Author Topic: Bladeless fan repair. Help needed.  (Read 2457 times)

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Offline Damian

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Bladeless fan repair. Help needed.
« on: August 06, 2017, 12:35:46 pm »
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 points :( Main voltage is rectified and smooth just fine. Regulated 5V in at the ground level.
3. Just replace the components. I've replaced LNK304PN (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?
« Last Edit: August 06, 2017, 12:56:21 pm by Damian »
 

Offline Damian

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Re: Bladeless fan repair. Help needed.
« Reply #1 on: August 06, 2017, 12:57:16 pm »
Detailed shots of chips and the controller.
 

Offline Cyberdragon

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Re: Bladeless fan repair. Help needed.
« Reply #2 on: August 06, 2017, 01:40:35 pm »
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.
*BZZZZZZAAAAAP*
Voltamort strikes again!
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Offline Damian

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Re: Bladeless fan repair. Help needed.
« Reply #3 on: August 06, 2017, 03:08:15 pm »
Quote
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.
I'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.

Quote
By no voltage do you mean no output or no input?
Both. 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.

Quote
P.S. You can check an inductor as it should read short or low ohms if working.
The inductor reads 1.6 ohms (in circuit).

Quote
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.
AFAIK the switching transistors are integrated in the LNK304PN.

Quote
Also check for shorts across the pins.
All 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.
 

Offline Nusa

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Re: Bladeless fan repair. Help needed.
« Reply #4 on: August 06, 2017, 03:21:10 pm »
What's going on at R38 at the edge of the last picture? There's solder all over the place.
 

Offline amyk

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Re: Bladeless fan repair. Help needed.
« Reply #5 on: August 06, 2017, 03:36:15 pm »
The FCM8201 appears to have a large crack in it.
 

Offline Damian

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Re: Bladeless fan repair. Help needed.
« Reply #6 on: August 06, 2017, 04:13:46 pm »
What's going on at R38 at the edge of the last picture? There's solder all over the place.
The FCM8201 appears to have a large crack in it.
Both cases - some flux and contrast lighting. After cleaning it out, everything looks perfectly normal.
 

Offline Damian

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Re: Bladeless fan repair. Help needed.
« Reply #7 on: August 06, 2017, 04:48:13 pm »
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... :/
 


Offline Damian

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Re: Bladeless fan repair. Help needed.
« Reply #9 on: August 25, 2017, 11:14:25 am »
StackExchange EE's user dim helped me to identify the unnamed chip as the FSB50250S. It seems that this chip is discontinued...

But the FSB50450 seems to be very similar. Do you think it can be used without any modifications of the circuit?
 


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