Just about any soldering iron should work. Chisel tips are better than round tips for most work. I really like J tips as well, they’ve got a range of usable surface sizes without having to change tip just by turning the iron around.
Put a piece of heat shrink tubing on one wire.
Strip the ends, and form a Western Union splice in the wires to hold them.
Set the iron to 350°C, and let it heat up. If your iron doesn’t have temperature control, it’s cheap crap and should probably just be thrown in the trash since it’ll tend to over-heat and lift pads when soldering PCBs. Continue for now, that doesn’t matter as much for soldering wires.
Then apply a tiny bit of solder to the tip of the iron so that it can make good contact, apply flux to the bit where the wires join (do NOT skip flux), touch the solder to the wires, and then touch the iron to the other side of the wires. The solder should quickly melt & flow into the joint.
Remove the solder, then remove the iron.
Let the joint cool, then slide the heat shrink up over the joint and shrink it with a heat gun.
Crimp connectors tend to be stronger and more vibration-proof than solder, but sometimes space constraints mean that soldered splices are necessary. Also crimpers are expensive, for many wire-to-wire crimp families the official crimpers are several hundred dollars.
The point of the diode is to prevent reverse current that gets induced when a (brushed) motor is turned off. It essentially turns into a small generator while spinning down, and the diode essentially short circuits that. It prevents damage to the rest of the circuit. If that motor is brushless (with an integrated control board), you likely won’t need it but it doesn’t do any harm either.
Doing some quick math, the transistor will have a base current of 5 milliamps, which a Pi should be able to supply. At a fairly typical beta of 100, the transistor could drive the fan at up to .5 amps, which is plenty for a small fan. A MOSFET transistor is generally better suited for switching high current loads, but for this a BJT (as drawn) should be fine.
On a KISS basis - I tend to just use a bimetallic switch or omit the temperature control and just run the fan from power up. It’s possible for a processor to suffer some non-handled exception where it no longer executes the temperature management routine.
Buy the JST plug with the right pin pitch (in your case 2mm), and grind it so it fits. You can find male to female cables, so you also don’t have to modify the original connector on your noctua fan.
I recommend EEVBlog’s OpAmp tutorial. His explanation is pretty simple to understand. Basically there are two rules (note these rules are ideal, but the exceptions can usually be ignored):
No current flows into the inverting and non-inverting inputs.
For negative and positive feedback circuits, the OpAmp wants to keep the inputs the same by changing its output, and will sink power to its positive or negative power rails to achieve this.
I work with a lot of particle detectors. Instead of this, I recommend a photo diode and laser diode. Light dispersal particle counting is relatively easy to pull off by comparison to scraping off coating and all that. You could even use a very small segment of solar panel and a light source or an IR detector and IR LED similar to a smoke detector.
The two through hole pads by C19/20 arent soldered and the one above it looks to be a bad joint
jumpers on the right arent connected in the same spot
extra traces by the IC
components can die, especially ICs and capacitors from ESD and drops respectively
PCBs themselves can sometimes just be faulty from the factory and have damaged traces.
Another thing is that small ICs like that tend to be fairly difficult to stick down all the pads. Reworking that might be a good option if checking the above doesnt work
Thank you, I will reflow C4 and add C16, but C10 and C14 look fine from the sides.
The messy/missing joints near C17, C19, and C20 are optional components for the other side. (Unused surface mount USB port with through-hole mounting pins and an unused jumper.) Right-hand jumpers are all optional and unused from an earlier prototyping stage.
What do you mean by extra traces by the IC? And you’re absolutely right about the small IC. It’s the MAX17640, and at 2mm x 2mm it’s a piece of work to land correctly.
I was referring to it more as a difference which might be the source of the issue. For example, one via is fairly close to the pad for C16 which could be shorted (probably isn’t, but still a good idea to check). It could be a wiring issue but could also be a board manufacture issue.
You can try checking whether the 54v supply has any voltage spikes if you haven’t already. 60-to-5 converter is most likely a switching converter and they draw high current instantaneously and can cause spikes if not filtered properly which may affect the functionality. This may not show up in DC voltage measurement, and daisy chained boards may still function if they are filtered well. One of the daisy-chained boards may be causing the disturbance too, and maybe top board is filtered well but bottom isn’t for some reason, maybe a soldering error(e.g. filter capscitor ground connection, poor soldering may be conductive but with high inductance, hindering filter functionality). So it is good to check supply quality. Also what do you mean by not powering up? Is 3.3v not working? What about 5v?
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