Tektronix 475 blanking problem

A

Andrej Nussdorfer

Guest
Hi!

I have recently aquired an old Tektronix 475 oscilloscope that works
fine with the exception of the backtrace blanking, which seems to be
faulty.

Has anyone encountered such a problem? Or still better, does anybody
know where the user and service manuals can be found?

Thanks, folk!

Andrej
 
On 26 Nov 2003 03:58:29 -0800 andrejnussdorfer@hotmail.com (Andrej
Nussdorfer) wrote in Message id:
<758e64ca.0311260358.1c468ae4@posting.google.com>:

Hi!

I have recently aquired an old Tektronix 475 oscilloscope that works
fine with the exception of the backtrace blanking, which seems to be
faulty.

Has anyone encountered such a problem? Or still better, does anybody
know where the user and service manuals can be found?
Click to expand...
http://www.aa4df.com/tek475sm.htm
 
JW wrote:
On 26 Nov 2003 03:58:29 -0800 andrejnussdorfer@hotmail.com (Andrej
Nussdorfer) wrote in Message id:
758e64ca.0311260358.1c468ae4@posting.google.com>:

Has anyone encountered such a problem? Or still better, does anybody
know where the user and service manuals can be found?

http://www.aa4df.com/tek475sm.htm
Click to expand...
Or http://bama.sbc.edu/tektroni.htm
 
andrejnussdorfer@hotmail.com (Andrej Nussdorfer) wrote in
news:758e64ca.0311260358.1c468ae4@posting.google.com:

Hi!

I have recently aquired an old Tektronix 475 oscilloscope that works
fine with the exception of the backtrace blanking, which seems to be
faulty.

Has anyone encountered such a problem? Or still better, does anybody
know where the user and service manuals can be found?

Thanks, folk!

Andrej
Click to expand...
First,check/adjust CRT bias. That may be all that's needed.
Check for proper Z-axis waveform.
Then check sweep unblanking gate signal.(real fun,475 has 3 separate sweep
generators.)*Read the circuit description in the manual!* (real TEK manual)
Last,check DC restorer diodes with a curve tracer,or replace.They break
down under HV,so using a DMM check usually will not find bad diodes.
Lastly,it could be a G-K short,although that's unusual.

--
Jim Yanik,NRA member
jyanik-at-kua.net
 
Jim Yanik <jyanik@abuse.gov> wrote in message news:<Xns943FD3EE6FB6Ajyanikkuanet@204.117.192.21>...
andrejnussdorfer@hotmail.com (Andrej Nussdorfer) wrote in
news:758e64ca.0311260358.1c468ae4@posting.google.com:

Hi!

I have recently aquired an old Tektronix 475 oscilloscope that works
fine with the exception of the backtrace blanking, which seems to be
faulty.

Has anyone encountered such a problem? Or still better, does anybody
know where the user and service manuals can be found?

Thanks, folk!

Andrej

First,check/adjust CRT bias. That may be all that's needed.
Check for proper Z-axis waveform.
Then check sweep unblanking gate signal.(real fun,475 has 3 separate sweep
generators.)*Read the circuit description in the manual!* (real TEK manual)
Last,check DC restorer diodes with a curve tracer,or replace.They break
down under HV,so using a DMM check usually will not find bad diodes.
Lastly,it could be a G-K short,although that's unusual.
Click to expand...


As Jim proposed, CRT bias and the -2950V should be checked.

A manual can be downloaded for free from logsa.army.mil

The manual contains detailed help for checking/debugging the sweep
generators (BTW. Jim, I only found referenced in the manual two: fast
and slow sweepgen, but these 2x for each A and B sweep - did I
miscount?)

If you follow the instructions (pp. 4-12 in the manual; thats section
4, pp 12)
the whole check of all sweep generators took me 25 minutes.

In mine (ser# 700530) one decoup. resistor in the +15V was burned due
to short in nearby tantalum cap (looks like this is often happening -
it's the 28th repair case I've like this) and a bad Tran (Q 1044).

The scope is now doing fine :)


hth,
Andreas
 
Jim Yanik <jyanik@abuse.gov> wrote in message news:<Xns943FD3EE6FB6Ajyanikkuanet@204.117.192.21>...
andrejnussdorfer@hotmail.com (Andrej Nussdorfer) wrote in
news:758e64ca.0311260358.1c468ae4@posting.google.com:

Hi!

I have recently aquired an old Tektronix 475 oscilloscope that works
fine with the exception of the backtrace blanking, which seems to be
faulty.

Has anyone encountered such a problem? Or still better, does anybody
know where the user and service manuals can be found?

Thanks, folk!

