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'[EE]: Transistor replacement'
2001\06\26@135948 by Sean Breheny

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HI all

My old Tek 7704A scope encountered a sudden problem last night. The display
suddenly (and permanently) shifted over to the right and compressed a
bit. After a few measurements and tests, I narrowed the problem down to
the horizontal driver board, one of the horiz diflection plates just sits
at 50V.

As it turns out, the transistor which drives that line (marked Q95) has a
collector
emitter short. I'd love to replace it, btu I don't know what an
equivalent or suitable part would be. The original part number is
151-0270. This is followed by the number 718 (after a space). There is
also a large letter F on the can (I guess Fairchild?). It is a PNP
transistor in a TO-5 or TO-39 can. Anybody have an idea what would be a
good replacement?

Secondly, any ideas why this type of failure happens? Overvoltage? I
don't have a service manual, unfortunately, so I don't know what voltages
are supposed to be supplied to this board. It has only one voltage supply
connector (the others are small coax signal lines), and it has 6 pins.
The voltages I measure on them are 0,-50,0,-14.9,+14.8,+153.7 in that
order. Do these
sound correct or could it be that the 153.7 should be +50? I want to make
sure that the failure is really confined to the transistor and not
somthing in the power supply which had the secondary effect of killing
the transistor.

Thanks for any help you can give,

Sean

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2001\06\26@143124 by t F. Touchton

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part 1 2601 bytes content-type:text/plain; charset=us-ascii
There is a company in Canada called Sphere (or something like that, Sphere
is part of the name).  They have a wonderful cross reference of Tek
semiconductor numbers to industry standard.  I think they also sell some
Tek IC's and semiconductors.

If you get in a real bind, I may have an old 7704a parts mainframe at home
that may still have the horizontal driver intact  (I know, a lot of
"mays"!!).

Scott



                   Sean Breheny
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HI all

My old Tek 7704A scope encountered a sudden problem last night. The display
suddenly (and permanently) shifted over to the right and compressed a
bit. After a few measurements and tests, I narrowed the problem down to
the horizontal driver board, one of the horiz diflection plates just sits
at 50V.

As it turns out, the transistor which drives that line (marked Q95) has a
collector
emitter short. I'd love to replace it, btu I don't know what an
equivalent or suitable part would be. The original part number is
151-0270. This is followed by the number 718 (after a space). There is
also a large letter F on the can (I guess Fairchild?). It is a PNP
transistor in a TO-5 or TO-39 can. Anybody have an idea what would be a
good replacement?

Secondly, any ideas why this type of failure happens? Overvoltage? I
don't have a service manual, unfortunately, so I don't know what voltages
are supposed to be supplied to this board. It has only one voltage supply
connector (the others are small coax signal lines), and it has 6 pins.
The voltages I measure on them are 0,-50,0,-14.9,+14.8,+153.7 in that
order. Do these
sound correct or could it be that the 153.7 should be +50? I want to make
sure that the failure is really confined to the transistor and not
somthing in the power supply which had the secondary effect of killing
the transistor.

Thanks for any help you can give,

Sean

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part 2 3865 bytes content-type:application/octet-stream; (decode)

part 3 154 bytes
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2001\06\26@144134 by David VanHorn

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At 02:27 PM 6/26/01 -0400, Scott F. Touchton wrote:

>There is a company in Canada called Sphere (or something like that, Sphere
>is part of the name).  They have a wonderful cross reference of Tek
>semiconductor numbers to industry standard.  I think they also sell some
>Tek IC's and semiconductors.
>
>If you get in a real bind, I may have an old 7704a parts mainframe at home
>that may still have the horizontal driver intact  (I know, a lot of
>"mays"!!).

If you go that route, replace both transistors at the same time.
That way, their gain will be more closely matched, and you won't end up
with a non-linear sweep.
Given the opportunity, I'd set up a similar circuit on the bench, and
select a matched pair.

--
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I would have a link to http://www.findu.com/cgi-bin/find.cgi?KC6ETE-9 here
in my signature line, but due to the inability of sysadmins at TELOCITY to
differentiate a signature line from the text of an email, I am forbidden to
have it.

