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Old 20-01-2016, 04:19 PM
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Moontanner (Ross)
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Replacement part for faulty PEC sensor in LX200GPS

Hi everyone,

I was using my scope recently and had the common ( in older scopes at least) "PEC not working" screen appear on the Autostar II. After doing a little research I found the problem was that the hall effect sensor had come loose and been damaged by the worm drive.

Does anyone know if it is possible to replace just the sensor component and if so, which exact component is needed?

Bintel can do it for a reasonable price but it looks like something I could fix at home without dragging the scope across town. I'd just need the right type of hall effect sensor to suit the electronics.

Thanks for any advice in advance.
Ross.
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Old 20-01-2016, 04:34 PM
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pdalek (Patrick)
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The LX200 schematic lists the original and replacement part numbers.
http://www.lx200classic.com/files/LX...sembly-Sh1.pdf
The LX200GPS is probably the same or very similar.
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Old 20-01-2016, 05:28 PM
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Moontanner (Ross)
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Quote:
Originally Posted by pdalek View Post
The LX200 schematic lists the original and replacement part numbers.
http://www.lx200classic.com/files/LX...sembly-Sh1.pdf
The LX200GPS is probably the same or very similar.
Thanks Patrick.
I'd already found the same schematic while searching around. As long as the parts haven't changed it should be all good.

If anyone can confirm that the parts are the same in the LX200GPS version that would be awesome.
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Old 20-01-2016, 06:35 PM
AndrewJ
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Gday Ross
The early LX200GPS units used an Allegro A44E ( ref my unit piccy ), but my understanding is that this is now superceded.
Many moons ago, on a forum far far away ( that i cant currently refind ), i lifted a post where someone had found an alternative unit
I can't vouch for the details, but it shld be easy to check
What i lifted

Quote:
Hi ,
The Hall chip attached to the Aluminum bracket that is adjustable is the one
that is working. It's the one on the worm gear frame that is not adjustable that
is not working. I used a needle attached to my VOM to check continuity from the
device pins to the 9 pin connector.
All good. I got hold of an engineer at Allegromicro and he said that their
A1104EAU-T is their replacement for this Hall device. (A44E). I also plan to
check the optical encoder in the Motor.
Manny
Andrew

PS full schematics for the LX200GPS/ACF are filed in the files section of the LX200GPS Moderated group if you are interested
https://groups.yahoo.com/neo/groups/...%20Schematics/

PPS, its not required that an "exact" match is achieved, just that the unit has a very "repeatable" trip.
The LX200s have an internal "fingerprinting" function that can allow the system to auto reset itself to suit how the sensor trips.
Attached Thumbnails
Click for full-size image (RA PEC Sensor.jpg)
57.3 KB49 views

Last edited by AndrewJ; 21-01-2016 at 07:35 AM. Reason: Piccy didnt load
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Old 01-02-2016, 04:31 PM
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Oh bother!

G'day Andrew, Thanks for the helpful info.

I managed to get my hands on a replacement sensor last week and swapped the crushed one out without too much trouble. It all went smoothly with the whole procedure taking about 20mins.
I managed to do the whole lot without pulling things apart or disturbing any of the other components. The only things I removed were the access panel on the base, the two cable ties holding the wiring loom and the wiring loom that connected the sensor to the board.

Unfortunately, the scope doesn't power up at all now and I'm stuffed if I know where to look next. It seems unlikely that I've fried anything else as the sensor itself should work the same as the original and was wired in exactly the same fashion.

My first thought is that jiggling the wiring loom has caused a fault or the old crushed sensor has shorted something when it went squish. Not that the scope stopped working at the time.

Anyway, I'm all ears if you have any recommendations about obvious starting points for trouble shooting. At this stage any expensive repairs will probably see me de-forking the OTA and mounting it on a AZ EQ6 (providing that's a suitable mount with some added futureproofing wiggle room).

Regards.
Ross.
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Old 01-02-2016, 04:44 PM
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Gday Ross
The fact that yr initial post mentioned "PEC not working" means it didnt fry at that point.
The main board will happily ( well almost ) start up with all the sub boards disconnected, so you can try disconnecting all the headers and then try to boot. If it starts, then the main board is OK.
If not, then it gets interesting.
Does the red panel light come on when powered up????
Can you measure the 5V rail to see if thats working????

Andrew
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Old 01-02-2016, 06:50 PM
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Hi Andrew,

Thanks for the speedy response. I only just noticed the notification in my inbox.

I'm not getting anything when I plug in the 12v power supply battery. No red light or anything to indicate a change when the switch is flicked.

