4 Sep
2009
4 Sep
'09
3:10 a.m.
Anyone got any ideas as to the oily film ?
Most likely it is from a capacitor.
If this is acting up, for testing purposes it would
seem to be safe
to remove it to see if the voltage changes (jumps back to around 12V) ?
No, that would remove all regulation from the 12V rail.
You can test this part out of circuit. Connect REF to K, pins 1 and 3 on
the TO92 part, and these two to +5V through a 680 or 1K ohm resistor.
Connect A, pin 2,to ground. With the 5V on you should read 2.495V +/-2%
between K and A.
This part can be replaced by a TL431, LM431 or equivalent.
So, suggestions, ideas on the film, and best way to go
about
troubleshooting the 12V rail are welcome :-)
An ESR meter to test caps is pretty much essential. Some obviously
fail but others can look fine but still be high R. Electrolytics
are by far the biggest single cause of switch mode supply failure.
Lee.