FT-847 repairs

FT-847

Sometime since I've written anything here, its not that I've been doing less on the radio front when the opportunity arises, Its just that I've not been as inclined to bother taking pictures then writing about it here.

Anyway sometime ago my FT-847 lost power on HF/Lower VHF, a tiny amount of RF was present (drive levels) finally upon investigation it was clear the Finals were out, and Torroids in the BPF were cooked well also.

One of either 2 things happened here, the famous 46 Mhz spurious emission cooked up the BPF upon amplification when operating on 70Mhz or I transmitted into the 6 meter antenna when I was on 4 meter or vice versa, I have no evidence of the later, but the FT-847 shares the same antenna socket for both the 6 and 4 meter bands.

Torroids, a Lovely shade of gray, one fell to powder upon removal, all 3 in that section of the BPF were replaced.

Next up the Finals.

All done, I used a slightly different material for the torroid replacement with better heat handling properties, other than that same RF wise.
New finals installed and the board ready to be reinstalled into the radio.
The cost of the new finals makes this a job you'd not want to be doing to often on a 15 year old radio, so I decided to take some precautions to prevent his happening again.

The SP2DMB supplied TX filter (circled) This should deal with the Spurious emission just below 46 Mhz.
http://www.sp2dmb.cba.pl/70e/FT847eng.pdf
I only installed the TX filter for various reasons.

Also visible in the picture is the G4FUF 4 Meter LNA daughterboard, which replaced an earlier 4 meter preamp effort.


When doing the solderwork on the finals I pondered how to split the 4 and 6 meter band antenna outputs, this was very simple to do, in the menu of the FT-847 the 6 meterband output can be selected between the HF socket and the dedicated 6 meter socket, as far as the FT-847 is concerned for the most part 4 and 6 are one big band so when you move the 6 meter band the the HF socket you move 4 also to it, so you can put a 50Mhz antenna on the HF socket and 70Mhz on the 50Mhz and change menu 28 each time you change bands, not ideal but better than screwing in and out PL259s eachtime.

I decided to disrupt this and split the outputs, so menu 28 does exactly what it says, it controls the output selection of the 50Mhz output leaving 70Mhz attached permanently to the 6 meter output.

I did this using a relay, and the old ALC power limiting transistor.

I can now have 50Mhz output on HF output and 70Mhz on the 50Mhz socket. or have them sharing the 50Mhz output as standard, the modification is easy to reverse.

Wire Menu 28 controls removed from socket.

Taken to a location at the front.

Orange Patchwire installed

 White wire is original menu 28 control, orange is a jumper back to the original socket, red is + for the relay and gray is the control logic, which comes into play when 70Mhz is switched in.

 Relay

Relay board eared onto the fan screw.

Control wire for relay from former ALC control Transistor.

I actually did this modification close to 1 year ago, and I can't imagine returning to the inconvenience of a shared 50/70Mhz antenna output again or fiddling with menu 28 each band change.