Meade LX90 DC Lead Polarity

[byronpaul]

Hi, can somebody please clarify for me the polarity of the DC Lead for a Meade LX90. :help:

At the scope end, is the "centre pin" postive or negative? I'd assume positive but I would like to be certain before making up a lead and causing damage to the scope.

I'd prefer to make up my own lead with better quality cable for my particular use rather than purchase the optional Meade #607 Power Cord.

I'm well aware that getting the correct polarity is critical.

Thanks in advance for all feedback/advise!!!!!

[bmitchell82]

Do you have a volt meter? that will tell you if its active or inactive (+ or -)

[AndrewJ]

The plug used is 5.5mm OD, 2.5mm ID centre positive
Also stick in a fuse ( 2A fast blow shld be Ok )
The scope has no polarity protection and no fuses built in.

Andrew

[xstream]

It's centre positive.

[mozzie]

ive had my pin broken at star parties by over excited public and after replacing a few the centre is positive take your time and check with multi-meter when finished
mozzie

[byronpaul]

Guys, really appreciate your prompt responses.:thumbsup:

Yes, I was definitely going to fuse the lead as well.

[AndrewJ]

Just for more info, as reversed polarity is a curse with the Meades
and you read about it all the time where people have blown the tracks off their pcbs
I made a simple polarity tester for 10c using 2 back to back LEDs
( then i found a 30c 2 leg, bicolour LED that did it in a single unit :P )
Have attached a piccy of the first and second prototypes
In the field, you just plug yr cable in and see what colour lights up
No multimeters, no fuss
If you have a fixed plug on yr cable, you can also build this directly into the cable itself
( just in case you connect the cable to a battery the wrong way round )
For 20c, everyone who owns a Meade should use something like this before using the scope as a "test fuse"

Andrew

[byronpaul]

Andrew,

thanks for the information and pictures. Very interesting.:P

I plan to run the scope off dedicated 12 volt power supplies (either caravan 12 volt socket or stand alone 240 ~ 12 Volt DC convertor). I'm 100% confident of the positive and negative from those supplies but hadn't thought about the situation if I ever used an independant power source.

I may need to build myself something like your little invention which will save having to use a multimeter at the time to determine positive and negative polarity.

[byronpaul]

Found this link tonight which has lots of information regarding LX90 pinouts, ports, cables and connections.:)

http://jan.eaglecreekobservatory.org/pinouts.html

[AndrewJ]

Hmm, my first reply didnt appear ??

Yep, that's one of the best for the LX90
Also
http://www.weasner.com/etx/menu.html
has a tremendous amount of info, esp related to the Autostar

Andrew