LB1668 2 phase motor controller

[okw]

Hello,
I have a fan with a faulty(?) controller. It is a YHWM-9733 DC18V 340mA fan. Sometimes it turns on and runs fine (inrush current 270mA, running at 195mA), but most times it's dead and draws only 8mA. If I manually spin it while energised, it kicks in and runs normal. The controller has a minimal circuit with LB1668, two resistors, one MLCC and one electrolytic (2.2uF) cap, a diode and some tiny 4 pin chip (designated H in the datasheet and connected to the amplifier in+ in- gnd and vcc), and an unpopulated inductor.
Any insight of what could be faulty? I measured the diode OK, the electrolytic is about 2.2uF and 8 ohms ESR (tried with two others at about 1 ohms, no solution).
My thoughts are the LB1668 or "H" (which I have no clue what is)

[fzabkar]

Datasheet:

https://media.digikey.com/pdf/Data%20Sheets/ON%20Semiconductor%20PDFs/LB1668_M_May2013.pdf

"H" would be a Hall Effect sensor. If you disconnect the power to the fan, and then rotate the fan by hand, you should see IN+ and IN- change state.

[okw]

Thanks. What could it indicate when the motor randomly doesn't start by itself, but needs a lilttle help? When it needs help, it's almost drawing no current, not does it "vibrate" like a normal motor struggling to start.

[fzabkar]

I would check the supply voltage and motor bearing. Compare the resistances of the two phases.

Monitor the Hall effect inputs and phase outputs with a scope while the fan is running.

Measure the C and RD pins when the fan is stopped.