at full intensity control position.

-Chuck Harris

Roger Evans via groups.io wrote:

I am not an expert on this, trained in physics not electronics. When you look at a low rep rate signal at 500ps/div the beam is on a very small fraction of the time, about 5ns every msec so one part in 200000. The readout is being triggered automatically and runs around 1kHz or so, I don't remember the actual clock speeds. So for the same brightness the signal trace has to carry maybe 1000 times the current compared with the readout, this means a higher density of electrons and the space charge can affect the beam focussing compared with a low current beam.

I tried putting a fast rise square wave into my 7904 at 1kHz and qualitatively I see what you see. I have to turn up the brightness a lot to see the trace at 1ns/div and it does defocus compared with the readout. I can improve the focus slightly and that worsens the focus of the readout significantly.

Maybe if we get some more comments we can decide who is unrealistic and who is easily satisfied. I have no idea what the factory specifications were.

Regards,

Roger




Re: Little ceramic trimmer caps that always break... A fix.

Stephen
 

On Wed, Aug 19, 2020 at 01:22 AM, Chuck Harris wrote:


Honestly, does it really matter that I mistyped FG504?
I make typos all the time. Especially with multi spellcheck in different languages. It writes whatever it wants... If I don’t double check...

Don’t worry, it’s okay. I understood you were talking about the FG504.
But maybe Colin did believe an actual FG540 existed and was confused when he did find it. Mistakes happen.


Re: Little ceramic trimmer caps that always break... A fix.

Colin Herbert
 

No, the typo doesn't matter in so far as that is what it was. I was just curious because I am trying to get a FG504 working correctly and not doing too well at the moment. I didn't mean to insult you or anything like that; please forgive me if that's what it came over as.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: 19 August 2020 13:22
To: TekScopes@groups.io
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix.

Honestly, does it really matter that I mistyped FG504?

I am talking about ceramic trimmers that exist in
hundreds of Tektronix instrument models.

-Chuck Harris

Colin Herbert via groups.io wrote:
Do you mean an FG504? I can't find any FG540 on TekWiki.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: 19 August 2020 05:15
To: TekScopes
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix.

Just to clear up some confusion:

This note is about subminiature ceramic disk type
trimmer capacitors. Tektronix equipment from the
1980's onward is littered with these little timebombs.

It is a "modernization" of the old style ceramic
trimmers that had a silver plated half circle on
the lid that was soldered to the adjusting screw.

In this case, the silver plating is inside of the
trimmer, and the ceramic disk is held on by very
temperamental magic. The moving ceramic disk sticks
to its ceramic base, and the magic disappears.

-Chuck Harris

Chuck Harris wrote:
Hi All,

Just a note. As happens to all of us, one of those
little ceramic trimmers in an FG540 was broken. The
screw turned and turned, but the ceramic disk on top
didn't. It was frozen solid.

Bother...

I didn't have a spare, so I removed the trimmer, and
found the ceramic disk frozen solid to the ceramic
base... no trimming going on here!

First, I put the capacitor into some IPA to soak for
a bit. There was more than enough stinky flux on
the cap, so I think the flux was gluing the cap stuck.

After it soaked for a while, I was able to turn the
disk with my fingers... don't use tools, it will break!

I put it in for some more soaking, and twisting, until
it was good and clean.

Next, I took a small dot of cyanoacrylate glue, and
spread it around the screw. A small dot, not a flood.
[If you can't control your glue bottle, put some CA glue
on a piece of plastic, and use a toothpick to bring a dot
to your trimmer.]

Then finally, I gave a rag a squirt of "Kicker", a CA
glue accelerator, and put the rag near the trimmer... The
kicker's fumes are enough to harden the glue almost
instantly. If you don't have any kicker, just let it set
a while, it will harden from the moisture in the air.

I gave the screw a twist, and all was back to normal.

-Chuck Harris










Re: Little ceramic trimmer caps that always break... A fix.

