Samsung DVD-4500 Dead / Intermitent PSU (SMPS) - Page 1
Forum section: electronics / repair

author: randoswift
author_rank: Contributor
timestamp: January 24, 2022, 01:42:24 am
content: I'm asking this here as I cannot find any help elsewhere. I have a samsung DVD-4800 that i took apart to remove a stuck disk and clean the lens (has been in use for quite a while). No power when I put it back together. I took it apart with gloves and no esd bracelet, which im guessing caused esd damage to the unshielded psu (I noticed esd buildup randomly when i had the gloves on). I'm getting 5.65v on the 12v output line on the psu, and 1.99v on the 5v output line on the psu. Checked most of the transistors off the board and they measure just fine, so I dont know what to do. Ive spent 15 or 20 hours so far on ithttps://drive.google.com/file/d/1nuCyl-xKemaK0QMi8WsMbmQSUagQqfAz/view?usp=sharingHere's the schematic to the PSU (page 55), and I have attached a picture of the board.

author: randoswift
author_rank: Contributor
timestamp: January 24, 2022, 06:46:57 pm
content: I forgot to mention the DVD VCR combo has been in use for 15+ years. When I took it down and took it apart it could have been the final straw for a capacitor. Many of the caps have a low voltage rating, and some of the ones I tested read -15-20% original value. I'm not sure if it would cause the low output power. Any help for how to troubleshoot smps psus would also be helpful.

author: commongrounder
author_rank: Frequent Contributor
timestamp: January 24, 2022, 07:46:02 pm
content: It is very likely the electrolytic capacitors. That is a very common problem for units of that age. Your voltage readings fit the symptoms. If it were me, I’d replace all of the caps on the power supply board. It’s inexpensive to do, and I’ll bet your supply will function normally again. ESD damage is not impossible, but unlikely.

author: randoswift
author_rank: Contributor
timestamp: January 24, 2022, 08:27:45 pm
content: Thanks heaps for the reply! I have a box of caps coming today I ordered for it. I'll replace whatever ones I can, starting with the power side on the schematic (transformer output is low)

author: randoswift
author_rank: Contributor
timestamp: January 25, 2022, 12:51:56 am
content: Just got done installing the caps, now i see a light on one of the inputs, but nothing on display. 0v output, transistor not getting warm so its not getting powered. I suspect its my horrible solder joints (as seen in the picture below

author: TheMG
author_rank: Frequent Contributor
timestamp: January 25, 2022, 12:54:32 am
content: Likely one or more of the smaller caps on the primary side, looks like things get a little toasty near those two transistors and heat makes capacitors fail sooner.Capacitors in the switching control circuitry going bad might cause the power supply to fail to start properly from a powered down condition so it keeps trying to start repeatedly but isn't able to, result is what appears as low output voltage as the PSU is actually rapidly starting/stopping constantly. Quite a common failure mode.An ESR meter would tell the whole story. Sometimes a capacitor will seem not too bad, even be within tolerance as far as the capacitance goes, but have ESR through the roof. ESR is the enemy in SMPS.

author: randoswift
author_rank: Contributor
timestamp: January 25, 2022, 01:18:13 am
content: It now flashes "AUTO" on the screen for a few seconds then shuts off :/ weird. I need to leave it unplugged for a bit then plug it back in before it does it again. I think the culprit might be a 250v 4.7uf cap i didnt have a replacement for, as it read 4.0uf.It doesn't turn on at all with the dvd drive plugged in eitherP.S. I replaced all 3 of those caps by those transistors

author: abdulbadii
author_rank: Frequent Contributor
timestamp: January 25, 2022, 10:14:46 am
content: might've not replaced cap with the same rated V, F of low ESR quality one. do so only

author: randoswift
author_rank: Contributor
timestamp: February 07, 2022, 04:46:06 am
content: Recapped everything I could, even went out and bought proper nonpolar capacitors to put in, all the output is slightly low still, im not sure why. However, it is outputting voltage on some rails it didnt previouslystarts off as 27.5 when first plugged in> goes down to 26.x, each .1v is slower than the last. stops flashing auto at at 27v. Heres the reading for all the pin outputs (im not sure what goes to what on the schematic)1-26.32-11.33-3.94-3.95-0.026-8.07-0.08-11.29-4.010-3.411-0.0And here's the readings after its unplugged-1-262-0.13-0.04-0.05-0.26-2.07-08-09-010-011-0

author: abdulbadii
author_rank: Frequent Contributor
timestamp: February 07, 2022, 04:53:05 am
content: Quote from: randoswift on January 24, 2022, 06:46:57 pmIt is, you're correct replace them all with that or greater/better than that rating, encouraged to test with a LCR/ESR meter on-board

author: randoswift
author_rank: Contributor
timestamp: February 07, 2022, 04:59:09 am
content: I recapped the questionable ones already, and i got a new meter which seems to read more accurately (although maximum range is 200uf) the most questionable cap (read 4.0uf on my old meter) now reads 4.7uf on my new one, which is what it should be.I don't feel like spending the money to recap everything

author: SeanB
author_rank: Super Contributor
timestamp: February 07, 2022, 05:16:12 am
content: I would say C1sr12 is the one most likely to be faulty.

author: randoswift
author_rank: Contributor
timestamp: February 07, 2022, 05:22:40 am
content: Quote from: SeanB on February 07, 2022, 05:16:12 amreplaced it yesterday, same value (but higher voltage) nonpolar cap.....I took the effort to buy the damn non polar ones!!(Not sure why one lead is longer than the other, theyre non polar..)

author: fzabkar
author_rank: Super Contributor
timestamp: February 07, 2022, 06:11:23 am
content: C1SF02 is my bet. That's the cap on the Vcc pin #6 of IC1SF1. These caps often cause hiccuping faults on these topologies.

author: randoswift
author_rank: Contributor
timestamp: February 08, 2022, 03:08:33 am
content: More recapping done, nothing seems to have changed. I noticed the 3.3v rail was just fine but all the others are bad. I attached a picture where i marked all the caps i replaced in redThe c1sf02 cap as mentioned above seems very suspect, but its just not on my psu. No similar value capacitor is either.

author: m k
author_rank: Super Contributor
timestamp: February 08, 2022, 02:43:15 pm
content: For the PCB in picture your ESD didn't do a thing.How you measure those voltages, against pin 12?Manual page 46 says that you have GND also at pins 1 and 8.Your measuring indicates that 11 is 12, 7 is 8 and 1 is missing.That lone 26V it also indicating that one power connector is misplaced.

author: fzabkar
author_rank: Super Contributor
timestamp: February 08, 2022, 09:00:23 pm
content: There are three different model numbers in this thread.This is the service manual for the DVD-V4800:https://elektrotanya.com/samsung_dvd-v4800.pdf/download.htmlDoes the PSU on page 55 match the subject player?

author: randoswift
author_rank: Contributor
timestamp: February 09, 2022, 01:48:34 am
content: Quote from: fzabkar on February 08, 2022, 09:00:23 pmThanks heaps, this is the correct one it appears. I could only find the v4300 which was pretty similar. The v4500 is model of my psu board, and the v4800 is the model of the player itself.