Hello all, Have a 7904A, low SN, 1982, stored for decades.
Usual cleaning of switches, contrlols, the CRT, bright and in focus.
But all surfaces, PCB, PS, HV, CRT are coated with dust.

Suggest I vacuum with brush nozzle, finish with compressed air? Which is better?

Am Wary of Air, Vacuum ESD, damage,
So, should use Metal nozzles , earthed?

Many thanks, Have an absolutely fantastic day

Jon

Be careful with compressed air. In another device, I broke several thin wires from transformers.

Check the dust with your fingers before going through a lot of effort. On most old gear I've seen, there is a "loose" dust coating that wipes or blows off easily, but underneath there's a gritty hard dust, grime, and corrosion coating that's tough, and needs solvent washing to get mostly off. Even then, it's hard to get perfectly clean like new, unless it was stored in very good conditions for its entire time. You can feel the surface to get an idea of what it will take.

For loose dust, I'd recommend a paint brush along with vacuum or compressed air, outdoors. Unless it's a very dry environment, I wouldn't worry at all about ESD. You can also dampen the brush a little with water or IPA to minimize static buildup. It would help the cleaning a little too, but might leave streaks that can look worse than a nice uniform dirt finish. Pretest all of your methods on a small scale before committing. Good luck.

In the old tube scope days it was common to give detergent and water washing, but I don't think it would be OK for newer stuff like 7K without some caveats. Maybe, maybe not - it would take some investigation to see. If you need to do instrument cleaning regularly, another option that's effective and totally dry is to invest in an air powered walnut shell blast cleaner. You can get the whole shebang at Harbor Freight, for instance. Years ago I got a vibratory tumbler cleaner and a huge box of walnut shell from them for cleaning ammo brass, but I've never tried it in an air blaster on surfaces. I believe that Tek used this method instead of water in the later years.

Ed

Forgot to mention - in real anti-static work environments it's common to have grounding leads or other conductors to keep any air or vacuum nozzles from charging. You can do that too easily enough, if there's a concern.

Ed

Hello all,

Many thanks for the tips
Was not so, bad nor encrusted, just a soft brush and gently blowing, then isopropyl alcohol. About ESD the scope was grounded, damp and rainy weather.

The upper Rear casting by HV section had embedded brown deposits, metal corrosion, I used fine steel wool!

Next to clean the HV to CRT connector and lead, then perform the CRT, HV and Z axis calibrations.

Enjoy

Jon

On Dec 26, 2024, at 13:47 , ed breya via groups.io <eb@...> wrote:

In the old tube scope days it was common to give detergent and water washing, but I don't think it would be OK for newer stuff like 7K without some caveats. Maybe, maybe not - it would take some investigation to see.

I tried it with a 7704A that was pretty filthy, after reading the article here on scope washing and noticing the photo on the last page is of a 7K scope being washed at the Factory Service Center:

https://www.byan-roper.org/steve/manuals/Tektronix/Tek%20Scope%20Cleaning%20by%20C%20Phillips.pdf

It also says "The 7000-Series plug-ins are washed with the side panels in place. This saves time and prevents a mix-up in panels." This gave me further confidence to try it.

After success with the 7704A, I did the same thing with a 7904, also with success. Unfortunately, the 7904 frame doesn't separate top and bottom to fit in the oven like the 7704A does, so I relied on summer heat to dry it.

I think Hypcon hybrids and elastomer switches are where washing becomes a bad idea, from my reading of the 7104 maintenance note, so did not try it with the 7104, 7A29, 7B10, etc (and would not with a 7904A, either).

https://w140.com/tekwiki/images/6/67/7104_maintenance.pdf

If you need to do instrument cleaning regularly, another option that's effective and totally dry is to invest in an air powered walnut shell blast cleaner. You can get the whole shebang at Harbor Freight, for instance. Years ago I got a vibratory tumbler cleaner and a huge box of walnut shell from them for cleaning ammo brass, but I've never tried it in an air blaster on surfaces. I believe that Tek used this method instead of water in the later years.

I'd like to try blasting for other reasons, but wonder about dust? Walnut and corncob both make a lot of really fine dust in my vibratory tumbler, but I'm lazy and tumble my brass too long.

thanks,
Adam