View Full Version : MR-03 steering problem

2016.04.03, 08:57 AM
I built an MR-03 from spare parts and a used board i bought, the ASF chase mode board which has coreless servo motor. upon testing, throttle works fine. steering does not.
1. steering responds to transmitter input. turn the wheel either direction and the servo motor moves appropriately. take the servo motor out of the servo gear assembly and it simply spins full tilt in one direction.
2. steering input will not turn the wheels right, only left. once left, the wheels remain at full lock left. i can turn the wheel right and push the servo horn the correct way as if it accepts my assistance however will not turn with enough force (maybe not overcoming running one direction full time as demonstrated when pulled out of the gearbox?).

1. no pinched, shorted, borken wires
2. servo will run in both directions with steering input out of the gearbox however neutral input results in motor constantly turning in the direction to steer left.
3. pot is aligned, clean, no gaps or spaces


2016.04.03, 09:59 AM
in testing a replacement servo motor, no change by the way, and putting the original back, the servo motor now only turns left. does not turn right with steering input any longer. seems i bought a bad used board i guess.

2016.04.03, 05:46 PM
Have you checked the pot and the pot wiring?

2016.04.03, 05:53 PM
yep. touched up any joints, tried swapping the servo motor out as well. don't have an extra pot.

Mike Keely
2016.04.03, 10:04 PM
Sounds like one of the steering fets are bad. I know that people have changed them out to fix this same issue.

2016.04.03, 10:28 PM
Sounds like one of the steering fets are bad. I know that people have changed them out to fix this same issue.
I smoked a steering FET on a clone MA-015 board which I believe is the same as MR-03 with different programming, do you have a suggestion for a replacement FET? I cannot find any information on the component on the board. I don't mind using a larger FET as there is quite a lot of extra room on the chassis for a FET to hang off the board.

2016.04.04, 06:26 AM
i've never dealt with replacing steering fet's before. there is always a first time for everything :p

2016.04.11, 12:30 AM
Any updates? Hope you get it sorted out...

2016.04.11, 06:55 AM
Nope, did some testing based on some other's experience with similar problems and the only fix for them was to send it in for repair/replacement. if anyone wants an ASF board for parts, send me a message. everything works but the steering. i bought a new board set so don't have any more time to deal with problematic board, cheaper for me in the long run to cut my loss and just replace it.

Mike Keely
2016.05.15, 08:37 PM
Try calling Maj's Hobby shop in NJ. They have needed to replace them before.

2016.05.28, 11:20 PM
Been searching all night to solve Phoenix's ASF board. I swapped polarity of the pot , but steering still stuck to one side..

I took out the servo assembly , switched the car on with transmitter on. Servo motor wil keep spinning unless I turned the pot to 90 degree, which is not the center position if we were to put the servo assembly back...

Any hint? Do you think I still have the pot cables swapped?

2016.05.29, 04:10 PM
if your board is still under warranty, i am aware of a case where they were able to correct the board.
if not a warrant repair, my only recourse was to replace the board in a similar situation. send me a message, i have a spare ASF brushed motor board i can send you.

2016.05.29, 09:54 PM
Thanks for the hint Ray. Let me check with the seller to see if they would accept exchange. If not it will be awesome if you have a spare asf board you can sell to us!

2016.08.20, 07:36 AM
swap the polarity of the motor. and if a fet is dead the motor won't spin at all (h-bridge requires 2 transistors).