Maker Pro
Maker Pro

cap plague

J

John Popelish

Jan 1, 1970
0
John said:

Last year, I was asked to recap a an obsolete and non
replaceable motherboard (would have required upgrading an
old system with a completely new version for big bucks and
new software). Several caps were bulged as shown in this
article and the values were low, making the regulators
unstable, but at least, none had yet vented.

Getting those leads out of a 6 layer, board without damage
was a real challenge. But new, high quality caps did the
trick and the board has been back in service for about a
year without any more problems.
 
J

Jeff L

Jan 1, 1970
0
John Larkin said:
Yes, that is / was a BIG problem. I've recapped several motherboards over
the years, as it was easier then replacing the motherboard with another
model and having to spend hours installing software.

I also recapped all the servo amplifiers (x 7?) in one of the machines we
have, as they all started leaking (120 some odd caps in total, some in very
difficult areas to reach, as large components had to be removed / desoldered
to get at them)

Another interesting failure I sometimes see is resistors with a large
voltage differential going open! Sometimes the resistor is dissipating
several watts, other times it's dissipating several uW. Removing the
resistors coating shows that the resistive material had disappeared in a
small area!
 
P

Phil Allison

Jan 1, 1970
0
"John Larkin"


** Had to perform some emergency surgery on my PC last Friday morning.

It refused to complete boot up and presented a totally black screen when
switched off & re-tried.

Same scenario repeated exactly after 20 minutes of being off.

Suspecting a " heat "issue - I got out the vac and gave the insides a
good clean, was pretty bad around the CPU heatsink & fan.

Tried again - same scenario.

Damn !!

Then, I noticed some VERY hot mosfets in the CPU regulators and some wonky
looking electros next to them - one 1000uF, 6.3 volt Sanyo and two 1200
uF, 6.3 volt " G S C " brand.

Extracted some similar electros from another ( unused) motherboard and
replaced the ones in my PC - these new caps tested extremely low ESR,
about 30 - 40 milliohms.

Voila - the PC works fine again and those mosfets now run only warm.

Checked out the faulty electros and found they were all open circuit, the
best showed an ESR of about 10 kohms !!!

How the heck could it function with O/C caps like that ??


Moral:

Check those hard working regulator electros from time to time and replace
them all at the first sign of cap bulging or hot mosfets.



........ Phil
 
R

Robert Baer

Jan 1, 1970
0
John said:
Last year, I was asked to recap a an obsolete and non replaceable
motherboard (would have required upgrading an old system with a
completely new version for big bucks and new software). Several caps
were bulged as shown in this article and the values were low, making the
regulators unstable, but at least, none had yet vented.

Getting those leads out of a 6 layer, board without damage was a real
challenge. But new, high quality caps did the trick and the board has
been back in service for about a year without any more problems.
Happened to my VIA P4PB 400-FL (rev B2) motherboard after around 2
years of service.
Had a bitch of a time finding a replacement MB that would run my
video card (AllInWonder TV in etc).
After trying many other vid cards in one of the MBs, research
indicated that *NOBODY* specifies which protocol / spec the video card
supports (most MBs seem to do that).
Real bitchy.
But i was lucky in that i found (new looking and sealed) VIA P4PB
400-FL (rev C2) MBs and got two.
Bought some chip caps to parallel the same-size large caps that went
bad on the original board.
Despite the 2-year time frame and knowledge of the bad cap problem,
VIA chose to use the *same* brand caps (GSC, one of the known offenders
as well).
Seems to me that a parallel chip cap will bypass those switching
spikes and so keep that stress away from the poor aluminums - and so
they should last a lot longer.
I posted the fix in ViaArena, attempting to use ASCII graphics.
Turns out their system ignores spaces between (?non-alfa?)
characters, so i tried another one that looked like a space in the
source,but got converted to a wierd character; so i gave up on that.
They do not allow pictures so too damn bad; if anyone in ViaArena
wants a picture they can either find me or attempt to complain to VIA.
 
