开云体育

--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...> wrote:

mtmpsmp@y... wrote:

I have a 454 that has no vertical deflection on ch1 or ch2, using
another scope I am able to trace signal from the preamps to the
deflection plates. The sweep appears to be in good shape and the
trace is centered on crt. ( position controls have no effect on
trace) What I don't understand is that I have a voltage imbalance

on

vertical plates and the trace is still centered!

Boy! I don't understand that either. I have to wonder if the

voltage

unbalance is actually getting to the deflection plates inside the

CRT.

Perhaps there is a broken connection INSIDE the CRT. If the

unbalance is

actually on the CRT plates, I don't see how the trace can be

centered

vertically . . .

Stan
w7ni@e...
.....................................................................

......................................................................
Stan,
Upon further investigation I have found that when the scope is
turned on the collector voltage is the same (74.6 volts) on each
output device. The voltage will stay in that condition ( flat
centered trace) until I start making voltage measurements with my
voltmeter ( high impedance digital) then the top connecter drops to
56.8 -62.0 volts and the bottom to 32.5 -29.8 volts, the voltage of
course being determined by position control. The trace is at this
point off screen in all modes ( chop, add ect) I can seem only to
bring this condition on by taking voltage measurement on either vert
plate.
Do you think maybe a bad output transistor? thanks for your help.
Mike

To unsubscribe from this group, send an email to:
TekScopes-unsubscribe@...



Your use of Yahoo! Groups is subject to

STunwall@... wrote:

mtmpsmp@... wrote:

I have a 454 that has no vertical deflection on ch1 or ch2, using
another scope I am able to trace signal from the preamps to the
deflection plates. The sweep appears to be in good shape and the
trace is centered on crt. ( position controls have no effect on
trace) What I don't understand is that I have a voltage imbalance on
vertical plates and the trace is still centered!

Boy! I don't understand that either. I have to wonder if the voltage
unbalance is actually getting to the deflection plates inside the CRT.
Perhaps there is a broken connection INSIDE the CRT. If the unbalance is
actually on the CRT plates, I don't see how the trace can be centered
vertically . . .

Stan
w7ni@...

To unsubscribe from this group, send an email to:
TekScopes-unsubscribe@...



Your use of Yahoo! Groups is subject to

I have a 454 that has no vertical deflection on ch1 or ch2, using
another scope I am able to trace signal from the preamps to the
deflection plates. The sweep appears to be in good shape and the
trace is centered on crt. ( position controls have no effect on
trace) What I don't understand is that I have a voltage imbalance on
vertical plates and the trace is still centered!

--- Im TekScopes@e..., msfix56@y... schrieb:

Hello All,

It was suggested that perhaps the nuvistors in the B channel were

the

cause of the drift. This does seem to be the case. In an attempt to
prove that case I swapped the tubes out and the drift changed
channels. I have tested the nuvistors in the scope and several of
them test weak including the front end of the channel B preamp

which

if you watch the tube test meter drifts up from about 3000 uMhos to
about 7600 uMhos before dropping off sporadically.

Have you tried to clean the connector pins of the Nuv?
Maybe the heater has a bad contact that could make unstable and
weak conditions.

The other tubes in
the scope vary from 10000 uMhos to 11500 uMhos. My question is that

The 8393 is exactly equal to a 7586 exept the heater voltage (13.5V)


Jorgen
dj0ud

An update.
I spent two hours in dismounting the vboard and un removing the pots
from it. What a nightmare! If any other people is about to start an
adventure like this, please be sure to have a perfect and efficient
unsoldering machine. I spent a lot of time trying to get rid of the
tin that was keeping the pots on the board. My solder sucking tool
was insufficient. I used a thin plaited wire to get the tin out of
the PCB holes by capillarity.
The pots are now in my hands and I am going to work on them the next
weekend (hopefully).
until next time
ciao

--- In TekScopes@y..., "Emanuele Girlando" <emanuele_girlando@y...>
wrote:

