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PPEC error on LX200 GPS

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#1 truman

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Posted 31 January 2019 - 07:56 PM

Hello all, I have an LX200  GPS and had some declination motor problems a while back. The little PPEC sensor on the drive had to be removed and i attempted to replace it but it has not worked correctly. Could someone point me toward someone I might be able to send the drive to have have the sensor replaced correctly?

Thanks

Truman



#2 OzAndrewJ

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Posted 31 January 2019 - 08:03 PM

Gday Truman

The sensor doesnt have to be very accurately positioned, as it is only a magnetic hall sensor.

As long as it is roughly under the magnet as it rotates, it should be OK.

 

Andrew Johansen Melbourne Australia


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#3 truman

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Posted 31 January 2019 - 08:09 PM

Thanks for your reply, It appears to be close enough to the magnet and i may not have even gotten the correct little component to replace the old one. I wired it exactly as the old one was but i receive an error in the scope initiation IF i have that function turned on. Just willing to sent it to someone and let them do it right   



#4 OzAndrewJ

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Posted 31 January 2019 - 09:08 PM

Gday Truman

 

What component did you get to replace it ????

My records show it was originally an Allegro A44E hall sensor.

 

A later post from a user on the Yahoo site stated

"I got hold of an engineer at Allegromicro and he said that their
A1104EAU-T is their replacement for this Hall device. (A44E)."

 

It is a very simple unit and you can test if it is working using a simple multimeter if required.

 

Andrew Johansen Melbourne Australia



#5 truman

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Posted 31 January 2019 - 09:11 PM

Andrew, thanks again. I do have a multi meter can you tell me what setting on the meter and which pins to check to be able to check the sensor?



#6 Dynan

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Posted 31 January 2019 - 10:14 PM

Follow the leads from the Hall Effect Sensor to their ends (both places on the board it's connected to is good. You might need a schematic for this). Set your VOM to Low Ohm Resistance. Connect your VOM to the leads of the sensor. Put a magnet (as strong as convenient) to the sensor. You should get a differential in OHM readings if the sensor is good.

 

You can also use the Millivolt Scale on your VOM. You should get a pulse of a few mv when the magnet is swiped near the sensor.


Edited by Dynan, 31 January 2019 - 10:15 PM.


#7 OzAndrewJ

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Posted 31 January 2019 - 10:25 PM

Gday Dynan

 

You might need a schematic for this

There are full schematics in the files section of the LX200GPS Yahoo group ( cant copy em sorry )

That said, on starting the detecting process, the motorcard PIC turns on the +5V power to the hall sensor and its output is held high by a weak pullup resistor.

All you need to do then is use the DEC slomo control to move the magnet across the sensor

and watch the output voltage.

It will toggle between 0 and +5 V  if working properly.

Sooo, first test is

a) does the hall sensor get power when starting the detect routine

Second test is

b) does the output voltage toggle as the magnet goes past the sensor.

Ref attached piccies of the wiring on my unit

 

Andrew Johansen Melbourne Australia

DecPecWires.JPG DecPCBWiring.JPG


Edited by OzAndrewJ, 31 January 2019 - 10:58 PM.

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#8 Dynan

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Posted 01 February 2019 - 01:45 PM

You've got it! Let me know how those tests go...



#9 truman

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Posted 10 February 2019 - 06:10 PM

thanks to everyone who offered to help with this. I drug the scope out and put it on the bench and started testing things. Where the hall sensor plugs into the board i get 5 volts but when i rotate the magnet i don't get a fluctuation in my DC reading. One more odd fact is that I am getting 5 volts to the negative side of the connection. in other words i when i put my ohm meter on the red and black leads on the board I get a -5 volts. If i swap the leads on the ohm meter where i put the ground from the ohm meter on the red wire and the red lead from the ohm meter on the black wire on the sensor i get +5 volts. but still no fluctuation in my reading when i rotate the magnet.

If i remove the connector and read the voltage I get -5 volts on the white wire and the black wire. I have to reverse the red and black on the board i get a + 5 volts when i touch the black to the white and the red to the black......oh and before anyone ask I DON"T have the wires plugged in backwards on the ohm meter,,,they are correct.....any ideas?


Edited by truman, 10 February 2019 - 07:01 PM.


#10 OzAndrewJ

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Posted 10 February 2019 - 07:24 PM

Gday Truman

Forget the colours, ( and where does white come from? ).

Meade do not wire stuff up like normal ( ie with red = +ve and black = ground ), they just do what they like.

I specifically annotated the pins on my piccy to show this

ie for the PEC sensor, the centre pin on the PCB connector is ground ( ie yellow in my piccy )

soooo, do you have a piccy of your connector so we can talk apples with apples.

 

 

Andrew Johansen Melbourne Australia


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#11 truman

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Posted 10 February 2019 - 08:50 PM

Hope this is what you were needing. The yellow wire is going to the center pin on the sensor. I can't get any readings on the ohm meter whatever i do. I don't remember with what or the part number was when i replaced it but i'm thinking ordering a new correct part and try a redo. Just want to make sure which color wire to put on which pin.

IMG_0884.JPG IMG_0886.JPG IMG_0887.JPG


Edited by truman, 10 February 2019 - 09:32 PM.


