EQ2 motor controller

[Doolsduck (Michael)]

For my first post I have a problem I bought a second hand eq2 mount of an upgrade to a cheap telescope. It looks like a single axis Skywatcher type. I checked the controller and drive were working. Later on I plugged it into my variable powersupply in my car without first checking the voltage. I put 12v though it and toasted something in the controller. I'm so grumpy at myself.
It's not worth having professionally repaired. I think I shorted out a couple of the transistors since two of them get quite warm when I plugged it into the correct power. Also they are reading no resistance on the multimeter. I'd like to try and repair it myself but I don't know where to get PCB components, don't know a lot about using the multimeter for diagnosing but follow instructions well and can solder OK. I was hoping to get some help, either online or in person as a little weekend project in exchange for a slab or a bottle thanks
Michael

[Nikolas (Nik)]

it's a 6 volt motor and you more or less fried it, they are not expensive to replace

[Doolsduck (Michael)]

Thanks Nikolas. I didn't have the motor attached so it is ok. I just toasted some components of the controller PCB. There's not that much to it. Replacing it will cost more than three times what I paid for the mount and drive so i'm just looking at options to fix the controller. thanks

Michael

[bojan]

Could you post a pic of controller, and transistors in question?


RS components is a good place to get components...
Or Element14 (however they charge the postage for small orders).

[Doolsduck (Michael)]

Thanks bojan, I could post a pic this afternoon. The number 8550 is printed next to the transistors but when I looked it up on Digikey there was even a bunch of different types under this number... I asked Skywatcher if they had a circuit diagram but they don't.
Michael

[bojan]

The type of transistor is not really important, as long as it is PNP (like 8550, data sheet attached) and capable of delivering enough current for motor (1.5A in case of 8550, more than enough).
Sharp picture of top and bottm side of the printerd circuit board can help reverse-engineer the schematic.

(BTW, is it 8550 o5 8050? The other one is NPN, more common in driver circuits like this one.. byt then again, it all depends on the design details).


Is this the controller?
More here.

I can't see the voltage regulator on the image... is it below the board?

If regulator is not there by design (to make it cheaper), 12V could have fried the processor (or Zener at the power input, it seems to be there), in which case you will have to try to find hand pad replacement.

[Doolsduck (Michael)]

Hi bojan, great that's the one all right. Or maybe not so great. I don't know what a voltage regulator might look like but I'd say given it stopped working after the application of 12v, it doesn't have one. I'm guessing the processor are those black rectangular items with lots of legs and they're not off-the-shelf? * Edit* OK, saw the link to more and that explained the processor. This is getting in over my head now, I didn't mind the idea of replacing a few simple components but a chip? This would mean it would have to be flashed with some sort of specific firmware or something hey?
cheers
Michael

[bojan]

Originally Posted by Doolsduck

Hi bojan, great that's the one all right. Or maybe not so great. I don't know what a voltage regulator might look like but I'd say given it stopped working after the application of 12v, it doesn't have one. I'm guessing the processor are those black rectangular items with lots of legs and they're not off-the-shelf?

cheers
Michael

Yes, processor is the longer one, other one (74LS05) is hex inverter.

Voltage controller usually looks like this but it could look like one of the transistors on board as well, it all depends on required power handling capacity.

Those processor could work at up to 6V, but not much more than that. And it seems there is none on your controller.


I have a similar controller for my LXD75 mount, however it is dual axis and it runs on 12 V, so it has voltage controller (under the main board, mounted on aluminium heatsink, mount screw is visible on image).

But the motor drivers are same, with H-bridge (designed with 8550 PNP and 8050 NPN transistors, just like yours.


There may be a way out, though - someone may have a spare controller box for your mount, or you can buy it on ebay, or you can build one yourself.

[Doolsduck (Michael)]

Thanks. I don't have the kind of brain that understands electronics very well (I'm amazed I even have a multimeter) I'll go hunting for one and lesson learned. thanks *edit. I found that chip online 2.7 - 6.0V
Michael