Magellan II handset circuit diagram?

Finite (John) · #1 26-03-2011, 11:41 AM

HI folks, John from the Waikato in NZ here. This is my first post so thanks for letting me into the forum. I must apologise my first post is an unglorified cry for help! I've recently got a LX50 (10") scope, having dabbled over the years with old newtonians, so am feeling quite chuffed, enjoying looking at it sitting imposingly in the hallway! To me it's neat, though it's an old clunker to most (rather like myself I suspect!) Anyway, it was the right price (for NZ) so into it. Now I'm hoping for some clever people to point me in the direction of where I might get a circuit diagram for the Magellan II handset which came with it. I've not had a lot of luck,- hang on, I mean I've had NO luck,- finding a circuit diagram anywhere on the internet.

The handsets problem is the LCD readout is super faint, can't read it. Sometimes is just visible though. The first time I connected it up to a portable power pack it lit up full strength immediately but subsequent times connecting it up it was back to being too faint again! It's not the end of the world, but it would be nice to get it sorted, so looking for advice....I'm not electrically smart, but want to get it to a repair place, hence a diagram would be helpful.

cheers,

Finite

Barrykgerdes · #2 26-03-2011, 11:49 AM

Hi John

I have searched for that circuit for years but no one has reverse engineered it that I know of like has been done with other Meade electronics.

However the brightness of the display is adjustable and the method is in the manual. Do you have the manual. It is available on Meade's site. I think it is a sequence of key presses with the mode switch selecting the blank menu screen, like the Magellan 1. I have added the section below

Barry

[1. Adjust Brightness Pressing ENTER in the blank mode will cause the "Set Brightness" message to appear. Pressing the PREV key will make the backlight display brighter, while pressing the NEXT key will make the backlight dimmer. There are 16 levels of brightness available. After the lighting has been adjusted for the best viewing, press MODE to exit this function.

Finite (John) · #3 26-03-2011, 12:36 PM

Thanks Barry, I tried that ta,... I can adjust the intensity of the orange background to the screen, but it's the actual grey LCD characters which are the problem. I'm hoping it's simply a faulty resister or so which dictates the strength of the output to the numerals....

Thanks for that info though, I appreciate you taking the trouble to type it up for me.

Barrykgerdes · #4 26-03-2011, 02:26 PM

Hi John

The LCD characters are not lit at all. If they are selected they just block the backlight. The contrast relies on the intensity of the backlight and shows as letters or numbers as black (grey?).

I have the same problem with the Magellan I the maximum brightness of the backlight is still quite dim at full on. So much so that I can't use it successfully due to my eyes not being as good as they were. I went out and bought an Argo Navis and made a patch cable to use the Magellan encoders with the Argo. Great improvement. It stores the time with its inbuilt clock and location so you don't need to re-enter everything when you turn on.

Barry

MrB (Simon) · #5 26-03-2011, 03:32 PM

Quote:

Originally Posted by Barrykgerdes

The LCD characters are not lit at all. If they are selected they just block the backlight. The contrast relies on the intensity of the backlight and shows as letters or numbers as black (grey?).

The LCD segments themselves have adjustable contrast too.
This is usually varied by a voltage applied to the driver IC, which in most cases is simply done with a multiturn trimpot set up as a rheostat(voltage divider), more clever versions will have a thermister included for temperature compensation.

Im not familiar with the Magellan, what type of LCD has it got?
2 line x 16 character? or 2x20 or 4x20 etc?
The only photo's I've been able to find are small, but it looks like a 2x16, which is likely to use the very common Hitachi HD44780 driver or a clone, in which case have a look at the circiutry hanging off pin 3.

Barrykgerdes · #6 26-03-2011, 04:36 PM

The Magellan II uses the same display as the LX200 and Magellan I as far as I can see. It is a 2 x 16 display. There is no ID on it that can be seen without disassembly.

However Pin 3 is shown on some circuits as being connected to a pot but this pot does not exist on the boards. The pin is just hard wired to 0 volts which I would expect is as black as it gets.

Barry

MrB (Simon) · #7 26-03-2011, 04:56 PM

Aha, thanks Barry
I would then check the soldering on pin 3 for a dry joint.
If all checks out, I'd just swap the LCD module as they can be had on eBay for only a few dollars.
Black with Red characters for $5.50

Finite (John) · #8 26-03-2011, 08:16 PM

Barry and MrB, thank you,- you guy's rock! Wish I had your ability. I'm a reasonably practical man but electronics on the level of your understanding is another language to me. Thanks for your input, it sounds hopeful that a successful repair may be had.

When I bought the scope the seller said that the characters take about half an hour to appear after turning the scope on, and that it never fails him. I found they did appear after about three hours but they faded away again after only a short period of time (maybe 10 minutes). Every other time I've turned it on, with the exception of only the first time I plugged it into a 12v power pack, I've got nothing in the way of readable characters. I must've looked a sight on my hands and knees in the hallway after dark, with a magnifying glass trying to see what's meant to be on the screen. I could make out the rectangles the characters form in against the screens background, and I did manage to get the background to adjust in those 16 steps of brightness.

As mentioned earlier, when I plugged the scope into a 12v power pack the numerals came up immediately, and solid and easily readable. Only on that day though and not since. I like the sound of a dry solder joint! That sounds very easily sorted. I have hope! I'm now going to have a look at those Ebay lcd screens.

My thanks, and kind regards,

john

Finite (John) · #9 28-03-2011, 09:28 PM

May be fixed, this pesky Magellan II handset. I had it in at electrical repair place to be checked over today, and they couldn't find anything wrong with it. But they didn't have the scope to run a test plugged in (I offered to bring that in for them also). I took it apart myself and found that if I pressed down on the left end of the screens mounting plate the characters came on, I let go and they go off! So I tightened the screws holding the screen mount in place and bobs your uncle! Been using it all evening. Now to see if it still goes when I switch it on tomorrow morning (when I have a quick look at Venus before heading to work).

MrB (Simon) · #10 06-04-2011, 06:28 PM