Re: 475 Probe Calibration problem with x10 probes

Colin Herbert
 

This might indeed help, but be cautious when doing it. There are posts on this forum where the correct technique is laid out - it is very easy to damage the cam-operated contacts. Also, note that the material of the attenuator board is a bit special and is easily damaged by heat and various solvents. Briefly, the technique is to put a little IPA (isopropyl alcohol) onto a sliver of ordinary paper and use that to clean the contacts. Check that the contacts are open, slide the ipa-wetted paper between them, close the contacts and then carefully pull the paper out level with the board, as far as possible. This can be done a few times to get all the contaminants off. You can probably ascertain which of the attenuator contacts need cleaning by checking in the service manual as to which attenuators are in circuit when the poor bandwidth is seen.
Good Luck, Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of ef804s tubes
Sent: 24 October 2018 14:27
To: TekScopes@groups.io
Subject: Re: [TekScopes] 475 Probe Calibration problem with x10 probes

I have two 475 scopes. Both have developed a similar probe calibration problem on one channel. I am using the scope calibration signal. I have verified results with multiple probes

First scope - Channel 1 probe calibration tests fine with x1 and x10 probles. Channel 2 calibration tests fine with a x1 probe but the waveform has a sloped rise and fall time when testing with a x10 probe on a vertical sensitivity setting of .5v/div and above.

Second scope - Channel 1 probe calibration tests fine with x1 probes but the waveform is a spike when testing with a x10 probe with vertical sensitivity setting of .5v/div and above. Channel 2 probe calibration works fine with x1 and x10 probes.

Has anyone seen this problem?

Mike N2MS

Hi,

please clean the attenuator contacts ans the pins of the attenuator blocks as well.

Fred

Join TekScopes@groups.io to automatically receive all group messages.