I confirm: "the pots are Allen Bradly, and have a double section";
one section seems unused (not connected).
I confirm: they are "the ones which you can nicely open with four
screws".
So your tips are very very useful.
For the sake of completeness and want to say that I have already
tryed to turn them back and forth a lot of times but with almost no
result.
Furtheremore it is impossible to squirt any form of conctact

cleaner

without opening them.
Thank you very much for your contribution, I'll keep the list

updated

on my activity.
ciao



--- In TekScopes@y..., pe1fbo@h... wrote:

--- In TekScopes@y..., Emanuele Girlando <emanuele_girlando@y...>
wrote:

Vertical position pots on my tek475 are so noisy to make my

scope

almost unusable.
Any suggestion on refurbishing those pots?
They are two sections pots, can I try to use the unused section?
Any source for them?
Thank a lot !
ciao

=====

Emanuele Girlando (IW1DHI)




__________________________________________________
Do You Yahoo!?
Get email at your own domain with Yahoo! Mail.

Hi Emanuele,

Those pots are probable Allen Bradly, and and have a double

section.

There are two type of AB pots, The plastic sealed ones, and the

ones

which you can nicely open with four screws. To clean the pot, you
have to take it apart (first remove them carefully from the

Vertical

amp board). Once you have opened them you need to cut the plastic
seal inside the black plasic section to get to the brown whiper
section.

If you have everything apart, remove all the old grease and clean

all

sections with alcohol. Mind you that the whiper has a tiny carbon
pallet, which comes loose very easy.

Once this is done you need to re-apply new grease. I use for this
purpose lithium based grease from Dow Corning, Molycote DX. Other
types of grease I cannot recomend to use. This is probably the

same

stuff that Bourns uses.

After this, everything has to be assembled again.

There is one small remark on this whole procedure, that is, if

the

carbon conductive film is worn out, the result will probably
disapoint you.

I have personally used this procedure on a lot of AB pots. They

are

the ones usuly having problems due to the aging of the grease.

And

can be restored most of the time with a good result.


- Fred de Vries

--- In TekScopes@y..., "Emanuele Girlando" <emanuele_girlando@y...>
wrote:

Referring to my other post "tek 475 vertical position pots", I am

now

required to dismount those pots. To do it (the one for channel 2 in
particular), I have to remove the vertical amplifiers board.
What I am afraid of is that it seems I have to desolder two

resistors

having one lead on the borad and one on the VOLTS/DIV rotary

switches.

Can I do it safely? Anything to be aware of?
Furtheremore, how can I safely dismount the BW/TRIG VIEW command
shaft from the switch it is linked to? Is it sufficient to unscrew
the tiny screws?
Thank a lot
ciao

Hi Emanuele,

You can safely desolder the two resistors. They are connected to the
input FET. Just make sure that your solderingiron ground is on the
same potential as the scope, otherwise you could damage the input FET
(2N5911 discontinued by VISAY). The BW trig view screw (I think allen-
key 1/16") is best taken loos at the switch.

On most 475s there is also a strap from the main board to the
vertical board which can easy be overlooked. It is close to the HV
section. You have to unsolder it as well. The same with the Delay
line which is normaly soldered to the vertial amp board.

Good luck.

Fred de Vries

Referring to my other post "tek 475 vertical position pots", I am now
required to dismount those pots. To do it (the one for channel 2 in
particular), I have to remove the vertical amplifiers board.
What I am afraid of is that it seems I have to desolder two resistors
having one lead on the borad and one on the VOLTS/DIV rotary switches.
Can I do it safely? Anything to be aware of?
Furtheremore, how can I safely dismount the BW/TRIG VIEW command
shaft from the switch it is linked to? Is it sufficient to unscrew
the tiny screws?
Thank a lot
ciao