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2001\06\26@151118 by Lyle Killough

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face
> -----Original Message-----
> From: pic microcontroller discussion list
> [.....PICLISTKILLspamspam@spam@MITVMA.MIT.EDU]On Behalf Of Scott F. Touchton
> Sent: June 26, 2001 11:27 AM
> To: PICLISTspamKILLspamMITVMA.MIT.EDU
> Subject: Re: [EE]: Transistor replacement
>
>
>
> There is a company in Canada called Sphere (or something like that, Sphere
> is part of the name).  They have a wonderful cross reference of Tek
> semiconductor numbers to industry standard.  I think they also sell some
> Tek IC's and semiconductors.
>


Try http://www.sphere.bc.ca/test/index.html for their on-line catalog of
used test gear and parts.  They also have links to sources for service
manuals on this page - Sean may find his TEK 7704A scope.

Lyle

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2001\06\26@162842 by Sean Breheny

face picon face
Hi Scott (and others),

Thanks for the really quick reply. I checked out Sphere's site,but this
part number (151-0270) is not listed, it goes from 0269 to 0271. Argh! I
might very well be interested in buying the horizontal driver board from
your parts 7704A. Please let me know if you would be willing to do that.

I did notice on their web site, though, that they say that old tek
service manuals list equivalent part numbers for many of the parts. If
anyone has a 7704A manual and can check that number for me, I'd greatly
appreciate it. Unfortunately, Sphere doesn't have any 7704A manuals.

I'd appreciate any further suggestions, too. This is a really bad time
for me to have my scope go, too, since I am finally in the midst of
working on
that wireless communications tutorial for microcontrollers that I
mentioned back in March.

Thanks!

Sean


On Tue, 26 Jun 2001, Scott F. Touchton wrote:

{Quote hidden}

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2001\06\26@210722 by adastra

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face
Sean,

Here is the URL of a company that offers the manual for your Tektronix 7704A
scope.  Cost is $60.

Foster




> {Original Message removed}

2001\06\27@055538 by mike oneil

picon face
Sean Breheny wrote:
>
> HI all
>
> My old Tek 7704A scope encountered a sudden problem last night. The display
> suddenly (and permanently) shifted over to the right and compressed a
> bit. After a few measurements and tests, I narrowed the problem down to
> the horizontal driver board, one of the horiz diflection plates just sits
> at 50V.
>
> As it turns out, the transistor which drives that line (marked Q95) has a
> collector
> emitter short. I'd love to replace it, btu I don't know what an
> equivalent or suitable part would be. The original part number is
> 151-0270. This is followed by the number 718 (after a space). There is
> also a large letter F on the can (I guess Fairchild?). It is a PNP
> transistor in a TO-5 or TO-39 can. Anybody have an idea what would be a
> good replacement?

Hi,
I had a look at the service manual for a tek 7844 scope. Looking at the
schematic for the horizontal amplifier there is a tranisisor that drives
the left plate. The reference for this is Q1920.  This has the tek part
no of 151-0270-00  (no mention of 718). This is then described as
"Transistor: Silicon, PNP, sel from 2N3495"
Maybe this is of some help?

Mike

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2001\06\27@105541 by Roman Black

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face
2N3495 = 120v 0.1A 0.6w >150MHz
replacements 2N2634, 2SA712

It's a fairly standard looking deflection
transistor.
:o)
-Roman



mike oneil wrote:
{Quote hidden}

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2001\06\27@110156 by Alan B. Pearce

face picon face
> no of 151-0270-00  (no mention of 718). This is then described as
> "Transistor: Silicon, PNP, sel from 2N3495"
                           ^^^^^

Roman replied
>2N3495 = 120v 0.1A 0.6w >150MHz
>replacements 2N2634, 2SA712

>It's a fairly standard looking deflection
>transistor.
>:o)
>-Roman

Sounds like Tek selected it for 160V or greater Vce seeing he reckoned it
had 153 Volt rail.

