Arfa Daily wrote:

"robb" wrote in message

I tested the L387 and i think it must be bad as i get more than
5v from the Vout ?

How much more ? A couple of hundred millivolts, says 5.25 V is OK.


i had already desoldered it from some previous suggestions about
isolating the different supply rails

so i tested by connecting 5V/1A DC source between Vin and
GND-Pin3 and i checked the voltage with DVM between Vout and
GND-Pin3 and i was getting 3.47 V

Pointless. It won't operate correctly with only 5V in. 3.47V is sort of what I'd
expect under those conditions. A linear voltage regulator has to have several
volts more on the input than the output to function correctly.


i changed to a 18 v/3.5A DC source and i was measuring 8.67 V
between Vout and GND-Pin3

L387 is cool and when i connected an LED load to Vout the L387 got very hot
very quickly so i suppose i at least need to get an L387 ?

What value resistor did you have in series with the LED ?


From that, it sounds as though the '387 is not doing its job correctly, so
replacing it would probably be a good move.

He didn't say if he had a resistor in series with the LED ! Could explain a lot.

Graham