My Drake R8B tuning sometimes gets lost when I spin the knob fast.
I'll be going up 7.2, 7.3, 7.4, 7.2 See? I expect this is a pretty
common prob.

Ok so unit is going to go back to Drake for fix and I will tell them to
go thru whole unit and check it out.

Any idea what they will charge me for this?


I finally got around to fixing the encoder problem (erratic tuning) that's
been bothering me for awhile.

Removal of the encoder board from the front panel was fairly
straightforward; just time consuming. The inner and outer panel came apart
surprisingly easy and making the repair somewhat enjoyable---re-assembly was
just as easy.

My first attempt was to unsolder the encoder from the board. However, like
many of you, I finally I bent back the tabs of the encoder with a small
screwdriver to take it apart. Even though I had a replacement encoder it
was difficult to unsolder the part from the board---plated through holes!
It might be that replacement of the entire encoder would be required at some
later date anyway.

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 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 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. I intend to experiment with
blue and white LED's as well as blue filters. The closest filter color I
had on hand to match the Drake blue on my vintage pieces of Drake gear is
the blue tab on 3-ring binder notebook separators or hanging file tabs. I'
ll take a tab to the art supply shop and see if I can match it.

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.

[Note: It's been three years since I cleaned the encoder---there has been no
recurrence of the problem.]

RG