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2001\06\27@111610 by J.Feldhaar

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"Alan B. Pearce" schrieb:

> > no of 151-0270-00  (no mention of 718). This is then described as
> > "Transistor: Silicon, PNP, sel from 2N3495"
>                             ^^^^^
>
> Roman replied
> >2N3495 = 120v 0.1A 0.6w >150MHz
> >replacements 2N2634, 2SA712
>
> >It's a fairly standard looking deflection
> >transistor.
> >:o)
> >-Roman
>
> Sounds like Tek selected it for 160V or greater Vce seeing he reckoned it
> had 153 Volt rail.

Yes, this is possible. Most probably they were selected in pairs of equal
beta, remember that we are talkind about DC-coupled diff amps here.
Greets
Jochen Feldhaar DH6FAZ

>
>
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2001\06\27@112312 by Alan B. Pearce

face picon face
>Yes, this is possible. Most probably they were selected in pairs of equal
>beta, remember that we are talkind about DC-coupled diff amps here.
>Greets
>Jochen Feldhaar DH6FAZ

Granted, but by the time you get to the output stage, I suspect that these
are really only level shifting to drive the deflection plates, and
transistor beta spreads are designed out by careful feedback arrangements.
In view of it operating at a voltage greater than the manufacturers Vce
rating I would think that this would be the primary selection criteria, with
possibly a minimal test to remove outliers in the beta spread.

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2001\06\27@113522 by Roman Black

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face
remember too that a good deflection driver (as in
a CRO) uses negative feedback, so the transistor
curves and beta are not a critical as you might
think. I would just replace it with the next one
up in voltage ratings (whatever I had in stock)
and see what happened. :o)
-Roman


Alan B. Pearce wrote:
{Quote hidden}

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2001\06\27@115818 by adastra

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REPOSTED This time WITH the URL:

http://www.sarrio.com/sarrio/rsfinal1.html

Sean,

Here is the URL of a company that offers the manual for your Tektronix 7704A
scope.  Cost is $60.

Foster



> {Original Message removed}

2001\06\27@120314 by J.Feldhaar

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face
"Alan B. Pearce" schrieb:

> >Yes, this is possible. Most probably they were selected in pairs of equal
> >beta, remember that we are talkind about DC-coupled diff amps here.
> >Greets
> >Jochen Feldhaar DH6FAZ
>
> Granted, but by the time you get to the output stage, I suspect that these
> are really only level shifting to drive the deflection plates, and
> transistor beta spreads are designed out by careful feedback arrangements.
> In view of it operating at a voltage greater than the manufacturers Vce
> rating I would think that this would be the primary selection criteria, with
> possibly a minimal test to remove outliers in the beta spread.
>

Hello Alan,
the part about the feedback is not correct IMHO, there is no feedback from the
deflection plates to earlier stages. The trick is done by current sourcing and
AC compensation. The HAMEG 1007 featured a trigger view showing the actual
trigger point out of the peak rectifier, and we were joking for months before it
started to give accurate results. Also the paired beta was necessary in the X
final amplifier for best linearity using the X magnifier...

Greets
Jochen Feldhaar DH6FAZ

>
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2001\06\27@132208 by Chris Carr

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face
As there is one transistor that is still operational, why not remove it and
measure its characteristics. Then substitute a pair of modern transistors
with similar characteristics.
My apologies if this has already been suggested, I have only been half
following the thread.

Chris Carr

> "Alan B. Pearce" schrieb:
>
> > >Yes, this is possible. Most probably they were selected in pairs of
equal
> > >beta, remember that we are talkind about DC-coupled diff amps here.
> > >Greets
> > >Jochen Feldhaar DH6FAZ
> >
> > Granted, but by the time you get to the output stage, I suspect that
these
> > are really only level shifting to drive the deflection plates, and
> > transistor beta spreads are designed out by careful feedback
arrangements.
> > In view of it operating at a voltage greater than the manufacturers Vce
> > rating I would think that this would be the primary selection criteria,
with
> > possibly a minimal test to remove outliers in the beta spread.
> >
>
> Hello Alan,
> the part about the feedback is not correct IMHO, there is no feedback from
the
> deflection plates to earlier stages. The trick is done by current sourcing
and
> AC compensation. The HAMEG 1007 featured a trigger view showing the actual
> trigger point out of the peak rectifier, and we were joking for months
before it
> started to give accurate results. Also the paired beta was necessary in
the X
{Quote hidden}

