I have just bought an 8591A that has an intermittent REF UNLOCK error message when I use the internal 10 MHz reference. The error comes every 0,5 to 10 second.
The internal reference is 10,000 MHz and the amplitude is around 350 mV peak to peak. The waveform is a bit distorted - not a clean sinus wave.?
The error REF UNLOCK disappears if I connect an external 10 MHz reference - If the amplitude is exactly 130 mV peak to peak.
If the amplitude is higher than 140 mV peak to peak, the intermittent error REF UNLOCK comes back.
Also if the external reference is adjusted lower than 9,98 MHz or higher than 10,02 MHz the error REF UNLOCK disappears even if the amplitude is higher than 140 mV peak to peak.
My 8591A has serial number 3122U01724 and software revision 7.5.91.
?
I have checked the Service Manual but it does unfortunately not contain any drawings of the A25 Counter Lock Assembly.
I am very grateful if anybody has any suggestions!