I confirm: "the pots are Allen Bradly, and have a double section";
one section seems unused (not connected).
I confirm: they are "the ones which you can nicely open with four
screws".
So your tips are very very useful.
For the sake of completeness and want to say that I have already
tryed to turn them back and forth a lot of times but with almost no
result.
Furtheremore it is impossible to squirt any form of conctact cleaner
without opening them.
Thank you very much for your contribution, I'll keep the list updated
on my activity.
ciao



--- In TekScopes@y..., pe1fbo@h... wrote:

--- In TekScopes@y..., Emanuele Girlando <emanuele_girlando@y...>
wrote:

Vertical position pots on my tek475 are so noisy to make my scope
almost unusable.
Any suggestion on refurbishing those pots?
They are two sections pots, can I try to use the unused section?
Any source for them?
Thank a lot !
ciao

=====

Emanuele Girlando (IW1DHI)




__________________________________________________
Do You Yahoo!?
Get email at your own domain with Yahoo! Mail.

Hi Emanuele,

Those pots are probable Allen Bradly, and and have a double

section.

There are two type of AB pots, The plastic sealed ones, and the

ones

which you can nicely open with four screws. To clean the pot, you
have to take it apart (first remove them carefully from the

Vertical

amp board). Once you have opened them you need to cut the plastic
seal inside the black plasic section to get to the brown whiper
section.

If you have everything apart, remove all the old grease and clean

all

sections with alcohol. Mind you that the whiper has a tiny carbon
pallet, which comes loose very easy.

Once this is done you need to re-apply new grease. I use for this
purpose lithium based grease from Dow Corning, Molycote DX. Other
types of grease I cannot recomend to use. This is probably the same
stuff that Bourns uses.

After this, everything has to be assembled again.

There is one small remark on this whole procedure, that is, if the
carbon conductive film is worn out, the result will probably
disapoint you.

I have personally used this procedure on a lot of AB pots. They are
the ones usuly having problems due to the aging of the grease. And
can be restored most of the time with a good result.


- Fred de Vries

--- In TekScopes@y..., Emanuele Girlando <emanuele_girlando@y...>
wrote:

Vertical position pots on my tek475 are so noisy to make my scope
almost unusable.
Any suggestion on refurbishing those pots?
They are two sections pots, can I try to use the unused section?
Any source for them?
Thank a lot !
ciao

=====

Emanuele Girlando (IW1DHI)




__________________________________________________
Do You Yahoo!?
Get email at your own domain with Yahoo! Mail.

Hi Emanuele,

Those pots are probable Allen Bradly, and and have a double section.
There are two type of AB pots, The plastic sealed ones, and the ones
which you can nicely open with four screws. To clean the pot, you
have to take it apart (first remove them carefully from the Vertical
amp board). Once you have opened them you need to cut the plastic
seal inside the black plasic section to get to the brown whiper
section.

If you have everything apart, remove all the old grease and clean all
sections with alcohol. Mind you that the whiper has a tiny carbon
pallet, which comes loose very easy.

Once this is done you need to re-apply new grease. I use for this
purpose lithium based grease from Dow Corning, Molycote DX. Other
types of grease I cannot recomend to use. This is probably the same
stuff that Bourns uses.

After this, everything has to be assembled again.

There is one small remark on this whole procedure, that is, if the
carbon conductive film is worn out, the result will probably
disapoint you.

I have personally used this procedure on a lot of AB pots. They are
the ones usuly having problems due to the aging of the grease. And
can be restored most of the time with a good result.


- Fred de Vries

At 3:56 PM -0800 2001/3/24, Emanuele Girlando wrote:

Vertical position pots on my tek475 are so noisy to make my scope
almost unusable.
Any suggestion on refurbishing those pots?

Surely any owner of "classic" equipment should have a can of good contact cleaner always at hand!!! :-) Perhaps even WD40 would work??? If the pot is just supplying a DC voltage, I guess you could always hang a big capacitor on the wiper!? Have you tried simply rotating the pot back and forth a few dozen times? This often helps, at least a bit.

