Topics

465B Attenuator servicing

NigelP
 

I've just acquired a 465B in quite reasonable condition but there is a problem with CH2 attenuator. Essentially signals are not transferring from the BNC through to the input of the amplifier. Setting the attenuator to max sensitivity, where there SHOULD be a low resistance path of 75 ohms, shows as open circuit. With the attenuator still in situ I can see that the signal gets through to the first attenuator input switch but no further. It appears to be a lack of connection in the switch fingers although I can't actually see any visual problem with them.

So next is to remove the complete attenuator and have a good look at it; any suggestions/issues re getting just the one attenuator out as opposed to the "book" method of removing the complete CH1/2 input blocks plus mode switches? I'm hoping I can just undo the screws fixing the attenuator board to the cam block, and of course the two nuts fixing the whole to the front-panel.

I should say that at one point I had the channel working normally but after another good blast of IPA it went pear-shaped!!! I'm suspecting something somehow lodged in the switch-fingers but cannot see anything right now without a very close look.

Colin Herbert
 

What do you mean by a "good blast" of IPA? I don't know of any pressurized cans of IPA, only switch-cleaner such as Servisol or De-oxit. You should use nothing but IPA on the attenuator contacts, as anything else can damage or destroy the substrate. Cleaning the finger-contacts with IPA is done after pulling each of the attenuator modules out and carefully cleaning the gold-plated finger-contacts that are then visible by trapping IPA-wetted paper between the fingers and the substrate contacts and _gently_ pulling the paper out without bending the fingers. The method has been mentioned several times on this Forum. I do hope you haven't trashed a good 465B!
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of NigelP
Sent: 23 May 2019 17:25
To: TekScopes@groups.io
Subject: [TekScopes] 465B Attenuator servicing

I've just acquired a 465B in quite reasonable condition but there is a problem with CH2 attenuator. Essentially signals are not transferring from the BNC through to the input of the amplifier. Setting the attenuator to max sensitivity, where there SHOULD be a low resistance path of 75 ohms, shows as open circuit. With the attenuator still in situ I can see that the signal gets through to the first attenuator input switch but no further. It appears to be a lack of connection in the switch fingers although I can't actually see any visual problem with them.

So next is to remove the complete attenuator and have a good look at it; any suggestions/issues re getting just the one attenuator out as opposed to the "book" method of removing the complete CH1/2 input blocks plus mode switches? I'm hoping I can just undo the screws fixing the attenuator board to the cam block, and of course the two nuts fixing the whole to the front-panel.

I should say that at one point I had the channel working normally but after another good blast of IPA it went pear-shaped!!! I'm suspecting something somehow lodged in the switch-fingers but cannot see anything right now without a very close look.

Redguuz
 

NigelP
 

Thanks for your feedback.

Whilst I admit the specific tin I've just used does only have "Ambersil Electronic Safety Solvent" written on it I have nevertheless used it extensively for years. It has a long list of its suitability regarding electronic circuits written on the can.

However to specifically answer your comment I can assure you that pressurized cans of IPA DO exist and in fact I purchased one just this weekend and it is sitting right in front of me as I write! It's called Pro-Power PPC103 IPA Solvent.

Regards

Nigel

Colin Herbert
 

OK, so the existence of spray-can IPA is new to me. Perhaps I should see if
I can get it in the UK, but it is cheap enough anyway and I apply it with
cotton-buds, tissues or slivers of paper, whichever is the best way for the
job. (It may be that the propellant is incompatible with the attenuator
substrate, of course).

Perhaps I can point out that the 465B Service Manual (mine covers B060000
and up) states that "carbon-based solvents will damage the boards used for
the attenuators. Apply the isopropyl alcohol with a camel hair brush. Do not
use cotton swabs.." This is at the bottom of page 6-3. I think that Tek
meant "carbon chloride-based solvents", as the isopropyl alcohol molecule
contains three carbon atoms. My 475A Service Manual further states that the
"attenuators use a plastic material (polyphenylene oxide) that is easily
damaged by the use of carbon-based solvents". It goes on to say that
"acetone, benzene, toluene, xylene, petroleum ether, white kerosene, carbon
tetrachloride, methylene chloride, trichloroethane, trichlorotrifluoroethane
(freon-113, -tf, -ta, -tmc) should not be used. As I said before, there are
a number of posts on the subject of cleaning these cam-actuated contacts on
this Forum. The gold-plated leaf contacts are delicate and easily damaged,
too. If you search, you should find the accepted technique - don't forget
that these cam-actuated contacts are common among most, if not all, of the
400-series portable scopes. I'm only trying to help to point you in the
right direction.

