There are times when it is desirable to remove the chassis or mainboard and
work on it in a convenient location without having to worry about the
equipment which will simulate the critical functions but this is rarely
an option for the doit-yourselfer.
|NotTaR of Television Sets : Troubleshooting a TV with the mainboard ..
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My approach is usually to do as much work as possible without removing the
main board and not attempt to power it up when disconnected since there are
too many unknowns. Professionals will plug the chassis into a piece of
equipment which will simulate the critical functions.
Note that if you have a failure of the power supply - blown fuse, startup,
etc., then it should be fine to disconnect the CRT since these problems
are usually totally unrelated. Tests should be valid.
However, if you really want to do live testing with the main board removed,
here are some considerations. There are usually several connections to the
CRT and cabinet:
- Deflection yoke - since the horizontal coils are part of the horizontal
flyback circuit, there could be problems running without a yoke. This
could be anything from it appearing totally dead to an overheating or
blown horizontal output transistor. There may be no problems. Vertical
and any convergence coils may or may not be problems as well.
- CRT video Driver board - pulling this should not usually affect anything
except possibly video output and bias voltages.
- CRT 2nd anode - without the CRT, there will be no capacitor to filter
the high voltage and you would certaily want to insulate the HV connector
REAL well. I do not know whether there are cases where damage to
flyback could result from running in thie manner, however.
- Front panel controls - disconnecting these may result in inability to
even turn the set on, erratic operation, and other unexpected behavior.
- Degauss - you just won't have this function when disconnected. But who
cares - you are not going to be looking at the screen anyhow.
- Remote sensor - no remote control but I doubt that the floating
signals will cause problems.
- Speakers - there will be no audio but this should not cause damage.
If you do disconnect everything, make sure to label any connectors whose
location or orientation may be ambiguous. Most of the time, these will
only fit one way but not always.
These include both controls accessible to the user (and often not understood)
as well as internal adjustments that may need to be touched up due to the
aging of components or following a repair.
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