I have 2 station OfficeServ 500 connected by PRI cards (3m cable)
Everythin works good but several times in day it stop working. I call this station as station A fnd station B.
So it works e.g. 2 hours and after it i can't call from the station B to station A, but i can call from station A to station B. After rebooting PRI cards everythin again works good.

But this trouble can happen in 5 minutes or in an hour or 2, 3, 4, but it happens every day.

Yesterday i have changed cable and PRI cards, but my broblem still exist.

What can i do in this case?

What version of software (MCP, PRI) are you use ?
Type of connection ? QSIG or pure ISDN ?

Station A
MCP 2 66 2006 7 20
PRI Cab 3 Slot 1 V 4 20 (2007 7 31)

Station B
MCP 2 69 2007 2 2
PRI Cab 1 Slot 1 V 4 20 (2007 7 31)

QSIG connection.

As a first step I would upgrade System A to v2.69 to match System B, or if it is available to you upgrade both to v2.72. Lastest version of tepri is 4.21, would also be worth doing.

Might be smart to put a VOIP card in the main 500 and put two VOIP phones in the second location then use the second 500 at another job.

Much cheaper solution.