>    problem as each pair of supply pins has 100n across them. The supply
>    comes from a 78L05 and the timing is courtesy of a three terminal (4MHz)
>    ceramic resonator.

> I don't know if this is relevant, but recently I ran into this:
> I have been building a PIC programmer, and I used a 7812 with
> a voltage divisor  to boost the voltage slightly (to 14 V).
>        _____            The voltage measured with a voltmeter
> _______|    |________   looked fine, but when I looked at it
>        |    |   |       with the scope, it was 14VDC plus a 10MHz
>        --+---   <       oscillation with 1 Vpp amplitude. Kind of
>          |      >       shook my confidence in 78xx parts. I suggest
>          |      <       you look carefully for a parasitic oscillation
>          |      >       (of course hooking scope probes could influence
>          +------|       what you are looking for---welcome to the
>                 >       wonderful world of analog).
>                 >       BTW, I ended up using LM317---works like a charm.
Hi,

You must make sure that the current in the resistor string in high enough
as well as putting decoupling capacitance on both sides of the regulator.
The oly time I had the problem you describe was with a LM723 regulator
working at 3 volts (near its limit of 2.7V) and driving a simple LED.
An LED has a funny VI characteristic and can cause funny effects in
regulators, the regulator would get very hot as well, putting the LED
before the regulator cured the problem.

--
Kalle Pihlajasaari     kalle@data.co.za
Interface Products     Box 15775, Doornfontein, 2028, South Africa
+27 (11) 402-7750      Fax: +27 (11) 402-7751