My 34970A just started to have a strange behavior...Sometimes let itself be powered, sometimes not! Although the self-test shows PASS, tested both ways - with and without 34901A card plugged into, intriguingly the unit fails to work after about 15 min, when the display starts flashing with all colorful LED segments. Once it started to flash, the on/off button is useless because the unit cannot be turned off anymore from the front panel. The only way it is to unplug the power cable! When re-plugged into the power socket, it won’t restart right away…; it takes about 30 min before being able to restart it. When running again self-test it shows the same outcome, - PASS. I am wondering if such occurrence has been heard before. What the cause could be?