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GM8 492 hand controller problem ?

 

I have a GM8 non-Goto 492 mount. Until recently everything was working fine. Last night, I could not get the mount to slew in RA. It was tracking fine in RA, so I don't think out is a problem with the motor. Moving in DEC was fine through the hand controller. I switched cables, and it didn't he change. So I think the problem is either in the hand controller or in the output from the 492 box. I am suspecting the hand controller since the 492 box is still sending tracking signals to the RA motor. Neither RA button on the hand controller is working. Does anyone have an idea how to further diagnose this problem? If it is a problem with the hand controller, can it be fixed, or is it possible to buy a new one from Losmandy? (I did not see an obvious replacement on the Losmandy site). Thanks for any advice you can give.
 

The 492 hand controller is a very simple electronic design. If you’re comfortable opening the case and checking continuity with a multimeter I’d suggest you do that. For now just check that the switches are making contact when pressed (they can get dirty or rust and not make contact). Also make sure all cables are connected to the pcb (there should be 6). If these steps fail to show the problem, then check the continuity on the cables from the pcb to the connector.


If all fail then the issue might lie in the mount controller, could be the connector, the pcb leads or other components inside. It’s best to try the easy stuff first and report back.

Good luck

Jonathan
 

Thanks. I'll open the case and see if I find anything suspicious.
 

Thomas
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see attached image.?? pressing the HC buttons places a "Low" out the HC RJ jack pins 3/4/5/6 to a resistor pack on the main board (RP1).?? All you have to do is take off the cover, connect pwr and HC and press Ra+ and measure at the points indicated and you should see the voltage go from 5V to "low" or 0V.??
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You can use the GND points I have shown
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Do this, get back with results, and we can help more.?? Most issues are HC cable problems (95%).??
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Lastly are your motor cables to Ra damaged.?? You said you changed the cable, which i assume the HC cable.? I also ask does the "G/S" LEDs change when you press the "G/S" button.? Yes motors do die, but its usually cable, swap Ra cable to DEC and visa versa...does the problem change from Ra to DEC??? Get back on all this
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Cheers
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Brendan
 

Thanks very much. Very helpful. I will do the tests and get report back. It may take a couple of days until I find the time.
 

This is the basic circuit.
HBX_ST4.jpg
The ports on the MCU are pulled HIGH. When a direction switch is actuated the port is pulled LOW. The MCU is going through it's routine about 4 million times a second and after ten or so cycles it sees the LOW port and executes a command to increase the pulse rate to the correct step motor.

I wouldn't say the handbox is bulletproof, but the switches are good?for 100,000nds of cycles. Every once in a while a cosmic ray hits a memory transistor and the routine becomes blind to the strings that have it look at the port, but if both RA ports are off that seems unlikely. Generally, drive faults are in electromechanical connectors. I'd suspect?that the pins or the sockets for the MCU have corroded a bit and are resisting moving current. Carefully pull the MCU and reseat it. See if that helps.

I've got three or four 492 controller circuit boards pulled for OnStep conversions, if need be. Or this would be an?easy conversion with a $20 FYSETC E4 3-D printer controller.?
 

Well, this is a bit embarrassing. I was about to open up the hand controller and I noticed that on the bottom of the HC there are two switches. I had never noticed them before. They control the directionality of the RA and DEC buttons. It turns out that the RA switch had gotten moved to an intermediate position, and in that position no commands are transmitted to the motors. I moved the switch to one of the sides and now RA slewing is working again.
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Thank you everyone for taking the time to explain how the HC works and for the willingness to help. If I ever need to do more serious investigation of the HC, I know where to turn. Sorry for the inconvenience.
 

Thanks got update Thomas. ?I have never seen a 492 HC with sw’s on the base. ? There are obviously many versions of them.?

cheers
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Brendan
 

Thanks for the moment of nostalgia.

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