Sharp LC-32sb28ut Power Supply has Pulsing DC Voltages

[Paul678]

Re: Sharp LC-32sb28ut Power Supply has Pulsing DC Voltages

One of the biggest load for the power supply is the inverter board. What happen if you disconnect the power to the inverter board.

Yes, I did that already. The inverter is totally disconnected,
and still the pulsing.

Big Bummer!!!

[tom66]

Re: Sharp LC-32sb28ut Power Supply has Pulsing DC Voltages

Is the PS-ON on main board pulsing too?

I cannot think of any way it is not the power supply. Perhaps it is a common fault. Or even what it does in standby, for example to save power?!

[Paul678]

Re: Sharp LC-32sb28ut Power Supply has Pulsing DC Voltages

Is the PS-ON on main board pulsing too?

I cannot think of any way it is not the power supply. Perhaps it is a common fault. Or even what it does in standby, for example to save power?!

The pin labeled "PS" on the power supply, which looks to
be the PS-ON, pulses from 3.1V to 0 V, again in time with
the blinking blue LED.

This PS-ON signal comes from the main board, right? So if it's pulsing,
perhaps that is why even the big main filter cap is pulsing as well,
because all it's doing is ramping ON and OFF.

Bummer, but perhaps I have two good power supplies I can sell....

[tom66]

Re: Sharp LC-32sb28ut Power Supply has Pulsing DC Voltages

That makes sense.

If it is anything like the cheap made in China TVs I have serviced, they will begin the power up, "crash" due to a fault, wait a few seconds then restart. Hence the pulsating DC, the entire PSU is being switched on and off. This isn't a real Sharp, so they haven't designed it well -- a good Sharp would go into lock out, blink an error code and everything would hopefully be easy to locate.

[budm]

Re: Sharp LC-32sb28ut Power Supply has Pulsing DC Voltages

Man, I feel bad not asking you to check the PS_ON signal!

[Paul678]

Re: Sharp LC-32sb28ut Power Supply has Pulsing DC Voltages

Man, I feel bad not asking you to check the PS_ON signal!

Yeah, it's amazing how you can veer off into the wrong
path completely!!

BUMMER!! Oh well, at least I can sell two good power supplies now!

And the inverter board is probably ok too, but I've had bad experiences
with Ebay buyers lately, so maybe I'll hold off......haha!

[budm]

Re: Sharp LC-32sb28ut Power Supply has Pulsing DC Voltages

Yep, I missed this one right here" Then I checked the +5V when I first plug it in (Red LED standby
mode), and it was at +4.1V" The main board is drawing too much current form the standby power supply (or the standby is not steady since it is not controlled by the PS_ON). It is not easy sometime when you do not have the board in front of you.

[Paul678]

Re: Sharp LC-32sb28ut Power Supply has Pulsing DC Voltages

Yep, I missed this one right here" Then I checked the +5V when I first plug it in (Red LED standby
mode), and it was at +4.1V" The main board is drawing too much current form the standby power supply (or the standby is not steady since it is not controlled by the PS_ON). It is not easy sometime when you do not have the board in front of you.

Sometimes it's hard even with the board in front of you......