Bad hotflash!

Hot-swapping and Boot-Block flash & Boot block flash and floppy support
KenH
Chip off the ol' block
Posts: 110
Joined: Wed Mar 30, 2005 7:11 pm

Do any of the electrolytic capacitors look bulged on top instead of flat,
even just remotely bulged.? I'd still suspect bad capacitors as CP
suggested..
I've lost count on how many boards I've revived by replacing most of
the capacitors on them, & I'm just a novice playing with this stuff for
fun...
If you do attempt to desolder some to test them, don't make the same
mistake I've made...
If there are places on the board that look like capacitors were marked
to go, but never used, color them in with black texta 1st before
de-soldering the one's that are there, you'll pull 9 to test them, then
realize there's places for 11 or so to go & think shite, what now...

I pulled 9 1000µF capacitors off a MS-6378 socket 462 board this
weekend just gone, all 9 were dead, some even spewed yellow goo
from under them yet look OK on top,
the board was given to me as it was dead, now I
have a working system...{ although no agp slot & 8mb onboard video
doesn't really excite me}{ hard to believe for a socket 462 board}

& just now thought I still have them plus some dead 1500µF pulled
from 5 acer veriton systems, so whilst writing this,I thought I'd test
a theory, sure enough, the dead ones I pulled wouldn't hold a 5v charge..
pulled some good ones out & found they held a charge even when
only connected for a split second...
In fact one of these dead ones got real hot just now connecting
5 volts to it for a split second so I wouldn't hold a charge on it for
much longer.
I've seen these things go off like a cracker...
cp
BIOS Guru
Posts: 1914
Joined: Mon Oct 21, 2002 9:07 pm
Location: Germany

yes, sorry, 3.3V is okay for that chip. i assumed a 5V type since you didn't specify the model.
looks like the voltages are all okay on your board. next thing would be to check the capacitors as KenOath already suggested. you can check the connectors for bend pins, too. but that's quite unlikely since the board died while it was in full use.
rapideyevj
New visitors - please read the rules.
Posts: 10
Joined: Sun Aug 27, 2006 1:46 am

If im using a multimeter, how would i test the capacitor?
Would i use the ohm setting to check resistnace, if so what am i looking for?
it does not have a mode for testing capacitance.

Also, should i test the mosfets also?
whats the best method (multimeter) for checking these?

heres the board:
Image

Thanks in advance.
KenH
Chip off the ol' block
Posts: 110
Joined: Wed Mar 30, 2005 7:11 pm

Unless the multimeter had a capacitor tester on it, I really don't know
how else you could, other than pulling them one by one & testing them
the way I posted above, that is - to induce a small voltage into them
making sure corect polarity when connecting, & checking to see if they
hold the charge...
Of the dead ones I have pulled within the last 6 months, none would
hold a charge.
Although that wasn't how I originally tested them, lucky enough I have
a capacitance meter..

& of the lot you show above, I'd be checking the lowest µF listed ones
1st.
Everytime I pull capacitors off a board to test them, I've not yet found
the large µF rated ones to ever be a problem, only the 1000 to 1600µF
units...
But again, i'm just a novice playing with this stuff in my spare time on
weekends, others here may know better...
rapideyevj
New visitors - please read the rules.
Posts: 10
Joined: Sun Aug 27, 2006 1:46 am

I have removed and cleaned up the 4x 16v 1500uF caps.
Im sorry, im rather new to using multimeters, am i correct in connecting the Black (COM) > negative pin, and the Red (VohmMA) to the positive on the cap.

Quick questions,
Which setting on the multimeter would give me the charge?
And then, which setting would i adjust to, to measure it with?

heres a pic of my multimeter:
http://www.honeytek.com/product/en/prod ... ductid=285

Ill spend some time over the next few days reading up on how to use them ;-)

Thanks in advance
cp
BIOS Guru
Posts: 1914
Joined: Mon Oct 21, 2002 9:07 pm
Location: Germany

your dmm can not test the capacitance. but as i already stated:
hmm..there are voltmeters out there that can check the capacitance. if your's does not there's an easy (and inacurate) method to check: get a battery and hook up a 2.2kOhm resistor in series with the capacitor. measure the time it takes to charge the capacitor to 63% of the battery voltage. following the formula T=R*C the time to charge a 2200µF capacitor should be close to 5s. so if you rearrange the formula to C=T/R you can roughly tell the (real) capacitance. Better than nothing i guess...
i would follow KenOath's advice and test if those caps hold the charge. just take a known good capacitor and look how it behaves. you might even use a resistor (>1M) to let it discharge slowly.

Code: Select all

time (T) for C1 to charge
to 63% of V(BAT):

    T=C1*R1
<=> C1=T/R1


 +---R2---+
 |        |
 +---C1---+
 |  -  +  |
 |        |
 |        R1
 |        |
 |        |
 +--BAT1--+
   -    +

1. hook up everything like shown with R2 ~ 1M and battery NOT connected
2. measure the voltage across C1 (the same as across R2)
3. connect the battery
4. measure the time it takes to charge the capacitor upto 63% of the battery voltage and calculate the capacitance according to the above equation
5. disconnect the battery
6. watch the voltage across C1, it should drop very slowly

the capacitors maked yellow are buffering the cpu voltage, so you might check them first.
cp
BIOS Guru
Posts: 1914
Joined: Mon Oct 21, 2002 9:07 pm
Location: Germany

i just got my hands on some bad capacitors today. some were bloated and leaking, others looked like brand new but were damaged, too! i hooked up a multimeter and a power source, connected the source to the capacitor and measured the voltage across it. then i removed the voltage source. on the bad capacitors voltage dropped immediately to less than half the voltage! i also tested a known good capacitor: when i removed the source the voltage didn't drop at all and even after some 10 seconds it was still at the starting level. just for your information: the bloated and leaking capacitors were 'Chhsi' (infamous already) and the good looking but damaged one was 'Taicon'.
rapideyevj
New visitors - please read the rules.
Posts: 10
Joined: Sun Aug 27, 2006 1:46 am

Ive just installed a full set of caps, brand new from shuttle.
the board has posted first time, and ive just finished a 12 hour burn in test.
Volts are looking good, temps are a little higher, but thats a shuttle for ya.

Ill run though all the shutlles old caps and see what i can find.
edwin
The Hardware Archivist
Posts: 6273
Joined: Wed Mar 20, 2002 7:11 pm
Location: Netherlands
Contact:

Well done 8)
edwin/evasive

Do not assume anything

System error, strike any user to continue...
cp
BIOS Guru
Posts: 1914
Joined: Mon Oct 21, 2002 9:07 pm
Location: Germany

that's good news! congratulations! please report back which caps were blown. maybe someone else could use that information, too. thanks.
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