Computer won't boot up - mobo?

CBFalconer wrote:
Pete Zahut wrote:
kony wrote:

... snip ...

Possibly a case standoff installed where there shouldn't be
one, or something else causing a short? Just grabbing at
straws, possibly the board has a broken solder joint(s) or
cracks in it and the different orientation or not being
screwed down has caused these broken part(s) of a circuit to
temporarily be continuous again.

You could well be right Kony, I'll have to see what happens
when I put everything back in the case again. It's now been
running a burn-in program for the last 12 hours without any
problems so I'll take this opportunity to say thanks very much
to all who replied and offered help - much appreciated.

No. First examine (with great care) all the areas where standoffs
touch the mother board, and examine the mounting screws too. They
may need insulating washers.

Good advice Chuck and I was going to do that anyway. I couldn't see anything
obvious but, working on the premise that insulating washers would do no
harm, I fitted them anyway and all is now well.

"Pete Zahut" dont@bother wrote in message
...
CBFalconer wrote:
Pete Zahut wrote:
kony wrote:

... snip ...

Possibly a case standoff installed where there shouldn't be
one, or something else causing a short? Just grabbing at
straws, possibly the board has a broken solder joint(s) or
cracks in it and the different orientation or not being
screwed down has caused these broken part(s) of a circuit to
temporarily be continuous again.

You could well be right Kony, I'll have to see what happens
when I put everything back in the case again. It's now been
running a burn-in program for the last 12 hours without any
problems so I'll take this opportunity to say thanks very much
to all who replied and offered help - much appreciated.

No. First examine (with great care) all the areas where standoffs
touch the mother board, and examine the mounting screws too. They
may need insulating washers.

Good advice Chuck and I was going to do that anyway. I couldn't see
anything obvious but, working on the premise that insulating washers would
do no harm, I fitted them anyway and all is now well.


It may not apply here. I did run across one motherboard a few years ago
that required chassis grounding via a screw through one standoff to the PC
chassis. I was using just stand-offs. PC would do nothing until I found
that ground requirement.
--
Dave

CDOs are how we got here.
A modified version, new taxes in the future, is how Congress will get us
out?

Lil' Dave wrote:

It may not apply here. I did run across one motherboard a few years ago
that required chassis grounding via a screw through one standoff to the PC
chassis. I was using just stand-offs. PC would do nothing until I found
that ground requirement.

Without proper grounding of the motherboard mounting points, the risk
also is transmission of radio frequency interference through any
transmissive voids of the enclosure. Also where external cables connect
to the motherboard, and are not immediately connected to case ground,
there is potential for these leads to further radiate RF acting as
external antenna.

The issue is not the usage of ground points (I use as many as I can),
but the application of screw heads and conductive posts that are too
large in comparision to the area allocated for them on the PCB, and
hence causing ground shorts to other components.

--
Adrian C

Lil' Dave wrote:
"Pete Zahut" dont@bother wrote in message
...
CBFalconer wrote:
Pete Zahut wrote:
kony wrote:

... snip ...
Possibly a case standoff installed where there shouldn't be
one, or something else causing a short? Just grabbing at
straws, possibly the board has a broken solder joint(s) or
cracks in it and the different orientation or not being
screwed down has caused these broken part(s) of a circuit to
temporarily be continuous again.
You could well be right Kony, I'll have to see what happens
when I put everything back in the case again. It's now been
running a burn-in program for the last 12 hours without any
problems so I'll take this opportunity to say thanks very much
to all who replied and offered help - much appreciated.
No. First examine (with great care) all the areas where standoffs
touch the mother board, and examine the mounting screws too. They
may need insulating washers.
Good advice Chuck and I was going to do that anyway. I couldn't see
anything obvious but, working on the premise that insulating washers would
do no harm, I fitted them anyway and all is now well.


It may not apply here. I did run across one motherboard a few years ago
that required chassis grounding via a screw through one standoff to the PC
chassis. I was using just stand-offs. PC would do nothing until I found
that ground requirement.

On the motherboards I've looked at, the mounting holes all have a
conductive ring (a so-called "plated hole") and the conductor
is connected to ground. That tells you that they want the motherboard
to ground to the chassis metal, at the nine mounting points.

If they really intended the motherboard to be insulated, they can remove
the plated ring and have bare, insulating PCB material. That would
easily result in perfect insulation. So the designers have added the
copper there, on purpose.

Ground is also established via the black ground wires in the main power
cable, so there is already a ground connection. Insulating all the
standoffs, should still allow the motherboard to operate, since it
has the black ground wires from the power supply.

The main value of ground points on the bottom of the motherboard,
is better control of electromagnetic interference from the PCB.

Similarly, there are "spring fingers" on the I/O plate, which
press on the metal housings of the I/O stacks. The spring fingers
are there to ground the housings, and better control EMI from the
I/O area.

Paul

On Fri, 27 Feb 2009 10:53:15 -0000, "Pete Zahut"
dont@bother wrote:

CBFalconer wrote:
Pete Zahut wrote:
kony wrote:

... snip ...