Chuck Harris
 

Honestly, does it really matter that I mistyped FG504?

I am talking about ceramic trimmers that exist in
hundreds of Tektronix instrument models.

-Chuck Harris

Colin Herbert via groups.io wrote:

Do you mean an FG504? I can't find any FG540 on TekWiki.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: 19 August 2020 05:15
To: TekScopes
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix.

Just to clear up some confusion:

This note is about subminiature ceramic disk type
trimmer capacitors. Tektronix equipment from the
1980's onward is littered with these little timebombs.

It is a "modernization" of the old style ceramic
trimmers that had a silver plated half circle on
the lid that was soldered to the adjusting screw.

In this case, the silver plating is inside of the
trimmer, and the ceramic disk is held on by very
temperamental magic. The moving ceramic disk sticks
to its ceramic base, and the magic disappears.

-Chuck Harris

Chuck Harris wrote:
Hi All,

Just a note. As happens to all of us, one of those
little ceramic trimmers in an FG540 was broken. The
screw turned and turned, but the ceramic disk on top
didn't. It was frozen solid.

Bother...

I didn't have a spare, so I removed the trimmer, and
found the ceramic disk frozen solid to the ceramic
base... no trimming going on here!

First, I put the capacitor into some IPA to soak for
a bit. There was more than enough stinky flux on
the cap, so I think the flux was gluing the cap stuck.

After it soaked for a while, I was able to turn the
disk with my fingers... don't use tools, it will break!

I put it in for some more soaking, and twisting, until
it was good and clean.

Next, I took a small dot of cyanoacrylate glue, and
spread it around the screw. A small dot, not a flood.
[If you can't control your glue bottle, put some CA glue
on a piece of plastic, and use a toothpick to bring a dot
to your trimmer.]

Then finally, I gave a rag a squirt of "Kicker", a CA
glue accelerator, and put the rag near the trimmer... The
kicker's fumes are enough to harden the glue almost
instantly. If you don't have any kicker, just let it set
a while, it will harden from the moisture in the air.

I gave the screw a twist, and all was back to normal.

-Chuck Harris










Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

Roger Evans
 

Luis,

Since both channels are equally affected the fault must be either in the beam switching circuitry (not very likely) or in the Y amplifier stages following the beam switching.

There is a fairly simple test on the beam switching that you can do with just a DMM. If you locate test points TP364 and TP 374 on schematic <3> and the example waveform shown in <21> and <22>, you should be able to replicate the DC values ( +1V and -1V) by setting the horizontal mode to ALT and the timebase to its slowest setting so the voltage flips every half second or so. Set both traces to somewhere near the middle of the screen and trigger to AUTO. This is not a definitive test but if these voltages are wrong the diodes may not switch correctly.

I only just now noticed you have Trig View option on the 465. Try feeding the calibrator signal to Trig In, set Trig Source to Ext or Ext/10. Push the trig view and you can move the trace up and down with the Trig Level control. Does the vertical height of the displayed trigger signal change with position in the same way as do the Ch1 and Ch2 signals?

If Q322 and Q324 are socketed then remove and test them. The Service manual schematic <3> shows various voltages around Q322 and Q324, set up the scope as best you can to the conditions defined in the manual at the start of the Schematics section under the heading 'DC Voltages'. See how well your measurements match the figures in the manual.

Farther down the Y amplifier chain there was a change from discrete transistors to an IC based Y amplifier. Which one do you have?

Regards,

Roger


Re: Little ceramic trimmer caps that always break... A fix.

Colin Herbert
 

Do you mean an FG504? I can't find any FG540 on TekWiki.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Chuck Harris
Sent: 19 August 2020 05:15
To: TekScopes
Subject: Re: [TekScopes] Little ceramic trimmer caps that always break... A fix.

Just to clear up some confusion:

This note is about subminiature ceramic disk type
trimmer capacitors. Tektronix equipment from the
1980's onward is littered with these little timebombs.

