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Cleaning plastic

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Cameron Kaiser

Nov 5, 1998, 3:00:00 AM11/5/98
This appeared on comp.sys.tandy and might be helpful for those of you
trying to clean up your equipment.

>Newsgroups: comp.sys.tandy
>Path: news!global-news-master!!!rcn!!!!!!nemesis!uhclem.dec98
>From: (Frank Durda IV)
>Subject: Re: How to clean 'yellowed' plastic?
>X-Newsreader: TIN [version 1.2 PL2]
>Organization: The Big Blue Box
>Message-ID: <>
>References: <71r0i8$r2q$>
>Date: Thu, 5 Nov 1998 04:36:47 GMT
>Lines: 78
>Xref: news comp.sys.tandy:29593

Steve Wilson ( wrote:
: I'm curious about the recommended method and materials for cleaning up
: the yellowed plastic that seems to grow on every piece of computer hardware
: I've ever owned that is more than 1 year old? I just received 2 M100's that
: could use a good scrubbing (not to mention 2 or 3 monitor cases
: around here)...anyone had any luck? TIA

There are two major sources of yellowing on the plastics Tandy and
other manufacturers used during the 1980s and early 1990s:

1. Tobacco smoke and other environmental hazards. Particularly on
monitors or computer cases containing monitors or open frame switching
power supplies, the tar from tabacco is electrostatically attracted
to these cabinets and not only coats the cases with a yellow film,
this film also captures dust, and is most evident in and around
CRT high voltage assemblies. Eventually, this can cause unexpected
high voltage arcing and component destruction.

Most common household cleaners, such as Windex (sprayed onto cloth
and THEN rubbed on the surfaces) will remove most of this material.
NEVER spray water-based surfacents directly onto computers as the
drips and overspray can get into the circuitry or cause staining.
Even after using a the cloth method, allow lots of time for any
stray liquid to evaporate before applying power.

This type of yellowing is usually uneven, and if it won't rub off
immediately when exposed to a mild cleaning agent, see problem #2.

2. Ultraviolet light. Most manufacturers (including Tandy and most of
its OEMs) did not bother to purchase plastics with UV stabilizing
compounds (it costs more or they originally planned to paint the case,
as was the case with all Tandy units made in late 1982 and early 1983,
when Tandy switched to non-gray cases).

Units that have been exposed frequently to direct sunlight (and
most types of flourescent lighting but at a slower rate) will
permanently change color, with the most frequently-used materials
moving eventually to a near-orange color. At the same time, some
materials will begin to shed/flake their outer finish, particularly
if the material was buffed, sanded or of a thermal setting plastic
type. In extreme cases, the plastic will become brittle. Early
symptoms of this will show at stress points, such as screw mounting
points, which will crack or break on the outer surfaces of the case
or points that are habitually rubbed, such as around buttons and other

There is no way to fix UV damage. You can conceal all but the latter
stages of deterioration by painting the surfaces with an oil-based
paint, except for transparent parts such as Model 100/102/200/600
screen covers. Most plastics will stop degrading when the source of
UV goes away.

As it turns out, the Tandy models that were spot-painted, either as
artistic trim or to conceal defects in the plastic moldings (these
include the Model 4/4D/4P/12/16/2000/6000/Coco II/III models) or
those that were completely painted (Model I/II/III/original Coco)
are protected from most UV damage, at least in the painted areas.
Go back to cause #1 on these cases, but don't rub too hard.

Some units contain plastic parts made from different types of plastic
which are affected by UV unevenly. The DMP 2200 is one such example,
and most units have now had their covers turn almond color, while the
bottom half of the plastic case looks the same off-white color as when
it was in the stores. This type of color change is entirely caused
by UV and the use of two different types of plastic or two different
batches of poorly mixed plastic, since both halves would have been
equally exposed to tabacco smoke and other airborne environmental

Frank Durda IV - only these addresses work:|"I picked up a Magic 8-Ball the
<> | other day and it said 'Outlook
| not so good'. I said 'Sure,
This Anti-spam address expires Dec. 31st | but Microsoft still ships it."
Copr. 1998, ask before reprinting.

Cameron Kaiser * cdkaiser.cris@com * powered by eight bits * operating on faith
-- supporting the Commodore 64/128: --
head moderator comp.binaries.cbm * cbm special forces unit $ea31 (tincsf)
personal page * "when in doubt, take a pawn"

Christopher A. King

Nov 5, 1998, 3:00:00 AM11/5/98
Cameron Kaiser wrote:

> This appeared on comp.sys.tandy and might be helpful for those of you
> trying to clean up your equipment.

Good information; thanks much for sharing this with us...

C.K. (original C-64 and 1541 are UV casualties)

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