-----------------------------------------------------------------
Michael Dunn | Surround Sound Decoder & Stereo Enhancer
Cantares | Self-Amplified Speakers, Test Equipment
74 George St. | Ambisonic Surround Sound CDs and Recording
Waterloo, Ont. | (519) 744-9395 (fax: 744-7129)
N2J 1K7 | mdunn@...
Canada |
-----------------------------------------------------------------

Vertical position pots on my tek475 are so noisy to make my scope
almost unusable.
Any suggestion on refurbishing those pots?
They are two sections pots, can I try to use the unused section?
Any source for them?
Thank a lot !
ciao

=====

Emanuele Girlando (IW1DHI)




__________________________________________________
Do You Yahoo!?
Get email at your own domain with Yahoo! Mail.

Michael,

I visited the site for you but unfortunately the 564 is not on that site
(also the one I was looking for the type 468 was not there)
Several others were.

kind regards,
Andre Roest

Michael,

I could download all the pdf files in holland.
Perhaps I can help you by sending you what is put there.
Can you give me a number you are looking for.

Kind regards,
Andre Roest

replacing the GaAs diodes with Schottkys sounds extremly
interesting. Could you write which type of Schottky diodes you
used? I think a lot of (potential) sampling plugin repairers
would appreciate this information, at least I would.

Thanks a lot,
Laurent Lamesch

Giving you part numbers would not be too useful, since the 1S1
still has the offset problems I mentioned.

maybe due to a unmatched set?


I got a couple of

different types through Digikey. If you want to experiment, I

expect

it's best to look for low-capacitance parts, say, 1-2pF. I'll get
back to the 1S1 when I have time. It *is* a weird circuit, and
difficult to troubleshoot, even with the manual!

I have tried a hp HSMS28xx (I don't remember the number but i can
have
a look, its a bridge-connected 4-diodes in one SMD housing) and a
(matched set) hp 5082-2815 in a a 3S76 a time ago,
as i mentioned in the tektronix-forum(@reprise.com) last year.
The balance and offset is ok, i have not checked the risetime and
aberations, because it was only a test. (My original sampling diodes
are OK)
I have tried those diodes because i have studied some service manuals
from samplingbridges in (vector-) voltmeters by hp. The HSMS28xx was
used up to 2 GHz in a hp VV-plug in, the 5082-2815 was used to 1 GHz
in 8405 VV and 3406 Sampling Voltmeter.

Jorgen
dj0ud

Hi Nick,

There is a list of vendors of Tek manuals at our web site. Try this URL:



If none of those guys can help, there is always eBay . . .

Stan
w7ni@...

nick weyland wrote:

What is the best way to get a service manual for
a 7104.

Thanks

__________________________________________________
Do You Yahoo!?
Get email at your own domain with Yahoo! Mail.

Hi Paul,

I have a real problem with the way Bill's and my forum works with my
computer. It takes forever to load and I just don't have the time to wait.
Bill says he can fix it as soon as he gets time to do it. In the mean time,
I have some info for you regarding your 454 nuvistors. See below:

msfix56@... wrote:

Hello All,

Please note that this is a copy of my post in the Tektronix Reference
materials forum with some comments removed as they would not make
sense here. If the bookmark is not in the bookmarks section here it
really should be added as they, (Stan Griffiths and Bill Den Beste)
have a wealth of good information available.

So here goes -

It was suggested that perhaps the nuvistors in the B channel were the
cause of the drift. This does seem to be the case. In an attempt to
prove that case I swapped the tubes out and the drift changed
channels. I have tested the nuvistors in the scope and several of
them test weak including the front end of the channel B preamp which
if you watch the tube test meter drifts up from about 3000 uMhos to
about 7600 uMhos before dropping off sporadically. The other tubes in
the scope vary from 10000 uMhos to 11500 uMhos. My question is that I
seem to be having a hard time finding the 154-0461-00 part number
tubes. According to the manual they cross over to an 8393

This is correct. 154-0461-00's are also known as 8393's.

and I have
found Tek part #157-0107-00 which also crosses over to the 8393. Is
there a significant difference in these two Tek part numbers?

