FY6600-60M Function Generator PSU Issue

Nice bit of kit, for a reasonable price, but watch out for the 90VAC on the BNC barrels. This post outlines the PSU problem and how a fix was implemented.

I've recently taken delivery of a "FeelTech" FY6600-60M signal / function generator. This is a cheapish, but pretty decent Chinese piece of test gear. This isn't the most up to date version, that's the FY6900, but it does what I need.

Searching around the internet indicated that this machine suffers from having stray 90V AC voltages on the BNC barrels. As supplied it only has a two line power cord and is not earthed in any way.

The consensus is that the ideal solution is to replace the PSU board, however YouTube channel TheHWcave has an excellent video where he analyses the problem and presents a quick and easy fix that reduces the barrel voltage to under 1V AC.  In a later video he designs and builds a replacement PSU.

I decided to go with the fix for now and only worry about replacing the PSU if it became necessary.

The core of TheHWcave's fix is to AC couple the signal ground to earth by replacing the Y1 capacitor between the high and low voltage sections of the PSU with two Y1 capacitors, connected to earth.

The following image from his video shows the principle.

The process is illustrated in the images below:

• The existing 2 pin mains plug is replaced with a 3 pin C8 plug.
  • The plug I obtained only required some enlarging of the existing plug mounting hole.
• The original Y1 capacitor, highlighted in one of the pictures, is replaced with two capacitors, paralleled to earth.
  • I connected the earth lead to the capacitors by screwing an old mounting post into an unused mounting point on the bottom of the case.
  • Be careful adjusting the new capacitor leads, I managed to twist the copper off the PCB!

The result was the reduction in the stray AC voltage from a measured 82VAC to 0.9VAC.