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Yesterday morning, I was preparing my tiller pilot (auto pilot for small boats) but it sounded like something was loose inside. When I opened it up, I found a damaged rubber sealing and the piece in the image below flying around loose. It is mechanically completely deformed and the legs are sheared off. I think it had two legs, but that's not certain. I have no clue how this could have happened, as the electronics is obviously designed around the mechanics. I cannot identify where the thing could have been on the PCB, as that looks unharmed. Also for some (magical?) reason, the pilot still(?!?) appears to work just fine.

Destroyed part Destroyed part, Side Open tiller pilot PCB, bottom side

The thing is about 5mm high and has a 5mm diameter.

What was this piece? A capacitor (what value)? I guess I should replace it if ever I find where it's missing. Elaborating on why the thing still works might be speculation, though.

The PCB (see images) looks unharmed, and the filter capacitors for the drive motor are still in place (those are very small ones, though).

PMF
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    Some more photos may be helpful (other angles of this component, and also the PCB). If you can't see anything missing from the PCB, then is there any chance this was never part of the autopilot device and somehow found its way in from outside? – Harry Jun 26 '22 at 08:42
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    Unlikely, the device has a waterproof sealing, as it needs to operate in rain and high seas as well. What could be is that (if it's a capacitor) it was attached directly to the driving motor as filter. But there's nothing obviously wrong there, too. I'll get some more pictures. – PMF Jun 26 '22 at 08:46
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    That component is an electrolytic capacitor; more pictures of the device are needed to assess the situation. Can you also explain how this device is powered? I think that small boats have a 12VDC system, like cars - but I might be mistaken. – Vladimir Cravero Jun 26 '22 at 08:55
  • @VladimirCravero That's correct, the device operates on 12V DC. – PMF Jun 26 '22 at 09:07
  • In the last photo, there is a black rectangular connection to a tiny flat orange ribbon cable. The ribbon destination is out-of-frame. Perhaps that capacitor is associated with devices at the end of that cable? – glen_geek Jun 26 '22 at 11:34
  • @glen_geek The thing at the end of that cable is an electronic compass sitting under the spindle. That piece is quite sealed and has no big components looking out. – PMF Jun 27 '22 at 19:46

2 Answers2

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It's an electrolytic capacitor. There is one place on the board with a corresponding PCB footprint and no capacitor (orange arrow).

enter image description here

It's probably the capacitor associated to the voltage regulator (blue arrow).

It used to look like that.

No idea why it came off the board, maybe a bad solder joint combined with vibrations. There's a motorized screw in there, so it probably got stuck in and squished, which would explain how it looks...

Since it's on the voltage regulator, it'll probably kinda work without it, but that will increase the chances of voltage being unstable, so your device could crash and reboot more often.

If you don't know that's a capacitor, you most likely don't have the tools to solder a new one back in, so I'd suggest bringing the board to someone who knows how to solder components. It looks like a standard 10µF or 100µF 35V cap. Doesn't look like a speial low-ESR model, just general purpose, so that's pretty easy to find.

The original should be measured with a caliper (or just the pad spacing on the board) to pick a replacement that fits.

The pads where it was soldered should be inspected carefully for damage. If they were ripped off the board, that's a problem.

Note this is a polarized capacitor, so it has to be put in the correct orientation. Normally there would be a silkscreen marking on the board to make the repair tech's life easier, but in this case there is not, so the polarity will have to be determined by looking at the circuit around it and probing for continuity between one of the pins and ground.

