"mottled effect" on anodized front panel


Sparky99
 

Hi everyone, I recently made a really great purchase of a Tektronix 536 together with a 132 (single slot plug-in power supply) and 5 plug-ins with 2 sets of all the manuals. Amazing most items are in extremely good condition, and 3 of the plug-ins even come with their original cardboard holders (which I presume were used when new - look old!) and even better the original sales receipt for when all the items were resold back in the 80's to the person I purchased them from. For me provenance is almost as interesting as the equipment itself, so this was a rare and good find!

In any case, coming to the point of this post - despite the good condition of all of the items, on closer inspection the scope has a slightly mottled effect on the anodized front panel. It does not show up well in a photo, but from most viewing angles the front panel seems to have lighter and darker areas - all the more noticeable on the 536 as large areas of the front panel are not used. Hence my description of a "mottled effect". The instrument has no corrosion or other indications of improper storage. I've tried the usual soapy water but it makes no difference. Anyone know what this may be, or have any ideas on how to remove it?

Thanks for your help.


Roy Morgan
 

Sparky99,

I have an R-390A receiver whose front panel has a circular grove worn deep into the front panel around the main tuning knob. This shows countless hours of use, more likely years, in signal intercept work.

Some folks might want to repair and refinish the panel to like-new condition, but I regard the deep shiny groove as a badge of courage and unusually long service in the line of duty.

Maybe your scope's mottled panel could be seen in a similar way.

Roy Morgan
K1LKY Western Mass

On Sep 11, 2021, at 5:38 AM, Sparky99 <jnolan@iprova.com> wrote:

Hi everyone, I recently made a really great purchase of a Tektronix 536 ... 5 plug-ins
...
the scope has a slightly mottled effect on the anodized front panel.
...


Sparky99
 

Thanks, but I'm sure these marks are not from use as they are distant from any of the controls - I checked and both plugs ins also have the same effect, so perhaps due to storage conditions but as I mentioned there are no signs of any corrosion elsewhere on the plugin.


 

Maybe they are etching from skin contact? Maybe the locations are BECAUSE there are no controls nearby, so that was the convenient place to push when installing the plug-ins, or to rest a hand while using the scope?

It’s too bad you can’t get a good picture of the effect.

— Jeff Dutky


stevenhorii
 

I’ve seen anodized aluminum exposed to the sun do this.

On Sat, Sep 11, 2021 at 14:24 Sparky99 <jnolan@iprova.com> wrote:

Thanks, but I'm sure these marks are not from use as they are distant from
any of the controls - I checked and both plugs ins also have the same
effect, so perhaps due to storage conditions but as I mentioned there are
no signs of any corrosion elsewhere on the plugin.






Roy Thistle
 

On Sat, Sep 11, 2021 at 02:38 AM, Sparky99 wrote:


on closer inspection the scope has a slightly mottled effect on the anodized
front panel.
I'm sure I've seen it too. A kind of mild staining? ... in some areas.
It could be, as suggested, and exposure to uv... but, that usually happens when the anodized part is colored. I don't think there is any coloring in these front panels.
The usual thing to do when anodizing aluminium is to seal the anodized part.
It could be that the particular batch that these panels came from did not get sealed properly. Then they would naturally get contaminated, in some areas, over time.
Perhaps these came from the factory with the defect(s) you observed?
It's also possible the scope had 'grime' on the front panel for a long time... that and perhaps a humid environment... that might have engendered an electro-chemically induced etch in some areas.
If you've tried a mild and neutral detergent (you say "soapy water") and it hasn't cleaned up... then anything harsher isn't recommended.
Anodizing... when done correctly, is supposed to to last for a long time. But, these panels have been around a long time already.
Perhaps one will have to live with it? ... or risk doing more damage.

--
Roy Thistle


Tom Norman
 

I recently acquired the calculator keyboard for my 7854 that had some mild mottling on the surface. The usual mild cleansers didn't help, so I tried using a very mild plastic polish with good results and the mottling has not returned. It didn't seem to hurt the silk screened characters at all. The product I used is called Novus, but I don't recall if it was the #2 or #3 (#3 is least aggressive). Your milage may vary, and just reporting what worked for me.

Tom


Sparky99
 

Hi everyone, thanks for your comments - @Roy Thistle, I agree - it's a mild staining which means that the panel is a bit "blotchy" where the finish varies from normal to a something a bit more matt/darker. I had a good look today and noticed that the same staining is present on both the 536 and also the T plugin, which presumably rules out a manufacturing defect. I tried again with soapy water to no avail, but will try the plastic polish if I can find some here - thanks for the tip. It's really odd - usually I would attribute this to poor storage conditions, but none of the other warning signs like rusted / corroded screws are present and even the original leatherette handle is in good shape with none of the usual corrosion signs on the metal structure. I'll try and get some photo's and post them tomorrow.

Sparky


Chris Wilkson
 

On Sun, Sep 12, 2021 at 09:34 AM, Tom Norman wrote:


The
product I used is called Novus, but I don't recall if it was the #2 or #3 (#3
is least aggressive).

Slight correction...Novus #3 is the MOST aggressive. Beware!

Novus #1 is for cleaning and polishing. It's non-abrasive and pretty safe.
Novus #2 is for fine scratch removal and heavy cleaning. It is mildly abrasive and will damage fine finishes and artwork.
Novus #3 is for heavy scratch removal. VERY ABRASIVE!! It will destroy the finish and remove artwork completely.

Novus is great for restoration and maintenance. Used extensively in pinball and video arcade hobbies and some automotive applications.
Always start with #1. Use #2 gently to remove fine scratches and blemishes. #3 is rarely used...only in extreme restoration cases.


Greg Muir
 

I’ve seen similar effects from contaminated anodizing solutions. If the rinse is inadequate after the item leaves the electrolyte bath some of the acid can remain in the porous aluminum oxide layer during sealing. Over time the remaining acid can slowly affect the finish.

Greg


Tom Norman
 

Thanks Chris for the correction. I went and took a look at my supply of Novus and it was the #2 that I used, just for confirmation.

Tom