Faulty EQ R.A drive - Advice needed!

[OptiGone]

Hi.

When i bought my scope the buyer said i could also take the below motor drive for free, so i did! Long story short he had a marriage break up and the scope was a gift didn’t want. The motor drive came with the scope when he bought it but he could not get it to work. And nor can I.

Ok here goes:

With both the battery wire and motor wire connected and the switch in the N postion ( northern hem.)

Then flick the on-off switch to ON - Nothing happens

Still with switch on 'ON' flick hemishpere switch to South - Nothing happens

NOW - If i now put the power switch to OFF and the change the hemisphere switch back to North before putting the power switch back to ON - i get a dull red LED - Progress!

At this point i still get no movement after pressing any of the direction buttons AND i can now flick the hemisphere switch between North and South and keep the red led alight. I can also now switch the power button on and off and every time it's in the ON position the red LED lights.

It will stay like this until i remove the battery wire then the process starts again...

To add even more confusion to this i have at some point a few months ago managed to get a yellow and green led to show.

Still never managed to get any movement out of it. Anyone fancy having a guess as to what could be wrong? N/S Switch?.

Just to be clear:

Batteries are mint (tested)

Have removed cover nothing has blown, no loose wires.

Removed motor case and can get motor to turn by hand so not seized.

Shame to just bin it.

[Earl]

I think you may of fried the handset with over voltage

[SpookyKatt]

Sounds like a bit of dodgy switch or cable ? Have you tried

wiggling the cable to the motor to see if that has any effect ?

Kathleen

[OptiGone]

Sounds like a bit of dodgy switch or cable ? Have you tried

wiggling the cable to the motor to see if that has any effect ?

Kathleen

It's had many wiggles even with me doing the wiggling and her doing the switching.

[OptiGone]

Just been having another play sometimes when powering up i do get a small pulse from the motor

[RikM]

When I got my EQ3/2 drives, I initially couldn't get it to work because the battery case clips hold the batteries so tightly that they didn't make good contact with the terminals. Now when I change batteries I shove them up tight to the terminal rather than rely on the spring to do it and haven't had a problem since.

Rik

[Talitha]

Try rubbing the battery contacts with sandpaper or an emery board...

maybe there's a bit of something on them, making the connection go wonky.

[berniew]

I have the same RA drive and the motor does move very slowly.

[SpookyKatt]

I take it that if you try depressing all the control box

buttons that the motor doesn't start moving ?

Kathleen

[OptiGone]

Ok quick update.

With repeated turning on and off I can sometimes get a green led, maybe once every 30 times. Still no movement after holding any buttons.

How hot do transistors get under normal condidions? i ask as there are two that are getting very hot (untouchable).

So in short:

I've never had any movement other than the odd 'pulse'.

Random LED colour and brightness (if any) when powered up

Wrist ache from manually tracking!

[SpookyKatt]

Hmmm it certainly doesn't sound healthy. Transistors could

I guess get quite warm depending on the voltage/current that

is passing through.

Does the motor get warm at all Matt ? what happens if you

disconnect and reconnect the motor with the power on ?

Kathleen

[OptiGone]

what happens if you

disconnect and reconnect the motor with the power on ?

Kathleen

OK I've pulled all the cases off everything and noticed when the power is on i cant turn the motor by hand. Disconnect the power and it spins freely.

Motor seems to be a sealed unit.

Think this is gonna end up on eBay for a pound BIN, see if someone else has any luck.

[Tinkerbell]

Just a thought, have You tried putting a marker on one of the cogs on the motor and leaving it for an hour and see if it has turned. They do tend to turn very slowly

[rwg]

Sounds like you might have a short circuit somewhere in there - that would account for the transistors getting very hot (high current flowing through them) and the motor being impossible to turn when on - you're trying to work it 'backwards' as a generator and it is trying to drive a current through the very low resistance of the short.

Robin

[OptiGone]

Just a thought, have You tried putting a marker on one of the cogs on the motor and leaving it for an hour and see if it has turned. They do tend to turn very slowly

Yep.

I have the gearbox removed also, so any movement should be visible

Sounds like you might have a short circuit somewhere in there - that would account for the transistors getting very hot (high current flowing through them) and the motor being impossible to turn when on - you're trying to work it 'backwards' as a generator and it is trying to drive a current through the very low resistance of the short.

Very possible but without the skills and knowledge to hand i wouldnt know where to start. I have looked over both sides of the PCB with a magnifying glass and cant see any signs of a short between any of the tracks or components.

The board does have 2 chips, a 20 pin and a 14 pin.

[OptiGone]

I'll put the thread on hold for a bit as forum member has very kindly said he will take a look at it.

[Glider]

OptiGone, I got the drive this morning and I've had it on the lab bench power supply and the oscilloscope.

The motor phases show a 15ohm impedance. At 6V I expect about 400mA to be drawn. I powered the motor controller with motor attached from the bench power supply set at 6Vdc. If the power is turned on and the controller LED doesn't light the current limiter came on, I had it set to 600mA'ish for safety.

If the LED came on orange the current drawn was only 50mA.

I couldn't get the LED to come on green.

I opened the motor controller and found a short, and 3 loose joints. I made them all good and tried again. Supply voltage stayed at 6V, LED orange.

No movement from the motor.

I got the datasheet for the Atmel AT89C2051 8 bit microcontroller and scoped around. The right supply voltages where at the right places. The crystal wasn't oscillating. None of the IO lines to the motor were toggling up and down.

Tried various things on the reset pin but no joy.

I think the micro is dead.

[OptiGone]

Glider,

Thanks very much for taking the time to have look at it. I'm guessing with a dead micro it's ready for the bin?

As it was freebie, I can't really complain. Shame it took me so long to decide to investigate the problem as I've seen a few of these going cheaply on eBay.