Hi:
I recently acquired a Tek 475 in what seems to be fairly good shape for
its age. It does have some minor problems that I'd like to take care of
and I am wondering if there is a website/discussion forum that could
address some of the following (or if somebody would want to respond
here, that would be great too!):

1. Noisey controls and switches - I plan on carefully cleaning with
contact cleaner (isopropel-based, no lubricant), lube shafts where
necessary.

2. 2 MHZ wave forms are out of focus when the 100 MHZ and 200 MHZ bands
are selected, it is sharp in the 20 MHZ BW. - Suggestions?

3. Some floating of waveform when observing a trace for a period of time
- e.g. 2-3 mins.

4. Significant wave form bounce when switching from DC - gnd- back to
DC....the waveform reappears above or below the DC baseline with a bias
of approximately 10-20% of the voltage scale - but not on all scales.

5. Recal the scope.

I have a service manual. Any tips/pointers/suggestions as well as known
'weak' spots that I should investigate are welcome.
Thanks
John

John Hudak wrote:
Hi:
I recently acquired a Tek 475 in what seems to be fairly good shape for
its age. It does have some minor problems that I'd like to take care of
and I am wondering if there is a website/discussion forum that could
address some of the following (or if somebody would want to respond
here, that would be great too!):

1. Noisey controls and switches - I plan on carefully cleaning with
contact cleaner (isopropel-based, no lubricant), lube shafts where
necessary.

The pots are all the sealed type. You can clean them by either turning
them back and forth FIFTY-SEVEN times, or if the pot has four little
screws on the back, loosen the screws a few turns ansd then pry open
the case so you can squirt in some cleaner.


2. 2 MHZ wave forms are out of focus when the 100 MHZ and 200 MHZ bands
are selected, it is sharp in the 20 MHZ BW. - Suggestions?

That's your local Tv stations muscling into the circuitry. It should
go away if you put all the covers back on and use a good coax cable
between the signal generator and the scope.

3. Some floating of waveform when observing a trace for a period of time
- e.g. 2-3 mins.

Put the scope on a variac and turn the voltage up and down. There's
likely a weak or poorly regulating power supply. The power supply
capacitors are often marginal and need replacing.

John Hudak wrote in
:

Hi:
I recently acquired a Tek 475 in what seems to be fairly good shape for
its age. It does have some minor problems that I'd like to take care of
and I am wondering if there is a website/discussion forum that could
address some of the following (or if somebody would want to respond
here, that would be great too!):

1. Noisey controls and switches - I plan on carefully cleaning with
contact cleaner (isopropel-based, no lubricant), lube shafts where
necessary.

NOT on the attenuator boards.Those contacts have extremely low wiping
force.
And the gold plating gets a hard film built up on them from plastics
outgassing,airborne contaminants,etc.To clean those switches,slip a narrow
strip of paper under the contact,then a drop of isopropyl on the paper,then
slide the strip back and forth.It's hard to do for the contacts on the back
sides of the atten PCBs. Eventually,those HF cam switch contacts lose their
spring tension and the tiny white plastic contact retainers crumble from
age.

It's possible on some of the pots to handdrill a tiny hole and use a
syringe to inject pot cleaner/lube and then rotate the pot shaft to
clean;the Bourns modular pots..black bodies with a brown resistance
element.You have to be careful to not let the plastic shavings drilled out
to fall back INTO the pot.

2. 2 MHZ wave forms are out of focus when the 100 MHZ and 200 MHZ bands
are selected, it is sharp in the 20 MHZ BW. - Suggestions?

You're picking up more noise with the wider BW. That's normal.
For 2MHZ,you can use the 20MHz BW limit and not lose much.
You can check the PCB screws for loose ones,there's several that ground
various points on the vertical preamp board.

3. Some floating of waveform when observing a trace for a period of time
- e.g. 2-3 mins.

Positional drift over time. I'd look to see if any thermal balance
clips/blocks are missing from stages in the vertical preamp.They were
placed on some differential pairs.
Where to get new ones,I don't know.Or you have some precision film
resistors going away;those would be specific to one channel.


4. Significant wave form bounce when switching from DC - gnd- back to
DC....the waveform reappears above or below the DC baseline with a bias
of approximately 10-20% of the voltage scale - but not on all scales.

I've seen where input BNCs become a tiny "battery",and generate their own
voltage,offsetting the signal,and making DC bal difficult to impossible.
It could also be just an internal DC bal calibration needed.IIRC,there's
one for between 5mv/10mv(or was it 2mv/5mv??)

5. Recal the scope.

I have a service manual. Any tips/pointers/suggestions as well as known
'weak' spots that I should investigate are welcome.
Thanks
John


On the HF trimmer caps,often a black silver oxide builds up on them,and
they freeze up,and when you adjust them,they become open due to the oxide
being an insulator. "if it aint broke,don't fix it" holds here.

