Re: 465B Attenuator servicing

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.

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