Benq W1090 - replaced power mosfets but... why won't it turn on? - Page 1
Forum section: electronics / repair

author: bombarie
author_rank: Newbie
timestamp: March 25, 2022, 10:00:31 am
content: My Benq W1090 projector broke. I've discovered and fixed (I think) one hardware fault but the next behavior has me shrugging.I'd had this projector (hanging upside-down) for about 3,5 years when the green status led stated blinking red upon turning it on. The machine would start up and shutdown again a few seconds later. I lazily 'fixed' this a few times by power cycling the projector and turning it on again... which worked a few times until it didn't anymore. Ultimately upon powering it up the fuses blew in my house! I thought the lamp must be broken, ordered a new one aaaand no, again the fuse blew.On Youtube I found the brilliant channel FixitFrank and the video below on ballast diagnosis and repair was bang on. 2 out of 4 power mosfets on the ballast board were broken -> short circuit between the legs. The mosfets on this board areSTP30NF20mosfets. I couldn't find these online and ordered someSIHP080N60E-GE3instead. I'm relatively certain that these should be suitable replacements, could anyone here take a look and let me know if I made a mistake here?I replaced the 2 broken mosfets, reassembled the projector and when I plugged it into the mains... nothing. Absolutely nothing. No blown fuse, that's nice. But also no status leds. I don't quite know what to make of this now.. Could the short circuit in the projector have irreversibly damaged the mainboard? Everything looks fine and clean. I haven't seen any blown caps or burnt IC's. I quite thorougly sniff-tested all boards for burnt smells but also - surprisingly to me - nothing. I really don't know what to try next, hoping for some tips from you. Thank you!

author: bombarie
author_rank: Newbie
timestamp: April 03, 2022, 05:35:42 pm
content: *bump*. Nobody? I'm still scratching my head, would love some help here.

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: April 04, 2022, 10:28:09 am
content: I am not looking at specs on either one.Things you need to know.When replacing, Rds is important never use higher, voltage/current can be higher.Always replace all outputs (matched) is best, mixed parts will cause problems.Unit could have other problems.Jeff

author: wraper
author_rank: Unknown
timestamp: April 04, 2022, 10:31:24 am
content: Why? Because when MOSFET blows, often some other not so obvious parts fail too. For example MOSFET gate circuity, including PWM controller. Not to say you need to measure voltages when connected to mains voltage to know what is happening in the circuit and if there is a rectified mains voltage on those MOSFETs to begin with.

author: bombarie
author_rank: Newbie
timestamp: April 05, 2022, 10:29:17 am
content: Quote from: Jeff eelcr on April 04, 2022, 10:28:09 amThanks for your answer. The original mosfet has Rds(on) of .0075Ω, the replacement mosfet has Rds(on) of .0070Ω with higher specs for voltage/current so if I understand you correctly that should be ok. I understand that it's better to have all the same components.I've since found that the main fuse at the primary power board has blown so gotta replace that one first.

author: bombarie
author_rank: Newbie
timestamp: April 06, 2022, 12:48:04 pm
content: The projector not turning on was the result of a blown fuse inside the projector. This must have perished together with my house's fuse tripping.From what I can see/measure it's a 5x20mm fuse and it reads 12AH250v. The fuse is ceramic and its leads are inherently part of its assembly.My question: are there particular design/electrical considerations which call for a single assembly fuse or could I solder in a fuse holder and place a replacement 12AH250V fuse?

author: Jeff eelcr
author_rank: Frequent Contributor
timestamp: April 06, 2022, 08:46:27 pm
content: No reason why you can not most likley it was chosen as it is one part rather than 3 parts.Jeff