On 3/10/2018 1:44 AM, Terry Schwartz wrote:
Are you certain there is no feedback? I've seen systems where the load driver, if overloaded, can truncate the PWM pulse from the low level driver circuitry and that circuit can sense it. Might want to put a scope on the enable and dim lines and see if anything like that is going on.


It's 2 am here now and I'm getting ready for bed. I don't know if
I'll have time to some more checking tomorrow. If not, it'll have
to wait for Monday.

I'm certain that the two lines coming from the control board go
to pins 13 and 16 of the inverter control IC OZ9933 via a few
passives. These are the DIM PWM and ENABLE pins respectively. The
tracks are easy to trace on the single-sided PCB and they are the
only lines of connection with the control board (except for the
5V supply and GND).

I downloaded the service manual a few days ago. But while it's
quite detailed about some things, it's sketchy about others or
entirely omits them. Same thing for the schematic.