RCA L32HD31 - Power led indicator but no display

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

Sounds good ill run it like that and let them inform me if anything happens.

I'm curious what did that fuse control? I'm having a hard time understanding the circuit. It looks like it went to the feedback of the ic, but the primary winding has two different windings. Are they both being run separately?

Here's the link to the schematic
https://www.badcaps.net/forum/attach...6&d=1375893777

[budm]

Re: RCA L32HD31 - Power led indicator but no display

The fuse is just the protection for the power supply for the PFC and the SMPS ICs. Looking at the BOARD layout, it looks like it used for powering the PFC controller IC and the SMPS IC for the 12V/24V through switched Transistor Q11 which is turned on (by OPTO IC6-B which is turned on by transistor QS3) by PS-ON signal to the Base of QS3 (Q12 is setup as 12V linear regulator to supply VCC to the 2V/24V SMPS IC).
The same AUX winding of the standby transformer is also fed to the other diode D82 for running the STBY IC once the circuit started up.
If you look at most of the power supply for TV, the power supply for running the PFC and other SMPS section is generated by the AUX winding of the STBY Transformer through a switched device..

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

Ah ok. Thing I'm stuck on is the AUX winding. How is it producing a separate signal from the primary winding? I'm thinking in simple terms how a transformer works. Primary induces voltage in secondary

[budm]

Re: RCA L32HD31 - Power led indicator but no display

The STBY transformer has one primary winding where the drive is applied, and it has two secondary windings, one for making 5V, and another one for making the VCC for running the SMPS IC.
Transformer can have more than two windings (primary, secondary) depends on how many outputs you want from the transformer,there are many form factor for the transformer windings.
http://www.edn.com/electronics-blogs...power-supplies
http://jandkaudiodesign.blogspot.com...ansformer.html

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

Ok but my confusion comes from seeing it on the schematic, it's showing the AUX on the primary side and in the circuit it's not on the secondary side of the board along with the 5vsb

[budm]

Re: RCA L32HD31 - Power led indicator but no display

Ok but my confusion comes from seeing it on the schematic, it's showing the AUX on the primary side and in the circuit it's not on the secondary side of the board along with the 5vsb

The location of the winding in the schematic symbol can be made any way you want, in this case it is on the left to make it easier to see what this winding is being used for.

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

Ok but even on the board it's how it looks in the schematic. So they can make a secondary side on the same side as primary?

[budm]

Re: RCA L32HD31 - Power led indicator but no display

That AUX winding is being used in the dc primary side of the circuit to supply the voltage to run the SMPS ICs in the primary side, that is all so the two pins of the winding is located in the hot side of the circuit this will allow it to pass creepage/clearance for safety compliance testing..

[caphair]

Re: RCA L32HD31 - Power led indicator but no display

I see. So are there two separate windings on the primary sharing the same core but only one is being pulsed?

[budm]

Re: RCA L32HD31 - Power led indicator but no display

There are three windings, one of them being driven (primary winding is the one that is driven), the other two are the two output windings for two power supplies. They all sharing the same core. You can also use the transformer in reverse and use other windings as the drive winding. It is just a transformer and how you want to use them and what safety requirement you need. Do not get confuse about the primary side of the circuit (dc primary circuit after the bridge rectifier that is fed by the primary AC line power source) and the primary winding of the transformer. primary winding can be driven by the the cold side of the circuit, I.E. Inverter transformer.