Priya,
You should be able to unscrew the aluminum cover over the cam switch. Then
the contacts are accessible but THEY ARE FRAGILE.

I believe the recommended cleaning procedure is to dip a piece of blotting
paper in 99% alcohol and gently place it between the contact and the PC
board and move it back and forth carefully to clean the contact. Turning the
cam to apply downward pressure on the contact is probably OK as long as the
blotter paper isn't to think.

This has worked for me but I always remember most important: THE CONTACTS
ARE FRAGILE. You never want to bend one. That would be bad.
Dennis

-----Original Message-----
From: Mover, Sent: Thursday, January 31, 2013 12:43 PM

My 5, 0.2, 0.1 and 50 mv deflection positions are noisy/jumpy (the readout
works fine) - the 10X attenuation is used only in these 4
volts/sensitivities so I assume that the contacts are dirty. I took off the
perforated side panels and lifted up the the readout board covering the
volts/div and AC/DC/GND/Offset cams.

Now to clean the attenuation switch contacts, do I have to take off the
cams, the knobs and the whole front panel? Just not certain how to get the
the spring loaded switches under the cam and clean the contacts. Really
don't won't want to open any more more than I have to.

Any advise or pointers to previous threads would be extremely valuable. I
assume that this is a common repair on these 1970s units.

Thanks,

Priya Jakatdar.

Thanks, Dennis. I was able to remove the aluminium cover and I can now clearly see the switches.

I'll try to verify the bad contact with an ohmmeter first. I'll also try to dislodge/dissolve the dirt with several drops of the Isopropyl Alcohol on the 10X contacts and move the rotary switch one step back and forth. If that does not work, I'll try the blotting paper.

Appreciate the good advise re: the delicate nature of the switches.

Priya.

--- In TekScopes@..., "Dennis Tillman" wrote:

Priya,
You should be able to unscrew the aluminum cover over the cam switch. Then
the contacts are accessible but THEY ARE FRAGILE.

I believe the recommended cleaning procedure is to dip a piece of blotting
paper in 99% alcohol and gently place it between the contact and the PC
board and move it back and forth carefully to clean the contact. Turning the
cam to apply downward pressure on the contact is probably OK as long as the
blotter paper isn't to think.

This has worked for me but I always remember most important: THE CONTACTS
ARE FRAGILE. You never want to bend one. That would be bad.
Dennis

-----Original Message-----
From: Mover, Sent: Thursday, January 31, 2013 12:43 PM

My 5, 0.2, 0.1 and 50 mv deflection positions are noisy/jumpy (the readout
works fine) - the 10X attenuation is used only in these 4
volts/sensitivities so I assume that the contacts are dirty. I took off the
perforated side panels and lifted up the the readout board covering the
volts/div and AC/DC/GND/Offset cams.

Now to clean the attenuation switch contacts, do I have to take off the
cams, the knobs and the whole front panel? Just not certain how to get the
the spring loaded switches under the cam and clean the contacts. Really
don't won't want to open any more more than I have to.

Any advise or pointers to previous threads would be extremely valuable. I
assume that this is a common repair on these 1970s units.

Thanks,

Priya Jakatdar.

?

?

I have become convinced that the plastic that holds the reed to the forked
tip is susceptible to chemical embrittlement.



As several have warned already they are very fragile. So use great care.



I have no absolute proof yet. However, as a guess; the ones that I have had
that fell apart from simply touching them (or were already in pieces) were
cleaned by someone spraying the once thought contact cleaner WD-40 in the
works. At least that is the odor I have attributed to it.



Anyway, paper and alcohol as described is the way to go. Perhaps De-Oxit on
the paper as well, suitably applied. I would refrain from sprays especially
any on the plastic.



Not trying to make you paranoid but I have not come up with a repair should
the plastic disintegrate as it has on a few of mine. Leading to a parts
unit..



Good luck

Rob

From: TekScopes@... [mailto:TekScopes@...] On Behalf
Of David C. Partridge
Sent: Thursday, January 31, 2013 8:25 PM
To: TekScopes@...
Subject: RE: [TekScopes] 7A18 volts/div switch contact cleaning

dip a piece of blotting paper in 99% alcohol

I would suggest you use regular cartridge paper, not blotting paper, as that
has too much tendency to shed. Also use isopropyl alcohol rather than
ethanol.

Dave

If you remove the left cover panel on your 7000 mainframe, you can
reach most if not all of the 7A18 calibration adjustments.

On Fri, 01 Feb 2013 04:11:48 -0000, "Mover"
wrote:

Thanks to everyone who responded - I was able to clean the 2 contacts for the 10X attenuation and the deflection now works fine. I put a few drops of isopropyl alcohol on the contacts with a small dropper and moved the knob back and forth 15 or 20 times. Never actually touched the contacts with anything per notes below.

So now that the gain is right, I have to adjust the compensation caps for which I need an extender. The one on eBay is far out of my reach financially. How do you guys set the comp caps without an extender card or extension cable?

Again, thanks for your assistance with the deflection contact points.

Priya Jakatdar.