Actuator/Positioner problem

[007.4]

I have a 1.80m PF driven by a 10 year old 24" jack actuator and a (21 year old) Pace MSP 200 positioner. It has been fine for many years but last night it stopped working.
I could hear the relay in the positioner click but the dish did not move.

I suspected the jack so stripped it down to check the connections etc. All looked well so re-assembled it but it was still appeared dead.

I then dug out my very old "Super Winch" 24" jack (why do they not make solid beasts like this anymore) and replaced the apparently defective one. It worked.
I then proceeded to set up East/West limits but on the second drive across the arc that too stopped working.

I checked the Pace MSP 200 service manual and that said for my symptoms (display OK, clicking relays but no movement) check fuse FS1 and/or short circuit on cable.
All fuses in the box are OK and a meter on the cable indicates no S.C.

However, I did check the output voltage and instead of 36V it was kicking out just over 50V (no load). Is this normal?
If not, I now wonder if the high voltage has damaged both jacks?

How can I further test which item is the cause of the problem? Obviously I do not want to buy another jack if it is the MSP 200 that is faulty for fear of damaging a new one and vice versa. I do not have another positioner (or 36v source) to test with.

Any ideas how I can proceed anyone?
TIA

 

[Terryl]

You need to check the voltage output with a load on it.

A resistor load can be subbed out for the jack, but you need to know two things first, one is the DC current load from the jack, and two is the DC voltage. (you know that is 36 volts DC)

So volts times amp equals watts, you need to know this to get the right wattage resistor or it will burn up.

Example: 36 volts times lets say 1 amp, equals 36 watts, so a 36 watt 36 ohm resistor will work out fine. (higher the resistance the lower the wattage)

Now if you don't have access to big power resistors, then three 12 volt automotive light bulbs tied in series will also work, this will load down the power circuit enough to give you a correct DC voltage reading, if it is over 36 volts by more then 3 or 4 volts then you have a problem.

Also check the DC output with the volt meter set to AC, you should read very little AC voltage (under 1 volt) if more then that then the voltage regulator circuit is FUBAR.

As to a 36 volt power source, 3 car or other 12 volt battery's can be used, tied in series they will supply 36 volts, but be careful, if the jack is shorted you may burn something up, look at the DC fuse rating on the positioner, (or its rated DC current output) use an inline fuse of the same rating to protect the setup.

 

[007.4]

Many thanks for your reply.
The output from the positionner is 3A. So does that mean I need a 100ohm, 100w rated resistor?
I've had a root through my "bits" box and do not have any high wattage resistors at all. I'll look in the garage tomorrow for some auto bulbs instead.

I'll also try and cobble together 3 x 12v batteries in series to test the jacks.

In the mean time I've tested the output with the meter in A/C mode (no load). It varies for the couple of seconds there is output and seems to flash momentarily to about 12v.

The MSP 200 service manual says to check the bridge rectifier (which is a KBL403) so I removed the board and (without load) this appears to be fine.
(0.48v and 0.503v on either side but zero across the A/C pins and zero in reversed direction).

Also, the manual states

"The output from the rectifier is unfiltered and unregulated DC to drive the motor. The output is nominally 36v DC but the actual voltage will vary depending upon load conditions"

Does this mean the voltage regulator is OK and just goes high (as expected) without a load?

 

[Terryl]

Yes, if the DC is unregulated then it can go as high as 50 volts DC without a load.

And a quick flash to 12 volts AC would be within any spec for an unregulated power circuit, now if it stayed at 12 VAC then you have problems.

Amps times volts equals watts, so 3 amps X 36 volts = 108 watts, it would be better to get some 12 volt auto bulbs and tie them in series, this would give you enough DC load to check the output.

 

[007.4]

I did some more testing today on the jacks. The first one was seized. However, I managed to free it off and got it moving (slowly) with a 12v garden tractor battery.
However, it is making a lot of noise, appears a little bit bent and I think the reed switch is faulty, so I've ordered a replacement.

The MSP 200 did drive it so I believe the positioner is OK. I should be able to confirm when the new jack arrives.

The old "Super Winch" seems to be completely dead but as it was raining I did not fully investigate. But again it is strange that it just stopped mid stroke.

If I do need to replace the the positioner I'm considering the Super Jack V Box 2 or the Moteck V Box II.
Is either one better or more reliable than the other?

 

[Burnham Beech]

I have a Moteck vBox II which is over 11 years old, and is still working ok.

I have no idea if the current supply is the same specification is the same as my old version.

 

[moonbase]

I have a Moteck vBox II which is over 11 years old, and is still working ok.

I have no idea if the current supply is the same specification is the same as my old version.

+1 for the Moteck V-BOX II.
They seem to be reliable and last a good while.