You could perhaps look at:

https://groups.io/g/TekScopes/message/144408?p=,,,20,0,0,0::Created,,cam+swi
tch+cleaning,20,2,0,11350196

(I hope the URL comes out ok).

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of NigelP
Sent: 24 May 2019 10:02
To: TekScopes@groups.io
Subject: Re: [TekScopes] 465B Attenuator servicing

Thanks for your feedback.

Whilst I admit the specific tin I've just used does only have "Ambersil
Electronic Safety Solvent" written on it I have nevertheless used it
extensively for years. It has a long list of its suitability regarding
electronic circuits written on the can.

However to specifically answer your comment I can assure you that
pressurized cans of IPA DO exist and in fact I purchased one just this
weekend and it is sitting right in front of me as I write! It's called
Pro-Power PPC103 IPA Solvent.

Regards

Nigel

Chuck Harris
 

Easy and cheap enough to get a pump sprayer bottle
from the store, and fill it with IPA. That is what
I do when I need to flood a circuit/switch/keyboard
with IPA.

-Chuck Harris

Colin Herbert via Groups.Io wrote:

OK, so the existence of spray-can IPA is new to me. Perhaps I should see if
I can get it in the UK, but it is cheap enough anyway and I apply it with
cotton-buds, tissues or slivers of paper, whichever is the best way for the
job. (It may be that the propellant is incompatible with the attenuator
substrate, of course).

Perhaps I can point out that the 465B Service Manual (mine covers B060000
and up) states that "carbon-based solvents will damage the boards used for
the attenuators. Apply the isopropyl alcohol with a camel hair brush. Do not
use cotton swabs.." This is at the bottom of page 6-3. I think that Tek
meant "carbon chloride-based solvents", as the isopropyl alcohol molecule
contains three carbon atoms. My 475A Service Manual further states that the
"attenuators use a plastic material (polyphenylene oxide) that is easily
damaged by the use of carbon-based solvents". It goes on to say that
"acetone, benzene, toluene, xylene, petroleum ether, white kerosene, carbon
tetrachloride, methylene chloride, trichloroethane, trichlorotrifluoroethane
(freon-113, -tf, -ta, -tmc) should not be used. As I said before, there are
a number of posts on the subject of cleaning these cam-actuated contacts on
this Forum. The gold-plated leaf contacts are delicate and easily damaged,
too. If you search, you should find the accepted technique - don't forget
that these cam-actuated contacts are common among most, if not all, of the
400-series portable scopes. I'm only trying to help to point you in the
right direction.

You could perhaps look at:

https://groups.io/g/TekScopes/message/144408?p=,,,20,0,0,0::Created,,cam+swi
tch+cleaning,20,2,0,11350196

(I hope the URL comes out ok).

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of NigelP
Sent: 24 May 2019 10:02
To: TekScopes@groups.io
Subject: Re: [TekScopes] 465B Attenuator servicing

Thanks for your feedback.

Whilst I admit the specific tin I've just used does only have "Ambersil
Electronic Safety Solvent" written on it I have nevertheless used it
extensively for years. It has a long list of its suitability regarding
electronic circuits written on the can.

However to specifically answer your comment I can assure you that
pressurized cans of IPA DO exist and in fact I purchased one just this
weekend and it is sitting right in front of me as I write! It's called
Pro-Power PPC103 IPA Solvent.

Regards

Nigel










Adrian
 

Hi Colin,

Yes you can, the Pro Power IPA is good I get 400ml spray cans from Farnell (or Element14 or whatever they want to be called today) or CPC (who are also Farnell) sometimes have offers on 10 packs of it. Farnell is around 3.75 GBP/can at 10 off I think.

Apart from the convenience I also work on the principal that if the pressure hasn't got out then the H2O has not got in!

I buy 25L bulk cans for the board washer on ebay where a bit of water is not an issue.

Adrian

On 5/24/2019 12:41 PM, Colin Herbert via Groups.Io wrote:
OK, so the existence of spray-can IPA is new to me. Perhaps I should see if
I can get it in the UK

NigelP
 

OK I think we bottomed out the IPA bit but what I really need to know is quite specific to the mechanics of the assembly. I may not have seen everything about this in the manual but the small bit I read implied that in order to service the actual attenuator board I need to remove the complete assembly of BOTH CH1 & CH2 attenuators including the mode switch which seems to come out as a complete system.

However looking at the mechs (and I have serviced similar Tek cam switches before) it would seem possible to undo just a few threaded bushes and remove the attenuator board on its own off the cam assembly without having to remove the whole lot as I've mentioned above? I do know that on some cam switches, if you are not careful you end up with some no-longer-captive nuts which can easily get mislaid!! Forewarned is fore-armed! I don't think the manual has an exploded mechnical assembly diagram which would shed light on this methodology, but I may have missed it.