It appears that the problem might be a total coincidence and the failure may be in the switch or some other simple component. I've got the schematics printed off and most of the scope's opened up ATM.

Leave it with me for a minute and I'll see if I can locate the problem. I'm pretty sure it's something to do with the power input part of the main board as I can't see (or smell) any fried components.
Corrosion on an old warhorse unit like this one is a strong possibility.

Speak soon.
Ross.
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Old 01-02-2016, 08:51 PM
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Gday Ross

I know its a suck eggs comment :-),
but do you have a blown fuse in yr power supply?????
I cant see how fitting the new sensor could do that
but its worth a check in case something else got moved
whilst you were playing.

Andrew
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Old 01-02-2016, 08:56 PM
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Partial success!

OK. The unit has been stripped down and put back together. This time it functions and has gone through the auto align sequence without a hitch.
I'm pretty sure there is a dodgy connector or wire around the 12v input and toggle switch. Definitely a problem for another day.

Getting back to the original repair, I'm very pleased with the result and how easy it was to sort out. Thanks for your help tracking down a suitable replacement Andrew.

$22 for 5 pack of sensors incl. p&p.
$5 approx. cost of sundries.
30mins if you don't count the secondary power issue.

The hall effect sensors only come in packs of 5 so if anyone needs one I have let overs.

Clear skies.
Ross.
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Old 01-02-2016, 09:05 PM
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Quote:
Originally Posted by AndrewJ View Post
Gday Ross

I know its a suck eggs comment :-),
but do you have a blown fuse in yr power supply?????
I cant see how fitting the new sensor could do that
but its worth a check in case something else got moved
whilst you were playing.

Andrew
First thing I checked. I wouldn't have been the first person to make that mistake if it was a fuse.

On the subject of fuses, what would be the best type for the LX200?
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Old 01-02-2016, 09:27 PM
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Gday Ross

Good to hear its back to life.
I know of several people who have reported failure of the switch itself, but i've never hit that yet. Another problem is sometimes the inbuilt switch in the 2.5mm connector jack that can be faulty.

Quote:
First thing I checked. I wouldn't have been the first person to make that mistake if it was a fuse.
Ahh but too many people use a std car cigarette adapter and dont realise it also has a fuse in it. Surprising how often that is the cause :-)

Quote:
On the subject of fuses, what would be the best type for the LX200?
I normally use about a 2.5amp fast blow
When i tested my scope slewing at max speed in both axes, it only draws about 1 amp, so the 2.5 is ample, and dies quickly.
If using a plugpack supply, i also try to ensure the fuse is rated well less than the output of the plugpack, just to ensure it blows.
Batteries will blow a fuse no matter what, but if yr plugpack is only rated to say 1.5Amp and you have a 5A fuse, it wont necessarily blow.

Lastly, as you have now effectively screwed up your PEC fingerprinting.
If you ever intend to do PEC training, you should reset it to zero and let it reconfigure itself for the new sensor.

Andrew
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Old 02-02-2016, 07:00 PM
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Quote:
Originally Posted by AndrewJ View Post
Gday Ross

Good to hear its back to life.
I know of several people who have reported failure of the switch itself, but i've never hit that yet. Another problem is sometimes the inbuilt switch in the 2.5mm connector jack that can be faulty.


Ahh but too many people use a std car cigarette adapter and dont realise it also has a fuse in it. Surprising how often that is the cause :-)


I normally use about a 2.5amp fast blow
When i tested my scope slewing at max speed in both axes, it only draws about 1 amp, so the 2.5 is ample, and dies quickly.
If using a plugpack supply, i also try to ensure the fuse is rated well less than the output of the plugpack, just to ensure it blows.
Batteries will blow a fuse no matter what, but if yr plugpack is only rated to say 1.5Amp and you have a 5A fuse, it wont necessarily blow.

Lastly, as you have now effectively screwed up your PEC fingerprinting.
If you ever intend to do PEC training, you should reset it to zero and let it reconfigure itself for the new sensor.

Andrew
Gdevening Andrew,

I'm pretty stoked about getting things up and running again.
It looks like it's an intermittent problem with the connector jack or the wiring that runs from the switch itself. The switch seems to check out.

Can you give me anymore info on the inbuilt switch in the connector jack you mentioned? I'm guessing it's similar to the one that fried my ETX when I hooked up the 12v input at the same time as having batteries installed.

Thanks for the tip on the fuse. That'll save me checking out the maximum draw of the unit when I'm trying to get do everything at once during a session.

I may also ask you about setting the PEC to zero shortly. Hopefully that part of things should be pretty straight forward. If it's anything that's not obvious in the menu settings let me know.

