Benq MP720p (9J.J2F77.BSE) - Page 1
Forum section: electronics / repair

author: ghorizo
author_rank: Contributor
timestamp: February 02, 2019, 05:49:53 pm
content: Hello, I have this projector MP720p (9J.J2F77.BSE) which won't power on and no sign whatsoever.I dismantled it to find a burnt capacitor, already a bit confused on the specs.My main question: is this feaseable to repair? Also my old iron broke. Would a cheap station be enough to solder on the pcb or I would need a hot air iron as I've been told by a friend?I know a bit of electronics and such but never worked with microelectronics.Btw just joined, pleased to find this nice forum!

author: highdesert56
author_rank: Contributor
timestamp: February 03, 2019, 05:54:25 am
content: Check this guy out:https://youtu.be/xqkXvmvuswsThe whole vid is interesting but at 33:30 he solders a surface mount cap about that size.

author: Armadillo
author_rank: Super Contributor
timestamp: February 03, 2019, 06:44:00 am
content: Hi;You certainly can desolder the cap with a just a soldering iron and a solder wick if you want to.The cap is the same as the rest of the other tantalum caps on the board - 100uf, 16volt 20% tantalum capacitor.But before you continue;If all the fuses are verified to be OK then,If the cap is shorted, then there will be no sign of life as you said.otherwise, if the cap is open, it should show some sign of life.So, with that said, use a multimeter to measure ohms across it to see if its shorted or not.If it is not shorted, then I am afraid this repair is not worth your time.If it is shorted, maybe, just maybe a simple replacement of the tantalum may be worth the risk and your time.HOpe it helps.

author: ghorizo
author_rank: Contributor
timestamp: February 03, 2019, 09:39:43 am
content: Hey thanks for the reply! The cap is indeed shorted out, as also the one right next to it!The mains fuse is still intact and no other signs of damage elsewhere.This is the replacement I'm thinking ofhttps://www.mouser.fr/ProductDetail/581-F911C107MNCandhttps://www.mouser.fr/ProductDetail/647-F931E475MBAMy friend will probably lend me his soldering station, but again he insists that pcb are not meant to be worked on with irons but with air guns as the iron can burn through the multiple layers of conductors inside the board.Should I risk it? The 20e shipping to Europe makes it more than just spare change for a chance to repair. :\Thanks highdesert, will take the time to watch more carefully later when I got more time!

author: Armadillo
author_rank: Super Contributor
timestamp: February 03, 2019, 09:44:51 am
content: Well Good,It should be 16V not 6V but don't buy yet;Take the shorted capacitors out of the circuit then power up your projector to see signs of life.Then you decide.

author: Armadillo
author_rank: Super Contributor
timestamp: February 03, 2019, 09:52:29 am
content: Your friend is not wrong, to use proper tools but not right as well.The cap is quite BIG, in my opinion.Show him how others do it;To desolder, you add leaded solder, yes you heard me right. Just like soldering you add flux and leaded solder until the 2 ends pools up large enough for your soldering irons to heat both ends at the same time, then you push with the soldering tip or you lightly pry with something.To the expert out there, they have done many donkey times.Practice with other spare boards to gain your confident. Watch the Youtube as to how others done it.The you wick the solder away so that the pad is flat, ready for new caps

author: Armadillo
author_rank: Super Contributor
timestamp: February 03, 2019, 09:57:28 am
content: If I were you in your situation, I will salvage the caps from some spare spoilt mobo or tv circuit boards and save the money on unnecessary postage charges.No need to be precisely 100uf, close enough will do.

author: ghorizo
author_rank: Contributor
timestamp: February 03, 2019, 10:11:10 am
content: That's very good advice! Thank you very much!Will go to the dump tomorrow to see what I can salvage.

author: Armadillo
author_rank: Super Contributor
timestamp: February 03, 2019, 10:15:24 am
content: For your info, there is one expert out there who desolder smd cap without even applying heat.I won't advice you doing that but some of you out there know who I am talking about.Good don't rush into things, practice makes you a better and more skillful than others.

author: ghorizo
author_rank: Contributor
timestamp: April 04, 2019, 03:22:14 pm
content: Soo I finally managed to get back at this and replaced the cap with equivalent. Now it turns on but output is pic related.Is this repair worth pursuing?By the way the image is static, menu keys don't do anything. Just the power key seems to be working.

author: ghorizo
author_rank: Contributor
timestamp: April 08, 2019, 04:19:42 pm
content: nobody that can give a little advice here?