It is a "modernization" of the old style ceramic
trimmers that had a silver plated half circle on
the lid that was soldered to the adjusting screw.

In this case, the silver plating is inside of the
trimmer, and the ceramic disk is held on by very
temperamental magic. The moving ceramic disk sticks
to its ceramic base, and the magic disappears.

-Chuck Harris

Chuck Harris wrote:
Hi All,

Just a note. As happens to all of us, one of those
little ceramic trimmers in an FG540 was broken. The
screw turned and turned, but the ceramic disk on top
didn't. It was frozen solid.

Bother...

I didn't have a spare, so I removed the trimmer, and
found the ceramic disk frozen solid to the ceramic
base... no trimming going on here!

First, I put the capacitor into some IPA to soak for
a bit. There was more than enough stinky flux on
the cap, so I think the flux was gluing the cap stuck.

After it soaked for a while, I was able to turn the
disk with my fingers... don't use tools, it will break!

I put it in for some more soaking, and twisting, until
it was good and clean.

Next, I took a small dot of cyanoacrylate glue, and
spread it around the screw. A small dot, not a flood.
[If you can't control your glue bottle, put some CA glue
on a piece of plastic, and use a toothpick to bring a dot
to your trimmer.]

Then finally, I gave a rag a squirt of "Kicker", a CA
glue accelerator, and put the rag near the trimmer... The
kicker's fumes are enough to harden the glue almost
instantly. If you don't have any kicker, just let it set
a while, it will harden from the moisture in the air.

I gave the screw a twist, and all was back to normal.

-Chuck Harris




Re: A possibly sick 7904A

Roger Evans
 

I am not an expert on this, trained in physics not electronics. When you look at a low rep rate signal at 500ps/div the beam is on a very small fraction of the time, about 5ns every msec so one part in 200000. The readout is being triggered automatically and runs around 1kHz or so, I don't remember the actual clock speeds. So for the same brightness the signal trace has to carry maybe 1000 times the current compared with the readout, this means a higher density of electrons and the space charge can affect the beam focussing compared with a low current beam.

I tried putting a fast rise square wave into my 7904 at 1kHz and qualitatively I see what you see. I have to turn up the brightness a lot to see the trace at 1ns/div and it does defocus compared with the readout. I can improve the focus slightly and that worsens the focus of the readout significantly.

Maybe if we get some more comments we can decide who is unrealistic and who is easily satisfied. I have no idea what the factory specifications were.

Regards,

Roger


Re: Little ceramic trimmer caps that always break... A fix.

Chuck Harris
 

Just to clear up some confusion:

This note is about subminiature ceramic disk type
trimmer capacitors. Tektronix equipment from the
1980's onward is littered with these little timebombs.

It is a "modernization" of the old style ceramic
trimmers that had a silver plated half circle on
the lid that was soldered to the adjusting screw.

In this case, the silver plating is inside of the
trimmer, and the ceramic disk is held on by very
temperamental magic. The moving ceramic disk sticks
to its ceramic base, and the magic disappears.

-Chuck Harris

Chuck Harris wrote:

Hi All,

Just a note. As happens to all of us, one of those
little ceramic trimmers in an FG540 was broken. The
screw turned and turned, but the ceramic disk on top
didn't. It was frozen solid.

Bother...

I didn't have a spare, so I removed the trimmer, and
found the ceramic disk frozen solid to the ceramic
base... no trimming going on here!

First, I put the capacitor into some IPA to soak for
a bit. There was more than enough stinky flux on
the cap, so I think the flux was gluing the cap stuck.

After it soaked for a while, I was able to turn the
disk with my fingers... don't use tools, it will break!

I put it in for some more soaking, and twisting, until
it was good and clean.

