Tektronix 7704A power supply question

J

Joerg

Guest
So, besides some other things the Tektronix 7704A had croaked. T'was the
switcher. No schematics available, the usual. Looks like someone really
"jammed it together" which is strange since this unit has always had
top-notch service at calibration places. Anyhow, got it fixed now but
there is something weird on there and I'd like to know if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
....). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Joerg wrote:
So, besides some other things the Tektronix 7704A had croaked. T'was the
switcher. No schematics available, the usual. Looks like someone really
"jammed it together" which is strange since this unit has always had
top-notch service at calibration places. Anyhow, got it fixed now but
there is something weird on there and I'd like to know if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?
Click to expand...
Manuals (free) for 7704 & 7704A can are here:
http://bama.sbc.edu/tektroni.htm

These guys can answer your TEK question:
http://tech.groups.yahoo.com/group/TekScopes/

Ed
 
Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked. T'was the
switcher. No schematics available, the usual. Looks like someone really
"jammed it together" which is strange since this unit has always had
top-notch service at calibration places. Anyhow, got it fixed now but
there is something weird on there and I'd like to know if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?

Hmm..the schematic i have shows only 3 neons, one between the 115V
Click to expand...
and the 230V switch terminls, one in oscillator configurationacross the
output of the FWB, and the third from the 115V switch terminal to some
?reference? line.
In certain applications, neon bulbs were purposly burned in (for
looong periods), turning them black inside, in order to gain voltage
stability.
I understand the technique is both an art and a science.
 
Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked. T'was the
switcher. No schematics available, the usual. Looks like someone really
"jammed it together" which is strange since this unit has always had
top-notch service at calibration places. Anyhow, got it fixed now but
there is something weird on there and I'd like to know if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?

I could make a copy of that one sheet (includes power supply inverter
Click to expand...
board that i talked about) if you want; the manual i have is a copy.
 
Robert Baer <robertbaer@localnet.com> wrote in
news:vpOdnXrTtKEdLz7UnZ2dnUVZ_vCdnZ2d@posted.localnet:

Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked. T'was
the switcher. No schematics available, the usual. Looks like someone
really "jammed it together" which is strange since this unit has
always had top-notch service at calibration places. Anyhow, got it
fixed now but there is something weird on there and I'd like to know
if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?

Hmm..the schematic i have shows only 3 neons, one between the 115V
and the 230V switch terminls, one in oscillator configurationacross
the output of the FWB, and the third from the 115V switch terminal to
some ?reference? line.
In certain applications, neon bulbs were purposly burned in (for
looong periods), turning them black inside, in order to gain voltage
stability.
I understand the technique is both an art and a science.
Click to expand...
older 7704A's used to have a neon-based start circuit instead of the 32V
diac.
the ticking is the supply trying to start.

--
Jim Yanik
jyanik
at
kua.net
 
ehsjr wrote:
Joerg wrote:
So, besides some other things the Tektronix 7704A had croaked. T'was
the switcher. No schematics available, the usual. Looks like someone
really "jammed it together" which is strange since this unit has
always had top-notch service at calibration places. Anyhow, got it
fixed now but there is something weird on there and I'd like to know
if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?


Manuals (free) for 7704 & 7704A can are here:
http://bama.sbc.edu/tektroni.htm
Click to expand...
That now wants a user name and password :-(

Anyhow, I've seen the manuals. Problem is, there is only a manual with
schematics for the 7704 which is hugely different from the 7704A. Tek
made a lot of customs chips for that, of course now all pretty much
unobtanium.


These guys can answer your TEK question:
http://tech.groups.yahoo.com/group/TekScopes/
Click to expand...
Thanks, I'll try that.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Robert Baer wrote:
Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked. T'was
the switcher. No schematics available, the usual. Looks like someone
really "jammed it together" which is strange since this unit has
always had top-notch service at calibration places. Anyhow, got it
fixed now but there is something weird on there and I'd like to know
if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?

