March 28, 2005
Broken Capacitor, K#135
Kinkajou #135, currently being using in the village of Digani in the Segou region, rattled when I picked it up. Attached are pictures of what I found inside. A capacitor had broken off the board, perhaps as a result of a bad solder connection and maybe some rough handling.
Board with missing capacitor
The capacitor
Attached is a technical assessment of the failure, and a recommendation for repair.
The 100uF capacitor that broke off is right after the on/off switch.
It's job is to:
- remove any electrical noise from the power pack connector,
- generally stabilize the 12V battery input, and
- satisfy peak power demands that a battery at the end of a 6 foot cable can't satisfy.
No decent power supply would be designed without such a capacitor. Is it absolutely, critically essential? Based on your empirical evidence, perhaps not. Should it be replaced? I would recommend yes because a noisy power supply could cause the projector to mis-behave or shut down if the power pack connector is disturbed.
We should have Emmanuel fix the cap, if only as an exercise. It is probably the easiest repair to do because it does *not* require that he remove the PC board. The cap is right at the edge near the cover (that's why it got damaged so easily).
This kind of feedback is important. Let's pay heed to this cap for the next round of builds. It could be as simple as gluing the part down.
Here are four photos documenting the capacitor replacement.
1. Preparation of leads w/dimensions
2. "Before shot" showing nearby via
3. Cap position prior to soldering
4. "After shot" showing finished work
The pads shown in photo #2 should be cleaned of any remains of the broken capacitor, and "tinned" (add solder so it is shiny). In photos #2 and #3, there are blue arrows that show a nearby "via" (i.e. hole). It is imperative that this via not be shorted to the capacitor. After the repair, if the technician has an ohm-meter, he should make sure there is no short between the via and the "-" lead of the capacitor. If he cuts the leads to 2.5mm lengths shown in photo #1, he shouldn't have a problem. Regarding polarity, the "-" side is marked in gray and is closest to the via. The "+" side is near to the edge of the board. The lettering on the cap are always oriented as shown, and can be used as a guide for orientation. In other works orient as shown in the photos.
Posted by Timothy Prestero at March 28, 2005 09:31 PM
