Steve -
Yes, it's quite possible that the internal Zener is 'sorta' conducting. They often fail in this
way. The internal Zener is 10V. Cold spray is often helpful in isolating the troublemaker.
How MUCH is the frequency shifting?
Other parts that can cause these kinds of problems are the capacitors, most often Dur-Mica (brown
dog-bone) type, and are np0 types.
The white tubular capacitors are temperature compensating caps, so care must be
taken in replacing them.
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Steve Wedge wrote:
I finally pulled my R-4A out of its place on my operating desk and got the covers off. As I was
undoing the nuts in preparation for PTO removal, I noticed that there was a 10V zener on the small
board that the wires from the PTO connect. I also noticed that one end was broken but still
touching its connection.
A couple of things come to mind. First, the schematic and comments I've heard from others on this
list strongly suggest that the zener should be inside the enclosure. Second, if that's true, then
a previous owner tried to correct my "frequency-jumping" problem by installing the zener
externally to the enclosure to avoid the extra work. Could it be possible that the zener inside
the enclosure is still behaving erratically and intermittently conducting at some voltage below
that of the external zener? I haven't pulled the receiver back off the desk (arggggh...) yet and
wanted to get a general opinion.
Am I right in assuming that this zener - which was installed on the back-side of the little board
- was added on?
Steve Wedge, W1ES/4
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