The Problem

A common issue with the Alinco DX-70 (all versions) is failure of the Multi-Function rotary control (S1001, the "sub dial" on the schematic). It is quite obvious when this control is failing, as the rig no longer responds reliably with every click of the multi-function control.

The part that fails is technically an "11mm vertical shaft 15 impulse 30 position incremental mechanical rotary encoder," Alinco part number UR009, manufactured by Alps as their part number EC11B15204. Though Alps has discontinued this item, the US Alinco distributor, REMTronix ( still has them in stock (at this writing). And, once their supply is exhausted, there is a good chance that another Alps decoder will be an acceptable substitute.
(Click here for a copy of the original Alps data sheet)

As you can see from the photo on the left, the encoder is physically very small. However, by following the instructions below, it is relatively easy to replace.

How the Encoder Works

Before we get started, let's discuss how an "incremental rotary encoder" functions, especially how it determines clockwise vs counterclockwise rotations.

Image two side by side single pole, single throw momentary switches. Call them A and B. Ground both of their two poles and connect the other ends to two inputs of a microprocessor (thus a total of three terminals for the encoder, A, B and Ground). A cam lobe half way around a rotary shaft operates the switches. The switches are so positioned so that when the shaft rotates in a clockwise direction the cam lobe will close switch A before it closes switch B. As you continue to rotate the shaft it should be obvious that switch A will also open before switch B. It should also be obvious that when the shaft rotates in a counterclockwise direction, switch B will close before A and will open before A.

Now, program the microprocessor to recognize that if A closes (or opens) before B, the shaft is rotating clockwise. Conversely, if B closes (or opens) before A, the shaft is turning counterclockwise. It is then a fairly simple programming exercise to execute the next routine down a list of routines if A closes or opens before B, and to execute the next routine up the list if B opens or closes before A.

Imagine now, not one cam lobe on the shaft, but 15 lobes (the 15 impulses mentioned above) and 15 valleys (15 "makes" and 15 "breaks" or a total of the 30 positions mentioned above). That's the rotary encoder used in the Alinco DX-70.

The problem with the Alps encoder in the DX-70 is that the A and B switches will eventually have trouble making contact reliably. The microprocessor in the head of the DX-70 always expects to see a B closure following every A closure and visa versa. If it sees two A closures in a row, or two B closures in a row, it gets confused and does nothing.

Replacing the Encoder

While cleaning the contacts with contact cleaner might work, it is sealed so well that you would have to remove the encoder and open it up to get to the contacts. At that point, you might as well replace it. Replacing the encoder is fairly easy, a low wattage soldering iron, a small Phillips screwdriver, a 1.5mm hex (Allen) wrench and a steady hand are all that is needed. Here are the steps:

1. Remove the head from the transceiver body, leaving the interconnecting wires attached to body.

2. Remove all six knobs from the front panel. All knobs except for the VFO simply pull straight off. The VFO knob is secured by one 1.5mm Allen screw.

Hint. If you don't have a 1.5mm Allen wrench, try a 3/64" wrench. It may work.

3. Remove the four small recessed Phillips screws from the back of the head.

4. You'll find that once the four screws have been removed the back panel of the head is still firmly attached to the plastic face housing. To release the back panel, insert a small screwdriver through the top cable slot and push up slightly on the top of the housing.

5. Lift out the CPU circuit board from the front housing.

6. The following steps remove the metal housing from the circuit board. Though not strictly necessary, removing the housing is highly recommended to avoid damaging the printed circuit board when the encoder is unsoldered.

a) Remove the nuts securing the volume and squelch controls and the VFO.

b) Remove the screw holding the VFO tension bracket and remove the bracket.

c) Remove the two screws on the rear of the circuit board that hold the metal
housing (click on photo 1 on the left) and remove the housing. The faulty
encoder is now fully accessible.

7. Position the circuit board so that the solder side is facing up. Using a small wattage soldering iron or desoldering tool, unsolder the two tabs that hold the encoder to the board (click on photo 2 on the left).

8. Now, unsolder the encoder's three leads (remember the A, B and ground leads discussed above?). Click on photo 3 on the left.

Hint. Rather than using an unsoldering tool, use a diagonal cutter to cut these
three leads right next to the body of the encoder. Click on photo 4 on the left). The
defective encoder will drop free of the board. Then, while grabbing each lead with a
tweezers (click on photo 5 on the left), touch a soldering iron to the same lead on
the opposite side of the board. The leads will come free of the board quite easily
without damaging the board's traces.

9. Clean out any remaining solder from each of the five holes that secured the encoder.

Another hint. An easy way to remove residual solder from printed circuit board
hole is with compressed air (e.g. from a "dust off" can). Spray the board with air on
the component side while heating the pad on the solder side with a soldering iron.
The compressed air will blow the solder from the hole.

10. With the faulty encoder removed and the holes clean, it is simply a matter of soldering in the new encoder and reassembling the head in the reverse order from disassembly. Two words of caution, though:

a) When reinstalling the metal housing, align the housing so that the push button
switches are centered in the housing's cutouts.

b) Do not over tighten the four Phillips screws that secure the back panel to the
head. Otherwise, you may crack the studs in the plastic face housing.

Click on any picture to enlarge it
Photo 1
Photo 2
Photo 3
Photo 4
Photo 5