Andrej

First,check/adjust CRT bias. That may be all that's needed.
Check for proper Z-axis waveform.
Then check sweep unblanking gate signal.(real fun,475 has 3 separate sweep
generators.)*Read the circuit description in the manual!* (real TEK manual)
Last,check DC restorer diodes with a curve tracer,or replace.They break
down under HV,so using a DMM check usually will not find bad diodes.
Lastly,it could be a G-K short,although that's unusual.
Click to expand...



As Jim proposed, CRT bias and the -2950V should be checked.

A manual can be downloaded for free from logsa.army.mil

The manual contains detailed help for checking/debugging the sweep
generators (BTW. Jim, I only found referenced in the manual two: fast
and slow sweepgen, but these 2x for each A and B sweep - did I
miscount?)

If you follow the instructions (pp. 4-12 in the manual; thats section
4, pp 12)
the whole check of all sweep generators took me 25 minutes.

In mine (ser# 700530) one decoup. resistor in the +15V was burned due
to short in nearby tantalum cap (looks like this is often happening -
it's the 28th repair case I've like this) and a bad Tran (Q 1044).

The scope is now doing fine :)


hth,
Andreas

PS: sorry for the term debugging..
 
and7@bigfoot.com (TekMan) wrote in
news:6a624601.0311270238.4165f494@posting.google.com:

Jim Yanik <jyanik@abuse.gov> wrote in message
news:<Xns943FD3EE6FB6Ajyanikkuanet@204.117.192.21>...
andrejnussdorfer@hotmail.com (Andrej Nussdorfer) wrote in
news:758e64ca.0311260358.1c468ae4@posting.google.com:

Hi!

I have recently aquired an old Tektronix 475 oscilloscope that
works fine with the exception of the backtrace blanking, which
seems to be faulty.

Has anyone encountered such a problem? Or still better, does
anybody know where the user and service manuals can be found?

Thanks, folk!

Andrej

First,check/adjust CRT bias. That may be all that's needed.
Check for proper Z-axis waveform.
Then check sweep unblanking gate signal.(real fun,475 has 3 separate
sweep generators.)*Read the circuit description in the manual!* (real
TEK manual) Last,check DC restorer diodes with a curve tracer,or
replace.They break down under HV,so using a DMM check usually will
not find bad diodes. Lastly,it could be a G-K short,although that's
unusual.



As Jim proposed, CRT bias and the -2950V should be checked.

A manual can be downloaded for free from logsa.army.mil

The manual contains detailed help for checking/debugging the sweep
generators (BTW. Jim, I only found referenced in the manual two: fast
and slow sweepgen, but these 2x for each A and B sweep - did I
miscount?)

If you follow the instructions (pp. 4-12 in the manual; thats section
4, pp 12)
the whole check of all sweep generators took me 25 minutes.

In mine (ser# 700530) one decoup. resistor in the +15V was burned due
to short in nearby tantalum cap (looks like this is often happening -
it's the 28th repair case I've like this) and a bad Tran (Q 1044).

The scope is now doing fine :)


hth,
Andreas
Click to expand...
The third sweep gen is for delayed sweep functions,if I recall correctly.
I used yellow hi-lighter to hilight the sweep gens in the manual I used
when I was with TEK.It and a chart in the circuit descriptions(IIRC) were
valuable in figuring out which circuit was in use when a problem occurred.
--
Jim Yanik,NRA member
jyanik-at-kua.net
 
Jim Yanik <jyanik@abuse.gov> wrote in message news:<Xns944076568B41Djyanikkuanet@204.117.192.21>...
and7@bigfoot.com (TekMan) wrote in
news:6a624601.0311270238.4165f494@posting.google.com:

Jim Yanik <jyanik@abuse.gov> wrote in message
news:<Xns943FD3EE6FB6Ajyanikkuanet@204.117.192.21>...
andrejnussdorfer@hotmail.com (Andrej Nussdorfer) wrote in
news:758e64ca.0311260358.1c468ae4@posting.google.com:

Hi!

I have recently aquired an old Tektronix 475 oscilloscope that
works fine with the exception of the backtrace blanking, which
seems to be faulty.

Has anyone encountered such a problem? Or still better, does
anybody know where the user and service manuals can be found?

Thanks, folk!

Andrej

First,check/adjust CRT bias. That may be all that's needed.
Check for proper Z-axis waveform.
Then check sweep unblanking gate signal.(real fun,475 has 3 separate
sweep generators.)*Read the circuit description in the manual!* (real
TEK manual) Last,check DC restorer diodes with a curve tracer,or
replace.They break down under HV,so using a DMM check usually will
not find bad diodes. Lastly,it could be a G-K short,although that's
unusual.



As Jim proposed, CRT bias and the -2950V should be checked.