Cheers.
Ross.
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Old 02-02-2016, 07:38 PM
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Gday Ross

Quote:
Can you give me anymore info on the inbuilt switch in the connector jack you mentioned?
The input jack on the panel is a std 2.5 x 5.5mm socket with inbuilt switch.
When no plug is inserted, a smal metal spring closes a switch and the +12V battery input is connected to the 12V in.
When a plug is inserted, the spring pushes open the switch thus disconnecting the battery, and the +12V then comes from the plug inserted into the socket. If that switch is damaged, it can cause grief.

Quote:
If it's anything that's not obvious in the menu settings let me know.
You cannot reset the "fingerprinting" data via the Hbx or any normal Meade programs.
You need to use my PEC editor to reset them to zero, and that will trigger the system to recalculate the offsets to suit your new sensor.

Andrew
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Old 03-02-2016, 05:33 PM
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Quote:
Originally Posted by AndrewJ View Post
Gday Ross



The input jack on the panel is a std 2.5 x 5.5mm socket with inbuilt switch.
When no plug is inserted, a smal metal spring closes a switch and the +12V battery input is connected to the 12V in.
When a plug is inserted, the spring pushes open the switch thus disconnecting the battery, and the +12V then comes from the plug inserted into the socket. If that switch is damaged, it can cause grief.


You cannot reset the "fingerprinting" data via the Hbx or any normal Meade programs.
You need to use my PEC editor to reset them to zero, and that will trigger the system to recalculate the offsets to suit your new sensor.

Andrew
G'day Andrew,

Your description of the connector jack switch mechanism leads me to believe I need to closely inspect that component.
Being that my background is not electronics I'll need to do a little research first. Thankfully, I'm very good at figuring out what makes active components tick.

Where can I find your PEC editor for the reset on the fingerprinting of the sensor? Please bear in mind that 6-7 years ago I was that guy in the night class that had to ask " what's Excel?" when prompted to open a blank spreadsheet in said program ( or is it an "app" now. Whatever).

Any instructions are welcome. This is my first time playing with the internals of this piece of equipment.

Regards.
Ross.
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Old 03-02-2016, 06:37 PM
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Gday Ross
Quote:
Being that my background is not electronics I'll need to do a little research first.
Its a very simple mechanical switch.
Look inside the connector, and on one side, you will see a flat metal tab protruding in through a slot. This is a simple spring mechanism.
With no plug inserted, the tab connects the battery ground to the socket ground.
When a plug is inserted, it pushes the tab outwards and thus disconnects the battery ground ( ie isolates the battery ).

Quote:
Where can I find your PEC editor for the reset on the fingerprinting of the sensor?
http://members.optusnet.com.au/johansea/
The help file describes resetting the fingerprints, but basically you start your scope. Then connect with my app and it will detect yr scope.
Use the PEC menu option to reset the fingerprints.
Reboot the scope and it should do its pec detection routine ( which will fail ) at which time it will invoke the fingerprinting routine. After that, its all resynchronised.

Andrew
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Old 03-02-2016, 07:53 PM
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Thanks Andrew. I really appreciate your help.

Everything is simple when you understand the task at hand.

This evening doesn't permit me the spare time to go about your recommendation for fixing the fingerprinting. That one will have to wait for another day.

Again, many thanks for your help to date. I hope I can pass the favour on some day.

Regards.
Ross.
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Old 21-07-2016, 09:54 AM
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Quote:
Originally Posted by Moontanner View Post
OK. The unit has been stripped down and put back together. This time it functions and has gone through the auto align sequence without a hitch.
I'm pretty sure there is a dodgy connector or wire around the 12v input and toggle switch. Definitely a problem for another day.

Getting back to the original repair, I'm very pleased with the result and how easy it was to sort out. Thanks for your help tracking down a suitable replacement Andrew.

$22 for 5 pack of sensors incl. p&p.
$5 approx. cost of sundries.
30mins if you don't count the secondary power issue.

The hall effect sensors only come in packs of 5 so if anyone needs one I have let overs.

Clear skies.
Ross.
Can you tell me the part numbers? I have a faulty sensor and need to replace it. How did you wire it up? Can I run the scope without it?
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Old 22-07-2016, 05:22 AM
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Hi Chris,

I've responded to your PM. For anyone else reading this, the part is:
Allegro Microsystems A1104EUA-T, Unipolar Hall Effect Sensor Switch 3-Pin Ultra Mini SIP, 3.8 → 24 V.

They can be purchased from RS components online.

Clear skies!
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Old 22-07-2016, 05:53 AM
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Thank you Ross!!

I ordered them from a local supplier. We'll see if it fixes my problem. I'll follow up when I get her working.

Take care,
Chris
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