Fixing a switching power supply - Page 1
Forum section: electronics / general

author: bsb0011
author_rank: Contributor
timestamp: December 01, 2013, 11:17:17 pm
content: A project I am working on requires 24VDC at around 1A.I have a Samsung HT-P38 DVD Home Theater system that has a power supply that produces +33VDC, and I have a 24V DC-DC converter. Only problem, is the power supply, while nice and modular, has a power-on circuit that does not make any sense to me. I have pulled the P-ON signal high, and Low, (Through a 10K resistor) and can not get the +33VDC to power up. However when connected back in to the rest of the system, it turns on with out any problems. I think a schematic of the power supply will get me quickly up and running.{edits - I originally listed this as a suggestion to link service manuals, along with a request for help with the HT-P38 listed above. I have since found that Dave already has a Wiki that includes links to manuals, so with that new information, I changed the Subject line and the contents of this first post as a request for help only.}

author: mariush
author_rank: Super Contributor
timestamp: December 02, 2013, 12:23:14 am
content: The one I usually check (and have account at) is elektrotanya.com - you can download some manuals for free but it's much better if you have an account... right now registrations are closed but sometimes you can answer to a series of electronics related questions to be able to signup or you can be invited by a current member.Here's what they have:http://savedonthe.net/a/samsung_ht-p38t-service-manual.rarIt's hp-p38t but maybe it's compatible with what you have.I'm also a member on badcaps.net :http://www.badcaps.net/forum/index.phpYou may get some help there if your post wakes up someone's interest... I've also set up a ftp server where several people from that forum have uploaded datasheets and service manuals. If you make an account there, you'll find the thread and the ftp address.

author: fluxcapacitor
author_rank: Frequent Contributor
timestamp: December 02, 2013, 12:31:06 am
content: You bet me to it mariush ,heres what i found .http://elektrotanya.com/?q=showresult&what=ht-p38&kategoria=&kat2=allhttp://elektrotanya.com/samsung_ht-p38t-service-manual.rar/download.htmlhttp://www.badcaps.net/forum/showthread.php?p=328584

author: bsb0011
author_rank: Contributor
timestamp: December 02, 2013, 03:42:33 am
content: Thanks for the quick replies guys!Got the first link to work for the rar file, and found the schematics file. Found 2 power supplies listed. I have the Samsung Bluetech P50 (page 12-6 in the Schematics.PDF file) . Never worked on a switching power supply before. Going nuts trying to figure this thing out. Embedded design is more my speed, my idea of a power supply is some form of 7805 or a LDO regulator. Kudo's to you guys that know more about these switching supplies!I've got power at all the supplies (on CN8 and CN4), but not the +36V outputs on CN7. I'm thinking I've got a problem related to the switching controller (KA5Q1265RF - U9) as I only have -.5VDC there. Only value I got from the data sheet is this has a MAX value of 40VDC.So anyone have any idea's on pointing me in the right direction to get this thing going? And while I'm asking for help - can someone explain to me how P-SENS and P-ON are intended to be used? I'm sure I'm missing something totally silly, but right now I am about to pull what's left of my hair out!

author: SLJ
author_rank: Frequent Contributor
timestamp: December 02, 2013, 04:50:33 am
content: Go to the EEVblog home page and check out the Wiki button at the top. Dave links resources by category already.Here's service manuals:http://www.eevblog.com/wiki/index.php?title=Service_manuals_and_repair_information

author: bsb0011
author_rank: Contributor
timestamp: December 02, 2013, 05:19:28 am
content: Cool, didn't see that - will defiantly check that out!