This page was created in july 2001.  the servicing details were 'scanned' by faxing them to a PC running DOS4 and emulating a fax machine.  The quality shows this.

FDK Multi750 * Mic wiring, Servicing and alignment details*



FDK750e and 430a 
The FDK Multi-750e was launched in the UK in 1981. A 2m ham radio multimode tranceiver, at a good price, and with a matching 70cm transvertor controlled from the front panel. There are still a good number around, but many have stopped working because of a very common fault - the potentiometers on the PCB were very prone to intermittent working - especially on the final amplifier board.
If you have one with problems, it really is worth giving all the pots a good clean, and sweeping the boards for 'dry' solder joints. Meanwhile I have a copy of the service manual as a series of GIF images which you can view and print out here.

The FDK750 is fitted with a 6 pin microphone socket.


FDK750e mic


used on packet or APRS A 2.5mm loudspeaker jack at the back of the FDK carries received audio to the TNC. Both TX and RX lines into the TNC are through a 180 degree 5 PIN DIN socket. The cable into the TNC is screened.

Clockwise from the indentation in the socket, looking at the radio mic socket:-

  1. Earth
  2. +5V
  3. Up
  4. PTT
  5. Mic
  6. (centre pin) Down

Multi 750e Servicing and alignment:


Click on each page to view it. These are GIF format files, and if you print them out- each should be put onto a single page of size A4- to give the best resolution.
All of the image files together add up to 2MB.

750 alignment page 1 PCB ref numbers
750 alignment page 2 Test gear
750 alignment page 3 Test gear
750 alignment page 4 Common fault areas
750 alignment page 5 Adjustment points
750 alignment page 6 Measurement points
750 alignment page 7 Adjustment procedure
750 alignment page 8 Adjustment procedure 2
750 alignment page 9 Adjustment procedure 3
750 alignment page 10 TX/RX DC switching
750 alignment page 11 TX/RX unit
750 alignment page 12 TX/RX explanation
750 alignment page 13 TX power unit
750 alignment page 14 TX power unit
750 alignment page 15 TX power unit
750 alignment page 16 PLL/SSB/Ch-SW unit
750 alignment page 17 Channel switching
750 alignment page 18 Channel switching
750 alignment page 19 Channel switching
750 alignment page 20 Channel switching
750 alignment page 21 Channel switching
750 alignment page 22 Channel switching
750 alignment page 23 Channel switching
750 alignment page 24 Channel switching
750 alignment page 25 Ch/SW display
750 alignment page 26 Ch/SW display
750 alignment page 27 PLL
750 alignment page 28 PLL
750 alignment page 29 SSB
750 alignment page 30 SSB
750 alignment page 31 SSB
750 alignment page 32 SSB
750 alignment page 33 Toneburst (1750Hz)
750 Circuit diagram (1)
750 Circuit diagram (2)
750 PLL circuit (1)
750 PLL circuit (2)
I'm pleased to report that this information has helped a number of 750e back into the land of the living. I'm afraid I have no other information - but if anyone has some details of the EXPANDER-430 Id gladly post them here.