Anyone know what point I could test for the 5v 0.33a fan?

[Shinai7047]

Been digging this out for a couple days now. I can find plenty of info on what replacement fans need to have in terms of wattage, however I am working on a damaged switch, and have replaced a couple of caps and res with the spec called for in the original. As this switch is a launch switch, I am also going to do a Trinket M0 install on it. At the moment, when I look at the connector that the fan goes into it has been singed a little bit due to the hot air rework of 2 Carbon Resistors at the Vol+/Vol- Strap. The pins on the connector still have continuity to the test points right behind it on the left (if the board is upright). Now what I am looking for is to test if there is a pad to check the continuity from the source to that pad? I have probably probed like 40 points with no success so far and its really tiring.

I have been up all night trying to probe this out, and at this point I think any help is appreciated. I just need somewhere to start. I have also ruled into the decision that the fan might just be shit and did order a replacement, so I will know by today at the latest whether or not the fan was broken after I drop a new fan in. If it isn't the fan though, not really sure what to do as if I cant guarantee the continuity between the source and the final pin then I can't confirm it'll get voltage at all (and apparently from what I can see while testing the switch doesn't spin fan up at boot, looks like it might only do it when it gets hot, however not sure what that process looks like and how the chips responsible calculate the heat and tell the system to engage/ramp up fan.

I'll be honest, I am a bit newer to switches, but not to soldering (although some of this SMD shit is fucking nuts), so the points do confuse me a bit, but I am a quick learner with this stuff and hopefully can move the question closer to an answer.

 

[FAST6191]

.33A@5V is enough that I might expect a modern chip to spit it out rather than tickling a transistor so that could be fun.
Curious that it does not spin on boot either, don't know if it does some kind of current sense for that matter (no fan detected/fan failed open/failed short sort of thing) that you could probe with a scope.
That said if boot does not work I would be inclined to leave it and see, maybe give anything with a heatsink a flash with a hot air station to help it along if you wanted. Nobody really does solely/primarily external sensing any more for stuff like this -- it is going to be on die, and while I can't guarantee the Switch has it then anything vaguely modern should also have thermal cutoff if it gets too silly.

If something is charred then my bigger concern is usually that carbon is conductive enough that shorts become a problem. Usually see it more for water damage but carbon is carbon in this case.

Alternatively have a nice series of pictures of the Switch boards being components removed and sanded
http://balika011.hu/switch/

 

[Shinai7047]

.33A@5V is enough that I might expect a modern chip to spit it out rather than tickling a transistor so that could be fun.
Curious that it does not spin on boot either, don't know if it does some kind of current sense for that matter (no fan detected/fan failed open/failed short sort of thing) that you could probe with a scope.
That said if boot does not work I would be inclined to leave it and see, maybe give anything with a heatsink a flash with a hot air station to help it along if you wanted. Nobody really does solely/primarily external sensing any more for stuff like this -- it is going to be on die, and while I can't guarantee the Switch has it then anything vaguely modern should also have thermal cutoff if it gets too silly.

If something is charred then my bigger concern is usually that carbon is conductive enough that shorts become a problem. Usually see it more for water damage but carbon is carbon in this case.

Alternatively have a nice series of pictures of the Switch boards being components removed and sanded
[removed]

Yeah I figured as much. Just wasn't sure if there was a good reference point that I could start at. mainly just trying to see if I can get the continuity to confirm no damage to 5v rail. I guess with all my previous work I just assumed that there would be a point, or a transistor that I could measure from that was slightly further away from the actual connector to check that the traces are still okay.

would be a bitch though if its the M92 chip, as I think that one spits some voltages, not sure on others. Either way, I have a friend in Can that is willing to probe it with an osc and check the chips. if it gets to the hopeless point, I'll send it his way.

Edit:

Thank you for that link, it is SERIOUSLY a godsend. I spent 15 minutes in there, checked pad to pad, from pads on opposite side of the board, etc and I am confident enough now to say that I do not believe the connector is causing any issue. Thanks!

 

[FAST6191]

Yeah I have not seen a repair manual or even much in the way of known failures here.

Anyway this sort of thing should be within the realm of poor man's oscilloscopes if you wanted to go there -- trashing an old CRT screen for the classic poor man's scope is probably not the done thing these days but a fan signal should be within the realms of a computer's line in (not like you are going to get a greater than 44KHz or crazy voltage signal* here for a fan) and that means you go to the cheap shop, buy a line in cable or headphones and slice that about a bit**, maybe a few resistors if you wanted and a copy of audacity if there is not a better alternative (granted audacity will record/capture for as long as you want, filter options and has a nice Fourier transform option as well).

*for the CRT and this you would tend to provide it a reference at a known voltage so as to establish a known position in addition to zero and everything else tending to fall from that.

**if it is an enamel coated affair do remember to remove said enamel. I like fire myself but sandpaper and sitting it ina blob of molten solder (throw solder away and clean iron afterwards)