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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only. |
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24th Mar 2017, 5:07 pm | #1 |
Octode
Join Date: Jul 2014
Location: Petersfield, Hampshire, UK.
Posts: 1,043
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LCD clock crystal
Hi
I have a couple of clock radios where the crystal won't oscillate When sprayed with freezer it then works for a while What's odd if I take the crystal out and put it in a another clock circuit it works fine ! If the crystal from the working clock is put in the faulty clock it won't run Is there a way of persuading the crystal to oscillate with this chip ? I have attached the circuit Cheers Pete |
24th Mar 2017, 5:24 pm | #2 |
Heptode
Join Date: Feb 2006
Location: Marlborough, Wiltshire, UK.
Posts: 915
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Re: LCD clock crystal
Sounds like the capacitors each side of the crystal are suspect, perhaps the trimmer is at one end, or it could be the chip. The caps form a voltage divider so if their ratio is far out, it can fail to oscillate or overdrive. I suggest you try replacing both cap/trimmer with fixed 22p as a starter. If that is no go, then suspect the chip.
Ken |
24th Mar 2017, 5:29 pm | #3 |
Octode
Join Date: Jul 2014
Location: Petersfield, Hampshire, UK.
Posts: 1,043
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Re: LCD clock crystal
Sorry I should have said I've dis the trimmer and put in two fixed caps
I also tried it with no caps I was hoping it's not the chip as it runs on its own 1.5 v battery so nothing to upset it |
24th Mar 2017, 5:42 pm | #4 |
Pentode
Join Date: Oct 2012
Location: Dorset, UK.
Posts: 240
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Re: LCD clock crystal
Make sure the board is spotlessly clean around the crystal and the relevent pins of the chip, with no flux deposits (modern "no clean" soldering processes) the slightest leakage will stop the crystal oscillating
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24th Mar 2017, 6:44 pm | #5 |
Octode
Join Date: Jul 2014
Location: Petersfield, Hampshire, UK.
Posts: 1,043
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Re: LCD clock crystal
I lifted the two osc pins from the PC to eliminate leakage problem ( connected xtal directly ) Still the same !
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