Frank said:
I think I have correctly diagnosed a problem with my PC. It now
completely refuses to start. I don't hear any beep shortly after
powering up - POST has not completed? Nothing appears on screen. So the
CMOS battery needs replacing??
My system is old (>10yrs) - ABIT KG7-Raid motherboard.
Fortunately I recently had the same problem but the system recovered so
I made a note of all the CMOS settings.
Assuming a correct diagnosis, I have 2 questions:
1> Battery: I have never replaced a battery before and the system is
more than a decade old. Is this lifespan normal? My system is up and
running for just a few hours a day. Are the batteries rechargeable?
(CR2032).
2> BIOS: At this point powering up does not activate anything on screen.
Is that normal, i.e. will replacing the battery get me back to where I
can get into the BIOS and re-fill the CMOS?
Thanks
Frank
There is a failure here, with bad caps (bulging or leaking capacitors).
http://www.badcaps.net/forum/showthread.php?t=1286
I wouldn't jump to any conclusions just yet.
Yes, a flat CR2032 can prevent *some* motherboard designs from starting.
And ten years of life for your CR2032 is pretty good.
If the +5VSB is available for the entire ten years, then no current
is drawn from the CR2032. The shelf life of the battery under no
load, might approach ten years. The motherboard is not allowed
to charge those batteries, because the battery would explode
if you did that. Really old motherboards used NiCd batteries,
which would leak and corrode the motherboard - but those actually
charged from the supply. CR2032's have to last all on their own,
no charging allowed. The max charge current allowed is 1 microamp,
so they're serious about allowing current to flow into them.
Current may only flow out.
If the operator turns off all power at the end of each day's eight
hour session, you might get three years from the battery before it is
flat.
If the fans spin when you turn it on, the power supply is making +12V.
But if the motherboard doesn't use the ATX12V 2x2 power connector, the
processor may actually be running off +5V.
With a multimeter you could check the power supply voltages,
just to get some idea. Power supplies are pretty unreliable,
so it could be the power supply which has the leaking caps.
I lost a couple Antec supplies that way.
Changing the CR2032 is certainly cheap, and they are readily
available. Don't buy them from sources that have known poor
turnover. (Like that battery store at the mall, that eventually
left the mall.) A big box store, might have a decent
turnover, so you get a fresh one, and not some old piece
of crap.
So try your idea out, with no guarantees.
1) Could be CR2032 is flat. Only a few motherboard designs
seem to stop dead when that happens. Many others, you can
set the clock in the BIOS (as it loses the correct time),
and boot with a flat battery. The power path there is dual
source, and the battery is diode ORed with a +5VSB derived
source of 3VSB. On my motherboards here (of which many will
have flat batteries), I just enter the BIOS, correct the
settings and they boot. They lose the time and all settings
at the end of the day, but the next day I can turn on,
press <Del>, enter the BIOS and set the BIOS up again, and
away we go. But a few motherboards will black screen like
yours.
2) Visually inspect motherboard for bulging/leaking tops of
capacitors. Especially on the VCore capacitors around the
CPU socket area.
3) If still no relief, pull the power supply, taking note of
where all the wires go, the polarity (which pin took yellow
+12V etc). Make sure AC is removed from the supply. Unscrew
the four top screws on the cover, and *just look*. If you
see rust colored stains on the top of the caps, put the
cover back on the PSU and replace it. For older systems, with
heavy 3.3 or 5V loading, you want a supply from an older era,
with "beef" on those rails. So if the supply does not use
the ATX12V type 2x2 power connector (two yellow, two black
wires), then look for a supply with perhaps 5V @ 25A.
Let's look at a supply, to see the potential problems.
http://images17.newegg.com/is/image/newegg/17-159-043-S04?$S640W$
Yes, 3.3V @ 30A and 5V @ 28A. I could run my Nforce2 motherboard
from that. Mine used to draw just over 20A on +5V, so that supply
appears to have just enough headroom. But be aware of the number
just below that. "Max combined power in watts on +3.3V and +5V
at any time = 130W". If the 5V load goes to max, there is zero
power rating left, to supply any 3.3V! Maybe that thing would
work, but I might want to look at some others.
Now if we look at my old fav, the B204
http://images17.newegg.com/is/image/newegg/17-103-013-S03?$S640W$
3.3V @ 30A, 5V @ 28A, combined limit 150W on both rails.
That leaves some room for both rails to get power.
The video card might draw 6A from 3.3V. And the processor
could be using the 5V.
Some other ones I looked at, are 3.3V @ 20A and 5V @ 20A,
and some of those might be marginal. Especially the 80+ Gold
supplies, where 3.3V and 5V were never intended for heavy
loads, and they actually use a separate regulator board
to convert the main 12V rail, into 3.3V and 5V. (That's
called two stage regulation, and the PSU designer intended
for those to be powering systems that mainly run off +12V.)
The Sparkle is not the worlds best power supply. It tends
to make my UPS beep when first powered. So it has a bit
of inrush current. But at least it's "headed in the right
direction". And this has relatively good reviews, compared
to some.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817103013
*Always* check the ratings in the advert, even if you think
its the B204. As power supply companies can change nameplate
ratings while the same SKU is still being manufactured. For
example, the supply you bought last week, with lots of
Molex connectors, you could buy one today and find nothing
but SATA hard drive connectors on it. It is definitely
a caveat emptor situation. Prepare to be dissatisfied.
Have fun,
Paul
