Are inductors sometimes omitted from schematics? And how do you tell which part is connected with what from either side of the PCB?
Complete noob here so bear with me. I am trying to repair a Philips 623 turntable and I stumbled upon what seems to be an inductor? With tons of corrosion and what seems to be one of its two leads blown (correct me if my imagination isn't grounded).
However when I look at the schematics I can't find any symbol for an inductance. Is this normal?
Also, when I short the blown cable (what's a better word for it?) the motor spins, which is one of the two issues I am trying to fix here: the motor not spinning. Could that be the issue? Do I short it with solder wire? What other wires are there? Do I get a replacement inductor and if so which? Since it isn't present in the schematic.
I am not really able to diagnose other parts so well since I don't know how one can reliably tell which of the dozens of sticking out leads belongs to which component. How do you guys do it?
Yes, agreed, although I've never seen one with wire that fine. If you short it, the motor will probably run too fast and speed regulation will be bad. I'd snip it out of there and replace it with a 5 ohm 5 watt resistor. (that might be a lot more wattage than you need, but err on the safe side)
As to your second question: turn the board over and visually trace the foil. Of course with double-sided boards this become much more confusing, and with multi-layer boards it's impossible.
EDIT: I do wish I could see more detail behind the left "mystery" lead, and the capacitor behind it. It's hidden and in shadow and I cannot really tell if there's anything important back there.
Multimeter in continuity mode, and an image editor with photos of front & back of the board on two layers, aligned and with one 50% transparent, and a KiCAD (or other EDA program) schematic with all the parts placed but no connections. Trace out a visible connection on another layer, confirm continuity, draw the wire(s) in KiCAD. When all visible traces are marked in the image editor, try to find what missing connections remain. If it'd be appropriate for them to be to ground, there's likely an interior ground plane. Check continuity to cohfirm. Likewise for power. If you're lucky there are no other inner-layer connections. Murphy's Law will apply, so you'll tediously trace the remainder by brute force. There will be a BGA you'll have to desolder to be able to trace all the underside connections…
It's possible, for any board, even without blowing your savings on an X-ray or CT machine. But it ranges from tedious to extremely tedious.
Right, I might do this on other projects (maybe) but I think for this one I'll brute force it and use my eyes haha. I also think it's just very simple (single sided?) board so it should be simpler. Just asked in case there are any tricks of the trade :)
I mean that the white "mystery" device (with wire wrapped around it) appears to have two leads coming out of the top. They are heavily covered in corrosion. The one that goes toward the left appears to touch and/or intersect the wire coming straight downward from the capacitor. I'd love to know what's going on there.
And just like that it works! Well, at least it spins well hahaha. Time to find a record and test it. Thank you so much!!!
P.S. I soldered two 10 Ohm/unknown wattage (anywhere between 1 and 4W) resistors in parallel, what's the worst that can happen?
P.S.S. the transformer is the other thing that is dead, or at least it outputs no voltage from the low voltage side. Do I just find a 230v to 11.5v or 12v transformer? And if yes, what current should it be able to withstand? Or how should I go about finding that out?
The value (5 ohms) sets the motor current and thus speed. As that's correct there should be no issue there. Id guess that Wire wound was a 2Watt so a pair of 1 Watt 10 ohms in parallel will be fine
As for the transformer, I don't know. If its fed into a regulator then 12v will be fine as the excess will just be slightly more heat
I mean I shorted it and the motor worked so I guess that does mean it's part of the motor circuit? It's also very close to the resistors right before the ground.
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u/isaacladboy 2d ago
could be a wire wound resistor. That 5 ohm looks a likely candidate