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rogersyd
02-03-2012, 11:23 PM
Well, I never thought I could be so careless, but the magic smoke has been released from my PPDB. Not a good way to start the weekend.

erco
02-03-2012, 11:29 PM
My condolences, rogersyd! Not a good Friday!

Speaking of which, any chance of resurrection? Looks like localized smoke. Sometimes the weakest (and hopefully replaceable) link lays down his life that other parts in the chain may live.

Duane Degn
02-03-2012, 11:44 PM
I agree with erco, I bet most of the board is fine.

I looked on my board to see what the little black chip was. It's a yellow tantalum capacitor. So the cap is shot and maybe the voltage regulator. Both very replacable.

Becareful if you need to remove the voltage regulator. I pulled some traces when I replaced one on a Prop Proto board. Hot air or ChipQuik (http://www.sparkfun.com/products/10925) should be able to remove it without damage to the board.

John Abshier
02-04-2012, 02:12 AM
I think I burnt out the same part. I sent it back and Parallax repaired it for a fee.

John Abshier

W9GFO
02-04-2012, 05:40 AM
I wonder, we picked up a PPDB on the UPEW freebie table with that exact same part missing. Replaced it with a new cap and it's been working fine.

rogersyd
02-04-2012, 12:06 PM
Thanks all, I'll contact tech support before I fire up the soldering iron.

erco
02-04-2012, 05:00 PM
It's a yellow tantalum capacitor.

So the tantalum threw a tantarum. Pa-dum-pum! Tip your waitresses, I'll be here all week. Thanks, you've been great...

rogersyd
02-06-2012, 11:41 PM
The rumors of my demise have been greatly exaggerated!

Nick in support suggested I just remove what was left of the cap. Pliers sufficed.

She is working like a champ once again.

Thanks again all.

Should I bother to replace that cap? I would imagine it was there for a reason...

erco
02-07-2012, 01:53 AM
Def replace. As Will Smith would say, "Pop a cap in its raggedy (buttocks) ."

Microcontrolled
02-07-2012, 02:18 AM
The same thing happened to my PPDB a while back. I thought it was completely dead, but after I pried off the cap it seemed to work just fine! I haven't replaced mine and it's worked fine for months, so I don't figure it needs replacing.

Dmashek
02-07-2012, 07:44 AM
I joined this club ( burned up part ) last summer on my PPDB. I tried to use it after the smoke, and that part glowed red. I then scraped out the burnt remains and I was back in business. Not sure of any negative consequences, but I don't leave the PPDB unattended and powered up.

davejames
02-07-2012, 04:33 PM
Should I bother to replace that cap? I would imagine it was there for a reason...


According to the PPDB schematic, this cap would appear to be C2 (10uF) that sits on the output of the +5V regulator VR2.

Yes - definitely replace it.

How to tell proper orientation? Use an Ohm meter to check for continuity to ground on one of the C2 pads.

A side note: I find it interesting that 4 other occurrences of this have happened, just from the previous posts.

Failure analysis time?

Duane Degn
02-07-2012, 04:51 PM
After looking at the traces on the PPDB, I think the cap is the 5V input cap.

I haven't checked the shematic yet, but it sure looks like it's connected to the 5V reg and the power jack.

Edit: After looking at the schematic, I'm sure of it now. It's C1 the input on the 5V regulator. I'm guessing low quality wall-warts are to blame for the failures. A lot of wall-warts' outputs don't match the specs printed on them.

davejames
02-07-2012, 05:13 PM
After looking at the traces on the PPDB, I think the cap is the 5V input cap.


I defer to your account, as I don't physically have a PPDB; was basing my presumption on the location of the cap in the photo.

Either way - it would be a good thing to replace the cap.

Duane Degn
02-07-2012, 05:48 PM
Either way - it would be a good thing to replace the cap.

I agree.

And I'd like to discourage the use of pliers for removing surface mount components. Components this small can be removed with a soldering iron. If need be, melt a bunch of solder so the solder is touching both sides of the component and it should just slide off.

Taking components off without heating them up is an easy way to pull traces on the circuit board.

Peter KG6LSE
02-07-2012, 06:11 PM
I wonder, we picked up a PPDB on the UPEW freebie table with that exact same part missing. Replaced it with a new cap and it's been working fine.

same :)

erco
02-07-2012, 07:04 PM
I agree.

And I'd like to discourage the use of pliers for removing surface mount components. Components this small can be removed with a soldering iron. If need be, melt a bunch of solder so the solder is touching both sides of the component and it should just slide off.

Taking components off without heating them up is an easy way to pull traces on the circuit board.

So using a hammer is "right out" ?

rogersyd
02-07-2012, 09:32 PM
Failure analysis time?

The failure in this instance was mine. The battery pack I loaded with AAs and connected to her was configured with a center negative plug. I don't ever recall soldering it up that way, but that may explain why it was at the bottom of my parts bin. I will never assume the polarity of a power supply again. Lesson learned. It was a dopey move on my part.