R

Robert Baer

Jan 1, 1970
0
Jeff said:
Yes, that is / was a BIG problem. I've recapped several motherboards over
the years, as it was easier then replacing the motherboard with another
model and having to spend hours installing software.

I also recapped all the servo amplifiers (x 7?) in one of the machines we
have, as they all started leaking (120 some odd caps in total, some in very
difficult areas to reach, as large components had to be removed / desoldered
to get at them)

Another interesting failure I sometimes see is resistors with a large
voltage differential going open! Sometimes the resistor is dissipating
several watts, other times it's dissipating several uW. Removing the
resistors coating shows that the resistive material had disappeared in a
small area!
Teleportation?
 
R

Robert Baer

Jan 1, 1970
0
Phil said:
"John Larkin"





** Had to perform some emergency surgery on my PC last Friday morning.

It refused to complete boot up and presented a totally black screen when
switched off & re-tried.

Same scenario repeated exactly after 20 minutes of being off.

Suspecting a " heat "issue - I got out the vac and gave the insides a
good clean, was pretty bad around the CPU heatsink & fan.

Tried again - same scenario.

Damn !!

Then, I noticed some VERY hot mosfets in the CPU regulators and some wonky
looking electros next to them - one 1000uF, 6.3 volt Sanyo and two 1200
uF, 6.3 volt " G S C " brand.

Extracted some similar electros from another ( unused) motherboard and
replaced the ones in my PC - these new caps tested extremely low ESR,
about 30 - 40 milliohms.

Voila - the PC works fine again and those mosfets now run only warm.

Checked out the faulty electros and found they were all open circuit, the
best showed an ESR of about 10 kohms !!!

How the heck could it function with O/C caps like that ??


Moral:

Check those hard working regulator electros from time to time and replace
them all at the first sign of cap bulging or hot mosfets.



....... Phil
Better yet, on a new system (or after replacement), parallel themwith
the largest physical chip cap that will "reach" the cap pins on the
bottom of the PCB.
Materially decreases switching (spike) currents thru the 'lytics.
 
E

Eeyore

Jan 1, 1970
0
Jeff said:
Another interesting failure I sometimes see is resistors with a large
voltage differential going open!

How large ?

Sometimes the resistor is dissipating
several watts, other times it's dissipating several uW. Removing the
resistors coating shows that the resistive material had disappeared in a
small area!

Electro-migration presumably.

Graham
 
P

Phil Allison

Jan 1, 1970
0
"Jeff L"
Another interesting failure I sometimes see is resistors with a large
voltage differential going open! Sometimes the resistor is dissipating
several watts, other times it's dissipating several uW. Removing the
resistors coating shows that the resistive material had disappeared in a
small area!

** There are two cases of ( usually open cct) failure I see quite a lot:

1. Metal and carbon film resistors ( 1/2W & 1 W) of from 22k to 220k with
applied DC voltages of from 50 to 250 volts - as found in power amps, tube
amps, scope vertical amps, SMPS kick starts etc.

2. Metal and carbon film resistors of 1M ohm to 22 Mohms with applied
voltages of 500 to 2000 volts - ie monitor focus dividers.





........ Phil
 
E

Eeyore

Jan 1, 1970
0
Phil said:
** There are two cases of ( usually open cct) failure I see quite a lot:

1. Metal and carbon film resistors ( 1/2W & 1 W) of from 22k to 220k with
applied DC voltages of from 50 to 250 volts - as found in power amps, tube
amps, scope vertical amps, SMPS kick starts etc.

I recall that original VOX AC30s commonly suffered from open 100k anode load
resistors. I have no idea if that was simply poor quality components though.
This is from memory from about 30 yrs back. Since the amps couldn't have been
older than 1961 vintage IIRC, that would have made them no more than 15 yrs old
at the time.

Their Hunts coupling 0.01uF paper caps' black plastic encapsulation used to
crumble too !

