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SynScan PIC tester

3 months ago 118
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Description

This schematic shows how to test PIC16F886 microcontrollers after downloading the .HEX file from MPLAB IDE.

It is a common problem with these motor boards, that the hand controller displays "No response both axles". This is usually caused if the serial communication fails on the microcontrollers. The board has 2pcs. PIC16F886 microcontollers, one for each axle. There axle stepper motors are bipolar, each coil has its own A3959SLBT stepper driver. The PICs has the same firmware, the 21st pin (RB0) tells the PIC, is it the RA or the DEC PIC. If the PICs failed, it is possible to replace and reload them. Be aware, every component on the PIC side of the board is glued onto the board. The easiest way to cut the PIC legs with a sharp knife right next ot the package and then the PIC can be pried up from the board with a screwdriver without damaging the delicate traces on the PCB! The firmware (.mcf) can be downloaded from Sky-Watcher website for the motor controller, butan an empty PIC cannot be downloaded with the Windows utility through the hand controller. Luckily, the .mcf file is a .bin file, which can be converted to .HEX, which can be flashed to the PIC from Microchip MPLAB X IDE. This conversion is not simple, some bin2hex converter work, some don't. I attached the HEQ5.HEX which worked for me. This is untouched, with code-protect flags set by Sky-Watcher. Code protect is not a problem, we don't want to read it from the PIC anyway.

Flashing the PIC with PICKit 3: IMG_20200812_185519.jpg If you are not familiar with PICs (like me), the PICKIT is not enough alone to download the firmware, you have to supply an external 5V (VDD) to the PIC to be able to download it. The simplest / safest is to supply from the USB 5V.

After flashing the firmware, it is possible to test the PIC,by connecting the hand-controller to the breadboard using this schematic. The +5V is supplied from USB to the breadboard. The hand-controller powered from this 5V source, through the 5-wire cable from the mounts power panel, and the HC is plugged into its original RJ-45 socket on it. DON'T connect 12V, this will damage the PIC and the USB port!!! If the programming was succesful, the HC will display "RA/Azm... No response!" if the PIC is in DEC mode, and "Dec/Alt... No Response!" if the PIC in in RA mode. In this case, the PIC is working and it is safe to solder it on the motor board.

IMG_20200813_103544.jpg

IMG_20200813_103612.jpg

(Ignore the ESP8266 @ Co. on the left side of the breadboard.)

Important! If the PICs are soldered on board, test the board with the motors connected. I don't know why, but the A3959SLBT motor driver ICs developed a short circuit inside, maybe because they were turned on without the motors connected and I had to replace them as well. I noticed later, that the motor driver ICs get HOT if the motors are not connected, or the OUT-A (pin16) or OUT-B (pin21) are not soldered properly on the PCB. Always check the motor controller ICs by touching, if everything is fine they shouldn't be hot!

More pictures of the HEQ5 motor board: https://photos.app.goo.gl/DFYHGF5gYhKZSGPw8

Documents

HEQ5

BOM

ID Name Designator Quantity
1 PIC16F886-I/SS U1 1
2 micro USBFemale USB1 1
3 SPDT U2 1
4 HDR-M-2.54_1x5 J1 1
5 20MHz X2 1

Attachments

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HEQ5.hex

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