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Upgrading Mainboard in Lecroy DDA-3000 (aka WavePro 7300a?)

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tautech:

--- Quote from: analogRF on January 01, 2020, 11:16:42 pm ---I have been running around all day and could not sit down and concentrate on this thing... :palm:

the cmos battery was 0V which I replaced. Reseated the CPU and memory and also used anther stick of memory instead...no change...it shuts down in a second and if I manually keep it powered on, there is nothing on display (not even back light) and nothing on VGA out. no beep sound from motherboard either.

I found out that if I keep punching the power switch repeatedly and quickly it finally stays powered on and I can also power it down by
pushing and keeping the power switch. of course the result is the same, no sound and no picture...all caps around the CPU seem ok.

EDIT: and jumpers are all in the right place

--- End quote ---
That screams of bad caps on the MoBo !
Had exactly this on a working (properly configured) PC and after a couple of hits from the PSU the bad caps would allow it to boot. Nearly burnt a finger on one and once all on the same power rail were pulled, checked and replaced the PC gave zero further issues.

analogRF:

--- Quote from: tautech on January 02, 2020, 12:17:34 am ---
--- Quote from: analogRF on January 01, 2020, 11:16:42 pm ---I have been running around all day and could not sit down and concentrate on this thing... :palm:

the cmos battery was 0V which I replaced. Reseated the CPU and memory and also used anther stick of memory instead...no change...it shuts down in a second and if I manually keep it powered on, there is nothing on display (not even back light) and nothing on VGA out. no beep sound from motherboard either.

I found out that if I keep punching the power switch repeatedly and quickly it finally stays powered on and I can also power it down by
pushing and keeping the power switch. of course the result is the same, no sound and no picture...all caps around the CPU seem ok.

EDIT: and jumpers are all in the right place

--- End quote ---
That screams of bad caps on the MoBo !
Had exactly this on a working (properly configured) PC and after a couple of hits from the PSU the bad caps would allow it to boot. Nearly burnt a finger on one and once all on the same power rail were pulled, checked and replaced the PC gave zero further issues.

--- End quote ---

mmm...sounds very reasonable. After I try the mobo alone with external PSU, if that fails, I will pull it out and check the caps.

Visually they all look good though. They may have killed the CPU  :scared: is that a possibility?

tautech:

--- Quote from: analogRF on January 02, 2020, 12:28:59 am ---
--- Quote from: tautech on January 02, 2020, 12:17:34 am ---
--- Quote from: analogRF on January 01, 2020, 11:16:42 pm ---I have been running around all day and could not sit down and concentrate on this thing... :palm:

the cmos battery was 0V which I replaced. Reseated the CPU and memory and also used anther stick of memory instead...no change...it shuts down in a second and if I manually keep it powered on, there is nothing on display (not even back light) and nothing on VGA out. no beep sound from motherboard either.

I found out that if I keep punching the power switch repeatedly and quickly it finally stays powered on and I can also power it down by
pushing and keeping the power switch. of course the result is the same, no sound and no picture...all caps around the CPU seem ok.

EDIT: and jumpers are all in the right place

--- End quote ---
That screams of bad caps on the MoBo !
Had exactly this on a working (properly configured) PC and after a couple of hits from the PSU the bad caps would allow it to boot. Nearly burnt a finger on one and once all on the same power rail were pulled, checked and replaced the PC gave zero further issues.

--- End quote ---

mmm...sounds very reasonable. After I try the mobo alone with external PSU, if that fails, I will pull it out and check the caps.

Visually they all look good though. They may have killed the CPU  :scared: is that a possibility?

--- End quote ---
So did the caps in the mobo I mentioned but running a finger around them confirmed they were not !
IIRC they were on a 5V rail but of course the CPU is normally on a lower voltage rail/s however I'd be checking those caps too.
Do you have a thermal camera you can run over the mobo to check if there's some temps way out of wack/normal ?

ollopa:
CPUs rarely fail but they can't operate if the mb is holding them in reset or failing to supply the required low voltage power rails.  In my experience it's usually the motherboard that is bad and it's usually a dried out, shorted, or leaking capacitor.  Most other failure modes including bad BIOS or damaged CPU tend to require help from a stupid user rather than develop on their own over time.

The power button is just a momentary contact to signal to the MB to latch the ATX PS_ON# pin low.  If the motherboard detects any faults or fails to start then it may let the pin float high again and the power supply turns off.  The CPU failing to boot is probably a symptom rather than the root cause.  Probably.

Use the process of elimination:
Can you power up a known good MB and CPU using the scope PS?  If so then PS is good.
Alternatively, can you power the scope MB using an external PS?  If so then the MB is good and the PS, switch, or a peripheral is a likely culprit.

All that being said, I did some experimenting on my old MB since I've upgraded the one in my scope.
1) If the 4pin CPU 12V power connector is not plugged in then it will turn on for a second and turn back off.  No beeping, even if RAM is removed.
2) With the CPU 12V connector and all RAM removed, it beeps as expected.
3) With the CPU removed it will not even attempt to power on, even for a split second.
4) Of course there is a +5VSTBY LED that is always on if the PS is on.

So double-check the auxiliary 12V supply.

analogRF:
all connectors are firmly in place.

I could only find the pictured power supply in my shop which was pulled from an old HP computer. Is it enough to power this mobo?

I took all the cards out and disconnected everything from mobo except hdd, ram, cpu and connected this PSU
as soon as push the power switch (or manually pull down the Vsb on the ATX connector) the cpu fan turns for <1sec
and shuts off and with that the PSU also shuts off and cannot be turned on again unless I pull the plug
(this PSU has a green led on the back that lights up when it is plugged in and that led turns off when I try to
turn on the mobo and then there is no Vsb afterwards until i cycle power)

Heh, now is it the board or is it this funky power supply?!  but the symptom is exactly the same with the lecroy power supply.
except the lecroy psu can be kept powered on if I pull the Vsb down manually. This PSU apparently shuts off and does not turn on again.

I will have to take the mobo out at this point and check the caps I think...

oh, when I had all the cards out and even the memory out, I also connected the Lecroy PSU back again and exactly the same thing.
Fans turn for <1sec and no beeps.

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