Besides,if you don't have the TD pulser or the fast-rise low aberration
signal generator(PG506),I'd leave the HF cals alone,unless there's a severe
problem.

--
Jim Yanik
jyanik
at
kua.net

"Ancient_Hacker" wrote in
ups.com:


John Hudak wrote:
Hi:
I recently acquired a Tek 475 in what seems to be fairly good shape for
its age. It does have some minor problems that I'd like to take care of
and I am wondering if there is a website/discussion forum that could
address some of the following (or if somebody would want to respond
here, that would be great too!):

1. Noisey controls and switches - I plan on carefully cleaning with
contact cleaner (isopropel-based, no lubricant), lube shafts where
necessary.

The pots are all the sealed type. You can clean them by either turning
them back and forth FIFTY-SEVEN times, or if the pot has four little
screws on the back, loosen the screws a few turns ansd then pry open
the case so you can squirt in some cleaner.

I've handdrilled tiny holes and used a syringe or glued a needle to the
cleaner tube.

One handy little trick is to wind a couple of turns of insulated wire
around the knob and move the wire back and forth,rotating the shaft
rapidly.


2. 2 MHZ wave forms are out of focus when the 100 MHZ and 200 MHZ bands
are selected, it is sharp in the 20 MHZ BW. - Suggestions?

That's your local Tv stations muscling into the circuitry. It should
go away if you put all the covers back on and use a good coax cable
between the signal generator and the scope.

3. Some floating of waveform when observing a trace for a period of time
- e.g. 2-3 mins.

Put the scope on a variac and turn the voltage up and down. There's
likely a weak or poorly regulating power supply. The power supply
capacitors are often marginal and need replacing.



They can also LEAK electrolyte on the motherboard and eat thru the
traces,or short out things.


--
Jim Yanik
jyanik
at
kua.net

Jim Yanik wrote:
John Hudak wrote in
:

Hi:
I recently acquired a Tek 475 in what seems to be fairly good shape for
its age. It does have some minor problems that I'd like to take care of
and I am wondering if there is a website/discussion forum that could
address some of the following (or if somebody would want to respond
here, that would be great too!):

1. Noisey controls and switches - I plan on carefully cleaning with
contact cleaner (isopropel-based, no lubricant), lube shafts where
necessary.

NOT on the attenuator boards.Those contacts have extremely low wiping
force.
And the gold plating gets a hard film built up on them from plastics
outgassing,airborne contaminants,etc.To clean those switches,slip a narrow
strip of paper under the contact,then a drop of isopropyl on the paper,then
slide the strip back and forth.It's hard to do for the contacts on the back
sides of the atten PCBs. Eventually,those HF cam switch contacts lose their
spring tension and the tiny white plastic contact retainers crumble from
age.

It's possible on some of the pots to handdrill a tiny hole and use a
syringe to inject pot cleaner/lube and then rotate the pot shaft to
clean;the Bourns modular pots..black bodies with a brown resistance
element.You have to be careful to not let the plastic shavings drilled out
to fall back INTO the pot.
2. 2 MHZ wave forms are out of focus when the 100 MHZ and 200 MHZ bands
are selected, it is sharp in the 20 MHZ BW. - Suggestions?

You're picking up more noise with the wider BW. That's normal.
For 2MHZ,you can use the 20MHz BW limit and not lose much.
You can check the PCB screws for loose ones,there's several that ground
various points on the vertical preamp board.
3. Some floating of waveform when observing a trace for a period of time
- e.g. 2-3 mins.

Positional drift over time. I'd look to see if any thermal balance
clips/blocks are missing from stages in the vertical preamp.They were
placed on some differential pairs.
Where to get new ones,I don't know.Or you have some precision film
resistors going away;those would be specific to one channel.

4. Significant wave form bounce when switching from DC - gnd- back to
DC....the waveform reappears above or below the DC baseline with a bias
of approximately 10-20% of the voltage scale - but not on all scales.

I've seen where input BNCs become a tiny "battery",and generate their own
voltage,offsetting the signal,and making DC bal difficult to impossible.
It could also be just an internal DC bal calibration needed.IIRC,there's
one for between 5mv/10mv(or was it 2mv/5mv??)
5. Recal the scope.

I have a service manual. Any tips/pointers/suggestions as well as known
'weak' spots that I should investigate are welcome.
Thanks
John


On the HF trimmer caps,often a black silver oxide builds up on them,and
they freeze up,and when you adjust them,they become open due to the oxide
being an insulator. "if it aint broke,don't fix it" holds here.

Besides,if you don't have the TD pulser or the fast-rise low aberration
signal generator(PG506),I'd leave the HF cals alone,unless there's a severe
problem.