Possibly a case standoff installed where there shouldn't be
one, or something else causing a short? Just grabbing at
straws, possibly the board has a broken solder joint(s) or
cracks in it and the different orientation or not being
screwed down has caused these broken part(s) of a circuit to
temporarily be continuous again.

You could well be right Kony, I'll have to see what happens
when I put everything back in the case again. It's now been
running a burn-in program for the last 12 hours without any
problems so I'll take this opportunity to say thanks very much
to all who replied and offered help - much appreciated.

No. First examine (with great care) all the areas where standoffs
touch the mother board, and examine the mounting screws too. They
may need insulating washers.

Good advice Chuck and I was going to do that anyway. I couldn't see anything
obvious but, working on the premise that insulating washers would do no
harm, I fitted them anyway and all is now well.



Insulating washers should not be needed, as Paul noted a
board is designed to be grounded through the standoffs.

What I'd meant in my prior remark about standoffs is that
possibly there is a standoff installed in the case that
shouldn't be there at all, with no corresponding hole in the
motherboard through which to secure it.

One common location where there might be such a standoff is
on the left-hand side, second hole up from the bottom of the
case (if it's a full sized ATX, not mATX board).

"Paul" wrote in message
...
Lil' Dave wrote:
"Pete Zahut" dont@bother wrote in message
...
CBFalconer wrote:
Pete Zahut wrote:
kony wrote:

... snip ...
Possibly a case standoff installed where there shouldn't be
one, or something else causing a short? Just grabbing at
straws, possibly the board has a broken solder joint(s) or
cracks in it and the different orientation or not being
screwed down has caused these broken part(s) of a circuit to
temporarily be continuous again.
You could well be right Kony, I'll have to see what happens
when I put everything back in the case again. It's now been
running a burn-in program for the last 12 hours without any
problems so I'll take this opportunity to say thanks very much
to all who replied and offered help - much appreciated.
No. First examine (with great care) all the areas where standoffs
touch the mother board, and examine the mounting screws too. They
may need insulating washers.
Good advice Chuck and I was going to do that anyway. I couldn't see
anything obvious but, working on the premise that insulating washers
would do no harm, I fitted them anyway and all is now well.


It may not apply here. I did run across one motherboard a few years ago
that required chassis grounding via a screw through one standoff to the
PC chassis. I was using just stand-offs. PC would do nothing until I
found that ground requirement.

On the motherboards I've looked at, the mounting holes all have a
conductive ring (a so-called "plated hole") and the conductor
is connected to ground. That tells you that they want the motherboard
to ground to the chassis metal, at the nine mounting points.


Imagine seeing this about 11 yeara ago for the first time after using
strictly standoffs for so many PC builds? No information in installation.
Trial and error. You get my drift...
--
Dave

CDOs are how we got here.
A modified version, new taxes in the future, is how Congress will get us
out?

"Pete Zahut" wrote:
Kony/Anna/Peter - not measured voltages because (at that time anyway) the
motherboard was still in the case and it was very difficult to get the
probes into the connector.

Acquire a short length of "twisted pair" solid telco cable (22 or 24ga).
Strip the outer sheath to expose the wires inside, and cut two six-inch
lengths. Strip a half inch off of each end, and curl one end up. Grab the
curled end in the alligator clips at the end of your multimeter leads, and
the other end will fit nicely into the PSU molex connectors (or most any
other little connector).

because faults don't just fix themselves - but it has.

You'd be surprised how many times things get fixed by just taking them apart
and looking at them. Sometimes I think they get lonely and break themselves
just to see if anyone still cares enough to poke around inside of them.

Jon

"Jon Danniken" wrote in message
...
"Pete Zahut" wrote:
Kony/Anna/Peter - not measured voltages because (at that time anyway)
the motherboard was still in the case and it was very difficult to
get the probes into the connector.

Snipped some


because faults don't just fix themselves - but it has.

You'd be surprised how many times things get fixed by just taking them
apart and looking at them. Sometimes I think they get lonely and
break themselves just to see if anyone still cares enough to poke
around inside of them.

Jon

That made me smile Jon.
And there`s a lot of truth in there somewhere. % )

Jon Danniken wrote:
"Pete Zahut" wrote:
Kony/Anna/Peter - not measured voltages because (at that time anyway) the
motherboard was still in the case and it was very difficult to get the
probes into the connector.

Acquire a short length of "twisted pair" solid telco cable (22 or 24ga).
Strip the outer sheath to expose the wires inside, and cut two six-inch
lengths. Strip a half inch off of each end, and curl one end up. Grab the
curled end in the alligator clips at the end of your multimeter leads, and
the other end will fit nicely into the PSU molex connectors (or most any
other little connector).

because faults don't just fix themselves - but it has.

You'd be surprised how many times things get fixed by just taking them apart
and looking at them. Sometimes I think they get lonely and break themselves
just to see if anyone still cares enough to poke around inside of them.

I had a networked printer twenty years ago that was bipolar. It would
work like a fiend for three weeks in a row, but would inevitably fall
into a funk. Fortunately, a few minutes of attention--pushing buttons,
unplugging cables, etc.--would bring it around again.