Crystals are glass and can be broken if dropped.  It's also
possible to damage them if you clip the leads with diagonal
cutters (the shock goes up the lead).  But also, crystals
can oscillate in an overtone (harmonic) which would give you
too high a frequency (that's the reason for the capacitors,
I hear).  Finally, with the oscillator's higher gain settings,
the circuit will likely oscillate on its own even without
a crystal so if the crystal is broken it may still
oscillate...somewhere...

Oh, put []'s around the PIC: and I bet a lot more people
will see your message!

Barry


At 10:31 AM 6/29/01 +0530, you wrote:
>Yeah, thats the most plausible explanation for
> Shane Bolton's Crystal Paradox(Don't I sound ridiculous ?)
> Anybody else has got a better theory ?
>
>Jeethu Rao
>
>
>-----Original Message-----
>From: pic microcontroller discussion list
>[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Douglas Butler
>Sent: Wednesday, June 27, 2001 8:49 PM
>To: PICLIST@MITVMA.MIT.EDU
>Subject: Re: PIC: F877 Wont Start
>
>
>It could be that the crystal was damaged and operating at a very
>different frequency.  Perhapse so high a frequency the the rest of the
>PIC couldn't handle it.
>
>Sherpa Doug
>
>> -----Original Message-----
>> From: Shane Bolton [mailto:Shane.Bolton@SUN.COM]
>> Sent: Tuesday, June 26, 2001 8:51 PM
>> To: PICLIST@MITVMA.MIT.EDU
>> Subject: Re: PIC: F877 Wont Start
>>
>>
>> Found the problem!!
>>
>> I pulled the chip out and put it in a breadboard.  put new
>> caps, crystal, pullups and hooked it up
>> to a power supply.  Works fine.
>>
>> I then replaced the chip into the board and started to change
>> components.  First the Crystal Caps -
>> no joy. Then the crystal - FIXED.
>>
>> I can't explain this, as it appeared that the crystal was
>> running (5 VAC on the CLK-OUT pin) but
>> obviously something was wrong.  I did not even re-program the
>> chip - it worked fine.
>>
>> Considering my total lack of concern for Static protection
>> etc. these PICs sure are tough!!!
>>
>> Just like to say thanks to everyone that responded with
>> suggestions - a very helpfull and
>> co-operative list.
>>
>> Shane Bolton

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