phillips 42pfl5609/93 no standby

[attainteddragon]

this psu has a blown fuse and is shorted somewhere.
all diodes test good.
fets seem good.
caps test good.
varistors measure 3.5 ohm in circuit (im not very sure about these, but doesnt that mean that they are cactus and could be causing my short!)
there are probably several other things that im missing here and look forward to learning some more!

[budm]

Re: phillips 42pfl5609/93 no standby

So the new fuse is blown right away and it is still blowing the fuse?
Since I cannot locate the diagram for this board, can you post lots of closed up section of the boards so we can clearly see the components and traces of the board?
There may be chassis number on the model tag that we may be able to use to locate the diagram fro this TV.
Also, use the Ohm meter to check the resistance on the two legs of each main filter caps that are laying on its side to see if shows really low resistance, no power applied when making resistance reading.
BTW, Does it blow the fuse if you power this board by itself?
You can connect about 75~100W lamp in place the fuse (lamp will be in series with the load) to monitor if the short still exist, if there is shorts, the lamp will stay brightly lit.

[attainteddragon]

Re: phillips 42pfl5609/93 no standby

i put 150watts of globes across the fuse and they power up very bright and strobe with the relay pulses and dont dull off. just continual strobbing effect. i only let it go for not even 10 secs, just in case.

[budm]

Re: phillips 42pfl5609/93 no standby

OK, power up the board by itself (nothing else connected to the board) to see if the lamp will light up, that way the power relay will stay off and the standby power supply will be the only section that will be getting the power.

[attainteddragon]

Re: phillips 42pfl5609/93 no standby

ok, powered up on its own and lights stay off and standby is present.

[budm]

Re: phillips 42pfl5609/93 no standby

Good, that means you have shorts circuit in the main power supply section.
So, use the meter in Ohm mode and report the resistance reading between the two inner pins of the bridge rectifier D804, then the resistance reading between the two outter pins of the bridge.

[attainteddragon]

Re: phillips 42pfl5609/93 no standby

ac legs 19.47m
dc legs 77.4k

[budm]

Re: phillips 42pfl5609/93 no standby

OK, no static shorts in the PFC Voltage booster circuit.
Next is the resistance reading at the positive and the Negative legs of C840 main filter cap.

[attainteddragon]

Re: phillips 42pfl5609/93 no standby

c840 is 23.44k
by the way, thanks heaps for your time and knowledge bud

[budm]

Re: phillips 42pfl5609/93 no standby

Hmm, the static readings are good.
So lets start disconnecting loads, lift one leg of the fusible resistor R941, and hook the cables backup because we need to activate the relay, see if the lamp will still stuck on bright when the relay kicks in.
BTW, you can also jump the relay contacts so the board can run by itself without having all the wires connected.
I will have to continue tomorrow, it is getting late here now.

[attainteddragon]

Re: phillips 42pfl5609/93 no standby

r941 is a jumper on this board but with one side lifted, lights still come on and flash with relays. it seems a bit slower and not quite as bright.

[budm]

Re: phillips 42pfl5609/93 no standby

OK, lift one leg of r863 next.

[attainteddragon]

Re: phillips 42pfl5609/93 no standby

ok, lifted a leg of r863 (i didnt reatatch r941), and my jumper globes only came on for a second with the relay and then went off.

[budm]

Re: phillips 42pfl5609/93 no standby

OK, that R863 feeds one of the switching power supply, if look at the one end of that resistor, it feeds one of the transformer pin which is driven by MOSFET Q803 (I cannot read the print on the board), so I expect that you have bad Q803, need to check that out. It loks like that is the circuit for the 24VDC for the main board through connector P802.

[attainteddragon]

Re: phillips 42pfl5609/93 no standby

q803 is k6a65d which is an n channel mosfet.
it read as follows
red on
g d ol
g s 1.939
s d .489
black on
g d ol
g s .662
s d ol

but as i was getting the mosfet code, i noticed that c 807 is cracked majorly down its side. cant believe that i missed that one.
it is a ceramic cap
l.y.
r1kv
331k

[budm]

Re: phillips 42pfl5609/93 no standby

That is the snubber cap connected between Source and Drain, commonly failed parts due to high voltage spike. Ceramic 330pF 10% 1000V, get 2000 V if you can. It should have shown shorted circuit which is the failure mode for ceramic cap.

[attainteddragon]

Re: phillips 42pfl5609/93 no standby

is there anything else i should look at, at this point?

[budm]

Re: phillips 42pfl5609/93 no standby

You can put the first jumper (which is for the backlights inverter circuit) I have you removed back in place since I believe you have found the cause of the problem now. The second jumper (r) is for the 24v power supply.
Oh, make sure R859 is not open circuit due to that bad cap, check the circuit around the Source pin, you can see the trace that runs to the Source pin which is connected to the resistor for the current sensing feedback, they may be OK.
BTW. that cap probably carbonized but the meter does not put out enough high voltage to cause the current to flow through, when when the TV is power up, about 380~400vdc will be applied on that cap.

[attainteddragon]

Re: phillips 42pfl5609/93 no standby

first jumper is back in.
should i leave the second jumper till i have tested with the new cap.
r859 (if i have this right) should be .47 5% (yellow, purple, silver, gold)
it measures .6 i should change it out too.
ill order parts tonight.

[budm]

Re: phillips 42pfl5609/93 no standby

OK, the Source resistor did not get damaged. Leave the second jumper out for now, you should be able to power up the unit, it will just be no 24vdc for now.