Reversed power, smoked a cap, part identification - Page 1
Forum section: electronics / beginners

author: Stonent
author_rank: Super Contributor
timestamp: July 12, 2014, 08:46:10 pm
content: I have a digital picture frame I picked up for cheap recently. It's an Ality AL-MD1 8" 800x480 display. It has an internal CF slot with a 512MB CF card in a CF to IDE adapter and external CF and SD.The screen appears to be VGA driven because if you unplug the cable from the main board it says "No Sync" on a blue background like a regular LCD monitor might.Anyway, I had it apart today and since I don't have the original cord, I'm using a different one with some alligator clips to power it. I wasn't paying attention and reversed power today and immediately head a short hiss and a puff of smoke coming from an SMD cap and it had glowing wire in it.I put power back to normal and it no longer powers up and the cap still glows inside. (EDIT: By no longer powering up I mean the LCD doesn't light, but since it draws power from the audio board that this cap went to, that could explain that part. The main board is separate)All the other caps on that board that are of the same physical dimensions are labeled 106 16k 643 and I zoomed in on this one with my camera and can faintly see a 106 under the charring so I'm pretty sure it is the same part. They are all pale orange with a dark stripe on one side so I'm assuming polarized.106 If I recall correctly means 0.01uF and 16K would mean 16 Volt Tantalum?So assuming that's right, since I don't have an SMD parts or any Tantalums, but have ceramics and electrolytics, do you think that might work as a substitute? Since it's on the ground of the input to the audio board I'm guessing it's just to smooth the power or react to sudden current changes, but I could be wrong.Here's the smoked cap:Here's the good ones elsewhere on the same board:

author: David_AVD
author_rank: Super Contributor
timestamp: July 12, 2014, 09:05:31 pm
content: "106" is 10 with 6 more zeros on the end. So that's 10,000,000 pF (10uF).You could substitute a regular electro there for testing, but i'm guessing you may have done a lot more damage.

author: Stonent
author_rank: Super Contributor
timestamp: July 12, 2014, 09:26:15 pm
content: Quote from: David_AVD on July 12, 2014, 09:05:31 pmOk you are right, it was 10uF. I was looking at the wrong column on a chart that I had.

author: Stonent
author_rank: Super Contributor
timestamp: July 12, 2014, 11:50:30 pm
content: With a 10uF electrolytic in place it does come up now but the backlight keeps turning on and off. It's LED based runs on 10V and rated to about 200mA. So at this point, not sure if one of the LEDs shorted and is causing an over current and shutting off or not.The voltage across the cap when it is on is 10.5V which I think is about right. I also checked the current across the cap and it looks like a little over 2 Amps, but I realize that may be a meaningless measurement since it could just be how much the cap can dump out into the multimeter and no indication of the rest of the circuit.

author: David_AVD
author_rank: Super Contributor
timestamp: July 13, 2014, 12:36:25 am
content: Check for any components getting hot.

author: Stonent
author_rank: Super Contributor
timestamp: July 29, 2014, 07:10:18 am
content: I messed with it again today and figured it out. Dodgy alligator clips. It worked fine today but when I wired it up again it kept cutting in and out like it did before. It turned out one of my alligator clips only had about 1 strand of wire making contact on one side.I was getting between 40 and 100 ohms on the clips depending on movement. After I pulled the wire back and made better contact, everything was fine.