Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

[Hazen]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

On Q602 the voltages to ground are

pin 1 (gate) 12.7 on/ 11.3 off
pin 2 (drain) 12.5 on/11.1 off
pin 3(source) 11.7 on/10.7 off

voltage g-s 1.8v, d-s 1.7v

[dick_barton]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

This is leading me back to IC1601. All the voltages being read are all low. I would have expected a voltage of approximately 350v at the junction of D1603/D1605 which would then push up all the other voltages read so far.
The circuit looks almost identical to the one in the application notes as shown on page 27 and this delivers approximately 400V.

There are two places in the circuit where higher voltages are given.
Q1704 Drain = 214V and Q601 Source = 231V.
Can you see what they currently read when ON.

[Hazen]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

On Q1704 drain, I have 164v, on Q601 source I have 0v checked when on. I also checked D1603/D1605 and have 164v at that junction.

[budm]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

OK, the power supply section where the ALL3.3V, AMP13V, P-ON21Vare generated by the IC601, Transformer T601, the output of the AMP13V, PON 21V will be at about 60% of normal Voltage when it is in standby due to feedback control on the REF DIODE D660 (431a) is set so those two Voltages will be low in standby. the 3.3V in standby is supplied by IC651 1117-3.3V.
When the PS-ON is present, Q653 will be turned on so the Voltage feedback through R666, 667 to D660 will be grounded by Q653 which will cause the power supply output to rise up and maintain the output of the +13v and the +21v Voltage. The 3.3V is then supplied by Q657.
This power supply section do not need the Boosted Voltage to produce the +13V, +21V. The +13V, +21V should go up to normal level when PS-ON is present.
The PFC IC will get the correct Voltage to run from the transformer winding pin 6, this Voltage will rise up to higher level to u run the PFC when the PS-ON is present.
So you need to find out if the DCV at the Collector of Q653 will change state in sync with PS-ON state.

[Hazen]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

So you need to find out if the DCV at the Collector of Q653 will change state in sync with PS-ON state.

I do see a state change with ps-on and when it is removed.

[budm]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

At the Collector? What do you see when PS-ON is not present and when PS-ON is present?

[Hazen]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

Ok, well something unexpected happened. After I posted about checking Q653 and toggling ps-on about 10 times to see the state change, I started checking other areas for voltages, and for some reason, I started getting the voltages I expect. I saw 21v at p-on+21v, and 12.8 volts at amp+13v. I connected everything back to the tv and my standby light came on, but would blink. I pressed the power button but it did not power on. But now it has went back to the state that was/is my original issue.

At the Collector? What do you see when PS-ON is not present and when PS-ON is present?

Yes, at the collector. The voltages were very small, around .005v with ps-on, but was stable. With it off, the voltages were still under 1v but fluctuating.

[budm]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

So it is switching, at this point we need to do more in-depth troubleshooting this power supply section to get the full 13V and the 21V output when PS-ON is present first.

[budm]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

BTW, so when you are running this power supply board by itself with the force on present, are the 3.3V, +13V/+21V (they are less right now since they do not kick up to higher Voltage) STABLE?

[Hazen]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

BTW, so when you are running this power supply board by itself with the force on present, are the 3.3V, +13V/+21V (they are less right now since they do not kick up to higher Voltage) STABLE?

Yes, they are stable at the lower voltages, other than the 3.3v, it is at 3v.

So it is switching, at this point we need to do more in-depth troubleshooting this power supply section to get the full 13V and the 21V output when PS-ON is present first.

That was the first time that I have seen it switch, and now I haven't been able to get it to do it again.

Where is the standby voltage produced? Since it's 3.3v, does it go through a switch? Once I connected the ps board to the tv, I got the standby light. Also, when I power on the ps I hear one slight click, when I was getting the correct voltages, I would hear 2 clicks.

[budm]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

IC651 1117-3.3V on the power supply board per schematic is where the 3.3V stby is from, it should be 3.3V since it is regulated.

"That was the first time that I have seen it switch, and now I haven't been able to get it to do it again." I do not understand, I thought you are doing the force on as shown in the link to force on the power supply without having the main board connected.

[Hazen]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

yes I am forcing it with the 1k resistor, but it was the first time seeing it switch to the higher voltages.

[budm]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

yes I am forcing it with the 1k resistor, but it was the first time seeing it switch to the higher voltages.

What do you mean switching to higher Voltage? So the +13V and the +21V go up to full Voltage when you force on with the resistor?

[Hazen]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

So the +13V and the +21V go up to full Voltage when you force on with the resistor?

Only during that one occurance. After I checked the voltages and state change of Q653 from post #24, I then started to notice the second click when I forced PS-ON. I started checking the voltages and found I was getting +13V and +21V, but again, only during that one instance. The 13v and 21v are no longer there when PS-ON, and I haven't been able to recreate the scenario to get them back.

[budm]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

Only during that one occurance. After I checked the voltages and state change of Q653 from post #24, I then started to notice the second click when I forced PS-ON. I started checking the voltages and found I was getting +13V and +21V, but again, only during that one instance. The 13v and 21v are no longer there when PS-ON, and I haven't been able to recreate the scenario to get them back.

So now you there are 0V for the 13V, and 21V and the 3.3V is only 3V?
Not making sense to me at this point, so you either have bad connections or something went out completely now..
if you are getting 3V then that section is still alive.

[Hazen]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

The trouble is where jt was originally when I first posted. I'm getting 6v at the 13v, 11v at 21v when forced on. I know its confusing because of getting the higher voltages, but it was temporary. I don't understand why it started working, and then why it stopped.

[vinceroger69]

Re: Emerson LF501EM4 s/n ds4 no standby light, and won't power on.

as per post 27 and checking Q653 voltage maybe check all around that area for bad/cracked as whilst you was probing for voltages etc you may of flexed the board or made a bad joint tempory good hence working for a short time.