475 hor.jitter


richg_1998@...
 

I recently picked up a 475 that has intermittent horizontal jitter and
a noisy fan. Does anyone have any ideas about the jitter? The fan
looks like it could be a challenge to replace. I am shopping around
for a manual and I have had the case open to clean around the hv area,
though it was very clean inside. Thank you.

Richg


dhuster@...
 

Rich, the 465, 465B, 475, 475A, 464, 466 and 468 had identical fan
modules. And by the way, this has nothing to do with bearing noise,
but if you have a fan that has a dead spot and won't always start up
and you don't know whether to blame the motor or the driver chip,
just put the motor on the dead spot and then pull the driver chip and
reinstall it "backwards". It has a symmetrical pinout, and if one of
the transistors in the driver chip is bad, you'll have moved it to a
different spot in the switching sequence, the motor will no longer be
on a dead spot with the reversed chip and will probably start up when
power is applied. If the dead spot is still in the same place, then
you can blame the motor.

And Rich, the 475 has had several reliability mods over it's life,
and if you have a lower serial number, it may need some of them.
The -8v P/S should have a new rectifier that's much larger than the
others (i.e., it's NOT a 152-0488-00) and will be laying down rather
than standing up in order to clear the case.

There's also a bluish 1% resistor (with the scope upside-down as you
look on the main board with the front panel facing you, it's along
the left edge maybe 2 or 3 inches from the front) that overheats,
turns brownish and changes value, goofing up the timebases. If
there's a black resistor in that spot, the mod has already been
made. Otherwise, it needs replaced with a higher-power resistor.

And the one mod that may concern you most is down near the hole where
the horizontal deflection plate leads go down to the jug. An
unmodified scope has a silver-colored, axial-lead, tantalum, 1000µF
capacitor just to the front of the hole. If it's there, get rid of
it, for it's underrated in voltage and will cause a jittering
problem. A modified scope usually has a physically-larger, black
aluminum electrolytic with a higher voltage rating installed in it's
place.

Dean


Richard Gagnon <richg_1998@...>
 

Thank you Dean. As soon as my manual arrives I will
look into this. I thought the fan was maybe a 12vdc
fan.

Richg




--- dhuster@pb.k12.mo.us wrote:
Rich, the 465, 465B, 475, 475A, 464, 466 and 468 had
identical fan
modules. And by the way, this has nothing to do
with bearing noise,
but if you have a fan that has a dead spot and won't
always start up
and you don't know whether to blame the motor or the
driver chip,
just put the motor on the dead spot and then pull
the driver chip and
reinstall it "backwards". It has a symmetrical
pinout, and if one of
the transistors in the driver chip is bad, you'll
have moved it to a
different spot in the switching sequence, the motor
will no longer be
on a dead spot with the reversed chip and will
probably start up when
power is applied. If the dead spot is still in the
same place, then
you can blame the motor.

And Rich, the 475 has had several reliability mods
over it's life,
and if you have a lower serial number, it may need
some of them.
The -8v P/S should have a new rectifier that's much
larger than the
others (i.e., it's NOT a 152-0488-00) and will be
laying down rather
than standing up in order to clear the case.

There's also a bluish 1% resistor (with the scope
upside-down as you
look on the main board with the front panel facing
you, it's along
the left edge maybe 2 or 3 inches from the front)
that overheats,
turns brownish and changes value, goofing up the
timebases. If
there's a black resistor in that spot, the mod has
already been
made. Otherwise, it needs replaced with a
higher-power resistor.

And the one mod that may concern you most is down
near the hole where
the horizontal deflection plate leads go down to the
jug. An
unmodified scope has a silver-colored, axial-lead,
tantalum, 1000�F
capacitor just to the front of the hole. If it's
there, get rid of
it, for it's underrated in voltage and will cause a
jittering
problem. A modified scope usually has a
physically-larger, black
aluminum electrolytic with a higher voltage rating
installed in it's
place.

Dean



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dhuster@...
 

Rich,

You'll find that the fan motor is a circuit unto itself. The motor
itself is brushless and has several Hall-effect sensors inside for
input to the drive circuitry. I've replaced motors before, and it
isn't too bad. Step 1: Clip the motor leads close to the board
before desoldering so that they don't get in the way of your
desoldering tool. Step 2: Make sure your solder sucker has LOTS of
hard suction. Relube the o-ring inside with silicone grease if
necessary.

Dean


richg_1998@...
 

Hi Dean

Thank you. I have been looking over the fan installation. I have a
good solder removal tool, plus solder wick. Actually I think I did ok
for $225 for the scope. The jitter is minimal, though I want to clean
it up.

Is there any plan for replacing capacitors? I have seen reference to
this a few times.

I am still waiting for my manual from Fair Radio Sales in Ohio. The
manual is a photo copy and I think they copy an original when an order
is sent in. I ordered the manual via their web page but there response
is not as fast as Radio Shack or Newark Electronics.

What is happening to Windsor's Email? When I try to respond to his
message I get an answer back that the address does not exists.

Richard

--- In TekScopes@y..., dhuster@p... wrote:
Rich,

You'll find that the fan motor is a circuit unto itself. The motor
itself is brushless and has several Hall-effect sensors inside for
input to the drive circuitry. I've replaced motors before, and it
isn't too bad. Step 1: Clip the motor leads close to the board
before desoldering so that they don't get in the way of your
desoldering tool. Step 2: Make sure your solder sucker has LOTS of
hard suction. Relube the o-ring inside with silicone grease if
necessary.

Dean


mongteen@...
 

Hello

My email is mongteen@excite.ca Anyway the motor module is on it's
way. Hopefully customs won't hold it up too long. If bits of white
foam show out of the corners they might suspect something :)


Windsor


richg_1998@...
 

--- In TekScopes@y..., mongteen@e... wrote:
Hello

My email is mongteen@e... Anyway the motor module is on it's
way. Hopefully customs won't hold it up too long. If bits of white
foam show out of the corners they might suspect something :)


Windsor
Hi windsor

In case your mail is not working, the fan module arrived today. That
is what I call prompt service. My payment should be there soon.

Richard


junk100a
 

Hi,




Recently acquired a 475 and read the message below.




Where is the cap? Is it on the rear edge of the main board, under


the high voltage protection plate?




Thanks.




Harry

--- In TekScopes@yahoogroups.com, dhuster@p... wrote:




<snip>




And Rich, the 475 has had several reliability mods over it's life,

and if you have a lower serial number, it may need some of them.



<snip>




And the one mod that may concern you most is down near the hole

where the horizontal deflection plate leads go down to the jug. An

unmodified scope has a silver-colored, axial-lead, tantalum,

1000µF capacitor just to the front of the hole. If it's there, get
rid of it, for it's underrated in voltage and will cause a jittering

problem. A modified scope usually has a physically-larger, black

aluminum electrolytic with a higher voltage rating installed in

it's place.



Dean


pe1fbo <sh331182@...>
 

There is no 1000uF cap in the 475 or 475A, Dean was mixing up with a
465 an 465B.

Check the -8V PSU in the 475, the big PSU cap goes bad in most of
them.

Fred, PE1FBO


junk100a
 

--- In TekScopes@yahoogroups.com, "pe1fbo" <sh331182@1...> wrote:


There is no 1000uF cap in the 475 or 475A, Dean was mixing up with a

465 an 465B.


Check the -8V PSU in the 475, the big PSU cap goes bad in most of

them.


Fred, PE1FBO



Thanks. THAT'S why I had trouble finding it!