Insignia NS-LCD19-09 no standby LED; (new problem)

[valvashon]

Having a new problem with the 19" Insignia that I modified with one of my automatic turn on circuits. That is now completely disconnected so that is not the issue. I was doing some modifications on that circuitry and managed to short something out on the underside of the power board.
Actually found and bought the service manual (who knew it was even available?!) which brought me to the High Voltage Startup Circuit controller chip.
Looking up that chip number- LD7575APS brought me to the attached datasheet. I have marked my voltage readings on the schematic sheet (open in new window to see voltages). I see good VCC (sort of) and good HV and maybe good voltage at the switching frequency pin (1) but variable voltages elsewhere (all are DC voltage measurements). I'm guessing that these are bad and the chip is toasted but there are no suggested voltages on the data sheet or the actual schematic which is almost identical to the data sheet circuit.
If anybody knows what those voltages should be I'd appreciate it. The external MOSFET could also be bad so I'd like to know these voltages first before I just start throwing parts at it.
Also, this is essentially obsolete but I can find replacements marked LD7575 not LD7575A. Any idea how much difference there is? Can't really find out from reading the two data sheets.
Thanks

[R_J]

Re: Insignia NS-LCD19-09 no standby LED; (new problem)

The service manual is available for free on line, the vcc voltage for the ic needs to be around 16v, if it falls below 10v it shuts down. C906 should be replaced as a it is likely weak. If the mosfet is bad it will likely be shorted, and R914 would likely be open.
My guess would be that you shorted the secondary diodes D908, D911, D909 or one of the zener diodes. Allso check R909 D902
The ld7575a will be fine, The LD7575APS is a sop-8 PB free, the LD7575APN is a DIP-8

Not sure what you shorted so it is hard to say what you damaged.

[valvashon]

Re: Insignia NS-LCD19-09 no standby LED; (new problem)

At the risk of violating copyright for the service manual I bought (which may be different than the one that is available for free online) I'm attaching part of it. I have checked everything on the "hot" side of the power board aside from a few very small value SMT caps.
Everything checks out as having the correct value; what I have measured is highlighted in yellow. Components circled with an X are not on the board. Unless I'm missing something the High Voltage Startup chip is the likely suspect. C 906 checked out at 2300 PF so I don't think that capacitor is weak. Unless somebody has any other ideas I will be replacing the LD7575 chip.

Val