no fan spin issue and solution

[dreamcat4]

ok i have now fixed my station. very happy about this 

To remind what the issue was: no fan spin

The very thin microscopic tin whiskers I noticed had bridged across the motor terminals. Normally you would expect the switching pulsed currents of the 3 phase BLDC motor to be strong enough to just burn them away like a fuse. And then keep on running.

However right next to the motor contacts are the hall sensors, and those connect back to the 3 sensor input pins of the BLDC driver IC chip. To get the timings input.

And according to the block diagram (in the data sheet). It looks like the middle IC, this BLDC driver chip includes some more delicate sub circuit inside of it. Like the input timing logic for example. So that seems more likely weak point than the mosfet. Which have their base protected away on other input side? Not that I understand enough about them. But if not the driver IC, then it could be one of the mosfet. Being the other most likely candidate.

Other deductions were to eliminate everything else:

Checked all the rest of the fan control circuitry. And really there was no problem with the PWM input control signal reaching this IC chip. It was just being clamped to +0.7v (transistor junction). So the current was transmitting through and getting to the controller chip all ok fine. And nothing else is actually on this part of the PCB, except also for the 3 dual mosfet chip. To output and power the motor.

However it turned out it was much easier to first get a genuine (quality) new motor driver IC from digikey, who still stocked it. Wheras the mosfets, not so easy to source of such a guaranteed quality, (at least not without searching for an alternative mosfet, with similar spec).

So 3 days later it came: Replaced the motor driver IC chip and it works now. Otherwise I would have also ordered some mosfet. But turned out it was the 1st guess

Also re-soldered the fan terminal. Original tin solder is gone now. Was replaced with Kester leaded solder, good quality. But it is also be worth it to make an extra protective barrier ontop. To make double sure they cannot short out again. Because you know...

It is less effort that way. More hassle to wait until it fails. Then have to order this special driver IC. Which may become discontinued. Maybe it is quite likely i think, they might discontinue it. Then if you cannot get it what will you do? Because I email BEST company some days ago (asking for replacement fan control board). And they did not reply back. (In fact it seems that BEST never reply back for anything).

So I recommend everybody do this.. to remove the fan control board. And check on the underside of the PCB, these solder joints on fan terminals underneath. Just clean them / scrub them. And then add some paint or suitable barrier to protect it better. That the contacts are fully isolated from each other. To get in the way of tin whiskers forming. Is probably worth it.

But you know.... you don't have to take my advice. Perhaps you will see for yourselves after longer time. If other units fails or not. It is just a friendly advice to save yourself and avoid the fault later on

 

[SteveyG]

Glad you have it working. So it was a faulty motor driver IC straight out the box?

[dreamcat4]

ah thanks for replying here steve, actually my comment was supposed to go to the main BST thread, nevermind

to answer your question: I purchased my unit here as parts not working on ebay. After somebody else had tried to repair it (but was unsuccessful). He said: "i tested the fan works but not inside the machine".

so after fixing i did message him to ask how many hours service life before the fault appeared. and the response was "well it broke 1st use". which to me is pretty strange. because you would expect this to develop slowly over a significant time

however he may have in turn received the unit as broken from somebody else (or new). i simply don't know, as did not receive a clear enough answer on that point. (Not for wanting to bother the guy too much about it)