LeCroy WaveSurfer 24MXs-B Motherboard

[tppc]

Hi there,
I just collected a non working LeCroy WaveSurfer 24MXs-B.
When turned on, the front panel buttons light up for 1 sec, fans do spin and that's all.

No beep, no boot, nothing except the fans and LCD backlight.
I connected an external VGA monitor, but no signal.

I read that the PSU on these WaveSurfer series was often an issue.
Not this time. Mine is OK, I tested all voltages (+3.3V, -3.3V, 5V, +12V, -12V, -6V) all measured OK.

I also tried powering the motherboard with an external ATX PSU and a VGA monitor.
It does not boot, and still no VGA signal. BIOS 3V battery is OK.

Conclusion, the motherboard is Kaputt!
I also read that this mobo is unobtainium.

Does anyone have a suggestion for a replacement solution?
The board is the first series with PS/2 port and PC104 slot.

Regards,
tppc

[Martin72]

Hi,

No beep

Got an onboard beeper ?
Possibilities to check CPU and RAM externally ?
Can you upload a pic from the motherboard ?

Martin

[tppc]

hi,
thanks for the reply.

no beeper on the mobo, the beeper is on the PC104 extension board.
I tried with and without the RAM, no difference.

I have no way to test CPU/RAM externally.

Here is a picture of the back of the board (I had it on my smartphone)

Will not be able to take a picture of the other side (for the moment) since I put it back in  the scope

[nctnico]

I'd try reseating all jumpers (if any) + changing the processor and memory first. But before putting a new processor in, check the processor's supply voltage & jumpers. I also spot some fuses on the back of the board; are these OK?

[Martin72]

I tried with and without the RAM, no difference.

Well, that´s not a direct indicator except the RAM got an short circuit.

Here is a picture of the back of the board (I had it on my smartphone)

Seems to be a µATX board with 20-pin ATX supply connector, would check the fuses too like nctnico suggest.

Will not be able to take a picture of the other side (for the moment) since I put it back in  the scope

A pic from the top-side of the board would be very helpful - For you, in the end..
(Because chances are high to identify it)

[tppc]

I tested the fuses and the aluminium electrolytic caps (onboard) with a capacity + ESR meter (DER EE 5000).
All tested OK. except 1 cap which mesured 8 ohms.
I desoldered it and it tested OK (capacity + ESR OK), with the cap out, I measured the same 8 Ohms directly on the board.

So I presume the board is bad, but I have no idea of what voltage on this cap should be (not indicated).

I don't know how to test processor supply voltages (not indicated on the silkscreen)

[tppc]

Seems to be a µATX board with 20-pin ATX supply connector, would check the fuses too like nctnico suggest.

A pic from the top-side of the board would be very helpful - For you, in the end..
(Because chances are high to identify it)

Yes, it is supplied with a 20 pin ATX connector.

Yes, I will post a picture, I just need some time to remove all other boards first 

[Martin72]

Hi,

I don't know how to test processor supply voltages (not indicated on the silkscreen)

Actually it´s not important, nctnico mentioned it in the case you change the mainboard and it´s an elder board with jumpers for voltages.
Main thing actually is to show the board form the top, with a little luck we can see the brand/model and even when it´s a OEM product, chances are good to find a suitable exchange for it.

Edit:

I just need some time to remove all other boards first

No problem, take your time.

[tppc]

OK, I' m returning to my lab, for a teardown...

[Martin72]

It´s a good scope and worth some efforts...

https://cdn.teledynelecroy.com/files/pdf/wavesurfer_mxs-b_datasheet.pdf

[TheBay]

Check across all the ceramic capacitors with a multimeter for shorts/low impedance. And then check the MOSFETS.

[tppc]

It´s a good scope and worth some efforts...

Much too good for me, will take me ages to read the manual 

[TheBay]

Lots of tantalums to check on the top side of that board!

[TheBay]

Also, depending on the configuration of that board and/or BIOS settings it might not display anything on the external VGA connector.
If you haven't already tried it might be worth removing the scope board off the motherboard to test it.

