LCD TV Power Supply Repair - Page 1
Forum section: electronics / repair

author: elliot42
author_rank: Contributor
timestamp: August 24, 2015, 03:18:11 am
content: So, my TV went out with a bang on the weekend so I opened it up and found a rectifier diode has gone, taking a ceramic capacitor with it (probably the source of the bang), and blowing the fuse. I've ordered a replacement fuse and capacitor and planned to replace the rectifier diodes (all 4 in the bridge) with 1N5408.The diodes in there I think are actually fast recovery diodes. Will it be OK to use the standard recovery diodes I already have on hand in the primary side of the SMPS? Or am I going to run into problems?The text on the diodes is "R208 SIYU"; I think it's this guy:http://www.dachang.com.cn/pdf/HER201.pdf(HER208). Possible replacements I could get areFR307 from Jaycar, orUF2008 from E14 (HER208G are a bit pricey).EDIT: FR307 actually look like similar response time to 1N5408

author: rickselectricalprojects
author_rank: Regular Contributor
timestamp: August 24, 2015, 03:34:04 am
content: no, keep all the ruined parts the same, don't change any partsi hope this helps

author: elliot42
author_rank: Contributor
timestamp: August 24, 2015, 03:37:43 am
content: OK, so I shouldn't try the 5408. But would UF2008 be fine to use instead? The specs seem identical to HER208.

author: rickselectricalprojects
author_rank: Regular Contributor
timestamp: August 24, 2015, 04:08:29 am
content: Quote from: elliot42 on August 24, 2015, 03:37:43 ami would look at the datasheets very carefully first but from the specs i looked at they seem very similar. i would still probably go with the HER208 just to be safe.i hope this helps

author: elliot42
author_rank: Contributor
timestamp: August 24, 2015, 04:40:44 am
content: Thanks, it does help. I'm still inclined to order the UF2008 instead though, it's a difference of $11 between it and HER208. This TV is a cheapie and only has to work for 5 more monthsThe only differences I can see are a higher typical thermal resistance for the HER208 (60C/W vs. 25C/W), and a slightly higher forward voltage at very low current for the UF2008 (both are 1.7V at 2A). And a difference in how the junction is created (diffused vs. glass passivated).

author: joao2004
author_rank: Contributor
timestamp: August 25, 2015, 12:55:49 pm
content: Hi,the 1N5408 will be fine...

author: rickselectricalprojects
author_rank: Regular Contributor
timestamp: August 26, 2015, 12:13:29 am
content: Quote from: elliot42 on August 24, 2015, 04:40:44 ami would still go with the HER208 as it was the original and it has a better thermal resistance.

author: elliot42
author_rank: Contributor
timestamp: August 26, 2015, 01:17:25 am
content: Isn't a lower thermal resistance better as heat will be dissipated more readily? Lower resistance == more flow?Anyway, I had some trouble ordering from E14, so instead ordered UF5408 from RS, which has the same specs as HER208 but higher current capacity and lower thermal resistance. The parts arrived this morning so I'll try the repair tonight. Hopefully it's just the obviously destroyed components that need replacing and nothing in the more complex switching circuit areas are damaged.

author: rickselectricalprojects
author_rank: Regular Contributor
timestamp: August 26, 2015, 02:31:34 am
content: Quote from: elliot42 on August 26, 2015, 01:17:25 amyes, my bad, a lower thermal resistance is better so you can use the UF2008