VNAV problem

[jolmos]

Takeoff, reached an altitude of 1500 'on the ground, the AP active and LNAV and VNAV. The first (LNAV) is successfully activated, but VNAV, no. I can not activate V / S. "Mysteriously" to a random altitude, I can activate the VNAV function. When I can not activate VNAV or V / S, light flashing alarm lights orange: A / P - P / RST. Can someone give me a help about it? Thank you in advance.
P / D: When taking off is armed the A / T and TOGO thrust.

[mmerelles]

Hi @jolmos please verify on the 737 left menu that the CWS slider is full to the right, otherwise any noise/signal coming from your hardware will keep disconnecting the A/P.

Moving the CWS slider full to the right you increase the null area where the A/P ignores any input from your hardware while A/P is engaged not to disconnect it.

 

Hope this helps

[jolmos]

The problem was in the FMC: discontinuities.

 

[mmerelles]

glad you figured it out!