Drake R8B --- Encoder Repair Notes
RadioGuy
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 bent back the tabs of the encoder with a small screwdriver
and pulled it apart for servicing. 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 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. 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.
R.
-----
starman
Nice detective work on the encoder. I suggest using a synthetic grease
called 'Superlube'. As for the backlight, mine now uses four white LED's
which give the display a blue color. I have a picture of it if you'd
like to see it. I found the instructions for the backlight mod' at the
following webpage:
http://homepages.ihug.com.au/~vk5vka/draklist.htm#R8BBacklightmodifications
RadioGuy wrote:
>
> I finally got around to fixing the encoder problem (erratic tuning) that's
> been bothering me for awhile.
snipped
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RadioGuy
starman <sta...@tech.net> wrote in message
news:3E3023C9...@tech.net...
> 1/23/03
>
> Nice detective work on the encoder. I suggest using a synthetic grease
> called 'Superlube'. As for the backlight, mine now uses four white LED's
> which give the display a blue color. I have a picture of it if you'd
> like to see it. I found the instructions for the backlight mod' at the
> following webpage:
>
>
http://homepages.ihug.com.au/~vk5vka/draklist.htm#R8BBacklightmodifications
Howdy Starman...
Thank you for the link to that R8B web site; I wasn't aware of it. I recall
J. W. Schermerhorn and his experiments with the R8B backlighting very well.
He regularly posted the results of his experiments to this newsgroup and
before I left it I remember he was trying different colored filters. I
haven't seen any posts from him recently. I was thinking of exchanging pc
boards instead of radical modification of the existing ones.
Yes, I remember you mentioning the synthetic grease to me in a previous
post. I had wanted to try it but then I thought that since the DeoxIT
contained a lubricant I figured I would use it by itself and see how it
worked before trying the grease.
You might have taken me to task regarding the base metal of the contact
fingers---I rather suspect it is beryllium copper instead of brass (I was
preoccupied with brass for some reason).
Well sure, if it is not to much of a bother please forward a link to the
photo of your display or perhaps post it to alt.test (?).
R.
-----
patgkz
these days! Such a crap-ola encoder in a $1400 radio.....geeeeez!
I own a SW-2 and R-8B.....replaced the encoder in the SW-2 years ago,
expecting it to be a cheap piece of crap in a cheap radio. Now I find out
that the same encoder is a little waiting "time-bomb" in the 8B....good
grief.
Pat WPE9JRL
"RadioGuy" <nos...@nospam.com> wrote in message
news:b0ncbs$92j$1...@slb0.atl.mindspring.net...
N8KDV
patgkz wrote:
> Typical Drake "quality".....Made in America doesn't seem to mean to much
> these days! Such a crap-ola encoder in a $1400 radio.....geeeeez!
>
> I own a SW-2 and R-8B.....replaced the encoder in the SW-2 years ago,
> expecting it to be a cheap piece of crap in a cheap radio. Now I find out
> that the same encoder is a little waiting "time-bomb" in the 8B....good
> grief.
Ahhhhhh, fixing a little 'ol encoder problem is nothing at all like having to
have all those mods done on an R75. ;-)
starman
A very similar encoder is used in the 909/398. I haven't heard about any
problems with those so it makes me wonder what the deal is with the
Drake encoder. As someone else said, it may have something to do with
the lubricant.
*****
N8KDV wrote:
>
> patgkz wrote:
>
> > Typical Drake "quality".....Made in America doesn't seem to mean to much
> > these days! Such a crap-ola encoder in a $1400 radio.....geeeeez!
> >
> > I own a SW-2 and R-8B.....replaced the encoder in the SW-2 years ago,
> > expecting it to be a cheap piece of crap in a cheap radio. Now I find out
> > that the same encoder is a little waiting "time-bomb" in the 8B....good
> > grief.
>
> Ahhhhhh, fixing a little 'ol encoder problem is nothing at all like having to
> have all those mods done on an R75. ;-)
Fcathell
encoder and the flip-flops. I don't know about the R-8B circuitry but the SW-2
has absolutely no de-bounce filtering after the encoder. The capacitor mod
I've posted in the past for the SW-2 does provide somewhat primitive de-bounce
filtering and it does help. If you look at the circuitry in the Lowe
receivers, for example, a very simple but effective R/C de-bounce circuit is
used and they have no problems at all with the encoders.
Frank
Llgpt
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From: fcat...@aol.com (Fcathell)
Newsgroups: rec.radio.shortwave
Date: 24 Jan 2003 14:24:18 GMT
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Frank
>>
I'll second that Frank, I've had several Lowe receivers, and no problems
whatsoever. Had two AOR AR 7030's, the first one was traded, so don't know
about that one, but the second had to have the encoder replaced (under
warranty). I never had any problems with my R8B which was purchased in
December, 1999.
The present Lowe, a HF-225 Europa is a fine, fine receiver. Works beautifully
from LF through HF with equal sensitivity.
By the way, those mods you sent for the HF-225E work great! Thanks.
Les