yes ... that's one of the first things I checked
the grounding of the instruments and the bench are ok ..
i also opened the tm504 to check the ground and a couple of resistors connecting the ground ... all ok
the pg506 has two floating masses .... at this moment I have the pg506 on the bench
if I measure the resistance between the two masses I read 10-11 kohm
I think it's not correct ... Eric has just measured an infinite value between the two masses on a working pg 506 .....
I performed the measurement between the two masses on C100 ....