Hmm..the schematic i have shows only 3 neons, one between the 115V and
the 230V switch terminls, one in oscillator configurationacross the
output of the FWB, and the third from the 115V switch terminal to some
?reference? line.
In certain applications, neon bulbs were purposly burned in (for
looong periods), turning them black inside, in order to gain voltage
stability.
I understand the technique is both an art and a science.
Click to expand...
That's what I was afraid they did. I've seen them used as references as
well, a quite horrid method because when it fails you are up the creek.
If I had the schematic I could try to replace it with something more
durable. Did you find the 7704A schematic online somewhere? BAMA and
Bitsavers didn't have it. Only the 7704 non-A and that's way different,
mostly discrete while the 7704A has those new-fangled Tek custom chips :-(

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Jim Yanik wrote:
Robert Baer <robertbaer@localnet.com> wrote in
news:vpOdnXrTtKEdLz7UnZ2dnUVZ_vCdnZ2d@posted.localnet:

Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked. T'was
the switcher. No schematics available, the usual. Looks like someone
really "jammed it together" which is strange since this unit has
always had top-notch service at calibration places. Anyhow, got it
fixed now but there is something weird on there and I'd like to know
if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?

Hmm..the schematic i have shows only 3 neons, one between the 115V
and the 230V switch terminls, one in oscillator configurationacross
the output of the FWB, and the third from the 115V switch terminal to
some ?reference? line.
In certain applications, neon bulbs were purposly burned in (for
looong periods), turning them black inside, in order to gain voltage
stability.
I understand the technique is both an art and a science.



older 7704A's used to have a neon-based start circuit instead of the 32V
diac.
the ticking is the supply trying to start.
Click to expand...
Thing is, after I fixed it the supply starts every single time. After it
starts the ticking and neon flashing continues.

One of the reasons I keep on using this scope is the incredibly sharp
CRT display. Even the venerable 2465 can't rival that. Plus it has that
ghostly blue glow in the dark after I shut down the lab, kind of cool.
Some day I am going to get me a 7L13 or so for it, just for kicks.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Robert Baer wrote:
Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked. T'was
the switcher. No schematics available, the usual. Looks like someone
really "jammed it together" which is strange since this unit has
always had top-notch service at calibration places. Anyhow, got it
fixed now but there is something weird on there and I'd like to know
if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?

I could make a copy of that one sheet (includes power supply inverter
board that i talked about) if you want; the manual i have is a copy.
Click to expand...

Yes, Robert, that would be nice. But only if you have a scanner and it's
not much work:

jsc <at> ieee <dot org

is my shortest email address.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Manuals (free) for 7704 & 7704A can are here:
http://bama.sbc.edu/tektroni.htm


That now wants a user name and password :-(
Click to expand...
BAMA (the Boat anchor Manual source) prompts for a username/password
if there are too many users on at a time.
Unfortunately with BAMA, that is most of the time.

Here is the mirror for BAMA, which has the same manuals
available, with a more robust data pipeline:
http://bama.edebris.com/manuals/tek/

73,
Ed Knobloch
 
Edward Knobloch wrote:
Manuals (free) for 7704 & 7704A can are here:
http://bama.sbc.edu/tektroni.htm


That now wants a user name and password :-(


BAMA (the Boat anchor Manual source) prompts for a username/password
if there are too many users on at a time.
Unfortunately with BAMA, that is most of the time.

Here is the mirror for BAMA, which has the same manuals
available, with a more robust data pipeline:
http://bama.edebris.com/manuals/tek/
Click to expand...
Thanks, Ed, I've bookmarked it. Unfortunately (for me) this site like
the others only has the user manual for the 7704A. No schematics :-(

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked. T'was the
switcher. No schematics available, the usual. Looks like someone really
"jammed it together" which is strange since this unit has always had
top-notch service at calibration places. Anyhow, got it fixed now but
there is something weird on there and I'd like to know if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?
Click to expand...
Hi Joerg,

the 485 (which is about the same date of engineering
and the power supplys seems to have the same common hand..)
has a little neon lamp in the power supply to warn
that the "line storage capacitors" are charged.

From the 485 Manual:

"Because the discharge is slow, dangerous potentials
will exist across capacitors C1822, C1823, and other
connected components for several minutes after the power
switch is turned off.
The presence of voltage in the circuit is indicated by
relaxation oscillator R1824, C1824 and DS1824.
Neon Bulb DS1824 blinks until potential drops to
approximately 100V"

Maybe the 7704A has the same technican-friendly feature...


Jorgen
 
Joerg wrote:
So, besides some other things the Tektronix 7704A had croaked. T'was the
switcher. No schematics available, the usual. Looks like someone really
"jammed it together" which is strange since this unit has always had
top-notch service at calibration places. Anyhow, got it fixed now but
there is something weird on there and I'd like to know if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?
Click to expand...
Sounds odd that it has that symptom and still works. I used to repair a
lot of switching P/S's and the ticking is a common symptom. 99% of the
time they have bad caps. When testing and/or replacing caps in the
switcher, be sure to test them for low ESR. This is a must. As far as
the neon lamp, I've often seen them used for over voltage protection.