Graham
 
P

Phil Allison

Jan 1, 1970
0
"Eeysore"
I recall that original VOX AC30s commonly suffered from open 100k anode
load
resistors. I have no idea if that was simply poor quality components
though.
This is from memory from about 30 yrs back. Since the amps couldn't have
been
older than 1961 vintage IIRC, that would have made them no more than 15
yrs old
at the time.


** I saw a bunch of early VOXs where 220kohm anode resistors had all gone
high - up to 1 or 2 Mohms.

But they were the notorious, C&N, carbon composition types.


Their Hunts coupling 0.01uF paper caps' black plastic encapsulation used
to
crumble too !


** Small matters compared to early VOX's penchant for delivering 300 volts
DC to the input jack ground connection.

Had a customer bring me one in that lethal condition complaining of no
sound....

A similar condition VOX laid Beatle John Lennon out flat on his back once
at a live concert - while the other Beatles played on in puzzlement.

Would have been very bad for business to have electrocuted a Beatle 20 years
before a demented Yank did so with a revolver.





........ Phil
 
M

MassiveProng

Jan 1, 1970
0
Getting those leads out of a 6 layer, board without damage
was a real challenge. But new, high quality caps did the
trick and the board has been back in service for about a
year without any more problems.


The trick to de-soldering such components in multi-layer, power and
ground plane included PCB assemblies is pre-heating the assembly so
the heat of your soldering station tip doesn't get "soaked out" too
quickly to do the job. About 180 F will offset from ambient enough to
allow you to do through-hole work. You can go higher, if you are
careful to observe what other parts are on the assembly that may not
like temperatures that are higher...

Working with mil, conduction cooled, ultra high density assemblies
has allowed me to learn a few tricks. This is but one.
 
M

MassiveProng

Jan 1, 1970
0
Had a bitch of a time finding a replacement MB that would run my
video card (AllInWonder TV in etc).


I have owned (still do) several ATI AIW cards of several different
busses, and have NEVER had a MOBO that they wouldn't run in.

The only problem is that ATI are snobs about providing fucking
drivers. So I quit buying their CRAP, because without comprehensive
driver coverage (Linux), the best piece of hardware is nothing more
than a total piece of shit when it comes to PCs.
 
M

MassiveProng

Jan 1, 1970
0
Would have been very bad for business to have electrocuted a Beatle 20 years
before a demented Yank did so with a revolver.


The world would certainly be a different place if the Beatles had
been taken from us at that time.

Damned shame that some stupid brit ambulance jock let Jimi drown in
his puke too. The world would be a different place if Jimi were still
around as well.

Today... thank god for wireless hooks on stage.
 
M

MassiveProng

Jan 1, 1970
0
Better yet, on a new system (or after replacement), parallel themwith
the largest physical chip cap that will "reach" the cap pins on the
bottom of the PCB.
Materially decreases switching (spike) currents thru the 'lytics.


Better still, pull the fucking EL cans and replace them with mil
hermetically sealed versions found at the surplus store!

They have 50 plus year life spans and NEVER... I repeat NEVER vent!
 
K

kell

Jan 1, 1970
0
On Apr 8, 5:43 am, MassiveProng
Damned shame that some stupid brit ambulance jock let Jimi drown in
his puke too. The world would be a different place if Jimi were still
around as well.
Jimi was dead long before anybody called an ambulance. The chick he
was staying with that night was a twitchy freak that ran away, and
spent the rest of her life in total denial.
 
M

MassiveProng

Jan 1, 1970
0
On Apr 8, 5:43 am, MassiveProng
Jimi was dead long before anybody called an ambulance. The chick he
was staying with that night was a twitchy freak that ran away, and
spent the rest of her life in total denial.


You may be thinking of Jim Morrison.

JIMI was still breathing when he was placed in the ambulance, and
regurgitated IN the ambulance, and drowned on it IN the ambulance.

That is the NEWS I remember hearing.
 
M

Martin Riddle

Jan 1, 1970
0
I believe it was Nichcon that had posted a warning on it web site about
cheap copies of its electrolytics. Not sure its related but the two seem to
go hand in hand.

Cheers
 
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