I have had a bunch of people asking for this MOD that can't get it off of the Yahoo Group so I'll try to put it on the Flex site that everyone should be able to get.
Hope this helps someone with getting rid of most of thier RFI.
The Problem: Basically what is happening is the Ground's ARE different on the Flex then the Yaesu.
The FLEX5000 requires a MIC- on PIN7 and a Chassis ground on PIN5 and ARE not the same thing as Yaesu uses because Yaesu radios do not have a MIC- input and have the pins reversed.
SO what is happening is that using the stock Yaesu cable it send all the noise on the MIC's shield into the FLEX5000 on the MIC- lead causing RFI right on the MIC- lead.
All the Mod does is it moves the MIC shield to the Chassis ground pin of the FLEX and off of the MIC- lead and uses the CUT OFF black wire in the HEIL CABLE as the MIC- and then on the MIC end it ties the black MIC- wire to the MIC- (not shield) on the MIC element and STILL has the shield going to the body of the MIC for chassis ground.
The MIC- wire (White wire) inside the MIC from the MIC elements does NOT do anything to shield or ground the MIC shell as far as I can see and is connected to PIN1 in the base of the MIC and after the MOD is not shorted to the Shield bust rather connects to the Black wire in the HEIL cable for a balanced output to the Flex5000.
After the MOD the main difference is that NOW a balanced MIC circuit from the MIC+ and the MIC- Elements to the Radio's MIC+ and MIC- connector on the FLEX thus letting the balanced mic wires inside the shield cancel out any interfering noise between the MIC and the Radio and the Shield IS NOW grounding the MIC body to the radio's Chassis Ground pin.
Here is the PIN outs for both the FLEX5000 and the Yaesu FT950 and many others Yaesu's for you to compare as you can see on the Yaesu they have the Screen/Earth (Shield) on the FLEX5000's MIC(-) pin which is where the main problem is and doesn't use the Chassis Ground Pin for the MIC's shield in the HEIL Cable on the FLEX5000 so the Cable Shield is floating on the MIC- Pin and is only Chassis grounded with the little wire under the Horse shoe cable restrainer clamp on the MIC connectors shell.
1 NC 1 MIC UP
2 +5 volts 2 +5 volts
3 N.C. 3 Down
4 N.C. 4 Fast Scan
5 Chassis GND (Shield) 5 Ground
6 PTT (+) 6 PTT
7 MIC (-) 7 SCREEN/EARTH (Shield)
8 MIC (+) 8 MIC
I have rewired 5 MIC's and Cables for the local guys now that had different degree's of RFI problems and ALL of their RFI issues are gone in ALL of them and their Audio sounds GREAT.
The RFI will manifest itself in a few different ways.
1: Just a bit of weird noise on different bands.
2: Echo on your voice audio.
3: A lot of distortion that is common on a station that doesn't have a good RF Ground.
This will NOT cure all your RF Problems but it will help track down one that you have been plagued with for a while.