[tppc]

some of the mosfets are not even accessible with standard test leads. (maybe with miniature test hooks)

As mentionned, I measured a suspicious 8 Ohms across an electrolytic cap (even with the cap removed)
The problem is that I have no idea of what supply voltage it should be.

No idea either of what components are supplied by this rail.
Maybe tens of them. Which one of them measures 8 ohms? No idea. 

[TheBay]

some of the mosfets are not even accessible with standard test leads. (maybe with miniature test hooks)

As mentionned, I measured a suspicious 8 Ohms across an electrolytic cap (even with the cap removed)
The problem is that I have no idea of what supply voltage it should be.

No idea either of what components are supplied by this rail.
Maybe tens of them. Which one of them measures 8 ohms? No idea. 

That could be a capacitor across a voltage rail and why I said check the ceramic caps and mosfets as there might be something gone s/c across the same rail.

[tppc]

Also, depending on the configuration of that board and/or BIOS settings it might not display anything on the external VGA connector.
If you haven't already tried it might be worth removing the scope board off the motherboard to test it.

Yes, I tried with the mobo out of the scope,
-PC104 removed,
- mobo powered with external ATX PSU (started by shorting green wire on the ATX connecor)
- external VGA monitor connected.
(also tried with the internal display)
Black screen, nothing, not even a cursor.

I did not test the tantalums yet, but thanks for the advice, I will test them all.

[free_electron]

https://www.ebay.com/itm/362087872172

[TheBay]

Also, depending on the configuration of that board and/or BIOS settings it might not display anything on the external VGA connector.
If you haven't already tried it might be worth removing the scope board off the motherboard to test it.

Yes, I tried with the mobo out of the scope,
-PC1014 removed,
- mobo powered with external ATX PSU (started by shorting green wire on the ATX connecor)
- external VGA monitor connected.
(also tried with the internal display)
Black screen, nothing, not even a cursor.

I did not test the tantalums yet, but thanks for the advice, I will test them all.

Did you try clearing the BIOS, as it might be set to the internal display, also plug in a PS/2 keyboard and see if the Num/caps/scroll lock LED's flash on and off when it powers up and if the num lock works on the keyboard as that will give you an idea if anything has initiated.

[Martin72]

Much too good for me, will take me ages to read the manual 

Duh, that is what I would call a real OEM board...
You won´t get an substitute except from lecroy itself.

I measured a suspicious 8 Ohms across an electrolytic cap (even with the cap removed)

Is it a constant value ?
Minus of the cap is connected to common GND ?
Then you can measure the ATX connector against GND, maybe you find the 8 Ohms on one of the pins.
Additional:
Take off CPU and RAM and measure the suspicious points again...

[tppc]

good point!
no I did'nt clear the BIOS, nor did I connect a PS/2 Keyboard.

I'm returning to the lab!

I'll be back

[tppc]

Is it a constant value ?
Minus of the cap is connected to common GND ?
Than you can measure the ATX connector against GND, maybe you find the 8 Ohms on one of the pins.
Additional:
Take off CPU and RAM and measure the suspicious points again...

OK, I'm going downstairs to check this too 

[tppc]

OK, I tested all your good ideas 

PS/2 Keyboard : Leds brieflly light up at power on but then no reaction to Caps lock/Num Lock
BIOS clear : no improvement.

Cap minus is connected to GND.
could not measure 8 Ohms on any pin of the ATX Connector.
Removed RAM + CPU, still measures 8 Ohms (constant) across the cap/rail

Looks like the damage is on the board, not the RAM nor the CPU.
Next step will be to test/unsolder tantalums and ceramic caps.

[tppc]

https://www.ebay.com/itm/362087872172

Hi,
thanks for the link, but this one misses the PC104 interface.
Thanks anyway.

[tppc]

Hi there,
just an update.

I lifted all tantalum caps + all mosfets on the mainboard.
none of them tested bad

And still this suspicious constant 8 Ohms measured over a large part of the capacitors on the board.

I don't think I can repair it.

Regards.