Yes. The 157-0107-00 is an aged and checked 154-0461-00 (8393). It has been
aged for 100 hours, checked for microphonics and grid current.

Can
someone tell me what the uMho readout for the 8393???s should be for
this application.

I don't think the transconductance of the nuvistor is very critical in this
application. I notice 8393's are not checked for transconductance when they
are selected to become 157-0107-00's. I believe the randomly varying
transconductance you see is related to the drift you see. I think the aging
process causes the nuvistors to eventually stabilize.

I notice that Tek uses two part numbers for the
8393???s in the 454 two of them are "aged" while the others are not.
Will this make a significant difference in the scopes performance or
will it just drift for a while until the tubes get "set in their
ways" :^) Thanks for reading all this and for all your help.

Paul

Paul, I would just use some plain 8393's in the input circuit of the 454 and
check them for microphonics by jarring the instrument slightly and watching
the trace for noise. I think the cal procedure calls out a test for grid
current. Grid current shows up as a vertical trace shift while grounding and
ungrounding the vertical input at the most sensitive position of the vertical
attenuator switch.

Hope this helps.

Stan
w7ni@...

Hello All,

Please note that this is a copy of my post in the Tektronix Reference
materials forum with some comments removed as they would not make
sense here. If the bookmark is not in the bookmarks section here it
really should be added as they, (Stan Griffiths and Bill Den Beste)
have a wealth of good information available.

So here goes -

It was suggested that perhaps the nuvistors in the B channel were the
cause of the drift. This does seem to be the case. In an attempt to
prove that case I swapped the tubes out and the drift changed
channels. I have tested the nuvistors in the scope and several of
them test weak including the front end of the channel B preamp which
if you watch the tube test meter drifts up from about 3000 uMhos to
about 7600 uMhos before dropping off sporadically. The other tubes in
the scope vary from 10000 uMhos to 11500 uMhos. My question is that I
seem to be having a hard time finding the 154-0461-00 part number
tubes. According to the manual they cross over to an 8393 and I have
found Tek part #157-0107-00 which also crosses over to the 8393. Is
there a significant difference in these two Tek part numbers? Can
someone tell me what the uMho readout for the 8393?s should be for
this application. I notice that Tek uses two part numbers for the
8393?s in the 454 two of them are "aged" while the others are not.
Will this make a significant difference in the scopes performance or
will it just drift for a while until the tubes get "set in their
ways" :^) Thanks for reading all this and for all your help.

Paul

Hi Terry,

Comments inserted below:

Terry Brown wrote:

Stan, I removed and reseated all the Nuvistors I could find and also checked
transistors in the sockets to see if loose. That seems to have solved the
drifting issue. I'll let it cool down completely and retry later.

That may be all that is required to fix the drift.

Are the 454's very sensitive to movement...i.e., do the
transistors/Nuvistors and other parts move around with just normal carrying and
storing of the scopes?

No, not normally. But you have to remember all 454's are now at least 30+ years old
and things like nuvistor sockets and transistor sockets can get a little oxidized
after that much time. Sometimes all that is required to fix an intermittant socket
is to remove and reinstall a transistor or nuvistor a couple of times.

I also noticed that the leading edges of the calibrator square waves have a
slight upward/downward curve to them (even using a straight patch cord in place
of probes). Is that normal or does it indicate some need for recalibration?

You may looking a the calibrator signal in the "AC" postion of the vertical input
coupling switches. (These are the horizontal lever switches near the input BNC
connectors.) Try the "DC" position and see if it doesn't look a little better.
The calibrator will look a little slanted in the AC position.

Glad to help, Terry. Let me know if I guessed this one right . . .

Stan
w7ni@...

Thank you, again, for all your help and sharing of knowledge.
Terry