Try adding a high value resistor (1-10MEG) across the xtal. This tends to
linearise the amplifier slightly, allowing a noise build up that starts
oscillation. (or something). We do it anyway and the accepted reason is that
it speeds the start-up of the xtal.

Also - 47pF caps is a bit strong - try 22 or 10pf instead.

Richard

> -----Original Message-----
> From: John Bes [mailto:jbes@E-TRADE.NL]
> Sent: Wednesday, August 25, 1999 8:19 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Please Help - Osc.Problem
>
>
> Hi all,
> I think I'm having a real serious problem now ;)
>
> I build a programmer and a separate test board for the 16c84.
> Programming went well, but testing doesn't. The program in
> the Pic is the
> famous flashing led.
>
> The problem seems to be the crystal. It doesn't oscillate very well.
>
> I have been working on this problem for 2 weeks now, and I get kind of
> desperate ;(
> Please let me now if you have a probable solution!
>
> Here are the facts:
>
> - my scope shows a mildly distorted sine wave between osc1
> and osc2 (pin
> 15/16).
> - when I connect the scope -> it works
> The scope has R=1M and C=33pF -> when I replace the scope
> with a R (1m)
> between pin 15 and 16 and parallel to that, a C (33pF)
> no result.
> - when I touch the GND side of the caps with my fingers,
> sometimes the led
> flashes up.
> - The R (10 Ohm) is implemented to reduce the current through
> the crystal.
> replacing it by a wire doesn't make a lot of diffenrence, it seems.
> - I tried several crystals (4 MHz) -> No go.
>
> - connection:
>
>         GND
>        __|__
>      _|      |_
>      _       _ 2x C=47pF
>       |       |
>       |_|X|_|
>       |      |_
>       |     |  | R=10 Ohm
>       |     |_|
>       |16   |15
>    _ |____|______
>    | Pic 16c84    |
>    ---------------------
>
> Thanx,
> John
>