Meade LX-200 Motherboard

[egoroff]

Hi folks,
This is my first posting, after an absence of many years I am enjoying being back in this hobby.

I have a Meade LX-200, recently acquired by me. The instrument had been in storage for more than 10 years, and in mint condition for its age. I am guessing it is an LX-200 classic, as it was built in the early1990's. It operated flawlessly for some 6 months before the main processor board failed. I diagnosed the problem to a tantalum capacitor, a common fault for this vintage of scope. However I had to replace a damaged IC in the process...and you got it, the chip is now obsolete, and no one wants to sell me just one chip....so I am after a replacement board.

Now I am having problems attempting to find someone who has a spare board, if it exists at all. Does anyone out there have contacts or know if I can get? Meade do not seem interested.

Thanks in advance.

[h0ughy]

not sure but contact BINTEL to see if they still can get a kit to repair the mount

[thunderchildobs]

Parts for LX200 classics can be tricky to find and will get harder. I have just lost a motherboard but luckily i had a spare. I am now considering getting new mounts for either the 10 and /or 12 i have and using the parts from one to keep the other going.

[mick pinner]

l'm with David try Bintel, if no good pm me.

[stephenb]

Hi Robert, I'd go with the above suggestions for BinTel and also try the Yahoo groups

http://tech.groups.yahoo.com/group/Meade-Uncensored/
http://tech.groups.yahoo.com/group/LX200GPS/ (I know it's the GPS version but they might be able to assist)
And perhaps Cloudy Nights thread: http://www.cloudynights.com/ubbthreads/postlist.php/Cat/0/Board/Meade

It sounds like Mick may recommend one of these anyway. Good luck.

[Barrykgerdes]

What is the chip that you cannot procure. I have some spares. The repair kits are no longer available but if you send the damaged board to Bintel it may be repairable (no guarantees).

There are still some boards around but I don't think repairs will be done for much longer as it is not ecconomical to repair the boards commercially. These days I recommend removing the OTA and puting it on an EQ6 or similar. The price is about the same as a repair.

Barry

[egoroff]

Hi folks,
Thanks to all for the speedy advice. Its a damn shame to have a scope crippled by what is ultimately a trivial issue...anyway.

The chip I seek is a UDN2993B, a servo motor amplifier chip. If anyone has a dead board from which I could scavenge the part then what would work too (I am a qualified tech).

Moving to the EQ6 Mount is a good idea, in the longer term. How good is the engineering in these mounts, tracking-wise? Articles seem to say good, but not the best.

Newbie question , who is BINTEL?

Cheers

[Barrykgerdes]

Binocular and Telescope shop in Sydney

Your info is correct that chip UDN2993B is obsolete. However I doubt whether that is your problem. That chip is only used to drive the focus motor if fitted and I am pretty sure that the rest of the board will work without it.

You say you damaged the chip. Have you removed it from the board. What are the exact symptoms of the fault otherwise.

Barry

[egoroff]

Hi,
its definitely the chip, I desoldered it to isolate a short on the supply rail. As mentioned earlier it was proved to be the dc decouple capacitor on the 12v DC in rail. The cap showed no obvious signs of failure and was failing intermittently, to boot just to make it fun. I have never seen a tantalum capacitor do that before!

I removed the IC (and others) as a final attempt in isolating the fault. Unfortunately the chip cracked as lifted it out (yeah, surprised me too). So there have it. one dead IC, no spare....

I was curious on its function as I identified two other chips as the servo motor driver. So you reckon it will work without it...now that is interesting!!

Cheers

[Barrykgerdes]

There were some mods to the motherboard some time ago that added some high wattage ballast resistors

Go to http://thadlabs.com/Meade-service.pdf

Read through the service slips and see what stage your board is at. I prepared this pdf from my notes and Thad kindly offered to put it on his web site. check that the ROM's are series 3.xx. If they are 2.xx you have a very early model and need an upgrade kit, also not available.

Clean up the board and make sure there are no other shorts and reconnect everything on the scope and see if the handbox gets past the "meade" stage . If so try a dummy alignment using polar mode. Use polar mode and just accept every request with a press of the enter key. This will give a dummy alignment. If this works you can put everything back together properly. If not give me a full run down on the symptoms.

Barry

[hikerbob]

Robert I've not worked out how to tell what package is being ordered but I did notice plenty of suppliers saying they had stocks of the UDN2993B . I suspect that a lot are geared for industry rather than single sales but the first site has a note on the site for no minimum orders at the moment.
http://store.americanmicrosemiconductor.co m/udn2993b.html

Several listings at http://www.ic2ic.com/search.jsp?sSearchWord=UDN2993B&prefix=U but I've never worked out how to use their listings.

http://www.sierraic.com/pnresults.asp?part=UDN2993B&btnsearch=Search claim to have 60,000 of them but I suspect that they may be geared to manufacturers rather than single sales.

Bob

[egoroff]

Hi folks,
Yes, I did try a lot of suppliers, most didn't even bother replying. Others said they would sell me a batch of about 10 for US$50 each. No thanks, US$500 for a two bit chip is a bit too much for me.

Ok. I fitted the sevo chips back in, inspected the board, all looks ship shape. I will drop the board back into the scope on Sunday or Monday, when Dad/husband duties are complete.

FYI, the board is running version 3.30 on the EPROM's, and their appears to be low ohmage resistors tucked in behind the servo chips, guess they could be ballasts. Couldn't open your recommended link, but I am at work at the moment. I will let you know how everything pans out.

Cheers

[Barrykgerdes]

Hi

That board is one of the older unmodified boards. The two low ohmage resistors have been replaced by two 10 watt resistors that are now attached to the side of the scope (see the fitting sheets that are in the reference I posted) and snubber diodes fitted to the U11 74LS14 data lines to the handbox. At the same time the matching 74LS14 in the handbox also had snubber diodes fitted. The same mod made some changes to the supply of U15 but I ignore that one as it is too difficult to remove the pin from the board.

The circuit diagrams are readily available from mapug but I can send them if you email me PM.

Barry

PS if you have trouble down loading the pdf from that site I can email that also if you can take a 9MB attachment.

[rogerg]

Such a shame how the electronic failures has let this scope down. Mine was out of action for 9 months after a lightning strike a couple of years back. BINTEL and fellow IIS members saved me, two repair kits, a hand controller and new front panel later.

I'd love to see instructions on how to replace the electronics of the LX200 classic with a Gemini kit. I'm sure it must be possible seeing as the Gemini can be configured to different worm configurations etc.

Roger.

[egoroff]

Hi back again.

Just giving you all feedback on progress. Well I fitted the board and powered things up, I got to the "Meade" message, and nothing beyond that. So I am assuming the motherboard is dead. Look like a new mount will be in order.

Thanks for ever-ones input on this. The help has been well appreciated.

[mick pinner]

l'm pretty sure l've got one laying around, let me know if your interested.

[DavidU]

The IC is here
http://www.partsvault.com/list/49/84/

[egoroff]

Hi,

If you have a motherboard to suit this old lady then I would be interested.

Let me know if you find something.

Cheers.

[altazman606]

Hello everyone.
I just registered with your forum. I have both an LX200 classic and a gps. Havnt used either much though yet. My classic is missing a hand pad and im trying to get it computer controlled. Any help from you guys would be appreiciated.
To Egoroff; I have a mother board from and LX50 will and of the parts on it help you or I can check for them around here let me know

[Barrykgerdes]

If you haven't got a handbox you will be in a bit of bother. The computer control can't be activated till a respose has been had from the handbox (even a faulty handbox will work sometimes)

Barry