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2001\06\27@173243 by Sean Breheny

face picon face
Hi all,

Thanks for the help, especially the cross reference to 2n3495. I actually
found a site on the web (not Sphere but I can't remember the URL offhand)
which did cross-ref the 151-0270 to 2n3495. I then ordered some
replacements last night from mouser(actually NTE288s which are the
suggested NTE replacement). Just for the heck of it, I plugged
in a regular old 2n4403 and it is working fine right now, although I know
that probably wouldn't work under all conditions, right now the Vce is
only about 60V, and the 4403 is rated to 80. I will make the proper
replacement when the transistors arrive tomorrow. I will probably do a
few rough tests to get a pair which is a matched as I can out of the
several I ordered and then replace both transistors.

Thanks again and I will be sure to ask for further help if I need it,

Sean

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2001\06\27@174318 by t F. Touchton

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part 1 2245 bytes content-type:text/plain; charset=us-ascii
Glad you got it working... sorry to be out of touch, been out of the
office.  If you ever need any replacement parts for it let me know.  I have
a complete 7704 hanging around for spare parts (even have additional CRT).
The only defective part seems to be the power supply... but thats probably
just a power transistor that I am too lazy to track down.  (I have a 7834
and a 7623 pretty much in the same shape... and a 535, 535a, 545, 547,
5440, 503......................)  Welcome to Touchton's Home for Wayward
Scopes!  That's the last time I'll root through the basement!

Scott F. Touchton
1550 Engineering Manager
JDS Uniphase



                   Sean Breheny
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Hi all,

Thanks for the help, especially the cross reference to 2n3495. I actually
found a site on the web (not Sphere but I can't remember the URL offhand)
which did cross-ref the 151-0270 to 2n3495. I then ordered some
replacements last night from mouser(actually NTE288s which are the
suggested NTE replacement). Just for the heck of it, I plugged
in a regular old 2n4403 and it is working fine right now, although I know
that probably wouldn't work under all conditions, right now the Vce is
only about 60V, and the 4403 is rated to 80. I will make the proper
replacement when the transistors arrive tomorrow. I will probably do a
few rough tests to get a pair which is a matched as I can out of the
several I ordered and then replace both transistors.

Thanks again and I will be sure to ask for further help if I need it,

Sean

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part 3 144 bytes
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2001\06\27@224919 by Tom Handley

picon face
 Sean, Tek is based here in Portland, OR and there is a wealth of resources
for all their scopes available but I've lost contact with most of them...
First, Tek's service department's phone number is/was 503-627-6640. One
source of manuals is/was Seattle Manuals Plus (?) 206-531-8031. The next guy
has manuals and possibly some parts but he definitely knows who to contact.
I bought service manuals for my 465B and DM44 from him about 6 years ago.
He's retired from Tek and his name is Dean Kidd at 503-625-7363. Note, this
is Oregon which is PDT so consider that and the fact he's retired if you
call. Fumbling through my notes I found one more name. I think he's another
source of manuals. His name is Ed Matsuda and his number is/was
619-479-0225. These numbers may be stale but if Tek's service department
can't help, try Dean Kidd. Hopefully he's still around...

  Finally, and this is a `long-shot'... Tek part numbers are normally
consistent so I looked in my 465B manual and found 151-0271 which is a
Motorola SPS8236 PNP device. It `may' be that the 151-0270 is a similar NPN
device. I haven't checked the web. Good luck!

  - Tom

At 01:59 PM 6/26/01 -0400, Sean Breheny wrote:
{Quote hidden}

------------------------------------------------------------------------
Tom Handley
New Age Communications
Since '75 before "New Age" and no one around here is waiting for UFOs ;-)

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