[AZ-Observing] Re: Cable Gone Out
- From: Gene A Lucas <geneluca@xxxxxxxxxxxxx>
- To: az-observing@xxxxxxxxxxxxx
- Date: Mon, 27 Jul 2009 21:21:47 -0700
Regarding the Meade LX-series cables and electrical problems...
There are actually TWO types pf cables -- the one for the hand paddle,
which uses a "standard" RJ11 telephone-type plug, with four connectors,
and the second one, for connecting the DEC motor circuits to the base
computer, which is a similar plug, but with two additional connectors.
They are NOT interchangeable, and, amazingly enough, the smaller hand
paddle cable WILL plug into the middle part of the DEC cable. This is
NOT good, as it WILL burn out some components in the DEC motor circuits
(possibly in the base computer !!) I would not have believed that
connection was possible, except that a friend of mine plugged in his
spare hand paddle cable into the DEC motor circuit, with disasterous
results!! Furthermore -- the DEC cable would appear to be similar to a
CAT5 / CAT6 type computer data cable... BUT -- it is of the
"cross-over" circuit type -- the wiring reverses end-to-end at the
connectors. This is because there is a pass-through connector installed
in the DEC fork arm, which requires the circuit reversal.
On the subject of making your own replacement cables.... unless you have
LOTS of experience, AND the required (expensive!) crimping tools, I
would not recommend trying it. Another tool that is useful (but also
expensive) is a cable checker box. But this is not economical for a
single replacement cable.
So far as I can determine, the LX-series hand paddle cable is wired the
same as a standard RJ11 telephone handset cord -- so replacement cables
of longer length, white insulation instead of black, etc. should work
o.k. FOR THE HAND PADDLE. And these are widely available and economic.
The rotating connector gadgets available for telephone plugs are
probably not a good idea, as they use cheap sliding contacts which are
known to be "noisy" in phone service, and therefore probably not
suitable for the hand paddle to computer circuits on the telescope.
FYI, the connector on the base computer for hooking up to a computer
serial port -- the so-called RS-232 port -- is NOT 'standard" RS-232...
Moreover, the circuit diagram for the series connection cable in the
older version of the Meade manual is incorrect ! Also, that plug
carries plus and minus 12 volts on the outer two pins - again, not
standard, and very easy to short out! BTW, any intermittent shorts or
grounds on the 12VDC input WILL "kill" the computer in the base...There
is no buffering or protective diodes on the power input circuits -- that
means the accessories, such as the reticle light and the focus motor
connector, are tied right onto that circuit, too!!
Much information on these subjects (and many others) is available on the
MAPUG web pages:
http://www.mapug-astronomy.net/AstroDesigns/MAPUG/ArhvList.htm
Dr. Michael Covington has some suggestions about modifying the 12VDC
input circuit (which I won't go into here; this is for the
electronically experienced!):
http://www.covingtoninnovations.com/astro/powerinlet.html
...plus lots more tips:
http://www.covingtoninnovations.com/astro/links.html
I cannot recommend buying parts from Radio Shack.... At most of the
stores I have visited, their stock is very limited (compared to the olde
days), and some of the components are not of the best quality -- you
have to know what you are looking for... They do have many useful
connector adapters, for say, audio and TV. Lately my impression is that
they are getting out of the hobby electronics business, and
concentrating mainly on iPods and cell phones and accessories. They
have even dropped much of their inventory of TV and audio components....
It is fairly easy to order electronic components over the internet, or
if you are in Phoenix and don't mind a cross-town drive, you can visit
one of the Fry's Electronics stores -- they still carry a large
selection of components. Circuit Specialists in Mesa is a big player on
the internet now... but the store on Country Club is not a walk-in shop
anymore... There used to be a couple of stores in west Phoenix that
carried fairly broad lines of components...
FYI, my experience is primarily with the LX200 "classic" telescopes...
Cheers,
Gene Lucas
(17250)
Stan Gorodenski wrote:
> Thanks, Steve. Stan
> Steven Dodder wrote:
>
>> My original reply was overquoted, so rejected.
>> What it said was, be careful with Radio Shack telephone plugs if you use
>> one. Be sure to check the polarity of the connectors. I wrote a procedure
>> for you, but if you're in contact with Gene, he can describe it for you.
>>
>>
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