[sdiy] crystal oscillator oscillator seeming to run at wrongfrequency

[Needham, Alan]

So the PAL crystal frequency is a little high and the NTSC crystal is
almost spot-on to what the -PAL- frequency should be?
I assume your frequency measurement won't be loading the oscillator
circuit and pulling the frequency (and is reasonably accurate)?
I wouldn't have thought the crystal would be at fault, you say both are
wrong - they are almost bomb-proof these days; you need to really abuse
them to crack or chip the crystal.
I am a bit surprised that the circuit uses a normal inverter - I thought
it was standard practice to use a Schmitt gate?


-----Original Message-----
From: synth-diy-bounces at dropmix.xs4all.nl
[mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of dragons
Sent: 15 November 2009 19:23
To: synth-diy at dropmix.xs4all.nl
Subject: [sdiy] crystal oscillator oscillator seeming to run at
wrongfrequency

Hi,
sorry if this question is off topic.
I've been looking at a video generator board that has two crystal 
oscillators on it, one is at 14.318 Mhz and 17.734 Mhz.
( these are for the ntsc and pal standards ).
both use a 74lcx04 ic with 1Mohm feedback resistor and 22pf caps.
but the frequency of the 14.318 crystal measures 14.322 , the other is 
much closer to the 14.318.
the chip the clocks drive is the  Epson S1D13806
supply voltage is 3.3 volts.
I just wondered if it is possible that this might be a design fault with

the circuit ? I've got a replacement crystal on order.
the video card would normally be used set to the Pal output but when I 
use it with a multistandard monitor and set it to ntsc the ntsc light on

the monitor doesn't illuminate.

regards Peter B



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