614L-8 ADF Control Head Hacking, Part 1

Collins 614L-8

This is the ADF Control Head that I chose form my project.  It is a Collins 614L-8. they are plentiful on Ebay.

The Analysis    The Unit is tuned via a 400hz syncro transmitter. So it looks like I will have to find a replacement for the syncro.  The Loop Switch in the upper left must be rewired and the switch logic for the Band Selector Switch behind the Tuning Knob seams ok, but that will have to be verified. The Gain Control is just a 5k pot,  and the Function Switch behind it just need some pull-up resistors. It looks like I can drive the Tuning Meter with a PWM signal from the controller.  Also there is a BFO Switch which induces 142.5 Khz signal on top of the audio.

The Plan   Well first I need to score a copy of the maintenance manual they are kind of pricey on Ebay so I dug a little more. In the military the Control Unit is part of AN/ARN-83 and I found pdf copies of TM 11-5826-225-12 and TM 11-5826-225-35 with schematic, part diagrams, etc. Also you can score the operators manual here.

Next we have to identify the goes inta and the goes outas, so here goes:

Connections Map
PIN	I/O	DESCRIPTION	CPU PORT	CPU PIN
	O	Loop Ant, Right Step
	O	Loop Ant, Right Slew
	O	Loop Ant, Left Step
	O	Loop Ant, Left Slew
	O	Function Switch, ADF
	O	Function Switch, ANT
	O	Function Switch, LOOP
	O	Range Switch, 190 – 400
	O	Range Switch, 400 – 850
	O	Range Switch, 850 – 1750
	O	BFO Switch
	O	Gain Control, Bottom
	O	Gain Control, Top
	O	Gain Control, Arm
	I	Tuning Meter
		GROUND
	P	Dial Lamps
	P	Panel Lamps

The Tuning Meter is a dc micro-ammeter requiring 100 micro-amps for full scale deflection.