bobflux
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  • Thanks, that could really be it. I didn't consider the possibility that it was mechanically destroyed _after_ it already fell off the PCB. That motorized screw has a rated thrust torque of 77kg, so very likely enough to make it look the way it does. – PMF Jun 26 '22 at 09:49
  • I do know what electrolitic capacitors are, but I've never encountered this form, and I was unsure because it does not have the capacitance printed on it. I even have some spare ones around, and a soldering iron. The main problem is that I'm rather bad at soldering... – PMF Jun 26 '22 at 09:51
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    Your assumption agrees with a previous observation: Last year, the pilot suddenly experienced the problem of regular restarts, particularly when the engine was running. I then "solved" that by wiring a new and thicker power cable. – PMF Jun 26 '22 at 09:53
  • OK! So if you have a multimeter with continuity/diode mode, you can probe between Ground and both capacitor pads, one of them should be ground. That's probably the one on the right since it has a via to what looks like a ground plane on a layer below. Then the power that comes in from the connector should go through the SMD diode just left of the voltage regulator, so the pad on the left should read about 0.5-0.6V in diode mode with the red probe on the power input and the black probe on the left pad of the cap. – bobflux Jun 26 '22 at 10:00
  • @PMF It does have the capacitance printed on it. It is just difficult to read because the markings are scratched. I guess it might read 100 on the top line which would be the capacitance in microfarads, and 35 on the second line could directly indicate voltage rating. – Justme Jun 26 '22 at 10:00
  • @bobflux Something is fishy about those pads. They don't seem to be conductive at all, even if I put both probes on _one_ of them, I get no measurement. Also they're to far apart for what the would have been, and are larger than any others. They have no signs of anything having been soldered there. Unless of course it was some manufacturing error that there was no (or not enough) solder applied there. – PMF Jun 26 '22 at 10:22
  • If the solder was broken then oxidized it would look matte/grainy and would be difficult to make contact. You can clean them up by adding a bit of new solder. – bobflux Jun 26 '22 at 10:25
  • I don't trust my soldering skills enough to try to fix this now, particularly since it's basically working for me. If it fully breaks, I'm really doomed. I will have to fix it with the help of somebody better at this. Thanks anyway, that was a great diagnosis! – PMF Jun 26 '22 at 10:45
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    Found this video: https://www.youtube.com/watch?v=tYc45QJNc5w. At 09:30 one can quickly see that that capacitor really should be there. One last question: Does the black marking on these capacitors mark the positive or the negative lead? – PMF Jun 26 '22 at 10:54
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    If pads are not conductive, they might be ripped off with the capactor. The picture looks like there is a copper trace leading to a pad but it has risen up. So the pads may be gone but feel free to take a photo with the pads cleary visible to confirm. Electrolytics have black marking on negative terminal. – Justme Jun 26 '22 at 11:29
  • @Justme it's probably just oxidized, scratching a bit seems to help. But even I can't see the details clearly. I need to get a magnifying glass to check the status of the trace (and whether that's thorn off as well). But today is sunday. – PMF Jun 26 '22 at 11:41
  • as for why it works: an open line is a very very low capacity, bordering 0. – Trish Jun 27 '22 at 09:32
  • The pads and the absence of leads suggests that this is an SMD component. – Simon Richter Jun 27 '22 at 17:58
  • My two cents here: I agree with @Justme that the pads were ripped off. Zooming on the last image makes it look like a copper trace lifting from the gray areas, which should be the bare PCB substrate without the copper pad. It's hard to see from the capacitor photos if the pads are still attached to the component, though. If this is the case, fixing it will require more work than just soldering a replacement. Maybe the clearance from the mechanism is a bit tight and the moving parts were responsible by the damage? – ricardomenzer Jun 27 '22 at 18:54
  • @ricardomenzer No, nothing is still attached to the capacitor (the legs are cut off _very_ close to the case) and I didn't find any remnants of the solder that should be there. Maybe that fell out when I opened the thing last time but I didn't notice or couldn't make sense of it. – PMF Jun 27 '22 at 19:57
  • @ricardomenzer There's nothing in there that can move in another direction than in our out, but I cannot really see how much space there is when the PCB is mounted. – PMF Jun 27 '22 at 19:59
  • If the capacitor legs were sheared off its body then the "feet" are probably stuck in the solder on the pads. That would be good news for repairability: if this is the case, the pads need to be cleaned and the remains of capacitor pins removed, but the PCB should be fine. Note these caps usually sit on a square piece of black plastic that serves to hold the legs, and yours has this piece missing. It's probably still wedged somewhere inside the device, or crushed into several pieces. – bobflux Jun 27 '22 at 21:28
  • @bobflux Status report: Now that I would finally have someone to solder a new capacitor on there, the whole thing has died. The electronics is just acting up, and the PCB shows traces of severe corrosion :-( Need to get it serviced by a professional or get a new one, I'm afraid... – PMF Sep 06 '22 at 16:57
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I agree with bobflux' answer that the component is most likley a 100uF 35V electrolytic capacitor. But I think it came from pads in the large copper area near the yellow Data push-on connector.

My guess is that someone fell against the pilot and distorted the polished cylindrical guide rails within the unit. This allowed the screw-jack traveller to hit the capacitor. The guides will have to be straightened lest the problem re-occur.

Happy sailing.

Richard
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    The other answer provides the correct place where the capacitor was. It is confirmed by comment pointing to a video. – Justme Jun 27 '22 at 13:15
  • That's unlikely. The mechanics still works fine. Such a big mechanical shock would also have to destroy the plastic housing. – PMF Jun 27 '22 at 17:33
  • Ah. Hadn't seen the video. It looks like you are right. I was surprised that the tracks leading to the pads were so fine for a reservoir cap. Maybe they are wider on another layer. – Richard Jun 27 '22 at 19:22
  • Well. If the mechanics are fine (hurrah! hurrah!) I also guess the cap _was_ poorly mounted and the damage occurred after it fell off. I have used such tiller-pushers; I am sure you are aware how vulnerable they are to someone falling (or sitting) on them in a seaway. – Richard Jun 27 '22 at 19:33
  • @Richard Well, I did manage to break the wooden tiller itself by falling on it... and the pilot mount was also fixed several times, but luckily the pilot itself never had a mechanical problem so far. – PMF Jun 27 '22 at 19:52