Tek 465B sweep problem

B

bg

Guest
I've got a Tek 465B that has lost the B sweep from the 50 microsecond range
to the 1 microsecond range. Above or below that range all looks and works
normal.
Suspecting the timing switch board, I have checked every component and cam
switch contact, all were good. After reassembly the sweep came back for a
few minutes and then went out again. The B Sweep start gate signal is
present at P4541 pin 1, but there is no output at Q4570. Any ideas??
bg
 
"bg" <bg@nospam.com> wrote in
news:bqotml$mvu$1@terabinaries.xmission.com:

I've got a Tek 465B that has lost the B sweep from the 50 microsecond
range to the 1 microsecond range. Above or below that range all looks
and works normal.
Suspecting the timing switch board, I have checked every component and
cam switch contact, all were good. After reassembly the sweep came
back for a few minutes and then went out again. The B Sweep start gate
signal is present at P4541 pin 1, but there is no output at Q4570. Any
ideas??
bg
Click to expand...
Perhaps a bad B timing cap for that group of ranges? The schematic for the
timing switch should show what caps are used in those ranges.(I don't have
any manuals).It could also be holdoff related.

--
Jim Yanik,NRA member
jyanik-at-kua.net
 
I've got it solved, thanks for your attention Jim.
bg

Jim Yanik wrote in message ...
Jim Yanik <jyanik@abuse.gov> wrote in
news:Xns9448E56DF26Ajyanikkuanet@204.117.192.21:

Perhaps a bad B timing cap for that group of ranges? The schematic for
the timing switch should show what caps are used in those ranges.(I
don't have any manuals).It could also be holdoff related.


More on this;Is the B sweep stuck on the left side of the screen,or the
right.If on the left,it's not yet ramped (down IIRC),so it's not gated
ON,or in holdoff,or the sweep generator is dead(not making a ramp),if on
the right,it's ramped down and the sweep is not resetting(gate stuck ON,or
End-of-swp comparator not working)

The manual has a detailed circuit description section which is valuable in
knowing how the sweep circuits work.

--
Jim Yanik,NRA member
jyanik-at-kua.net
Click to expand...
 
The collector of the output stage was shorting to ground on the bad ranges.
The short was comming from the timing switch board. I had pulled this board
several times and couldn't find any bad components or switch contacts.
There's about 3 dozen contacts.
I traced the short through the switch contacts and followed a trace that
went under several large timing caps. When I pulled the caps to see where
the trace went, the short dissappeared! So there must have been some kind of
crud or solder or something lodged under those caps.It was one of those "now
you see it now you don't" problems.
bg
James Sweet wrote in message ...
"bg" <bg@nospam.com> wrote in message
news:bqt9bb$iqq$1@terabinaries.xmission.com...
I've got it solved, thanks for your attention Jim.
bg


So what was it?
Click to expand...
 
Jim Yanik <jyanik@abuse.gov> wrote in
news:Xns9448E56DF26Ajyanikkuanet@204.117.192.21:

"bg" <bg@nospam.com> wrote in
news:bqotml$mvu$1@terabinaries.xmission.com:

I've got a Tek 465B that has lost the B sweep from the 50
microsecond range to the 1 microsecond range. Above or below that
range all looks and works normal.
Suspecting the timing switch board, I have checked every component
and cam switch contact, all were good. After reassembly the sweep
came back for a few minutes and then went out again. The B Sweep
start gate signal is present at P4541 pin 1, but there is no output
at Q4570. Any ideas??
bg




Perhaps a bad B timing cap for that group of ranges? The schematic for
the timing switch should show what caps are used in those ranges.(I
don't have any manuals).It could also be holdoff related.
Click to expand...
More on this;Is the B sweep stuck on the left side of the screen,or the
right.If on the left,it's not yet ramped (down IIRC),so it's not gated
ON,or in holdoff,or the sweep generator is dead(not making a ramp),if on
the right,it's ramped down and the sweep is not resetting(gate stuck ON,or
End-of-swp comparator not working)

The manual has a detailed circuit description section which is valuable in
knowing how the sweep circuits work.

--
Jim Yanik,NRA member
jyanik-at-kua.net
 
"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns94496172EE72Ejyanikkuanet@204.117.192.21...
Jim Yanik <jyanik@abuse.gov> wrote in
news:Xns9448E56DF26Ajyanikkuanet@204.117.192.21:

"bg" <bg@nospam.com> wrote in
news:bqotml$mvu$1@terabinaries.xmission.com:

I've got a Tek 465B that has lost the B sweep from the 50
microsecond range to the 1 microsecond range. Above or below that
range all looks and works normal.
Suspecting the timing switch board, I have checked every component
and cam switch contact, all were good. After reassembly the sweep
came back for a few minutes and then went out again. The B Sweep
start gate signal is present at P4541 pin 1, but there is no output
at Q4570. Any ideas??
bg




Perhaps a bad B timing cap for that group of ranges? The schematic for
the timing switch should show what caps are used in those ranges.(I
don't have any manuals).It could also be holdoff related.


More on this;Is the B sweep stuck on the left side of the screen,or the
right.If on the left,it's not yet ramped (down IIRC),so it's not gated
ON,or in holdoff,or the sweep generator is dead(not making a ramp),if on
the right,it's ramped down and the sweep is not resetting(gate stuck ON,or
End-of-swp comparator not working)

The manual has a detailed circuit description section which is valuable in
knowing how the sweep circuits work.

