Philips Brilliance 420p Fluctuating PSU Voltage

[tom66]

Re: Philips Brilliance 420p Fluctuating PSU Voltage

Relays can fail, but that is rare.
You can check the relay by putting a 9V battery across its coil when removed from the board, it should make a "click" sound.

[NipZ]

Re: Philips Brilliance 420p Fluctuating PSU Voltage

ok , thanks I'll give that a go tomorrow

[budm]

Re: Philips Brilliance 420p Fluctuating PSU Voltage

You can check to see if one of them has 5VDC, and another one has 12vdc on the coils, if they do but the relays do not close the contact, then I would expect bad relay. You can test them off the board as Tom suggested also.

[NipZ]

Re: Philips Brilliance 420p Fluctuating PSU Voltage

I have taken both relays out of circuit and tested using 9v battery as suggested by Tom and both relays are clicking.
My next step was to remove the 2 transistors BC557B and BC547B and try to test these. I followed a guide on youtube here http://www.youtube.com/watch?v=b0jCUsenNsY but I am not getting readings the guy is saying to expect. Every way round I try my leads I am getting OL, not a high ohm resistance. 1 is NPN and the other PNP going by datasheets I have googled. I suspect I am doing something wrong or coincidentally both transistors are bad(which I doubt?).
Can you suggest a better way to test these please?

Never mind, I have tested them on diode test and I'm getting a voltage drop of around 0.7 from base to collector and base to emitter and nothing across collector and emitter. They both appear to be good

[budm]

Re: Philips Brilliance 420p Fluctuating PSU Voltage

Right now do you know which of the two relays on the board is clicking on? You can monitor which one has the DC voltage on the coil, once I know which one is working then I can guide you to find out why the other one is not working.

[NipZ]

Re: Philips Brilliance 420p Fluctuating PSU Voltage

After messing about with this today I now think both relays are clicking, so I think the theory of not bypassing the variable resistors is out of the window.
That brings me back to square one, I have fluctuating voltages and don't know why, even at pin 1 of the bridge rectifier the voltage can vary +/- 25v that follows through to fluctuation at the pfc ic +/- a few volts, and all the way to the 380v output.
Any ideas I can try?