Huangyang vfd rpm readout

I am using one of the Huangyang 1.5Kw drivers with RS485 comms and it is working fine except the spindle rpm or the drive rpm display is 20% slower than what it should be.

If I reprogram drive parameter PD144 to 3000 which is the rpm at 50Hz the speed is then correct. I can cut power to the drive then power up again and things will still work at the correct speed.

If I close Linuxcnc and restart it, PD144 is reset to 2400 and the spindle is slow again.

Can anybody give me a clue where to find whatever needs changing to stop this happening.

it is strange, it seems that it is linuxcnc to change parameter 144.
it should only do so if you specify the -s motor speed option.
have you looked here? linuxcnc.org/docs/html/man/man1/hy_vfd.1.html

I haven't used this machine for a long time and getting the spindle to work used to be a real faff. I am still specifying the max spindle speed as a parameter as before.
It used to be ok but now I am using another computer with a 2.7 version of Linuxcnc, not sure exactly which version because I am not with the machine at the moment. I think it used to be on a 2.6 version.

I just cloned the 2.8 repository and checked the source code that sends the PD144 value to the drive and it all checks out ok so I will install 2.8 tomorrow and see what happens.

It may just be a default setting somewhere in the 2.7 version that I used.

Just in case this shows up in a future search for somebody else, the problem exists in ver 2.7.0 of Linuxcnc. The value sent to PD144 gets mangled somewhere.

After an update to version 2.7.14 and presumably newer versions when released, the problem is gone, the spindle works properly.

Well! But I did not have this problem with the latest versions. I had problems with the rs485 usb sticks that burned, then I discovered that it was the power supply of the PC not connected to the ground -DC tomorrow I think I try.