Pendulum | CNT-90 - TimeBase

[liszt955]

Hi guys!

Recently, I've been changing the TimeBase of my second-hand CNT-90 by replacing it with an OCXO, and When calibrating with a GPSDO, I encountered the problem "Impossible to calibrate timebase. Bad reference signal?"

I have followed the methods found online and have already changed the software options to option 30.

I would like to ask everyone, what methods are there to solve this problem?

By the way, how do I insert pictures? It's my first post.

[coromonadalix]

normally  as a first   do not double post, it is not appreciated,  you already posted in the repair section, and the guy hasn't showed for 2 years there

[liszt955]

I'm sorry.
I tried to remove this topic,
but it seems unsuccessful.
I deeply apologize for the inconvenience caused.

[liszt955]

HI，guys:

The issue has been resolved. I found a document for the Fluke PM6690. The key to this problem was that my OCXO, pin 2, Vref could not output voltage.

However, during calibration, or when the OCXO is operating normally, Vref must output a 5V voltage. (Page 85 of the document)

I added a variable resistor between pins 3, 2, and 5 of the OCXO to allow Vref to output a 5V voltage.

When it can output 5V, I was able to correctly calibrate the time base.

[liszt955]

Because the document is too large, I will upload it in two parts. This is the second part of the document.