Benq T905 power supply repair
 

Phil Allison wrote:
Jeroni Paul wrote:
Here is its schematic:
http://www.rom.by/files/q9t4-fp91g-power_bd_1.pdf


** If the mosfet blew, R615 must have too.

Did you maybe replace it with a wirewound type ?

That would explain most of you symptoms, running OK at low loads but failing if the current in the switch is higher - also made worse if the AC supply voltage is lower as it will be with a lamp in series.

R615 ( 0.22 ohms 2 watts ) must be a metal film or composition type.

IOW *low* inductance is crucial.


..... Phil

Thank you Phil.
The resistor you mention was good and is the original. Finally I got it working by wiring 4 100W bulbs in parallel, so I removed the bulbs and all is fine.

Benq T905 power supply repair
 

Jeroni Paul wrote:


** If the mosfet blew, R615 must have too.

Did you maybe replace it with a wirewound type ?

That would explain most of you symptoms, running OK at low loads but failing if the current in the switch is higher - also made worse if the AC supply voltage is lower as it will be with a lamp in series.

R615 ( 0.22 ohms 2 watts ) must be a metal film or composition type.

IOW *low* inductance is crucial.



Thank you Phil.
The resistor you mention was good and is the original.
Finally I got it working by wiring 4 100W bulbs in parallel,
so I removed the bulbs and all is fine.


** That SMPS is unusually sensitive to low AC supply voltage.

Normally they work from 85V and up.



..... Phil