Equivalent to STU418S from Samsung TV BN44-00265A Rev 1.1 - Page 1
Forum section: electronics / repair

author: edy
author_rank: Super Contributor
timestamp: June 27, 2025, 04:33:02 am
content: I'm currently working to fix my old Samsung TV (circa 2009) which I noticed randomly powering off. Just before the first time it powered off, I heard a crack/snap/pop and then a few minutes later the TV turned off. I could turn it on again and it worked, but I didn't want to keep pushing it. When it has happened before on my other old Samsung's it would get worse and worse, shutting down within less time, until eventually have a lot of trouble starting up (red light blinking, not coming out of stand-by mode). Then I'd open it up, notice some caps bulging and replace them, TV worked fine again.This particular TV is a first fail, I'm surprised it lasted this long to be honest. I don't want to risk running the TV and possibly causing more damage, so I figured I'd open it up and look at the power board but I found no obvious leaks or bulging caps, smell test also negative. I know caps can fail without obvious signs (although I'm still perplexed as to the origin of the snap/crack/pop sound I heard). I decided to pull most caps to test out-of-circuit. I also noticed some "browning" on the board opposite this N-Channel MOSFET (STU418S) and thought maybe it overheated and released the magic smoke on the underside, but when I removed it to test there appeared to be no damage and it seems to test ok on my LCR-T4 MTester.All the caps I've pulled show correct capacitance but ESR on the 1000 uF caps (10V and 25V) ranged from 0.15 ohm to 0.17 ohm, while the 47 uF 50V caps were ESR=0.99 ohm to 1.1 ohm (except for one 47 uF cap that was ESR 2.3 ohm). The 10 uF cap was ESR=0.83 ohm. These also look to be fairly normal. So I may be doing all this replacement soldering for absolutely nothing.With respect to the STU418S, I cannot find any data on it. I could put the original one back on the board but if I'm going to place an order and it's cheap I may as well just get a replacement. Does anyone know what equivalent modern part would be? Seems to be a "SamHop Microelectronics Corp N-Channel Logic Level Enhancement Mode Field Effect Transistor". TO-252. A search on Google gave an "AI" answer as follows, which I am not sure if I trust:"The STU418S is a N-Channel Logic Level Enhancement Mode Field Effect Transistor in a TO-252 (also known as DPAK) package. It features a 40V drain-source voltage and a 30A drain current, capable of handling 50W of power. Electronicservice.ro provides a cross-reference for the STU418S, listing D418S, STU9916L, and D9916L as equivalents or replacements." I looked on Digikey and cannot find anything related to 418S or 9916L.So I looked up MOSFET on Digikey and chose "N-channel", "MOSFET" and 40V for "Drain to Source" , clicked all options for 30A continuous current drain, and 50W power dissipation, "Surface Mount" and "Package/Case" TO-252-3, DPAK (2 Leads + Tab), SC-63 and ended up with the following:DigiKey Part Number: STD30NF04LT-ND - Tape & Reel (TR)Manufacturer: STMicroelectronics (STD30NF04LT)Description: MOSFET N-CH 40V 30A DPAK (N-Channel 40 V 30A (Tc) 50W (Tc) Surface Mount DPAK)But then it said this product is NO LONGER MANUFACTURED!3 substitutes showed up at the bottom of the page:1. AOD454A Alpha & Omega Semiconductor Inc. 785-1223-1-ND(N-Channel 40 V 20A (Tc) 2.5W (Ta), 37W (Tc) Surface Mount TO-252 (DPAK)) <-- not high enough power rating or current2.DMN4030LK3-13 Diodes Incorporated 31-DMN4030LK3-13CT-ND(N-Channel 40 V 9.4A (Ta) 2.14W (Ta) Surface Mount TO-252-3) <-- not high enough power rating or current3. DMN4040SK3-13 Diodes Incorporated 31-DMN4040SK3-13CT-ND(N-Channel 40 V 6A (Ta) 1.71W (Ta) Surface Mount TO-252-3) <--- not high enough power rating or currentAny idea how I'm supposed to get this part? None of the above "substitutes" are rated for the current/power that the original part is supposed to handle. And that is assuming my current part is bad, but I don't know how to make out my MTester result as it seems fine, it's getting a threshold turn-on voltage Vt of about 1.8V and getting some small capacitance of 2.17nF so it might just be fine, as are all my caps which seem to fall within a normal range. Am I on a wild goose chase? Perhaps the TV turned off for a completely different reason. Any help would be appreciated. I've never ordered for DigiKey before and want to pick these parts up along with a bunch of Tantalum caps to fix my Apple Macintosh suffering from the "Simasimac" issue.I found some other MOSFET's in stock but wanted some advice on whether I should increase the current/power rating as a substitute, if this is still ok. For example, this one is in stock:STMicroelectronics STD44N4LF6 (DigiKey: 497-11098-1-ND) N-Channel 40 V 44A (Tc) 50W (Tc) Surface Mount DPAKThis one is even closer in specs but part of "Marketplace" which means I have to order $50.00 or more from them to get free shipping:AM40N04-30D (DigiKey Part Number 5318-AM40N04-30D-ND)Manufacturer: Analog Power Inc. MOSFET N-CH 40V 33A TO-252 (N-Channel 40 V 33A (Ta) 50W (Ta) Surface Mount TO-252)The only one in stock in DigiKey that is close is the following:RD3G03BBGTL1 (DigiKey Part Number: 846-RD3G03BBGTL1CT-ND - Cut Tape (CT))NCH 40V 65A, TO-252, POWER MOSFET (N-Channel 40 V 35A (Tc) 50W (Tc) Surface Mount TO-252)This one says 35A at T=25C but the silicon can handle up to 65A.