More parts I need to replace on the VT100 - test-drb@ccmp.vtda.org

30 Nov 2005

...
 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