On 8 Aug 2011 05:47:44 -0700 Winfield Hill
wrote in Message id: :
JW wrote...
Winfield Hill wrote,
The optical shaft encoders were originally made by HP, but now of
course they're made by Avago. Sometimes they call these a digital
potentiometer or a "Panel Mount Optical Rotary Encoder". For
example, the HRPG-AD16 product line, about $34 each at Mouser.
http://www.mouser.com/Search/Refine....word=HRPG-AD16
http://www.avagotech.com/pages/en/mo.../hrpg-ad1616c/
Since they use an optical 2-bit quadrature grey-code (as opposed
to using a pair of switch contacts), they're supposed to be
extremely reliable.
But recently I've encountered two instruments with identical
tuning-knob failures, one in an elegant 33250A 80MHz model
that's on my bench, and the other in one of our standard
33120A 15MHz instruments.
In both cases the knob seems 'stuck" and not to work as you
turn it, except every now and then you'll get one or two
increments or decrements. Totally useless.
I'm wondering if anyone else has encountered this failure?
I have not seen a failure on the 33XXX series of generators, but
the part # is 0960-0892. Looking at the picture on the find-a-part
website shows it as a mechanical encoder.
http://www.home.agilent.com/myagilen...te=u4p3ex5iq_4
Indeed.
Which is obsolete and replaced by 0960-2545, also a mechanical one.
It looks like its the same as used on the 65XX and 66XX power supplies.
I do know that the older 65XX and 66XX do use the (obsolete) optical
ones. It is possible to use the mechanical ones to fix the obsolete
optical ones with a bit of hacking, but the mechanical ones need more
turns to change the output of the supplies for a given amount.
Thanks, great info!
You're welcome.
Are you sure it's an optical encoder you're looking for?
No, and as you say, the service manual identifies the mechanical
one as the part, now that I bothered to look. Given the failures,
perhaps being mechanical makes sense.
Could be, but I've yet to see a mechanical one go south unless there was
some abuse. Even then they are sometimes repairable. The bend over tabs
that hold the encoder together come apart a bit when the shaft is hit at a
right angle, which seems to happen all the time on the power supplies I
mentioned. I've lost count on the number of times I've repaired them.
After repair I solder two 24ga pieces of bus wire across the top from tab
to tab which helps sturdy them up a bit.
I had just assumed that
because HP long-ago developed and manufactured a fine optical part,
they'd use it in their expensive premium instruments. Heck, I've
long used their expensive optical encoder in my own designs!
The mechanical part looks much smaller than the optical one, which
might not fit as an upgrade replacement.
If you *do* have an optical one, it may depend on whether it solders
directly to a PCB, or is panel mounted. If the latter, it probably has a
cable which attaches to a PCB, and you should be able to adapt the
mechanical one. If you go that route, I've found that it is important to
ground the case of the encoder. You'll probably have to fiddle around with
the wires to get the order right. Trial and error...