Brushless laptop fan motor how to repair PCB controller - Page 1
Forum section: electronics / repair

author: axero
author_rank: Regular Contributor
timestamp: July 11, 2016, 12:06:11 pm
content: I have a broken fan for a Fujitsu-Siemens Amilo Xi2550 (part no 28G200750). Initially I wanted to replace the whole fan with housing but a replacement costs $25-30 which is way too much and I'm not sure that it is the fan that is broken in first place. I'm only willing to pay up to $12 to figure out whether that is the case.I tried hooking up the fan to an ATX power supply on the 5V rail. When doing that, it spun up initially and then died. I felt a burning smell from the spindle of the fan afterwards so I figure that there must be something broken in the circuitry of the fan. The fan blades can move freely without any obstruction, btw just to be clear about that.Is there a way to replace the motor/PCB? It is glued somehow to the housing and I'm not sure how to get it loose. I suspect that it is some epoxy that keeps it together. I also don't know how to find appropriate spare parts. Not sure hwat search criteria to use for such replacement parts. Perhaps the surface mounted components can be replaced, if they are identifiable and not ASICs.Edit:I have now managed to get it loose. Thankfully, it is not epoxy. It is some tar like substance from the looks of it.The first circuit with 4 pins only has the denomination ".SE", or rather "·SE". I'm not sure what that means. The second circuit has three rows of characters. It looks like that the first row says "H67", second row says "9 9", "9.9", "909" or "90.9". I believe that the circle is just a residue from the forging process of the encapsulation though. The last row says VM. So I'm assuming that it either says H6799VM, H679.9VM, H67 99 VM or H67 9.9 VM. I get no clues from Google.The picture of the whole PCB has "E250336" on it. Also here, no clues from Google.

author: axero
author_rank: Regular Contributor
timestamp: July 13, 2016, 11:19:56 am
content: I have looked more carefully into the circuitry of the PCB. The main circuit that runs the fan is the H67 circuit i.e. IC2. Lets assume that schematic of IC2 as illustrated in first picture. Pin 6 +5V and pin 8 is -5V/GND, between these pins is also a capacitor. Pin 5 is connected to the counter (yellow cable). Pin 1 is connected to the coils. Pins 2-4 are connected to IC1.Pin 7 doesn't appear to be connected to anything(see Edit below).IC1 is apparently a Hall sensor circuit for the RPM counter I imagine.The coil circuit has three pins,both areconnected to pin 1 of IC2,this doesn't seem right perhaps a short circuit somewhere?The third pin of this circuit is unconnected.In the other enclosed picture is shown a piece of copper conductor being torn off of the PCB. I think this is the major culprit. It connects pin 5 of IC2 to +5V. That and fixing the short circuit will most likely repair the motor.Edit: After having removed the coil circuit, the short circuit is within this circuit. I don't know whether this is a true short circuit or normal condition inherent in coil circuits. I imagine that the inductance would create a delay before the multimeter detects it as a short circuit, but then otoh the inductance may be very low...So pin 1 of IC2 is connected to one pin of the coil circuit, and pin 7 is connected to another pin of the coil circuit. The third pin of the coil circuit is unconnected and it is not "shorted" against the other two pins of the circuit.The third image shows the coil circuit I'm talking about here.

author: amyk
author_rank: Super Contributor
timestamp: July 13, 2016, 11:25:46 am
content: First result for "H67 brushless fan controller":http://rohmfs.rohm.com/en/products/databook/datasheet/ic/motor/fan/bh6799fvm-e.pdf

author: axero
author_rank: Regular Contributor
timestamp: July 13, 2016, 11:53:34 am
content: Thank you, I couldn't find it myself!Some updates here; bypassing/bridging the severed connection did not help.Feeding 5 volts directly to the coil circuit / DC motor makes it twitch so I assume that it is working normally. So I suspect that I have a fried fan controller to boot. I tried resoldering the circuit but it didn't help.

author: axero
author_rank: Regular Contributor
timestamp: July 13, 2016, 09:44:47 pm
content: Does anyone happen to know where and how to buy such chips? It doesn't seem to be available on eBay or Ali-express. The "BH6799FVM 5V Single-phase Full wave Fan motor driver" that is.

author: edavid
author_rank: Super Contributor
timestamp: July 13, 2016, 10:22:52 pm
content: Quote from: axero on July 13, 2016, 09:44:47 pmDigikey...http://www.findchips.com/search/bh6799fvmBut, it's likely that the chip blew up because of the shorted coil.

author: axero
author_rank: Regular Contributor
timestamp: July 13, 2016, 11:11:12 pm
content: I suspect that I blew the circuit when I accidentally reversed the voltage. I didn't figure it would matter so much since it's "only 5V", but when reading the datasheet it appears that the circuit is sensitive to wrong polarity. It says on page 4 on the datasheet:"Take a measure against Vcc voltage rise due to reverse connection of power supply and back electromotive force."and the PCB has no protection circuitry against wrong polarity.But maybe the coil has shorted. It had no problems cranking the fan blades when I fed 5V directly to the coil though so it appears to be normal.There is MathJax support, yay!\({{\left( \sum\limits_{n=1}^{\infty }{\left| {{x}_{n}}+{{y}_{n}} \right|} \right)}^{{1}/{p}\;}}\le {{\left( \sum\limits_{n=1}^{\infty }{{{\left| {{x}_{n}} \right|}^{p}}} \right)}^{{1}/{p}\;}}+{{\left( \sum\limits_{n=1}^{\infty }{{{\left| {{y}_{n}} \right|}^{p}}} \right)}^{{1}/{p}\;}}\)