DECmate III and Rainbow 100+

From: jpero_at_sympatico.ca <(jpero_at_sympatico.ca)>
Date: Fri Feb 25 20:38:07 2005

> From: "Geoff Reed" <geoffr_at_zipcon.net>
> Sent: Thursday, February 24, 2005 11:38 AM
> > At 07:39 AM 2/24/2005, you wrote:
> > >Geoff Reed wrote:

> > >>> > And yes, the whole thing is powered, rather poorly, from 12 volts.
> > >>> > (Poorly: if you flip significant quantities of white pixels on and

> > >>>I've never had this problem. Are you sure you've not got some dried-up
> > >>>capacitors somewhere?

> > >>> > off, the scan area expands and shrinks very noticeably. So clearly
> > >>> > the supply regulation is seriously inadequate.)

> > >>the VR 201 monitors have a couple of points of failure, the most common
> > >>is a coil (IIRC) in the vertical that is potted in wax, they potted this
> > >>-before- soldering, and wax tended to get down into the solder joint
> > >>making a bad joint that fails after a while, there is a resistor right

> Basically you are referring to cold solder joints, the bane of classic
> hardware.
>
> I tell people that it is usually caused by vibration, invariably they say
> "what vibration it just sits there".
>
> Randy

I have no problem with wax *but* one material I'd stomp on their
countless feet if they are caught using is hot glue to secure
components! Total reliablity nightmare and costs maker in warranty
claims.

One particluar maker was notorious for this till late 2002 for
decades.

What happens at first often certain components and crimped on wire
stakes (these looks like a crimped terminal with connector missing,
just a tiny barb on the end to lock into thru hole). Then
they're secured with hot glue (usually!) in certain spots. Solder
wave is then performed successfully. Over time. subsonic
vibrations, thermal and expansion cycles worked many ways to make
solder bond fail caused by hot glue flowing into "break" and slowly
working through the solder & copper or brass "junction" bond.
Eventually fails, ranging from minor fix for little cost all the way
to $300 bill and multi parts replacement. Multi parts blown very
common in some TV designs, just one part lost the solder bond and one
part ahead of it gets dirty signal and fails, taking out other parts
along with it. Zzzzzzt, finally usually fuse goes if the owner
didn't heed the power supply screaming as sign to yank that power
cord out of that socket!

Usually this happens
ranging from 3 months to 10 years. Always failed at the component
leads or stakes where solder wets that leads. Never the trace lands.

Every time, granteed. The ONLY solution was desolder them and pull
all the parts that was "slopped on" with glue and scrape off glue and
clear the thru holes of those horrible glue.

Simply resolder those parts without hot glue clean up will earn you
call backs or fails again just after the repair warranty. Not nice
and learned that hard way.

Right now we're busy making good money with this! Just this! Along
with occasional items that has true failures not from glue, other
normal causes like bust flyback transformer, badly installed
transistor on heatsinks, maybe a burst capacitor or dried up.

What I think was that your monitor might have another type of equally
nasty glue, that starts out very light tan, very strong bond and very
stiff stretchy like gum but much stronger bond. This does very
poorly with heat, as it ages with heat, glue hardens and turn brown,
in extreme cases went black. Some has specific formulations that is
is equally nasty it turned corrosive after a time as glue breaks
down. Some went conductive causing wildly interesting cases. Some
turns so brittle that crumbled when scraped off like a burnt
bread.

Make sure that coil coated in this is really wax. If it is hot glue
or other kind, get that freaking thing OFF!! After soldering parts
in, sometimes needs to be secured with silicone which is good. Great
for stopping whistling noise or shrieks, high pitched buzz parts.
Like loose ferrite beads on component leads, other items, transformer
cores is ideally with hard or very firm curing glue or varnish for
those.

By the way, watch for new no lead solder problems to roll in! This
late 2004 and later begun to use those, there will be problems I
promise you! I just starting to see the potiential problems with
this. :-( No lead solder doesn't solidfy nicely like a normal
solder did. Still mushy, dull look and poor stress resistance
compared to good old lead-based solder. I know lead is really bad
and those bastards is too cheap to properly recover all the lead
before going to dispoal. Old type of solder does melt rather easily.
 In fact you can melt solder without burning plastic if thermal
control is controlled tightly.

Cheers,

Wizard (TV servicer).
Received on Fri Feb 25 2005 - 20:38:07 GMT