TM500 Mainframe Tester, BNC grounding issue fix.

Jared Cabot


I have just taken a couple photos of the BNC in my TM500 mainframe tester.
Some were having issues with the BNC being grounded to chassis, which is incorrect and can cause erroneous readings etc.
I didn't catch this as I used a scrap PCB to aid in aligning the connectors (not required, just made assembly easier for me) so my BNC was insulated from the start.

The fix is to install some sort of insulating washer, like a fiber or nylon washer or similar, and if possible, enlarge the hole in the aluminium panel to provide clearance.
Then the shell of the BNC connetor is connected to the provided pad on the Front Panel PCB to connect it to the LO terminal on the front panel.

Here are some detail photos of how mine is constructed:

I'll update the manual with these details in the next few days.