Sounds prudent to replace the cap. Ill be sure to do that.

Thanks again all for the advice.

Bits
02-07-2012, 11:44 PM
That capacitor is not needed in a hobby environment so, replacing it it not critical. In fact careful study of the parts data sheet will confirm my statement. Now if this were a customers board then I would consider replacing it.

erco
02-08-2012, 05:21 PM
OK, the board still works without the cap. But someone put it there for a reason. I'd replace it.

If nothing else, the cap's fireworks show provided a clear alert that something (polarity or other) was wrong, thus prompting you to immediately remove power. It may have acted as a fuse and protected something more critical downstream. Without it, next time you may leave power on for a longer time and do some real damage. Like it or not, there's always a next time. Pretty cheap insurance IMHO.

The PPDB costs $150.

How much does a cap cost? A nickel?

John Abshier
02-09-2012, 02:42 AM
My failure was also due to reversed polarity of the power source.

John Abshier

RDL2004
02-09-2012, 05:08 PM
I kind of wonder why Parallax uses the LM108x regulators on many boards instead of the LM2940 which has much better input protection and is used on the Board of Education.

erco
02-09-2012, 05:54 PM
Protection diode: 5 cents
Peace of mind: Priceless

RDL2004
02-09-2012, 06:48 PM
That's my point. The PPDB has no input protection diode. The LM2940 has built in reverse polarity protection for itself and all downstream regulated circuitry. It just seems a little odd to me that Parallax doesn't use the 2940 for all their 5 volt regulator needs. There's probably a reason, but I don't think it's cost.

rogersyd
02-09-2012, 09:50 PM
That's my point. The PPDB has no input protection diode. The LM2940 has built in reverse polarity protection for itself and all downstream regulated circuitry. It just seems a little odd to me that Parallax doesn't use the 2940 for all their 5 volt regulator needs. There's probably a reason, but I don't think it's cost.

I would imagine that the PPDB was designed for real professionals who wouldn't do such a dopey thing, so there was probably no design requirement to make the thing idiot proof.

davejames
02-09-2012, 10:56 PM
I would imagine that the PPDB was designed for real professionals who wouldn't do such a dopey thing, so there was probably no design requirement to make the thing idiot proof.

I am presuming that was intended 'tongue-in-cheek'?

erco
02-10-2012, 04:27 PM
I'm seeing new opportunities for semiconductor firerworks shows. Destruction art, choreographed to blow up various electronics components in visually interesting ways by applying way too much reverse voltage to a component. Who among us hasn't done a DEMO (literally) to someone, hooking a tiny LED directly to a 9V battery. You get at least a brief flash, but some explode with a nice pop.

I will need a multichannel high voltage controller for this, and a grab bag of cheap low-voltage semiconductors... :)

wildpony
02-17-2012, 02:15 AM
I just had the same thing happen to my PPDB tonight. That'll teach me to wire things when I'm half asleep....
Anyway.... Does anyone have a part number for the Capacitor in question?
Looking at the position on the board between the two regulators and the schematic I would say this is the c2 cap.
I'll try just removing for now, but would like to replace it.
Thanks

Duane Degn
02-17-2012, 02:41 AM
It's C1 on the schematic. The 5V input cap.

wildpony
02-17-2012, 02:31 PM
It's C1 on the schematic. The 5V input cap.
Are you sure? Cause if you look at the schematic C1 is non polarized and c2 is a polarized one. Also looking at the data sheet for a LM1085 regulator the right pin is the input and the middle pin is the output. And the output goes from the 5V to the 3.3 Volt and this cap is right in the middle.....
Just seems more like it's C2....

Duane Degn
02-17-2012, 03:21 PM
Are you sure? Cause if you look at the schematic C1 is non polarized and c2 is a polarized one. Also looking at the data sheet for a LM1085 regulator the right pin is the input and the middle pin is the output. And the output goes from the 5V to the 3.3 Volt and this cap is right in the middle.....
Just seems more like it's C2....

Follow the traces on the board. The cap in question has a thick trace that travels to the switch in one direction and the right pin on the 5V regulator in the other direction (the trace passes under all three pins).

The larger cap under the 5V regulator in connected to its center pin (output) which is also connected to the right pin on the 3.3V. This larger cap is C2.

Do you need help finding a replacement at Digi-Key? I know I've purchased tantalums about this size from them before. I could run through their search engine if your not familiar with the different terms (it took me a while to figure it out). I don't know what the voltage rating on C1 is. I couldn't read it on my PPDB. I think I'd try to find a cap with 20V or more rating. I would have thought the C1 cap would be a higher voltage rating than C2 but C2 is larger which I associate (probably incorrectly) with a higher capacity or higher voltage rating. Since both C1 and C2 are 10uF, I don't understand why C2 is larger than C1.

rogersyd
02-17-2012, 10:13 PM
I just had the same thing happen to my PPDB tonight.

Bummer man!
I finally replaced the cap as suggested and the board is fat and happy. Good luck with yours.