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Old 9th Mar 2009, 5:18 pm   #4
julie_m
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Join Date: May 2008
Location: Derby, UK.
Posts: 7,416
Default Re: Alpine 7148L Car Stereo digital Tuning Fault

Quote:
Originally Posted by 'LIVEWIRE?' View Post
The +5v supply to the uP is present, as are both the permanent and accessory +12v supplies, but the 4.5MHz Crystal Controlled Oscillator doesn't appear to be working, and the o/ps from the uP to the display are all at zero.
If there's no oscillation, then that is most probably your problem; don't expect anything else to work.

Just probing around a crystal oscillator often gets it working, but it's a bit impractical to have to get an oscilloscope out every time you want to listen to the radio A crystal or ceramic resonator is basically a delay element, wired between the output and input of a Schmitt-trigger NOT gate. So, one lead of the crystal is driven high; and after awhile, the other lead goes high -- now the output of the NOT gate changes to low, and after awhile the other lead of the crystal goes low; and the output of the NOT gate goes high again. You should see a nice square wave (the drive signal) on one leg of the crystal and a rough sine wave (the delayed signal) on the other end. Re-soldering the joints on the crystal and/or any nearby capacitors (usually a few pF on one or both leads of the crystal) might fix it. Otherwise, replace the crystal.
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