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 Bad caps also afflict computers
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 Return to top of page · Post #: 1 · Written at 5:54:39 AM on 17 August 2016.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 729

Had a PC have screen blackouts that lasted about a second or two, and I'd get reports that the Intel video chipset driver had crashed and was restarted. Well, you'd figure that there is something wrong with that driver. Boot the PC in "safe mode" and the VGA screen was stable. After much SW mucking around, took the PC cover off and looked for loose connectors and such. I did spot several electrolytic caps with bulged tops, a definite sign that they are bad. Removed the motherboard (that was an adventure in figuring out what I had to do to get it removed...) I replaced the bad caps. (I also managed to damage a fine PCB trace, but it looks to serve only an expansion option socket I'm not using and unlikely to ever use... so left it). Still Sad Anyway, the computer stopped blacking out (Windows 7 did have to run a repair session, I must have messed something up when chasing the SW angle) Anyway, it straightened itself out, and this PC looks to be healthy again. The solder work is a bit ugly, but secure (I didn't want to muck with the board too much trying to clear through part PCB holes, so I just beaded some solder on the board topside and soldered the cap leads to that, a little like surface mounting). You get a little gun shy after damaging fine traces...

To bring this back to radios, well, caps can be the fault in modern electronics as well.


 
 Return to top of page · Post #: 2 · Written at 9:04:32 AM on 17 August 2016.
Johnny's avatar
 Location: Hobart, TAS
 Member since 31 July 2016
 Member #: 1959
 Postcount: 323

It just goes to prove that a good visual inspection is always recommended before diving in with the soldering iron.
I've found that in modern electronics 9 times out of 10 a fault has been electros.
And if the visual does not show a problem the next best thing these days is an ESR meter, which can be used in circuit and quickly
test all electros in situ. Mind it's not invallible, but a very valuable tool for modern fault finding.
JJ


 
 Return to top of page · Post #: 3 · Written at 9:15:38 AM on 17 August 2016.
Brad's avatar
 Administrator
 Location: Greenwich, NSW
 Member since 15 November 2005
 Member #: 1
 Postcount: 5562

Capacitors in switchmode power supplies act like suicide bombers at the best of times. This goes back to the days of the 386 - caps inside the power supply itself and amongst the capacitor array on the motherboard itself would blow their tops for no good reason, aside from poor quality which wasn't bad considering a half decent IBM-compatible computer at that time was around $5,000.00 and all that got you was the box and the monitor. In some cases even the hard disc was an add-on.


‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾‾
A valve a day keeps the transistor away...

 
 Return to top of page · Post #: 4 · Written at 9:22:49 AM on 17 August 2016.
GTC's avatar
 GTC
 Location: Sydney, NSW
 Member since 28 January 2011
 Member #: 823
 Postcount: 5300

And then there was the capacitor plague: https://en.wikipedia.org/wiki/Capacitor_plague


 
 Return to top of page · Post #: 5 · Written at 9:38:14 AM on 17 August 2016.
Marcc's avatar
 Location: Wangaratta, VIC
 Member since 21 February 2009
 Member #: 438
 Postcount: 3786

I can relate to that: Someone deliberately left a dodgy formula on a computer to be hacked. Those caps did Muti millions of dollars in damage & I spotted a couple of them recently in a No Break that I had built, dating into the 90's. I have seen them in situe, all over the mother board.

Good battery in no break; dated 1998 (I labelled it: so its fact). I ran it to flat it went for the right time, so I serviced the module (new electrolytic's) put all back together & let the module recharge the battery (current limited).

That spy idea is not new I am given to believe that the English designed a magnificent battle ship during WWII with the full intent for the spy within to get it for the enemy.

Espionage can have its failings: Obviously things were not checked in the excitement, when it was built. It was deliberately designed to be "top heavy" and due to perfect design, heeled & sank during a turn, when sea trialed.


 
 Return to top of page · Post #: 6 · Written at 10:30:57 AM on 17 August 2016.
Robbbert's avatar
 Location: Sydney, NSW
 Member since 18 September 2015
 Member #: 1801
 Postcount: 1094

Electros in computers are always the weak point, especially the ones that are right next to the hot CPU. Poor quality ones never last.

I've got some old Compaq computers made in 1999, and they used good quality electros, and I reckon those pc's will still be working after I've gone.


 
 Return to top of page · Post #: 7 · Written at 4:26:55 AM on 18 August 2016.
Wa2ise's avatar
 Location: Oradell, US
 Member since 2 April 2010
 Member #: 643
 Postcount: 729

I tested the bad caps for grins. They read about 1% of their rated capacitance. And the "D" factor was also poor (used a BK Precision 878 LCR meter). Computer is behaving itself well, now.

Brand of two of the bad caps is "KZG"


 
 Return to top of page · Post #: 8 · Written at 4:40:06 PM on 17 October 2016.
Little Nipper's Gravatar
 Location: Australia, SA
 Member since 21 December 2011
 Member #: 1047
 Postcount: 85

Yes, you have to be careful, these are six layer boards.

The idea is to heat one leg up until loose, then bend the capacitor over all the way so the leg clears the hole in one action. Don't let it stop halfway.

Also if you are ESR testing, make sure they are filter capacitors. There are few DC blocking (coupling) capacitors that are naturally high in ESR especially around the audio section. These may be a different colour.


 
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