SRK71 MHI Split System Inverter shutting down after startup

[Donno63]

Hello, I have just replaced the Gate Transistor and Switching Diode on Inverter PCB, tests ok, New Fan motor, On switch on, comperessor runs ok for a short time then shuts down,, Comp Fan does not rotate but has the correct Voltages 330V and 15V as per the Service Manual.. 4-way valve is operating when switching between cool and heat,, It appears that Speed control Voltage Signal (VSP) is not evident,, Does this mean the Main PCB (MCU IC) is damaged beyond repair? Indoor unit runs ok on fan only, responds to remote when changing modes etc.. Compressor tested ok across the windings and equal..1 ohm each.. so I am confident Compressor is ok and just shutting down in response to safety control, as no fan motor operating.
Any sugestions or advice would be greatly appreciated.

[Donno63]

Just an update on this problem,, After replacing the schotky diode and switching transisitor, This unit still will not run. I have found 5v and 15V correct on the main PCB control side. The indoor unit responds correctly to remote control signals. I have also replaced the outdoor fan motor. Compressor starts up, then shuts down soon after due to no fan motor Vsp. I have checked the voltages at the compressor when starting up, each line has 15-20V equally.. Would I not expect more Voltage here? My refridge tech has told me these boards are not repairable, but I feel I must try as it's not me to give in and replace. I also checked Voltage at the Power inverter o/p and each line showed 11.2V when I disconnected them from the compressor. Does anyone have experience in these boards.

[Tayters]

Can't say I've delved this deep on an MHI unit but have you got a speed signal coming out of the motor when spinning and also command signal from the PCB?

Not sure what they should be but as far as I'm aware you get a square wave from the motor which changes duty cylce with speed and the same or perhaps a 0 to 5V signal from the PCB as the speed command.
If you have nothing from the PCB side of things then I'd imagine short of replacing standard parts you'd be hard pushed to get the actual IC concerned.

Inverter voltages seem low but this all depends on inverter frequency and how quick your test meter picks them up. Search for inverter testing to get details of static checks you can do with the diode function of your meter.

Cheers,
Andy.

[ozairman]

More Questions for you
1 What is the full model number ie SRK71xxx /SRC71xxx?
2 What model remote control are you using?
3 What was the original fault?
4 Have you accessed service mode yet and checked the most recent stop codes (Cooling mode, Lo fan, 21, 22 23 setpoint)?
If not go here http://mhiaa.com.au and go to the downloads page and download the service support handbook. There are instructions there on how to access service mode, two big hints for accessing service mode:
A It's easier with a helper to turn the isolator on whilst you are holding the On/Off button down on the Indoor unit
D Don't count the initial long flash of the Run and Timer light when you are counting the number of flashes.
Come back with some answers soon :)