Replacing R8B encoder:

R8 optical encoder -- ID from Drake:  
The encoder can be purchased through e-sonic, http://www.e-sonic.com and digi-key, http://digikey.com. The part number is ENA1J-B28-L00128.  Allied stock # 70154375 $34.03; Avnet $29.32; Digi-Key and Mouser higher.  Distributors showing obsolete.

R8B service manual calls R8B encoder EC24B100B-9 (Drake P/N 3260015)

Latest R8A encoder part info (1/9/13)  
	RL Drake Part number: 3260013  $12 plus shipping
	Contact: Debbie @ 732 679 4000 x 4256
 
If you can solder well and know how to disassemble electronic equipment, the encoder replacement is quite easy. It starts with removing all the knobs, top/bottom covers, and the front (black) panel. Then you remove the nut that holds the encoder shaft in the hole of the chassis. Unplug the encoder wiring harness from the PC board and remove the encoder assembly through the bottom of the chassis.

I suggest you order just the encoder without the PC board. It's about half the price of the original assembly. As I said, the PC board is no longer necessary. The new part # is 3260012. The price was $11.51 about three years ago. You will have to remove the wiring harness from the old encoder PC board and solder the three wires to the matching terminals on the new encoder. Follow the circuit traces on the old encoder PC board to determine where each wire goes on the new encoder terminals.

There was a thread on this group more than a year ago where we discussed why this encoder fails. Myself and another contributor came to the conclusion that the factory lubricant (grease) causes the encoder contacts to become less conductive, possibly oxidized. I disassembled an R8B encoder which was acting like yours, cleaned/degreased it and relubed it with a synthetic grease. It's been working fine for several years now.

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You probably won't have any problem with the new encoder but I've found a way to make it last much longer. This involves taking it apart and thoroughly degreasing all the internal parts, especially the contacts.  Use a good electrical cleaner such as DeOxIt. Then relube the internal parts with an *all synthetic* grease. I use a grease called 'Superlube'.  It may be hard to find in your part of the world but you can order it online.  The encoder in my R8B has lasted several years since I did this maintenance. I think Drake may have done something about this encoder problem because the new ones seem to be lasting longer.

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Drake Service indicated the replacement encoder is not the same type as the original.

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As I had mentioned in a previous post, I was interested in learning why the encoder failed. After removal of the encoder wheel from the body of the encoder I examined the contact surfaces under stereo microscope (Leica SZ-4) at 40X magnification. I could plainly see what appeared to be normal wear patterns in the conductive surfaces that matched the position of the contact fingers in the mating part.

The contact fingers were examined next. Using similar magnification and upon carefully rotation of the part, I could plainly see that the contact points were worn through their silver plating and well into the brass base metal. The contact surfaces were burnished to a bright, mirror finish. Furthermore, the first two contact points were clean with a clear grease residue while the third inner contact (electrical common?) had a dark brown/black greasy residue about its contact surface.

With the realization that I rarely used the tuning knob I wanted to understand why the wear on the contact fingers seemed, in my opinion, excessive. I observed that the third contact finger (electrical common?), the one with the dark residue, was in continuous electrical contact with the wheel more so than the other two fingers that rode on the 'spokes' of the wheel. Furthermore, the surface that the contact was moving against had a rough surface consisting of striated tooling marks with uniform depth and spacing that suggested the result of rough polishing or grinding. Close study of the wear patterns on the wheel clearly revealed hills and valleys and that the hills were the surfaces that had been worn into the wheel by that contact finger but had not yet reached the depth of the valleys. It was this observation that led me to think that the brown/black residue on this particular contact was an accumulation of silver and brass particulate from the contact finger and wheel that had oxidized and mixed with the grease. The rough surface of the wheel was simply acting as an abrasive surface and was wearing the contact points.

I thought I would reuse the old encoder and see how long it would last after a bit of maintenance. I cleaned the encoder with electrical solvent cleaner and with the help of a very fine brush I cleaned the contact fingers as well. The parts were carefully blown dry then re-examined under the scope and were found clean. A small drop of DeoxIT contact cleaner was placed on the wheel surfaces then worked by pressing the assembly together and rotating the wheel against the contacts.

There was another problem with the encoder that I need to take care of as well. Ever since I got this receiver I had been bothered by the viscous, squishy feel of the tuning knob. While I had the encoder opened I carefully cleaned it of all grease with electrical cleaner. The designers of the encoder had used a relatively large quantity of grease to gain the damping action that had bothered me. On the reverse side of the wheel (shaft end) the grease was easily removed with a probe and the remainder was readily soluble in the electrical solvent. However, before re-assembly, I placed a very light film of fine grease on the shaft. After the front panel was replaced I placed a small felt washer on the encoder shaft. The knob was positioned against the felt washer to get the desired feel. Now the knob turns with a dry, positive, precise, clean feel with no wobble or endplay. Furthermore, I replaced the R8B knob with that of the R8---the aesthetic enhancement that the old R8 knob adds to the receiver is remarkable!

While the front panel was detached from the chassis, I also removed all controls and added a drop of DeoxIT into them and worked it in. The tone control was beginning to get scratchy and I've had a problem with the volume control in the past.

In the process of working on the front panel I learned how the readouts are backlit---just a bunch of green LED's on a circuit board. I have always been upset by the lime-green color of the display. Drake had been known for decades for their use of a distinctive blue for illuminating the meter and dial displays of their older equipment and I liked it very much. I guess when the receiver was designed there weren't any blue or white LED's and those that are available now are expensive. 

The receiver has been re-assembled and everything is working properly; tuning is as it should be. It will be interesting to see how long the repaired encoder lasts. I had the encoder replaced under warranty repair by Drake twice before.

In summary; apparently the encoder failed as a result of intermittent electrical contact resulting from dirty contact surfaces. Others have suggested contact bounce and poor electrical design. My personal opinion, although based on this one example and comments from others, suggests that the encoder is poorly designed or not able to take the continuous wear and tear it experiences in its application as a main tuning control for a radio receiver. Quite possibly it should be replaced with a part more suited to the task.

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