Servo Died??
Servo Died??
by fnastro
Sat Sep 16, 2006 12:55 am
Hi all. I was working on adding a servo for head rotation for my RN-1. (Pics to be posted once I'm done). All of a sudden my left shoulder servo does not work. No sound no nothing. Capture does not seem to work either. I get no reading. The wires and connections look good. Any Ideas
by hivemind
Sat Sep 16, 2006 1:27 am
You either have a dead servo or dead wire. Take it off and check the h-bridge and the motor, it could be either, or both. If you arent getting even sporadic movement (like a bad wire) then chances are its a bum servo. You will most likely need to contact Hitec and send it in for a replacement. I wish these servos didnt fail so often 
were you just working with 6v?
were you just working with 6v?
by i-Bot
Sun Sep 17, 2006 3:28 pm
When you have the bottom cover removed, you will see at one end a large hole in the PCB with the end of the motor visible through it. The surounding 3 large terminals in solder pads connect to the motor. The one at the end is a ground connection.
If you measure the resistance between the other two on the sides, then a good motor has a resistance of about 4.5 ohms. A shorted motor will be pretty much zero, this will have taken out one or more of the H bridges.
The H bridges are the two 8 pin devices on the board by the motor. They are unlikely to fail unless the motor shorts.
To get to the other side of the board it is necesary to unsolder the 3 motor connections. This only gains access to the procesor chip, regulator, and the connections from the feedback pot and the servo lead. Best to leave alone, these servos are not realistically user serviceable.
Best to just measure the motor, so you know if that was cause. Buy another servo, beacause you will need a spare if you are serious in this. Then send the dead servo to Hitec for replacement.
If you measure the resistance between the other two on the sides, then a good motor has a resistance of about 4.5 ohms. A shorted motor will be pretty much zero, this will have taken out one or more of the H bridges.
The H bridges are the two 8 pin devices on the board by the motor. They are unlikely to fail unless the motor shorts.
To get to the other side of the board it is necesary to unsolder the 3 motor connections. This only gains access to the procesor chip, regulator, and the connections from the feedback pot and the servo lead. Best to leave alone, these servos are not realistically user serviceable.
Best to just measure the motor, so you know if that was cause. Buy another servo, beacause you will need a spare if you are serious in this. Then send the dead servo to Hitec for replacement.
Where can you buy new.
by Gort
Sun Sep 17, 2006 4:15 pm
Everyone seems too be out of stock for robonova servos. 
Mike
Mike
by Ray
Sun Sep 17, 2006 5:01 pm
from my experience, first of all,
do you have many motion in the arm?
if yes, it is likely a boken wire of the signal side,
---- to confirm, just use a digital multimeter to measure both end of the
long servo wire (of course you should open the case),
do it 3 time for each wire, it should should less than 6 ohm for each wire.
if the resistance of the wire is small, try measure it when you shake the wire, if no change, then you may have the MOSFET (H - Bridge) Driver burnt. (the two 8 pins surface mount IC --- Si9958DY)
Replacement: IRF7389 x 2 pieces
Location: http://www.rs-components.com/index.html
That's all.
(If the motor was died, the two SMD IC should be burnt and bad smell
should be come out already)
do you have many motion in the arm?
if yes, it is likely a boken wire of the signal side,
---- to confirm, just use a digital multimeter to measure both end of the
long servo wire (of course you should open the case),
do it 3 time for each wire, it should should less than 6 ohm for each wire.
if the resistance of the wire is small, try measure it when you shake the wire, if no change, then you may have the MOSFET (H - Bridge) Driver burnt. (the two 8 pins surface mount IC --- Si9958DY)
Replacement: IRF7389 x 2 pieces
Location: http://www.rs-components.com/index.html
That's all.
(If the motor was died, the two SMD IC should be burnt and bad smell
should be come out already)
by pepperm
Sun Sep 17, 2006 5:16 pm
You can test the connectivity of the servo to the CM-5 by either writing your own or using one of the robot test programs (with maybe the servo number being changed) that turns on and off the servo's LED. If the LED turns on and off then the cable, voltage regulator and processor circuitry within the servo are working. If not then I would look at the cable then voltage regulator first.
Also with the motion editor, the servo will not report in as being present if the cable, regulator or processor are screwed.
If all that works then start looking at the motor and the 2 motor drive ICs. At this point it could also be the voltage regulator circuit that is made around the two SMD transistors on the servo PCB. I haven't worked this circuit out exactly yet but it sits between the +ve trace and pin 1's of the drive ICs. I think the SMD components are transistors but could be wrong.
Hope this helps a bit.
Mark
Also with the motion editor, the servo will not report in as being present if the cable, regulator or processor are screwed.
If all that works then start looking at the motor and the 2 motor drive ICs. At this point it could also be the voltage regulator circuit that is made around the two SMD transistors on the servo PCB. I haven't worked this circuit out exactly yet but it sits between the +ve trace and pin 1's of the drive ICs. I think the SMD components are transistors but could be wrong.
Hope this helps a bit.
Mark
by i-Bot
Sun Sep 17, 2006 5:41 pm
The servo schematic is here if you need it:
http://web.ukonline.co.uk/r.ibbotson/fi ... 0Servo.pdf
The H-Bridges are normally the IRF 7389, not the siliconix part I reference in the text.
If you suspect a broken wire, then the 3 wires are soldered through the board and do appear on the bottom. The three larger blobby pads in line with the servo cable are the ones. The top one closest to the cable inlet is the positive supply, the top one in line with this at the opposite side from the cable is Gnd, and the one on the bottom right is the signal. ( all viewed from bottom of servo.
If you do want to remove the board completely unsolder all three motor connections and the board can be removed. The motor seems not to slide out of this servo still connected to the PCB, like some of the other Hitecs.
http://web.ukonline.co.uk/r.ibbotson/fi ... 0Servo.pdf
The H-Bridges are normally the IRF 7389, not the siliconix part I reference in the text.
If you suspect a broken wire, then the 3 wires are soldered through the board and do appear on the bottom. The three larger blobby pads in line with the servo cable are the ones. The top one closest to the cable inlet is the positive supply, the top one in line with this at the opposite side from the cable is Gnd, and the one on the bottom right is the signal. ( all viewed from bottom of servo.
If you do want to remove the board completely unsolder all three motor connections and the board can be removed. The motor seems not to slide out of this servo still connected to the PCB, like some of the other Hitecs.