Economy EQ-1 RA drive Motor Dead !!

[Mr TamiyaCowboy]

well it died, 

i have used this unit about three time maximum for around 10 mins at a time.

over the past year  i had it.

went to set up the mount to track the moon with my dlsr attached.

new battery , secured and fitted correct to the mount, i switched the unit on.

power light glows red but there is No motor sound, the pot adjustment has no effect and the motor drive does

not work.

So i take off the cover to find a Very Very crude PCB board. lots of resistors a regulator and a reverse flow diode ( i think)

with some type of 4-6 pin chip.

the power goes to the regulator, then into a series of tracks to the resistors and the small chip.

then onto the power light / switches and the driver pot. i dont have a multimeter but i do have an arduino uno

is it possible to mimic the crude PCB board using my arduino instead ?

i can get images of the board and its components if needed.

[Mr TamiyaCowboy]

i took some photos of the said drive unit. 

as you can see it is a crude set of electronics to drive the dc motor and the gearbox (not shown)

but either one or more of these components are knackered, but i do not know what one.

there is no sign of burning, no magic smoke, no smell of fried components.

when powered the top right switch turns the unit on.

the switch below is north/south, just flips the motor from clockwise to anticlockwise.

the power led works and lights up. 

the motor does not turn ( it should turn as soon as the on switch is active)

and the pot on the left under the led does not have an affect ( it speeds up or slows down motor)

the parts i think are dead are : the pot - the motor 

so what do you techy people think , i dont have a multimeter, it died a 11.1v death but it was a good 10yr old.

and i am in hope father chrimbo maybe brings me one. i am stuck without the eq-1 drive it powers the 114mm scope

[woodbob123]

Try testing motor on a battery  to check it is working first, does it have a gearbox this may be seized try a squirt of wd40 or some thin oil, if ok check bottom of board for bad solder joints if not sure put a photo up, are there any numbers on chip and what may be a transistor next to it. 

[Mr TamiyaCowboy]

Try testing motor on a battery  to check it is working first, does it have a gearbox this may be seized try a squirt of wd40 or some thin oil, if ok check bottom of board for bad solder joints if not sure put a photo up, are there any numbers on chip and what may be a transistor next to it. 

hello and thank you for the reply. 

no numbers or markings on the chip itself, the transistor beside it is a three pin regulator what it looks like.

possible its used to govern the voltage to system. 

gearbox is of a sealed design, in the first image you can just see the motor tab and a small solder blob with a

very fine wire ( below the chip) . there is a spring clip that holds the PCB tight to the motor/gearbox, with a good amount of some sort of semi hard

stiff epoxy/rubberised glue. the rear of the PCB is covered in a type of soft servo foam the battery sits between the rear of the board and the gearbox casing.

no markings on motor either around the can so am even unable to replace motor without knowing what it is.

the unit was brought from Wex ( over 25 quid not cheap either) and was branded skywatcher on the site. what i have in my hand resembles some

backyard shed tinkering not something from a named scope builder/seller.

has anyone at a guess  a rough idea what the chip used could be, i have arduino uno so could build/copy the PCB

on a bread board maybe make it better than the original design, it lacks function, the pot drive is very fiddley 

so a better designed rotary slider would be better, the on/off could be intergrated into the north/south motor reverse.

three way switch, off is centre , left is on south - right is on north. and its size to.

These things dont fit correct and when the scope slews round on the RA axis ,the scope/balance bar / mount head collides with the

motor unit itself. with mount north you can only really use the east RA side, the west is impossible without collision of the drive/mounthead

[NEM]

Can you attach a photo of the track side of the board?  That might give a clue to the type of chip used.

Noel

[Alien 13]

 A wild guess would be a 555 timer fot the chip

[Mr TamiyaCowboy]

trawled the internet could not find anything much about these devices.

so i took my anger out on it and sort of tossed it into the  things i want fixed but dont have a clue

how to box. 

about three mins later theres this very annoying like ginding motor sound,

bit like when your feeding a motor a low current and it skips like judders.

so back to the things that i want fixed but dont know how to box and low and behold

The darn thing is ALIVE. 

so the motto of these things is, if it breaks lob it into the corner, it may start working again

or better advice would be " buy something better " and leave these simple things alone. 

My guess is the dry gearbox and it being a sealed unit is at cause.

the quality of the PCB is nasty hand soldered affair, so i would guess the

reducing gearbox is very cheap and nasty to ( its not exactly smooth running)

[Squagnut]

I'm glad it's working - as I was taught at an early stage of finding out how to fix things, "If in doubt, give it a clout". Very often there's just something stuck which needs to be dislodged. In general, of course, this is very poor advice for pricy astro kit, but if "turn it off and turn it back on again" doesn't work first or second time then you soon find yourself looking at circuit boards you don't understand.

To help you understand how the board works, first ignore the build quality. As long as all connections are sound, it doesn't matter if it's been hand-soldered or whatever. It's much more likely that the fault you experienced was mechanical (stuck gears, etc.) rather than electronic, especially if the LED comes on. Next, look at what the board does, from a user point of view. It has a potentiometer, and adjusting that changes the speed at which the motor turns, right? This suggests that it's a PWM circuit, or pulse width modulator (which, in turn, suggests that Alien13 is correct, the chip is a 555 timer IC, used in PWM circuits everywhere - you've probably used at least three devices today which depend on the 555 chip to function). That might sound complicated, but it really isn't. You know that the motor needs power to make it turn, and you know that the speed at which the motor runs can be changed. Rather than changing the voltage which gets to the motor, the PWM circuit sends the rated voltage (I believe these motor units run off a 9v battery? If so, 9v in this case), but if you want the motor to run slowly, the PWM breaks up the power output into a rapid succession of on-off-on-off... pulses. To make the motor run faster, the "on" phase is held for longer, while it's shorter to make the motor slow down. This length of on-time is what the potentiometer adjusts. If you think of this as a graph, with time on the x-axis and on/off status on the y-axis (on = 1, off = 0), you'll find it makes a square wave, and as you turn the potentiometer, the length of the "on" time changes ... or, to put it succinctly, the width of the pulse can be modulated.

PWMs are used all over the place. Dew heater controllers, LED dimmers, electric cookers and so many other things use PWMs.

You asked about using an Arduino to replace the drive unit's board. This would be very much possible, and by doing so you would open up a range of possibilities. An Arduino can carry out all the PWM functions of a 555 chip and much more besides - but you'd be using a sledgehammer to crack a nut if you had only this one application for it, and Arduino boards aren't cheap, unless you make your own (which is astonishingly easy to do).

[Mr TamiyaCowboy]

i have a arduino Uno board. 

i also have a populated arduino type PCB this runs the ATmega chip from the Uno, but

also has a barometer added, also runs a digital compass , 3 axis accelrometer and a 3 axis gyroscope (ITG3205 )

the idea was to use the aircraft flight controller to run the ALT AZ part of the scope ,

then have the baro give pressure data , the gyros to feed the alt and dec data,

and the acceleometers to measure and govern the speed rate of slew and tracking..