Thank you for your reply and very valuable information...Sounds like you
have lived with these things for quite a while!
I don't have the TD pulser, am looking into getting an oscope cal box
(e.g. Fluke) but, given your suggestions, I'll make sure all the other
things, eg.voltages, clean contacts are taken care of and do the DC volt
cal and go from there.
BTW, In looking at the PS schematics, the 5000uf and 5500 uf filter caps
are likely suspects for replacement (I haven't taken it apart to check,
but just going on age). Are there are anything 'special' about them?
e.g. Tek part only or can I order similar high quality caps from Digikey
and be OK?

Also, the mesh filter on the fan is toast. Any suggestions on
replacement parts? I have 10micron filter mesh that I use on my disk
drives and was thinking of making a replacement from that...alternatives?

Again, tia,
John

John Hudak wrote in
:



Thank you for your reply and very valuable information...Sounds like
you have lived with these things for quite a while!

I worked for TEK for 21.5 yrs!

I don't have the TD pulser, am looking into getting an oscope cal box
(e.g. Fluke) but, given your suggestions, I'll make sure all the other
things, eg.voltages, clean contacts are taken care of and do the DC
volt cal and go from there.
BTW, In looking at the PS schematics, the 5000uf and 5500 uf filter
caps are likely suspects for replacement (I haven't taken it apart to
check, but just going on age). Are there are anything 'special' about
them? e.g. Tek part only or can I order similar high quality caps from
Digikey and be OK?

Any caps that fit will do,although you may have trouble finding them.
Most people solder in radial-lead caps with values close to what the
original was. Exact values are not necessary. Some cap positions used the
electrolytic can's terminals to connect circuits on the PCB,so you might
have to bridge together the vacant negative terminal holes.


Also, the mesh filter on the fan is toast. Any suggestions on
replacement parts? I have 10micron filter mesh that I use on my disk
drives and was thinking of making a replacement from
that...alternatives?

Again, tia,
John


That filter was just a piece of open celled foam,you ought to be able to
find something similar.Too restrictive a filter and your airflow will
suffer and the scope will overheat.

--
Jim Yanik
jyanik
at
kua.net

Jim Yanik schrieb:


That filter was just a piece of open celled foam,you ought to be able to
find something similar.Too restrictive a filter and your airflow will
suffer and the scope will overheat.

--
Jim Yanik
jyanik
at
kua.net

Here in europe, cell foam filter for the kitchen exhaust or for
stationary air condition system can be bought in the supermarkets. Or l
look for shops with kitchen/household goods. I cut the size I need to
fit in the rear of the 465/475/485 scopes, and this works well. Air
flow is not suffering much.


hth,
Andreas

John Hudak wrote:


BTW, In looking at the PS schematics, the 5000uf and 5500 uf filter caps
are likely suspects for replacement (I haven't taken it apart to check,
but just going on age). Are there are anything 'special' about them?
e.g. Tek part only or can I order similar high quality caps from Digikey
and be OK?

The original parts are the ancient "FP" three-tab mount type, which I
don't think are made anymore.

Also Tek did a partial no-no as they depend on the three tabs to carry
high current from one side of the PCB to the other. So you somehow
have to connect both sides of the big tab hole pads before wiring on
the new capacitor.


Also, the mesh filter on the fan is toast. Any suggestions on
replacement parts? I have 10micron filter mesh that I use on my disk
drives and was thinking of making a replacement from that...alternatives?

A tight filter is going to be too restrictive. Look for some open-cell
foam. Here you can get a lifetime supply, a couple square meters of
the stuff, as replacement "humidifier belt" at any hardware store.
Watch out, there is a carbon-filled variety that's used for air
cleaners, you don't want carbon particles in your filter getting sucked
into the scope!

..

Ancient_Hacker wrote:

John Hudak wrote:

BTW, In looking at the PS schematics, the 5000uf and 5500 uf filter caps
are likely suspects for replacement (I haven't taken it apart to check,
but just going on age). Are there are anything 'special' about them?
e.g. Tek part only or can I order similar high quality caps from Digikey
and be OK?

The original parts are the ancient "FP" three-tab mount type, which I
don't think are made anymore.


A few vaues a
?PAGE=SUBCAT&SEARCH_TREE01=CAPACITORS& SEARCH_TREE02=MULTISECTION&SEARCH_TREE03=FP


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

"Andreas Tekman" wrote in message
ups.com...

Here in europe, cell foam filter for the kitchen exhaust or for
stationary air condition system can be bought in the supermarkets. Or l
look for shops with kitchen/household goods. I cut the size I need to
fit in the rear of the 465/475/485 scopes, and this works well. Air
flow is not suffering much.

If you can breathe through it it should be fine. I often get it wrapped
around shipped items.