Probe problem?

JohnInTX

Joined Jun 26, 2012
4,787
A 10X probe will present a 1/10 signal to the scope input. Many scopes have automatic sensing and automatically adjust the vertical scale accordingly. If your scope doesn't have auto sense inputs and/or your probe is not compatible with auto-sensing, yes your signal will be 1/10 of what you might expect. If this is the case and you read .63V, the actual was 6.3V - not unreasonable for 8Vcc on the 555.

A 10x probe also requires input compensation to present a true signal. If its not right, the signal will show a peaked or rolled off signal depending on which way the compensation is off. Most scopes have a probe test pin that issues a square wave at some convenient frequency (1KHz is common.) To adjust the 10x probe, connect it to this signal and adjust the trimmer screw on the probe for a good square wave. Then assign the probe to that input only.
 
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