Backwards electrolytics (again)

You IDIOT!!!

Good grief man, take some digital pix before you take it apart - at least until you get over your brain fades.

G=B2

"Jeff Liebermann"

** With all those damn electros installed in reverse polarity, be a damn site easier to alter the DC rails to suit - wouldn't it ??

..... Phil ;-)

Yeah! And take a video for us to see what happens when you power it up. Extra points for audio. Make sure you use a 600W or better supply, fold-overs just won't cut it. ;)

On Mar 31, 6:36=A0am, "Phil Allison" wrote: .

mn

Geez Phil, what kind of Phil Allison answer is that? And a smiley emoticon? Since you're off your game, I thought I'd take the liberty and reply to Jeff in the proper Allison manner:

"Jeff LIeberfool"

** Are you f**king blind?

** Twice? What kind of moron are you? ** Yeah, like retire you idiot!

...Phil

How did I do?

Edwin

"Stroonz"

How did I do?

** Just as psycho, brainless and retarded as ever.

I thought you would be amused. I don't think that the IC's would appreciate the reversed power supply polarity.

It took me about 45 minutes to tear down the XPS-200, replace 11 caps, reassemble, and test. It's now running an overnight burnin. I also fixed two of the other machines in about 30 minutes each (fewer caps to replace). What I found interesting was that the XPS-200 again worked for about a week with reverse polarized caps. My usual 24 burnin is probably inadequate as I didn't bother doing a visual or thermal inspection after the burnin.

Yes, I also learn from my mistakes.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Welcome to Learn By Destroying(tm).

I take photos of every customers machine I work on. I blow off the dust outside (so that it doesn't trash the office), take a few photos, and then proceed to work on the machine. This has ended a few debates over missing accessories, mechanical damage, etc. Sometimes, I use one of the particularly disgusting photos as wallpaper on the repaired machine. I also take some more photos when I'm done.

However, these were my machines, not customers, so I didn't bother with the photos. Most were rescued from the recyclers and all of them had bulging caps. Since these were mine, not customers, all my customary precautions were ignored. Out of about 7 machines, I managed to reverse the caps on 4 of them. All had the silk screened stripe marking the "+" end instead of the usual "-" end. I didn't see the "+" silk screened marking or bother checking the square pad, until Phil Allison pointed it out in the first photo. The brain isn't fading, but the eyesight is certainly going down the drain. Assumption, the mother of all screwups, is also fully functional.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

An infra-red camera might be of use...or wet-touch each cap after its been running a while (without exploding).

John :-#)#

--
    (Please post followups or tech enquiries to the newsgroup)
  John's Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9
  Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
                     www.flippers.com
       "Old pinballers never die, they just flip out."

BTW, not all Dell mobos are marked that way.

Do you mean you don't write a red dot next to the positive lead when you remove each capacitor? :) I do that because I've come across circuit boards that were marked wrong.

Yep. This is the first time I've seen boards marked that way and I've been dealing with PC's since the Apple ][.

I usually take a photograph. For major repairs, such as laptops, I also print the photo, and mark any parts I replace. However, I haven't found it necessary to mark the capacitor polarity. I have run into some that were marked backwards, but that was maybe 10 years ago. More commonly, capacitors where the silk screened markings are UNDER the capacitor, where they can't be seen. When I do mark something on the board, I use a UV pen for the top, and whatever I have handy for the bottom (which can't be seen).

Worst case are some video cards, where the annular ring around the solder bad is so narrow, that any attempt to solder the pad will result in a guaranteed solder bridge. These also tend to have no visible polarity markings of any kind, which adds to the challenge.

The problem here was that these machines were mine, not my customers. So, I simply ignored all of this, and blundered onward with no photos or markings.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com               jeffl@cruzio.com
# http://www.LearnByDestroying.com               AE6KS

I use a cheap IR thermometer with a bit of creative optics to narrow the viewing angle, or a thermocouple thermometer. I need my finger tips functional for playing piano, organ, synth, etc. What I found odd on the GX-520 board with the backwards capacitors, was that they did NOT become warm:

I measured the temperature and the capacitors were the same temperature as the surroundings. I would have expected them to get warm, but apparently not. My guess(tm) is that the plastic insulator, between the foil wraps and the aluminum case, is also a fair thermal insulator. While the electrolyte is getting hot and boiling off belching gasses, there is little heat transfer to the case.

If you haven't broken it and then fixed it, you don't understand it.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com               jeffl@cruzio.com
# http://www.LearnByDestroying.com               AE6KS

"Jeff Liebermann"

** As is usually the case when the reverse voltage is only 3.3 or 5 volts. ** Not IME at such low voltages. ** No way - boiling electrolyte would make the whole cap too hot to touch. Electro caps are almost like living things - when faced with reverse polarity, they try to re-form as reversed caps. There is a limit, of course and much heat will be generated if the voltage is more than a few volts.

Anecdote:

The most alarming example of a reversed electro I ever came across was inside a *new in carton* 300 watt per channel power amplifier made by Jands Electronics here in Sydney (a model J600).

One of the two 8000uF, 80V filter chassis mount electros had been installed in reverse in the factory but the darn thing actually worked for a few minutes until the AC fuse blew. Some clear liquid was split round the bottom of the case. On correcting the error - the thing worked OK. Of course, it got a new cap from me.

Although the amp was new, it had apparently not been used in 8 or 9 years since manufacture. So I rang Jands and gave them the serial number. According to their records the particular amp had " gone missing" from the factory and was never sold to any customer. An "inside job " was suspected.

My customer professed total innocence.....

..... Phil

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

They now make "fairly low cost" handheld IR scopes for firefighting use; I saw one demonstrated on the local TV news,and it was sensitive enough to see a 3-sec handprint on a wall. It could easily show up hot components on a PCB.It was the size of a handheld portable spotlight. It might be worthwhile reaserching,particularly if one has a small production business.

--
Jim Yanik
jyanik
at
localnet
dot com

Ok. I was assuming that the gas necessary to blow the lid off the capacitor and spew brown goo was accompanied by heating. That seems to be a bad assumption as the gases can probably be produced without any heat. Time for a reverse polarity bench test with the proper instrumentation. (Probably this weekend).

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com               jeffl@cruzio.com
# http://www.LearnByDestroying.com               AE6KS

FLIR makes these:

Their lowest cost model is about $1000. Office next door does home energy assessments and has one of these.

However, they won't let me borrow it any more after it got trashed by someone else. While I had it, it was wonderful for finding shorted power supply traces, overheating components, and CPU cooling problems. I don't see myself spending $1000 for one in the near future.

However, I have built several IR flying spot scanners, that might suffice. Basically just a far infrared photo detector chip, a rotating mirror ripped out of a laser printer or supermarket scanner, and some optics. I've built several of these over the years, with assorted problems. All of them worked, but the response time was awful compared to the various FLIR arrays. Thermal noise was also bad.

The problem was that the caps really did not get warm. Per comments by Phil Allison, little heat is not required to produce the gasses that a bulging the case. I don't think the FLIR camera will show anything useful.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com               jeffl@cruzio.com
# http://www.LearnByDestroying.com               AE6KS

Thing is, Jeff hasn't disagreed with Phil, or said something that Phil disagrees with. Phil reserves his insults for what he regards to be their proper use - as a debating tool.

Sylvia.