Hello members-

Recently Oscilloscoped the X1 and X2 Clock Input of a special purpose microprocessor within one of main control boards of Tascam Cassette Deck.

The signal level on one ( X1 or X2 ) was a nice sinewave with accurate enough frequency, however , the voltage High and Low levels appeared questionable. The other X1 or X2 Clock Input measured a digital float or approx. 1.5 - 2.0 volts steady DC level.

These X1 and X2 are taken directly from a Ceramic Oscillator (Crystal ) with parallel small capacitors.

I had always thought their was supposed to be a Sinewave measured on both pins of the Ceramic or Crystal Oscillator component.

Anyway, the unit is operating fine ! As Is.
Just ran across this being curious.

Any suggestions . . .

 

The capacitance of the probe can be enough to stop the oscillator when connected to the input of the oscillator circuit which I think is what happened when you saw the DC level. A X10 probe may give better results but it will still disrupt the oscillator to some extent.

 

You will often see a square wave, as explained here: https://www.edaboard.com/showthread...orm-of-a-crystal-oscillator-always-a-sinewave

The inverter in a PIC MCU oscillator is non-linear.


Do you have a block diagram for the oscillator of your microprocessor?

 

Thank you for replies thus far.

Attached you may find a snapshot of the Schematic section which is where the ceramic crystal located.

 

Hello Again -

I Oscoped these X1, X2 signals on another unit and both signals appeared as what I am used to seeing on uP Crystal Oscillator Input Pins.
Both signals were a slightly distorted Sinewave at exact 4.20 MHz with a slight positive (maybe .25 volt) DC offset from ground.

I believe that the first unit which started this thread _ I later found that possibly the weird signal levels were due to the Scope Probe, Scope Probe Ground or that Probe or Oscope was set on the X10 scale.