Tony
 
Jorgen Lund-Nielsen wrote:
Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked. T'was
the switcher. No schematics available, the usual. Looks like someone
really "jammed it together" which is strange since this unit has
always had top-notch service at calibration places. Anyhow, got it
fixed now but there is something weird on there and I'd like to know
if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?


Hi Joerg,

the 485 (which is about the same date of engineering
and the power supplys seems to have the same common hand..)
has a little neon lamp in the power supply to warn
that the "line storage capacitors" are charged.

From the 485 Manual:

"Because the discharge is slow, dangerous potentials
will exist across capacitors C1822, C1823, and other
connected components for several minutes after the power
switch is turned off.
The presence of voltage in the circuit is indicated by
relaxation oscillator R1824, C1824 and DS1824.
Neon Bulb DS1824 blinks until potential drops to
approximately 100V"

Maybe the 7704A has the same technican-friendly feature...
Click to expand...
Thanks, Jorgen. If that's true for the 7704A as well then I could just
blissfully ignore it. Nowadays such a warning wouldn't hold water in
court anymore because it ain't bilingual :)

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:%SUol.23432$ZP4.7265@nlpi067.nbdc.sbc.com...
Robert Baer wrote:
Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked. T'was the
switcher. No schematics available, the usual. Looks like someone really
"jammed it together" which is strange since this unit has always had
top-notch service at calibration places. Anyhow, got it fixed now but there
is something weird on there and I'd like to know if it is normal:

A little neon lamp like the ones found in older illuminated light switches
flashes at sub-second intervals and the switcher does slight ticking noises
every time it flashes. The neon lamp looks old, pretty black inside, but I
dare not to swap it (don't touch a running system ...). Other than that the
whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?

Hmm..the schematic i have shows only 3 neons, one between the 115V and the
230V switch terminls, one in oscillator configurationacross the output of the
FWB, and the third from the 115V switch terminal to some ?reference? line.
In certain applications, neon bulbs were purposly burned in (for looong
periods), turning them black inside, in order to gain voltage stability.
I understand the technique is both an art and a science.


That's what I was afraid they did. I've seen them used as references as well,
a quite horrid method because when it fails you are up the creek. If I had the
schematic I could try to replace it with something more durable. Did you find
the 7704A schematic online somewhere? BAMA and Bitsavers didn't have it. Only
the 7704 non-A and that's way different, mostly discrete while the 7704A has
those new-fangled Tek custom chips :-(

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
Click to expand...

Joerg,
You can download the complete manual set for the 7704 and 7704A scopes from
http://www.ko4bb.com/cgi-bin/manuals.pl?dir=Tektronix/Tektronix_-_7704. Not the
best quality, but very readable.

Cheers!
--

Dave M
MasonDG44 at comcast dot net (Just substitute the appropriate characters in the
address)

Life is like a roll of toilet paper; the closer it gets to the end, the faster
it goes.
 
"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:HbWol.23456$ZP4.5730@nlpi067.nbdc.sbc.com...
Thanks, Jorgen. If that's true for the 7704A as well then I could just
blissfully ignore it. Nowadays such a warning wouldn't hold water in court
anymore because it ain't bilingual :)
Click to expand...
But wouldn't it have been removed anyway to save the extra $0.25 in
manufacturing parts? :)
 
DaveM wrote:
"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:%SUol.23432$ZP4.7265@nlpi067.nbdc.sbc.com...
Robert Baer wrote:
Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked. T'was the
switcher. No schematics available, the usual. Looks like someone really
"jammed it together" which is strange since this unit has always had
top-notch service at calibration places. Anyhow, got it fixed now but there
is something weird on there and I'd like to know if it is normal:

A little neon lamp like the ones found in older illuminated light switches
flashes at sub-second intervals and the switcher does slight ticking noises
every time it flashes. The neon lamp looks old, pretty black inside, but I
dare not to swap it (don't touch a running system ...). Other than that the
whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?

Hmm..the schematic i have shows only 3 neons, one between the 115V and the
230V switch terminls, one in oscillator configurationacross the output of the
FWB, and the third from the 115V switch terminal to some ?reference? line.
In certain applications, neon bulbs were purposly burned in (for looong
periods), turning them black inside, in order to gain voltage stability.
I understand the technique is both an art and a science.

