Emaching bad power suppy

  • Thread starter Thread starter Brian Cloutier
  • Start date Start date
B

Brian Cloutier

I have a friends PC at my house to check out. It would not boot, no
activity, (Power supply fan not turning) no post no nothing. I had a 235
watt power supply laying around and replaced the 250 watt that was in the
PC. The 235 I put in powers up but still no post, no beeps, no nothing. Is
it possible that the 235 is not enough watts? I also disconnected the 2 cd
drives and just left the HD and floppy connected, still no post or beeps.

Thanks,

Brian
 
Both learn how the power supply 'system' works AND identify
the failed part before swapping anything. Previously posted
are "Computer doesnt start at all" in alt.comp.hardware on
10 Jan 2004 at
http://tinyurl.com/2t69q and
"I think my power supply is dead" in alt.comp.hardware on 5
Feb 2004 at
http://www.tinyurl.com/2musa

Takes a long time to read. Procedure can determine the
problem in but minutes. Notice the 'system' has handshaking
between PSU and controller. The 'system' is composed of three
components.
 
There is a red light on the motherboard that is on and the power supply fan
as well as the CPU fan. That is all that will work. I hooked up an extra
hard drive to one of the connecters and it spun up fine. Took out video
card to try a get some beeps still nothing. Is it worth it to try another
PS? May a 350?

Thanks Brian
 
I was walking down the street, minding my own business, when on Sun,
I have a friends PC at my house to check out. It would not boot, no
activity, (Power supply fan not turning) no post no nothing. I had a 235
watt power supply laying around and replaced the 250 watt that was in the
PC. The 235 I put in powers up but still no post, no beeps, no nothing. Is
it possible that the 235 is not enough watts? I also disconnected the 2 cd
drives and just left the HD and floppy connected, still no post or beeps.
Click to expand...

It's more likely the cheap ass mobo in the E-machine was fried by the
PS as it died. Time to get a new machine, not worth fixing.
 
Brian said:
I have a friends PC at my house to check out. It would not boot, no
activity, (Power supply fan not turning) no post no nothing. I had
a 235 watt power supply laying around and replaced the 250 watt that
was in the PC. The 235 I put in powers up but still no post, no
beeps, no nothing. Is it possible that the 235 is not enough watts?
I also disconnected the 2 cd drives and just left the HD and floppy
connected, still no post or beeps.
Click to expand...

Maybe the first PSU fried because the mobo became bad (capacitors
leaked or bulged -- see www.motherboardrepair.com) or shorted against
the case. PSUs in major brand computers are normally really high
quality and can't be damaged by the mobo, but eMachines seems to be an
exception and sometimes uses even Powmax PSUs, which are among the
worst.

If the HD spun up, it probably means that the +12V and +5.0V rails are
OK, so that leaves the +3.3V rail in question, but I have a feeling
that it's OK, too, although I had a cheapo PSU where only it failed
(when a memory module plugged in backwards). A voltage meter will tell
you for sure, and even the cheapest digital one (not analog) is very
accurate.

That 235W PSU is probably powerful enough, at least for testing the
mobo without any CD or hard drives connected, unless it's a realy bad
brand. What brand is it, anyway?
 
The 235 watt is an a-open. The original PS did not fire up at all. At
least the 235 spins the fans. However it did not power up the cd drives or
the floppy. I am begining to wonder if the original PS took out more than
the MB?

Brian
 
The cd drives both work as well as th HD's. There is no speaker on this
cheap ass machine so that is why I get no beeps. The red light on the MB
still lights up so does that mean anything?

Thanks,

Brian
 
Every device required voltages in limits. But how far
outside of those limits does the peripheral device still
function? In this case, the HD may work at voltages too low
but CD and floppy would not. Moreso, the LED will always work
when voltages are too low.

BTW, this is an example of ternary logic. You are trying to
use binary logic to solve the problem. Will not work.

Again we are back to the same problem. Wild speculation
because we do not have numbers. You have a procedure up top
that could have answered these questions in less time than it
took to post. If you really want to fix the problem AND come
out smarter, then get the meter and follow those simplistic
procedures.

"I think that the MB took out the original PS" is wrong.
Basic knowledge: Intel even defines the size of the wire that
must short out all power supply outputs ... and still a power
supply must not be damaged. This was defacto standard for
power supplies even 30 years ago. A motherboard can only
damage a power supply that was defective when purchased (IOW
bought by a bean counter mentality). Yes there are power
supplies that can be damaged by the motherboard only because
Asian manufacturers have discovered a large number of bean
counters pretending to be computer experts. Such supplies
sell at prices such as $25 and $40. But it is not the
motherboard that damages. Damage due to a bean counting
human. That type of failure is more often a complete burn out
- not your symptoms.

Get the meter and get those necessary numbers. Determine
power supply integrity in but a minute. End all these silly
speculations by having numbers.
 
The cd drives both work as well as the HD's. There is no speaker on this
cheap ass machine so that is why I get no beeps. The red light on the MB
still lights up so does that mean anything?
Click to expand...

The red light could be the indicator that the mobo is getting +5V power
from the purple standby wire, which is supposed to be live whenever the
PSU is receiving AC from the wall outlet.
 
w_tom said:
Every device required voltages in limits. But how far
outside of those limits does the peripheral device still
function? In this case, the HD may work at voltages too low
but CD and floppy would not. Moreso, the LED will always work
when voltages are too low.
Click to expand...

I'm no expert, but whenever the +5V or +12V rails were lower than
specs, I've never had an HD spin when the CD drive wouldn't work (i.e.,
not play music), but I have had CD drives work when the HD wouldn't
spin. As for the mobo LED, every +5V standby rail I've measured either
worked within specs or put out 0V, nothing in between, except in the
case of one cheapo PSU where it would drop to +4V and then to 0V after
being loaded to less than half capacity for about 30 seconds.
"I think that the MB took out the original PS" is wrong.
Basic knowledge: Intel even defines the size of the wire that
must short out all power supply outputs ... and still a power
supply must not be damaged. This was defacto standard for
power supplies even 30 years ago. A motherboard can only
damage a power supply that was defective when purchased (IOW
bought by a bean counter mentality).
Such supplies sell at prices such as $25 and $40. But it
is not the motherboard that damages. Damage due to a bean
counting human.
Click to expand...

How is the average person supposed to know if a PSU is defective before
purchase, especially if it came with a major brand computer? All retail
PSUs are claimed to be protected against overloads, whether that
protection works or not, and reviews aren't reliable because only 2-3
websites apply full loads the PSUs. And prices mean little -- my
$10-25 PSUs were able to out out more than their rated power and
withstand shorts, and one even survived an accidental short to ground
of its high voltage MOSFETs. OTOH a fairly high priced 500W Ultra
Connect-X recently failed during one magazine's 350W load test.
Get the meter and get those necessary numbers. Determine
power supply integrity in but a minute. End all these silly
speculations by having numbers.
Click to expand...

He said that two PSUs were tried (at least one is known to be high
quality), and mobo doesn't fully turn on with either of them. That's
why I suspect the mobo.
 
Thanks for the post. The original PS was dead. The A-open I tried worked
but MB did not respond.
 
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