Sony tv power board - Page 1
Forum section: electronics / repair

author: onis_uk
author_rank: Contributor
timestamp: March 20, 2022, 06:36:52 pm
content: 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.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: March 20, 2022, 08:06:57 pm
content: 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

author: inse
author_rank: Super Contributor
timestamp: March 20, 2022, 09:21:20 pm
content: 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.

author: onis_uk
author_rank: Contributor
timestamp: March 20, 2022, 09:35:13 pm
content: Quote from: Jeff eelcr on March 20, 2022, 08:06:57 pmAh yeah sorry Jeff, its a GL72 variant board APDP-225A1 I believe to be the PN.

author: onis_uk
author_rank: Contributor
timestamp: March 20, 2022, 09:38:49 pm
content: Quote from: inse on March 20, 2022, 09:21:20 pmI 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!

author: inse
author_rank: Super Contributor
timestamp: March 21, 2022, 05:28:20 am
content: The 68uF look normal to me, do the PCB traces confirm the diodes are arranged as bridge?

author: onis_uk
author_rank: Contributor
timestamp: March 21, 2022, 08:50:03 am
content: Quote from: inse on March 21, 2022, 05:28:20 amnot 100% sure to be honest, best I can do it hold it up to the light, but I think so yes.

author: xavier60
author_rank: Super Contributor
timestamp: March 21, 2022, 11:21:59 am
content: It's normal for the secondary of a resonant converter transformer to be full wave rectified.

author: onis_uk
author_rank: Contributor
timestamp: March 21, 2022, 11:38:33 am
content: The diodes have LT7114 SB5150 on them, possibly this datasheet.https://www.wontop.com/uploadfiles/56/sort_excel/pdf/sb5150.pdfCould someone assist me in picking an equivalent on RS as I can't find the exact same part!

author: onis_uk
author_rank: Contributor
timestamp: March 21, 2022, 11:44:05 am
content: Found these but only 3A not 5A....https://uk.rs-online.com/web/p/schottky-diodes-rectifiers/1656559

author: onis_uk
author_rank: Contributor
timestamp: March 21, 2022, 11:50:58 am
content: Maybe this is closest?!https://uk.farnell.com/multicomp-pro/htg5150/schottky-rect-single-150v-5a-do/dp/2750944

author: Mike_NZ
author_rank: Newbie
timestamp: July 09, 2022, 04:39:10 am
content: I wonder if the power board has been fixed? My TV has exactly the same problem