Instructables

Meade LX200 motor controller chips needed - L2724 (sip9)

My scope has gone awol and I can't locate these chips anywhere. L2724 made by STI. They were apparently end-of-life'd.

I hate the idea of a $4000 paperweight sitting in my garage. Any ideas where I can find 2 of these chips? My astrophotography is impossible till I get this fixed.

Chariot4121 year ago
Thank you for the prompt reply! I replaced a blown capacitor on the main board, afterwards, ended up with run-away ra and decs motors. Adjusted the pots on both and got them under control. My hand controller checks out fine in all regards except the N,S,E,W slew. It's a known problem where the scope thinks a CCD camera is connected because a short on U11/U12. I believe replacing the L2724 chips has helped others. Anyone have a source for those? Thanks.
Dark Light (author)  Chariot4121 year ago
The L2724 chips were end-of-lifed years ago. I went with an L272 (8 DIP) from LittleDiode.com, the link for the part I used is here.

Although it is pin-compatible with the original 2724, it's a different form factor. I made a small socketed circuit board for the chip, then extended the leads out via wires. I had to cut off the orginal 2724 on the main board, then solder on the wires from this new chip. I mounted the circuit board inside the scope case. There was room behind the control panel. After re-trimming my pots on the dec motor, the scope is working just fine.

If you go this route, double check your connections with a meter, and make sure you find a way to heat-sink this new chip.

Good luck.
Chariot4121 year ago
Hey guys, I need the same 2 chips for my LX200; N,S,E,W slews not working. Where did you find them please?
Dark Light (author)  Chariot4121 year ago
Chariot,
When my chip blew, I still got movement, it just "stuttered and stalled", and unless you took an electrical or lighting strike, the chances of both of yours blowing is probably slim. I got mine at the "Little Diode Shop" in England, and had to make up a little circuit board to make them work. I can share what I did if you end up getting the same chips.

It sounds to me like your keypad (hand controller) or keypad cable is dead. Have you checked them? Do you have any display on them? How about the fuses?

Check your keypad and cable again. I'd bet money the caps in blew, and it's a simple fix if it didn't damage anything else. There's also a guy in Mass. I think that I used to repair my keypad. Note that you'll probably need an scope to check the trim pots after replacing either the keypad or the motor controller chips.

So...we need more details about your problem, then I can try to help.
Dark Light (author) 1 year ago
Thanks to steveastrouk, I've been able to locate a couple of replacement chips. See why I love this place?
Dark Light (author) 1 year ago
Thanks, Steve. I've been watching Ebay, not finding what I need yet. And honestly, I'm not sure what is pin-capatible with these chips. Two of them are soldered into the motherboard of my scope for the motor control. I have no schematics or anything other than a datasheet I downloaded on the chip itself. I can easily resolder an exact replacement chip, but I have no idea how to find an alternative replacement for it.
You MIGHT struggle to get "pin compatible", but see if the Ebay site really does have a couple of the chips you need. That link I sent you claimed to have more than two in stock.
Dark Light (author)  steveastrouk1 year ago
I didn't get any link. But thank you so much for the information!
Orange text on instructables are links.
Dark Light (author)  steveastrouk1 year ago
DOH!!! It doesn't show that I'm new here, does it? LOL

Thank you again.
Also the L165, single channel opamp
Dark Light (author)  steveastrouk1 year ago
You sir, are a GOD! Thanks so much for your suggestions. I really hate to see my expensive scope and so many good photo ops going to waste. Thanks very much, Steve. I owe you one.
Bear in mind they're both SINGLE channel amps - you'll need to hack together a board with two on, for each L2724

You'll have to mess around a bit, but the OPA548 is powerful enough
Ebay ?

Its only a power op-amp, there are alternatives if you have to.