Phillips Magnavox 42MF438B/F7 does not power up

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

Please see the attached picture.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

After looking at the newly mounted chip the IC's pinouts are correct based on the slant.

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

OK, so now we need to figure out why you have this new problem with losing the 3.3V when the main board is connected.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

what is the possibility now that the IC is funtioning that there maybe a leaking capacitor with the additional load or attempt to power up the 12v and 24v power supply area.

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

If you do not have 3.3V for the processor to run, this processor sends the PS_ON signal to turn on the 12/24V power supply section, that is why we have to have the 3.3V working again to see if the new IC fixes the 12/24V section.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

Where is the best area to start with troubleshooting?

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

When testing shorts to ground, below what resistance measurements is considered a short to ground? A resistor with bands I can get the resistance for but other devices or components like diodes.

I probably will remove the IC chip off the board and see if I get the constant 3.3v and the powering on of the PS.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I removed the IC chip and still the samething, the relay latches on then off adn loss of the 3.3V.. I am wondering now whether I have an issue on the main board. What would be teh obvious things to check for, diodes,regulators??

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

anyone have any advice???

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

Without having the Main board connected to the power supply board, put 4.7 Ohms 5 Watts as a dummy load for the 3.3V Standby power supply out put to see if it can handle this load and stays at 3.3V output.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

the only resistor I found at radio shack was a 10 ohm 10 watt wirewound would this suffice..Also I assume the resistor will be coming off the 3.3v line then going to ground?

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

Get two of them then. Yes 3.3V pin and the chassis ground. Try one resistor first and see what happen.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

the first resistor still had the 3.3v. 2 resistors in parallel still yielded a 3.3v

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

Well. that is about 0.6A load and it can handle that OK. On the power supply board, does it have any printing on the board that show the Voltage and current rating of each voltage outputs? It is not going to be easy to find out which part of the main board is drawing to much current.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I did order a power supply board yesterday and it should be in tomorrow. I am baffled at how this thing went from having that voltage to not after the IC swap.. as I was thinking more about what could possibly have changed, soemthign dawned on me aafter I removed the IC chip with my hot air station. I noticed that the board lifted up in that area as though it seperated apart ( underneath the IC chip). could there be a possibility that there is a short or discontinous trace that I did not notice? maybe this may have been a coincidence to what happened.

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I think it may be co-incidence because the 3.3V standby power supply is separated from the section you are working on which is the 12/24 power supply section.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I still would like to get this board fix even if the repalcement works out well. I am going to comb the booard over and resolder some of the main areas just in case there maybe a solder joitn issue.

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I received the PS today and hooked everything up and the TV powered up and works well. The main baord is good.. I would liek to fix the old PS..do you thin there might be soemthign going on on the primary AC side of the board like the new rectifier could be leaking or the 3.3v PS is the culprit?

[mike123333]

Re: Phillips Magnavox 42MF438B/F7 does not power up

I through components and compared them to the good board but could not find anything that faulted... I am not sure whether a capacitor is leaking or any other component with the limited testing I can do on the board.

[budm]

Re: Phillips Magnavox 42MF438B/F7 does not power up

You can shot gun it by replacing a set of caps, otherwise, good diagram to understand how the circuits are hooked to really get to the root cause will be the next thing.
At you got the TV again now, good job.