More parts I need to replace on the VT100

[Julian Wolfe]

Your point is well taken.  I'm going to examine those schematics a bit more
closely tonight.  I also have a friend who has been building electronic
projects for Atari computer systems for a very long time now, and hopefully
he can give me a second opinion too.

> -----Original Message-----
> From: cctalk-bounces at classiccmp.org [mailto:cctalk-bounces at classiccmp.org]
> On Behalf Of Dwight K. Elvey
> Sent: Wednesday, November 30, 2005 4:57 PM
> To: cctalk at classiccmp.org
> Subject: RE: More parts I need to replace on the VT100
> 
> >From: "Julian Wolfe" <fireflyst at earthlink.net>
> >
> >The burned out resistors wouldn't have had anything to do with the blown
> >flyback or the shorted components I replaced on the video board?
> >
> 
> Hi
>  They could but you still need to look at the schematics to
> see how they may have done this. It is possible that the
> power supply failed in such a way that it blew up the
> parts on the video board. If so, simply replacing the resistors
> may make expensive smoke of your replacement flyback
> and other parts.
>  It is always wise to evaluate the root cause of each
> known bad component. If the resistors are in series with
> the load, it is likely that the shorted parts on the
> video board may have caused the damage. If you see the resistors
> in other paths, look to see what in the supply might
> have also caused the failure.
>  As an example, the series pass transistor in a regulator
> output stage could have gone short. This would cause the
> voltage to go way above what the flyback was designed for.
> It shorted some turns that cause the horizontal output
> transistor to go short from excessive power. Now a
> resistor that was used in series with the supply's output
> might smoke because there was nothing else limiting the
> current. This is only an example of thousands of possible
> problems.
>  In other words, you need to look at the failures and
> justify the cause. Resistors burn up because they
> have excess power dissipated. This is caused by the voltage
> going up across them for some reason.
> Dwight
>