#12 OzAndrewJ

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Posted 10 February 2019 - 10:25 PM

Gday Truman

OK, so the connector in the first piccy is wired the same as mine

sooo

Red    = +5V

Yellow = ground

Black = data

That said, the pictures you show are for the RA motor card???

You started the thread saying it was DEC that was playing up????

Either way, to test the board, you need voltage mode on your meter and

you measure with meter ground to YELLOW and meter red to RED

When detecting the sensor, this should show +5V, then it switches off.

BLACK is always held up at +5V by a weak pull up resistor so will always be at +5V

unless the sensor is energised and the magnet trips it.

i'm thinking ordering a new correct part and try a redo. Just want to make sure which color wire to put on which pin.

Have added a markup of the spec sheet for the alternate Allegro chip i noted above.

I marked the pins with the wire colours that match your board connector functions/colours.

You can see its colours/functions line up with those coming out from under the worm in my piccy

Soooo, thats the way to wire it up :-)

Andrew Johansen Melbourne Australia

Hall Sensor.jpg

 

 


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#13 truman

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Posted 11 February 2019 - 09:26 AM

Thanks Andrew. Never got the terminology correct with DEC and RA. This is my drive that makes the scope go clock wise and counterclockwise. What first brought this to my attention was that during alignment when rotating clockwise the motor would sound like it was in a bind just for part of the rotation then it would speed back up to normal. What puzzled me about this is that if i held the control on the key pad and had it rotate in the same direction i would never hear the motor go in to the bind. Just would hear the bind during auto alignment. Anyway I have the part ordered and should get it about wednesday or so. Thanks so much for all the help and the diagrams I will keep you up on whats happening

Truman



#14 OzAndrewJ

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Posted 11 February 2019 - 03:52 PM

Gday Truman

This is my drive that makes the scope go clock wise and counterclockwise.

OK, so that is the azimuth/RA drive. The PEC sensor is identical there so no problems re my prev diag.

I have attached a clear view of what an RA drive looks like ( as i got good piccies of mine when i had to replace the worm bearings).

Also ensure your magnet hasnt fallen out, as some people have reported that for RA drives in the past.

What first brought this to my attention was that during alignment when rotating clockwise the motor would sound like it was in a bind just for part of the rotation

In that case, it may be lubrication or clearance.

The RA drive is springloaded, but must be able to pivot a little bit to account for eccentricity etc in the worm wheel. In the attached piccy, you can see the RA spring loading system.

The large alloy spigot can be moved up/down as required to compress the spring by an amount required to give a good "spring" preload.

After setting that, the little grubscrew is then positioned such that the worm carrier can move the worm away from the wormwheel enough to allow for imperfections, but not far enough to allow the worm to disengage. ie a mm or so is heaps.

If that grubscrew is a tight fit, you can get binding in the worm.

 

Andrew Johansen Melbourne Australia

RA Drive PEC Sensor.jpg

RA Drive Clearance Adjust.jpg

 

 


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#15 truman

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Posted 11 February 2019 - 10:45 PM

Thanks again Andrew. I don't think it's the worm gear adjustment. In my mind the scope would sound like it was binding whether or not you were doing an alignment or just manually rotating the scope. Like i said it only sounds like it has a slight slow down in the motor while it is self leveling and during the auto align process. I can hold the rotation button from stop to stop and the motor never slows down at all. Any way the pictures you sent and the drawing you sent are great. I should get the hall sensor in a day or two and will let you know how it goes. And yes the magnet is in place and has not fallen out

Thanks again

Truman  



#16 Dynan

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Posted 12 February 2019 - 03:23 AM

THAT looks like a VERY badly engineered application of that spring! noway.gif



#17 truman

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Posted 13 February 2019 - 11:25 PM

Got the sensor today 2-13-19, soldered it in and .............................................IT WORKED

no more PPEC Error in RA or DEC...Thanks so much for all the help everybody offered....especially Andrew Johansen

for the detailed pictures and drawings

Truman


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#18 OzAndrewJ

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Posted 13 February 2019 - 11:55 PM

Gday Truman

Good to see it worked.

Saves a heap of dollars and risk in transporting the scope to a repair shop.

 

Andrew Johansen Melbourne Australia



#19 Joe Bauman

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Posted 17 July 2019 - 11:41 AM

Andrew, I'm extremely grateful for your help. I have two other questions: where do I get a sensor, and how do I connect it to the scope's wires? Best wishes, Joe



#20 orangeusa

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Posted 17 July 2019 - 04:10 PM

I could be wrong, but it appears that Newark has them..

 

https://www.newark.c...0-ma/dp/31K6578



#21 OzAndrewJ

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Posted 17 July 2019 - 04:17 PM

Gday Joe

Where to get?? no idea

Down here, everything comes via a little white van after you order it on the net .

As to connecting, the sensor has long legs and you just solder the wires to them

then insulate with heatshrink.

 

Andrew Johansen Melbourne Australia



#22 Joe Bauman

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Posted 22 July 2019 - 05:40 PM

One more question and I hope I'll be able to start soldering: how do I tell the top from the bottom of the A1104EAU-T? Both sides have letters impressed on them. I expect the top is the side with the minute A, but I'm not sure. Thank you, Joe




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