There's no switching happening on the main transformer on this LG 1953T. no 12V out, no 5V out.
I put a scope on U101 which is a FAN7601 PWM controller:
pin 1 -Start up- getting 160VDC off the bus (bus reads fine at 167VDC)
pin 2 - Current Sense/Feedback - is 0.13V so it is not being shut down here (>1V will shut it down)
pin 3 - Latch/SS - comes up to 1.5V as expected during start-up then goes to 0V (over 75ms)
pin 4 - RT/CT - is clocking
pin 5 - ground
pin 6 - Out - nothing... flat line.. I want a square wave here to drive the FET. I can see some noise on here when it first connects to AC but then it goes away and never comes back.
pin 7 - VCC - is going from 8V to 12V as expected, it looks like the Startup current is charging the cap. It drops from 12V to 8V over the 75ms startup time.
pin 8 - Vref - steady 5V.
Schematic attached. FET checks out - no shorts.
pins 5/6/7 are not shorted so the internal transistors seem to be ok. Looking for some thoughts before I go to the trouble of ordering another FAN7601.
THanks!
PS. I do this in my spare time for a non-profit ethical computer recycling organization that provides these monitors to low income families, schools, etc.
I put a scope on U101 which is a FAN7601 PWM controller:
pin 1 -Start up- getting 160VDC off the bus (bus reads fine at 167VDC)
pin 2 - Current Sense/Feedback - is 0.13V so it is not being shut down here (>1V will shut it down)
pin 3 - Latch/SS - comes up to 1.5V as expected during start-up then goes to 0V (over 75ms)
pin 4 - RT/CT - is clocking
pin 5 - ground
pin 6 - Out - nothing... flat line.. I want a square wave here to drive the FET. I can see some noise on here when it first connects to AC but then it goes away and never comes back.
pin 7 - VCC - is going from 8V to 12V as expected, it looks like the Startup current is charging the cap. It drops from 12V to 8V over the 75ms startup time.
pin 8 - Vref - steady 5V.
Schematic attached. FET checks out - no shorts.
pins 5/6/7 are not shorted so the internal transistors seem to be ok. Looking for some thoughts before I go to the trouble of ordering another FAN7601.
THanks!
PS. I do this in my spare time for a non-profit ethical computer recycling organization that provides these monitors to low income families, schools, etc.
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