Next, I took a small dot of cyanoacrylate glue, and
spread it around the screw. A small dot, not a flood.
[If you can't control your glue bottle, put some CA glue
on a piece of plastic, and use a toothpick to bring a dot
to your trimmer.]

Then finally, I gave a rag a squirt of "Kicker", a CA
glue accelerator, and put the rag near the trimmer... The
kicker's fumes are enough to harden the glue almost
instantly. If you don't have any kicker, just let it set
a while, it will harden from the moisture in the air.

I gave the screw a twist, and all was back to normal.

-Chuck Harris




Re: Little ceramic trimmer caps that always break... A fix.

Chuck Harris
 

Hi John,

This is normal stuff when you calibrate an instrument for the
first time in decades.

These little subminiature trimmer caps break all the time. Every
time I try to turn one for the first time, my jaw clenches up,
and I give it a gentle turn. Either the ceramic part breaks free
and the cap turns, or the screw breaks free of the ceramic disk.

It is fixed, and the generator impedance is now adjusted. I am
about half way through the calibration adjustments...

All is good. I just like to put out repair notes as my local
reality reminds me of them.

-Chuck Harris

John Ferguson via groups.io wrote:

Wow, Chuck, it was worse than I thought, but it sounds like you have prevailed.

john


Re: Little ceramic trimmer caps that always break... A fix.

Chuck Harris
 

Trimmer caps is short for trimmer capacitors.

-Chuck Harris

keantoken via groups.io wrote:


You mean these trimmers?
https://www.mouser.com/ProductDetail/?qs=HHuYZtQ5iDWVDisM2QQAHw%3D%3D

I had them fail in 2 ways. The caps became loose so the wipers had no contact, or they get dead spots which don't seem to be reversible at all. I want to replace these with sealed Bourns trimmers as possible. My FG504 came very clean and new looking and with a calibration sticker, like it had been used in a climate controlled building. In my 465B scope, one of them had the cap break off in the middle where the shaft is. I didn't have a replacement so I wedged something between the trimmer and some wires in that area to keep it in contact. And there it remains to this day.
The brown cap is plastic, not ceramic. They seem to get brittle over time, perhaps accelerated when exposed to chemicals. I wonder how long yours will last after this treatment.


On Tuesday, August 18, 2020, 08:51:04 PM CDT, Chuck Harris <cfharris@erols.com> wrote:

Hi All,

Just a note.  As happens to all of us, one of those
little ceramic trimmers in an FG540 was broken. The
screw turned and turned, but the ceramic disk on top
didn't.  It was frozen solid.

Bother...

I didn't have a spare, so I removed the trimmer, and
found the ceramic disk frozen solid to the ceramic
base... no trimming going on here!

First, I put the capacitor into some IPA to soak for
a bit.  There was more than enough stinky flux on
the cap, so I think the flux was gluing the cap stuck.

After it soaked for a while, I was able to turn the
disk with my fingers... don't use tools, it will break!

I put it in for some more soaking, and twisting, until
it was good and clean.

Next, I took a small dot of cyanoacrylate glue, and
spread it around the screw.  A small dot, not a flood.
[If you can't control your glue bottle, put some CA glue
on a piece of plastic, and use a toothpick to bring a dot
to your trimmer.]

Then finally, I gave a rag a squirt of "Kicker", a CA
glue accelerator, and put the rag near the trimmer... The
kicker's fumes are enough to harden the glue almost
instantly.  If you don't have any kicker, just let it set
a while, it will harden from the moisture in the air.

I gave the screw a twist, and all was back to normal.

-Chuck Harris







Re: Little ceramic trimmer caps that always break... A fix.

Stephen
 

On Tue, Aug 18, 2020 at 03:21 PM, keantoken wrote:



You mean these trimmers?
https://www.mouser.com/ProductDetail/?qs=HHuYZtQ5iDWVDisM2QQAHw%3D%3D
I believe he’s talking about precision adjustable capacitors, not trim pots... 🤷‍♂️

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