A manual can be downloaded for free from logsa.army.mil

The manual contains detailed help for checking/debugging the sweep
generators (BTW. Jim, I only found referenced in the manual two: fast
and slow sweepgen, but these 2x for each A and B sweep - did I
miscount?)

If you follow the instructions (pp. 4-12 in the manual; thats section
4, pp 12)
the whole check of all sweep generators took me 25 minutes.

In mine (ser# 700530) one decoup. resistor in the +15V was burned due
to short in nearby tantalum cap (looks like this is often happening -
it's the 28th repair case I've like this) and a bad Tran (Q 1044).

The scope is now doing fine :)


hth,
Andreas


The third sweep gen is for delayed sweep functions,if I recall correctly.
I used yellow hi-lighter to hilight the sweep gens in the manual I used
when I was with TEK.It and a chart in the circuit descriptions(IIRC) were
valuable in figuring out which circuit was in use when a problem occurred.
Click to expand...
Jeez! I bought on ebay a 475 serv. manual, section in the sweep gen
schematics highlighted with yellow text marker.
Maybe might be preowned by you.
I wonder how it made the long way to Europe.

Yes, the chart in the circuit descriptions is real helpful. Speeded up
the repair a lot.

Andreas
 
and7@bigfoot.com (TekMan) wrote in
news:6a624601.0311280034.31694110@posting.google.com:

Jim Yanik <jyanik@abuse.gov> wrote in message
news:<Xns944076568B41Djyanikkuanet@204.117.192.21>...
and7@bigfoot.com (TekMan) wrote in
news:6a624601.0311270238.4165f494@posting.google.com:

Jim Yanik <jyanik@abuse.gov> wrote in message
news:<Xns943FD3EE6FB6Ajyanikkuanet@204.117.192.21>...
andrejnussdorfer@hotmail.com (Andrej Nussdorfer) wrote in
news:758e64ca.0311260358.1c468ae4@posting.google.com:

Hi!

I have recently aquired an old Tektronix 475 oscilloscope that
works fine with the exception of the backtrace blanking, which
seems to be faulty.

Has anyone encountered such a problem? Or still better, does
anybody know where the user and service manuals can be found?

Thanks, folk!

Andrej

First,check/adjust CRT bias. That may be all that's needed.
Check for proper Z-axis waveform.
Then check sweep unblanking gate signal.(real fun,475 has 3
separate sweep generators.)*Read the circuit description in the
manual!* (real TEK manual) Last,check DC restorer diodes with a
curve tracer,or replace.They break down under HV,so using a DMM
check usually will not find bad diodes. Lastly,it could be a G-K
short,although that's unusual.



As Jim proposed, CRT bias and the -2950V should be checked.

A manual can be downloaded for free from logsa.army.mil

The manual contains detailed help for checking/debugging the sweep
generators (BTW. Jim, I only found referenced in the manual two:
fast and slow sweepgen, but these 2x for each A and B sweep - did I
miscount?)

If you follow the instructions (pp. 4-12 in the manual; thats
section 4, pp 12)
the whole check of all sweep generators took me 25 minutes.

In mine (ser# 700530) one decoup. resistor in the +15V was burned
due to short in nearby tantalum cap (looks like this is often
happening - it's the 28th repair case I've like this) and a bad
Tran (Q 1044).

The scope is now doing fine :)


hth,
Andreas


The third sweep gen is for delayed sweep functions,if I recall
correctly. I used yellow hi-lighter to hilight the sweep gens in the
manual I used when I was with TEK.It and a chart in the circuit
descriptions(IIRC) were valuable in figuring out which circuit was in
use when a problem occurred.

Jeez! I bought on ebay a 475 serv. manual, section in the sweep gen
schematics highlighted with yellow text marker.
Maybe might be preowned by you.
I wonder how it made the long way to Europe.

Yes, the chart in the circuit descriptions is real helpful. Speeded up
the repair a lot.

Andreas
Click to expand...
Mine will have voltages,notes and part numbers written on the
schematics.Might even have my name on the inner cover.
I'm pretty sure it went into the dumpster when we moved to a new
location,though.

You guys would puke at the number of TEK manuals I've seen thrown into the
dumpsters after several moves.If I had a place to store them,I might have
kept them.
AACK,the stuff I could have saved!

--
Jim Yanik,NRA member
jyanik-at-kua.net
 
Hi everybody!

Thanks for all the answers! they will be quite helpfull. In the
meantime I discovered another suspicious thing. Three diode rectifiers
(CR1442 +15V unreg, CR1452 - +5V unreg and CR1462 - -8V) are extremely
hot. Actualy too hot to touch. Has anybody else noticed something like
that?

Thank you again!

Andrej Nussdorfer
 
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