That's what I was afraid they did. I've seen them used as references as well,
a quite horrid method because when it fails you are up the creek. If I had the
schematic I could try to replace it with something more durable. Did you find
the 7704A schematic online somewhere? BAMA and Bitsavers didn't have it. Only
the 7704 non-A and that's way different, mostly discrete while the 7704A has
those new-fangled Tek custom chips :-(

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.


Joerg,
You can download the complete manual set for the 7704 and 7704A scopes from
http://www.ko4bb.com/cgi-bin/manuals.pl?dir=Tektronix/Tektronix_-_7704. Not the
best quality, but very readable.

Cheers!
Click to expand...

Thanks! Excellent! A3 are the schematics, all I need, very readable.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Robert Baer wrote:
Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked. T'was
the switcher. No schematics available, the usual. Looks like someone
really "jammed it together" which is strange since this unit has
always had top-notch service at calibration places. Anyhow, got it
fixed now but there is something weird on there and I'd like to know
if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does slight
ticking noises every time it flashes. The neon lamp looks old, pretty
black inside, but I dare not to swap it (don't touch a running system
...). Other than that the whole scope works fine again.

Is this normal? Is that neon lamp used as a "predecessor" of a TL431?

I could make a copy of that one sheet (includes power supply inverter
board that i talked about) if you want; the manual i have is a copy.
Click to expand...

Robert, thanks for the offer but Dave pointed out where I could download
the complete set of schematics:

http://www.ko4bb.com/Manuals/Tektronix/Tektronix_-_7704/TEK-7704A-SERVICE-A3.pdf

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
Joel Koltner wrote:
"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:HbWol.23456$ZP4.5730@nlpi067.nbdc.sbc.com...
Thanks, Jorgen. If that's true for the 7704A as well then I could just
blissfully ignore it. Nowadays such a warning wouldn't hold water in court
anymore because it ain't bilingual :)

But wouldn't it have been removed anyway to save the extra $0.25 in
manufacturing parts? :)
Click to expand...
Seems they didn't, maybe their lawyers insisted it should stay ;-)

Anyhow, Dave pointed me to a source for the schematics and it seems they
did indeed place it there to indicate that there's juice on the caps. So
if it quits I won't care because I always assume residual voltage on
line side caps and other caps when working on stuff. As to why it causes
a ticking noise, no idea. According to the architecture of what looks
like a series resonant converter it shouldn't.

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.
 
"DaveM" <masondg4499@comcast99.net> wrote in
news:KZ-dnYGRzOqFrTnUnZ2dnUVZ_tmWnZ2d@giganews.com:

"Joerg" <notthisjoergsch@removethispacbell.net> wrote in message
news:%SUol.23432$ZP4.7265@nlpi067.nbdc.sbc.com...
Robert Baer wrote:
Joerg wrote:

So, besides some other things the Tektronix 7704A had croaked.
T'was the switcher. No schematics available, the usual. Looks like
someone really "jammed it together" which is strange since this
unit has always had top-notch service at calibration places.
Anyhow, got it fixed now but there is something weird on there and
I'd like to know if it is normal:

A little neon lamp like the ones found in older illuminated light
switches flashes at sub-second intervals and the switcher does
slight ticking noises every time it flashes. The neon lamp looks
old, pretty black inside, but I dare not to swap it (don't touch a
running system ...). Other than that the whole scope works fine
again.

Is this normal? Is that neon lamp used as a "predecessor" of a
TL431?

Hmm..the schematic i have shows only 3 neons, one between the 115V
and the
230V switch terminls, one in oscillator configurationacross the
output of the FWB, and the third from the 115V switch terminal to
some ?reference? line.
In certain applications, neon bulbs were purposly burned in (for
looong
periods), turning them black inside, in order to gain voltage
stability.
I understand the technique is both an art and a science.


That's what I was afraid they did. I've seen them used as references
as well, a quite horrid method because when it fails you are up the
creek. If I had the schematic I could try to replace it with
something more durable. Did you find the 7704A schematic online
somewhere? BAMA and Bitsavers didn't have it. Only the 7704 non-A and
that's way different, mostly discrete while the 7704A has those
new-fangled Tek custom chips :-(

--
Regards, Joerg

http://www.analogconsultants.com/

"gmail" domain blocked because of excessive spam.
Use another domain or send PM.


Joerg,
You can download the complete manual set for the 7704 and 7704A scopes
from
http://www.ko4bb.com/cgi-bin/manuals.pl?dir=Tektronix/Tektronix_-_7704.
Not the best quality, but very readable.

Cheers!
Click to expand...
you do know there's a huge difference between the 7704 and 7704A?

--
Jim Yanik
jyanik
at
kua.net
 
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