1. Home
  2. Electronics Repair
  3. Testing a crystal.

Testing a crystal.

I have a device where the crystal and associated network is external to the CPU. Which isn't working. Looking across the two connections with a scope there's no approx 30 kHz as should be - but what looks like very dirty mains hum. Any way of easily testing the crystal other than by substitution?

--
*Why is the man who invests all your money called a broker? *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.
Reply to
Dave Plowman (News)
Loading thread data ...

You need a special probe to keep from loading down the circuit, and if it is a typical 32.768 kHz watch crystal the waveform isn't clean even when it is working properly. It is a tuning fork type of crystal, not the typical cut used at higher frequencies. A high input impedance FET amplifier with a fraction of a pF coupling capacitor is typically used to prevent loading, but you can often see a waveform at the drive side of the crystal. They use an unbuffered inverter and a resistor to bias it into the linear range, but the AC voltage in the circuit pushes it out of the linear range.

--
http://improve-usenet.org/index.html

aioe.org, Goggle Groups, and Web TV users must request to be white
listed, or I will not see your messages.

If you have broadband, your ISP may have a NNTP news server included in
your account: http://www.usenettools.net/ISP.htm


There are two kinds of people on this earth:
The crazy, and the insane.
The first sign of insanity is denying that you\'re crazy.
Reply to
Michael A. Terrell

The easiest test that I can think of is to breadboard a CMOS oscillator circuit. Use one inverter out of a hex inverter like this:

View in a fixed pitch font such as Courier

|\\ +--| >0---+----> OUT | |/ | | | +--\\/\\/\\--+ | 1 Mohm | | | | \\ | / 2.7 kohms | \\ | / | | | Xtal | +---|[]|--+ _|_ _|_ 55pf ___ ___ 60pf _|_ _|_ \\ / \\ /

If the circuit oscillates at the crystal frequency, then the crystal is likely good. If it doesn't oscillate at all, or oscillates at the wrong frequency, then it's likely bad.

--
Dave M
MasonDG44 at comcast dot net  (Just substitute the appropriate characters in the 
address)

Life is like a roll of toilet paper; the closer it gets to the end, the faster 
it goes.
Reply to
DaveM

Testing crystals,ceramic resonators and filters Signal generator (RF) and scope. Connect the grounds together and then connect the sig gen to the scope via the crystal. Sweep the oscillator and resonant response at fundamental and overtones will show on scope trace. Use a f counter as well if f is required. If testing while in circuit (unpowered) use less then 1V sig gen o/p . The response may be muted comnpared to free component especially for ceramic resonators.

from my tips files below

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

formatting link

Reply to
N_Cook

...and the device number for the gate needs to have a "U" in it (for "unbuffered").

Reply to
JeffM

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.