During standby operation test of RH thrust reversers per amm 78-31-00-735-033 REV MAY 25/2008 the reversers locked out usually around the 3rd cycle of operation.

They would no longer operate with the standby system. They would operate with system B hydraulics.

After several minutes they would operate again using standby for two or three cycles before locking out.
The standby pressure system fuses where tripping. The fuses where swapped per amm 78-34-07, test failed. System B shuttle valve was replaced per amm, test failed.
Theust reverser control valve module was replaced, test successful.
It appears that the module was allowing too much flow using the alternate system which was tripping the fuse.
Thanks to Boudewijn d .S. for his input.

> FOR INFORMATION ONLY. UNCONTROLLED DATA !.