Sony tv power board

[onis_uk]

A friend of mine said his Tv just went off and won't come back on and asked me to have a look as I have some small modicum of electronics experience.

The main power board has 2 failed diodes in the bridge rectifier, just wondering what could cause this kind of damage? Would just swapping them out be likely to fix it?!

I was drawn to the top left diode as there is clear heat damage on the legs but the lower left is also open circuit.

[Jeff eelcr]

I would replace all 4 and check electrolytics after them.  it is a good idea to post model number, chassis and board numbers on some types of equipment if not schematics to make it easier to tell whats going on.
Jeff

[inse]

Once again I am puzzeled by Sony engineering.
The diodes are in an area marked as "secondary", why would you have a bridge rectifier here?
The mains input is clearly on the left lower corner, but I can't see the bridge rectifier there (is it hidden under a heat sink?)
It is difficult to apply additional heat sinking to this diode package, I would replace them and hope for the best.
I would replace the electrolytics only if bulged, leaky or otherwise suspicious.
They apparently are quality parts, if you decide to replace them, select proper parts, not random stuff.

[onis_uk]

I would replace all 4 and check electrolytics after them.  it is a good idea to post model number, chassis and board numbers on some types of equipment if not schematics to make it easier to tell whats going on.
Jeff

Ah yeah sorry Jeff, its a GL72 variant board APDP-225A1 I believe to be the PN.

[onis_uk]

Once again I am puzzeled by Sony engineering.
The diodes are in an area marked as "secondary", why would you have a bridge rectifier here?
The mains input is clearly on the left lower corner, but I can't see the bridge rectifier there (is it hidden under a heat sink?)
It is difficult to apply additional heat sinking to this diode package, I would replace them and hope for the best.
I would replace the electrolytics only if bulged, leaky or otherwise suspicious.
They apparently are quality parts, if you decide to replace them, select proper parts, not random stuff.

I must admit this confused me too, there is rectification in DC side post transformer?!

All the caps on the board look ok, maybe the 2 brown 68μf caps look a little puffed up so might as well swap them out too!

[inse]

The 68uF look normal to me, do the PCB traces confirm the diodes are arranged as bridge?

[onis_uk]

The 68uF look normal to me, do the PCB traces confirm the diodes are arranged as bridge?

not 100% sure to be honest, best I can do it hold it up to the light, but I think so yes.

[xavier60]

It's normal for the secondary of a resonant converter transformer to be full wave rectified.

[onis_uk]

The diodes have LT7114 SB5150 on them, possibly this datasheet.

https://www.wontop.com/uploadfiles/56/sort_excel/pdf/sb5150.pdf

Could someone assist me in picking an equivalent on RS as I can't find the exact same part!

[onis_uk]

Found these but only 3A not 5A....

https://uk.rs-online.com/web/p/schottky-diodes-rectifiers/1656559

[onis_uk]

Maybe this is closest?!

https://uk.farnell.com/multicomp-pro/htg5150/schottky-rect-single-150v-5a-do/dp/2750944

[Mike_NZ]

I wonder if the power board has been fixed?  My TV has exactly the same problem