Bladeless fan repair. Help needed. - Page 1
Forum section: electronics / repair

author: Damian
author_rank: Newbie
timestamp: August 06, 2017, 12:35:46 pm
content: Hi all! I've been watching Dave's videos for a while, but this is my first post.I need your help in a repair of my bladeless fan (some polish clone of AM06 10 inch Desk Fan). Last season it was switching off itself several times. But after switching it on again, everything worked fine. Last time it switched off, and afer few seconds there was a rather quiet and soft pop sound. Now I'm stuck trying to repair it.Things I've done so far:1.Visual inspection. No apparent damage, no magic smoke smell.2.Thou shalt check voltages.No test pointsMain voltage is rectified and smooth just fine. Regulated 5V in at the ground level.3.Just replace the components.I've replacedLNK304PN(Energy-Efficient Off-Line Switcher IC),78M05(Positive voltage regulator), 3 electrolytic caps.No luck. I didn't replace the inductor - i have no clue what value it is/supposed to be.There is no voltage between leads of the 78M05 regulator. Do you have any suggestions what should I check next?

author: Damian
author_rank: Newbie
timestamp: August 06, 2017, 12:57:16 pm
content: Detailed shots of chips and the controller.

author: Cyberdragon
author_rank: Super Contributor
timestamp: August 06, 2017, 01:40:35 pm
content: Don't go replacing components until you have an idea of where the fault could be. It could just destroy new parts if there is some other severe problem. By no voltage do you mean no output or no input? If there is no input check everything in the path from the rectifier to the regulator, there may be some transistors switching the input voltage that blew. Also check for shorts across the pins. But how is it getting 5v if there is no voltage on the 7805, which is the 5v regulator?P.S. You can check an inductor as it should read short or low ohms if working.

author: Damian
author_rank: Newbie
timestamp: August 06, 2017, 03:08:15 pm
content: QuoteI'm aware of this. The total cost was far below 1$, so I thought I'll give it a shot and save some time. Sadly, no luck.QuoteBoth. The input voltage seems to be pulsing (auto-range indicator on my meter is pulsing ~ once pew two seconds). The voltage on the BP pin of LNK304PN is 5.8V, but the FB pin stays low (on DC range). There is some waveform of frequency of several kHz (multimeter readout), but I cannot tell more without a scope.Between D and S pins of LNK304PN I have 320V DC. Between BP and S: 5.8V. Between FB and S: ~0.06V, changing.QuoteThe inductor reads 1.6 ohms (in circuit).QuoteAFAIK the switching transistors are integrated in the LNK304PN.QuoteAll S pins shorted, but they should be. But there is 8.4 ohms between common and input of the voltage regulator, measured on the PCB, with the regulator removed. It's rather strange, isn't it?I do not fully understand the operation of LNK304PN. Should I expect any constant voltage on the FB pin? I guess not - I'm trying to reverse the power section, so far it seems very alike to the application note from page 4/5.

author: Nusa
author_rank: Super Contributor
timestamp: August 06, 2017, 03:21:10 pm
content: What's going on at R38 at the edge of the last picture? There's solder all over the place.

author: amyk
author_rank: Super Contributor
timestamp: August 06, 2017, 03:36:15 pm
content: The FCM8201 appears to have a large crack in it.

author: Damian
author_rank: Newbie
timestamp: August 06, 2017, 04:13:46 pm
content: Quote from: Nusa on August 06, 2017, 03:21:10 pmQuote from: amyk on August 06, 2017, 03:36:15 pmBoth cases - some flux and contrast lighting. After cleaning it out, everything looks perfectly normal.

author: Damian
author_rank: Newbie
timestamp: August 06, 2017, 04:48:13 pm
content: After reversing, I removed some components (D10, C24, 5V regulator). Still, there was ~8 ohms resistance between IN and ground of the 5V regulator. I traced (continuity) the paths from IN, OUT and ground of the 5V regulator. They all meet in the big IC, that seems to be some kind of regulator for the DC motor. They may be shorted (8ohm) internally in that chip. I have no other unit to compare. I have no schematics either.I guess I have to discard this board and come with my own DC brushless motor controller... :/

author: carl_lab
author_rank: Frequent Contributor
timestamp: August 06, 2017, 05:43:47 pm
content: https://www.fairchildsemi.com/application-notes/AN/AN-8201.pdfhttps://media.digikey.com/pdf/Data%20Sheets/Fairchild%20PDFs/FCM8201_Rev_1.0.4.pdf

author: Damian
author_rank: Newbie
timestamp: August 25, 2017, 11:14:25 am
content: StackExchange EE's user dimhelped meto identify the unnamed chip as the FSB50250S. It seems that this chip is discontinued...But theFSB50450seems to be very similar. Do you think it can be used without any modifications of the circuit?