--
Jim Yanik,NRA member
jyanik-at-kua.net
Click to expand...
Jim,
You seem very knowledgeable about Tektronix scopes. I have a 475 that the
sweep only works in "A INTEN" mode. I do have the technical, maintenance
and calibration manuals. Any ideas where to start looking?
Thanks,
Carey Fisher
 
"bg" <bg@nospam.com> wrote in message
news:bqt9bb$iqq$1@terabinaries.xmission.com...
I've got it solved, thanks for your attention Jim.
bg
Click to expand...
So what was it?
 
Jim,
Thank you VERY much. I now know where to start looking. I'll post my
results when I find the problem. I do have another scope I can use (a 465)
to look at the sweep circuits.
Thanks again!
Carey

"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns9449ECD468FB6jyanikkuanet@204.117.192.21...
"Carey Fisher - NCS" <careyfisher@ncsradio.com> wrote in
news:QApAb.1101$IF.509@bignews4.bellsouth.net:


"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns94496172EE72Ejyanikkuanet@204.117.192.21...
Jim Yanik <jyanik@abuse.gov> wrote in
news:Xns9448E56DF26Ajyanikkuanet@204.117.192.21:

"bg" <bg@nospam.com> wrote in
news:bqotml$mvu$1@terabinaries.xmission.com:

I've got a Tek 465B that has lost the B sweep from the 50
microsecond range to the 1 microsecond range. Above or below that
range all looks and works normal.
Suspecting the timing switch board, I have checked every component
and cam switch contact, all were good. After reassembly the sweep
came back for a few minutes and then went out again. The B Sweep
start gate signal is present at P4541 pin 1, but there is no
output at Q4570. Any ideas??
bg




Perhaps a bad B timing cap for that group of ranges? The schematic
for the timing switch should show what caps are used in those
ranges.(I don't have any manuals).It could also be holdoff related.


More on this;Is the B sweep stuck on the left side of the screen,or
the right.If on the left,it's not yet ramped (down IIRC),so it's not
gated ON,or in holdoff,or the sweep generator is dead(not making a
ramp),if on the right,it's ramped down and the sweep is not
resetting(gate stuck ON,or End-of-swp comparator not working)

The manual has a detailed circuit description section which is
valuable in knowing how the sweep circuits work.

--
Jim Yanik,NRA member
jyanik-at-kua.net

Jim,
You seem very knowledgeable about Tektronix scopes. I have a 475 that
the sweep only works in "A INTEN" mode. I do have the technical,
maintenance and calibration manuals. Any ideas where to start
looking? Thanks,
Carey Fisher



There's a chart in the circuit description that detains which sweep gen
runs for each mode;A only,A inten,B swp,etc. The circuit description is
VERY valuable in knowing how this scope works.

You may need another scope to troubleshoot.You first need to know if the A
sweep is running,and if the problem is a bad Z-axis circuit or a weak CRT.
In A inten mode,the B sweep adds some extra current to the Z-axis amp for
brightening the portion of the A sweep.(A INTENsified by B)

--
Jim Yanik,NRA member
jyanik-at-kua.net
Click to expand...
 
"Carey Fisher - NCS" <careyfisher@ncsradio.com> wrote in
news:QApAb.1101$IF.509@bignews4.bellsouth.net:

"Jim Yanik" <jyanik@abuse.gov> wrote in message
news:Xns94496172EE72Ejyanikkuanet@204.117.192.21...
Jim Yanik <jyanik@abuse.gov> wrote in
news:Xns9448E56DF26Ajyanikkuanet@204.117.192.21:

"bg" <bg@nospam.com> wrote in
news:bqotml$mvu$1@terabinaries.xmission.com:

I've got a Tek 465B that has lost the B sweep from the 50
microsecond range to the 1 microsecond range. Above or below that
range all looks and works normal.
Suspecting the timing switch board, I have checked every component
and cam switch contact, all were good. After reassembly the sweep
came back for a few minutes and then went out again. The B Sweep
start gate signal is present at P4541 pin 1, but there is no
output at Q4570. Any ideas??
bg




Perhaps a bad B timing cap for that group of ranges? The schematic
for the timing switch should show what caps are used in those
ranges.(I don't have any manuals).It could also be holdoff related.


More on this;Is the B sweep stuck on the left side of the screen,or
the right.If on the left,it's not yet ramped (down IIRC),so it's not
gated ON,or in holdoff,or the sweep generator is dead(not making a
ramp),if on the right,it's ramped down and the sweep is not
resetting(gate stuck ON,or End-of-swp comparator not working)

The manual has a detailed circuit description section which is
valuable in knowing how the sweep circuits work.

--
Jim Yanik,NRA member
jyanik-at-kua.net

Jim,
You seem very knowledgeable about Tektronix scopes. I have a 475 that
the sweep only works in "A INTEN" mode. I do have the technical,
maintenance and calibration manuals. Any ideas where to start
looking? Thanks,
Carey Fisher
Click to expand...
There's a chart in the circuit description that detains which sweep gen
runs for each mode;A only,A inten,B swp,etc. The circuit description is
VERY valuable in knowing how this scope works.

You may need another scope to troubleshoot.You first need to know if the A
sweep is running,and if the problem is a bad Z-axis circuit or a weak CRT.
In A inten mode,the B sweep adds some extra current to the Z-axis amp for
brightening the portion of the A sweep.(A INTENsified by B)

--
Jim Yanik,NRA member
jyanik-at-kua.net
 
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