I'm trying to determine my next steps in diagnosing and repairing an inverter drive module for a compressor in a heat pump.
Pool heat pump Model Astral Pool iHP170
Symptoms:
Shortly after turning on and after the compressor kicks in it stops with a fault; "F10 - Inv. Input Overvolt."
Apart from a range of sensors and relays, there are essentially 3 main components in the electrical side; Touch screen, main controller and the inverter drive module.
There are no obviously damaged components that I can see and no residual magic smoke smell.
![Inverter drive module overvolt fault 1608739-0](https://www.eevblog.com/forum/index.php?action=dlattach;topic=346618.0;attach=1608742;image)
The replacement cost from Astral pool for just the inverter module pictured is ~$2500! Repair it is.
I have had no success in determining an OEM for the part or anything related to the marking on it "SA.FNB75GW.1" except for parts listings in the various manuals for this heat pump presumably rebadged under a few names.
The main drive chip is a
mitsubishi pss35s92f6-ag, other component numbers can be provided where relevant.
I have determined that the communication between the controller and the compressor Inverter drive module is ModbusRTU over RS485.
After sniffing a bunch of the communication between the boards I have managed to reverse engineer enough of the communication protocol to control the inverter drive board directly from a laptop using a small application I wrote which polls the state of the module every 100ms.
I can instruct the inverter module to control the compressor on/off state, compressor frequency and fan speed and the inverter module will report:
"AC plate voltage", "Inverter DC Voltage", "Compressor frequency", "Compressor Current", "IPMTemperature" along with a bunch of error codes
While powered and with the compressor and fan off the drive module reports the AC voltage ~220v which is about 15v less than I measure on the terminals with my EEVBlog BM786 multimeter
![Wink ;)](https://www.eevblog.com/forum/Smileys/default/wink.gif)
it also reports the DC voltage as ~320v which seems to be about right for the given AC voltage.
When I send the "on" signal for the compressor, a few seconds later I see a jump in the reported compressor current and another few seconds later the compressor frequency begins to rise.
After around 5 seconds with the frequency generally about 25Hz, the reported AC voltage jumps from ~220v to ~320v; pretty much the same value being reported for the DC Voltage.
About 5 seconds later, the compressor cuts out and the "Inv. Input Overvolt" error is reported, at the same time the AC voltage drops to ~255v where it stays for the next 10 seconds or so before returning
to ~220v. The DC voltage remains around 320v throughout.
I've tried setting the initial compressor frequency to a number of values from 20Hz to 100Hz (all within range of the compressor's specs) and the behavior is fairly consistent.
So that's about as far as I can go on the software side, now I need to get into the electrics but not sure where to start.
The numbers above are all as reported by the inverter module itself via Modbus, not independently measured values.
Using the multimeter I do not see the spike on the AC input terminals reported by the module so I need to determine where the metering circuit might be on the module.
This is where I need help from more seasoned experts. Any suggestion on what to check next or where the AC metering circuitry might be would be very welcome.