FV-101DM VFO to FT-901DM radios

I have a FV-101DM and a FT-901DE (same remote VFO requirements as the FT-901DM and the FT-902 series). I've seen several notes from people who thought they would directly interface, and decided to dig into this and get mine working. After reading the notes around the web, I studied the schematics and realized that they are incorrect and would have 12vdc being applied to the VFO output and the wrong cable being modified for operation.

The FT-901Ds have a totally different interconnection design from that of the 101ZD's. The 101ZD's have two cables between the VFO and transceiver, the 901Ds utilize one. Additionally, the FV-101Z & FV-901DM have a different pinout on VFO port B than the FV-101DM.

After a bit of experimentation, I discovered the FV-101DM can be interfaced to the FT-901DM with a little work, and retain most of the functionality of the FV-101DM's original design. Here's what has to be done:

1- A jumper must be installed from pin 7 of port A to pin 1 of port B on the VFO.

2- The 6-pin cable supplied with the FV-101DM only utilizes 3 wires (with no shielded circuits for the VFO output), as it intends for the VFO communications to the 101ZD to be via VFO port A. For this reason, a new cable with 6-pin connectors must be assembled to connect from the FT-901DM to the FV-101DM VFO port B. Wire the cable, pin to pin (i.e. Pin 1 to pin 1, pin 2 t pin 2, etc). Use a piece of small coaxial cable with the center conductor connecting pin 1 to pin 1, and the shield connecting pin 2 to pin 2. Standard unshielded wire is fine for the other pins.

3- Assemble a power cord to plug into port A on the VFO, to supply an external 12 vdc source to pin 1. Include a fuse link at 250ma to protect the circuit in the event of a problem. Connect the negative of the 12 vdc source to the cabinet of the VFO (there is no ground connection in the socket for port A on the VFO).

That's it! Mine is working great, and has all functionality except the VFO memories can not be programmed from the FT-901DM, but can be programmed from the VFO just fine. This is because there is no feedback path from the FT-901's internal VFO to the FV-101DM VFO like there is with the FT-101ZD.


The FV-101 is a good cosmetic match, and works well with the 901 after these mods. Below is a pic of the reassembled VFO as paired up with my FT-901.


Dave WB4IUY
www.WB4IUY.net

My FT-901 back on the air!

After looking at my old Yaesu FT-901 in Studio "A" with a failed transmitter for several months, I decided to dig into it this past rainy Sunday and see what had gone wrong with it. I checked the usual things... the 6146's and 12BY7 tubes, bias, operating voltages in the RF cage, etc. All was normal. It was actually producing about 100mw, and all was loading up OK, she just wasn't pulling any plate current above idle, as if there was no drive. I broke out the scope and started poking around a little, and discovered the TX output from the RF board to be waaayyyyyy down. After some voltage drop checks, it looked as if one of the 3SK40L's N-Channel mosfets had failed.



I scrounged around in my Yaesu spare (junk) parts box, and found an RF board from a later model. Mine used the PB-1702, and I had a PB-2154A from a later (newer) model. You can see the two boards compared above, and the component layout (and overall design) to be very different. I compared the pinout on the edge connector between the two in my shop manual, and that seemed to be the same. The old board used two FETs in the mixer, the newer boards uses a diode ring mixer. I started to pull a FET from the new board, but a bit more reading on foxtango.org suggested the newer board would work and was an IMD improvement.



On the left, you can see the new version RF board plugged in for a test, with the red, yellow, and green cables plugged into the top. I plugged the new board in, flipped the switch for a smoke test, and she came alive with full output. Yipee!! All is well, and my old FT-901DE is back on the air with a newer version RF board to boot. Ya gotta love these old rigs for ease of service. My rig is one of the early serial #'s, produced sometime around 1978. Despite it's age, it was one of Yaesu's flagship contest rigs of the day, and still preforms pretty darn good today.

Dave WB4IUY
www.WB4IUY.net