This describes how to modify a Yaesu FT-817, so that the +12V appearing on the accessory connector switches on and off with the radio.

Normally, the +12V appears on the ACC connector when it has internal batteries fitted or DC plugged into the rig.

Accessory Connector

The +13.8V feed appearing on the accessory connector is “always on”. In other words, whilst the FT-817 is connected to an external PSU, or has its own internal battery pack installed (and charged), +13.8V will always appear on this pin.
For some applications, it is more useful to switch this +13.8V feed on and off with the radio. This then allows us to switch peripheral equipment on and off accordingly, such as a transverter.
Required Skill Level

Basic – intermediate: Requires SMD part removal, and fine soldering.
Time to complete: 5- 10 minutes.
Applicable version?

The Main Unit overlay in the downloaded FT-817 Service Manual pdf was found to be different to my FT-817 (purchased new, Feb 2011) in the vicinity of the accessory connector. Thanks Yaesu!

Luckily, this modification became much easier, and the Main Unit does not need to be removed, as first thought.

Everything can be done from the top side of the PBA.

How the Main Unit PBA markings relate to the “Lot” numbers on the different schematic versions, who knows.
If your FT-817 layout does not look EXACTLY like the pictures here, you have a different version, and should proceed with caution, and only once you have identified the correct point to break into the Accessory Connector pin.
Tools required

• Small Philips head screwdriver to unscrew case
• Tweezers, suitable to extract 0805 sized SMD part
• Soldering iron, with fine tip
• 20cm fine hook up wire
• Solder, preferably fine
• Side cutters, wire strippers
Procedure Summary
One 0R SMD link is removed, and a wire link is run to another part of the board – that’s it!
Detailed Procedure

• Unscrew and remove shoulder strap. It’s just easier to work inside the 817 without this on.
• Unscrew top cover’s seven screws (top cover is cover with speaker).
• Carefully lift the top cover off towards the RHS of the radio, mindful of the short speaker lead. Disconnect the speaker connector.
• Located near the antenna socket, identify the 0R link that needs to be removed, as indicated below.

• Using a fine-tipped solder iron and tweezers, carefully remove this 0R link

• Solder one end of fine hook up wire to the RHS pad as indicated by the arrow.
This pad goes to the +13.8V pin on the Accessory Connector.

• Solder the other end of the wire to the emitter of Q1082.
This is made easier, by temporarily disconnecting the coaxial connector plugged into J1.
Don’t forget to reconnect this plug, once you have soldered the wire!



Click for full size
Click for full size


Circuit Diagram

We get the switched +13.8V feed from the drain of Q1104, a 2SJ355 FET. Although this device is rated at 2A (with appropriate heat sinking), it would be wise to limit the current drawn from this point to 100 mA, or so.

This is perfect for activating an external relay in our peripheral device.

As Q1104 is on the under-side of the PCB, and difficult to get to, it is much easier to take this switched feed from Q1082 emitter, as described above.

Further Enhancement

If desired, there is sufficient room inside the FT-817, next to the accessory socket, for a miniature toggle switch.

The behavior of the +13.8V feed on the Accessory Connector could be changed from being switched (as per this modification), or continuous, as found standard, depending on requirements.

This article is available as a pdf.

 FT-817 13V Acc Mod by VK4GHZ