LeCroy WaveSurfer 24MXs-B Motherboard - Page 1
Forum section: electronics / testgear

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 07:59:29 pm
content: 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

author: Martin72
author_rank: Super Contributor
timestamp: May 08, 2022, 08:08:27 pm
content: Hi,QuoteGot an onboard beeper ?Possibilities to check CPU and RAM externally ?Can you upload a pic from the motherboard ?Martin

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 08:19:44 pm
content: 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

author: nctnico
author_rank: Super Contributor
timestamp: May 08, 2022, 08:24:54 pm
content: 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?

author: Martin72
author_rank: Super Contributor
timestamp: May 08, 2022, 08:37:53 pm
content: Quote from: tppc on May 08, 2022, 08:19:44 pmWell, that´s not a direct indicator except the RAM got an short circuit.QuoteSeems to be a µATX board with 20-pin ATX supply connector, would check the fuses too like nctnico suggest.QuoteA pic from the top-side of the board would be very helpful - For you, in the end..(Because chances are high to identify it)

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 08:40:11 pm
content: 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)

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 08:49:04 pm
content: Quote from: Martin72 on May 08, 2022, 08:37:53 pmYes, 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

author: Martin72
author_rank: Super Contributor
timestamp: May 08, 2022, 08:54:05 pm
content: Hi,QuoteActually 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:QuoteNo problem, take your time.

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 08:59:11 pm
content: OK, I' m returning to my lab, for a teardown...

author: Martin72
author_rank: Super Contributor
timestamp: May 08, 2022, 09:05:15 pm
content: It´s a good scope and worth some efforts...https://cdn.teledynelecroy.com/files/pdf/wavesurfer_mxs-b_datasheet.pdf

author: TheBay
author_rank: Unknown
timestamp: May 08, 2022, 09:15:44 pm
content: Check across all the ceramic capacitors with a multimeter for shorts/low impedance. And then check the MOSFETS.

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 09:17:11 pm
content: Quote from: Martin72 on May 08, 2022, 09:05:15 pmMuch too good for me, will take me ages to read the manual

author: TheBay
author_rank: Unknown
timestamp: May 08, 2022, 09:18:43 pm
content: Lots of tantalums to check on the top side of that board!

author: TheBay
author_rank: Unknown
timestamp: May 08, 2022, 09:22:42 pm
content: 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.

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 09:28:49 pm
content: 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.

author: TheBay
author_rank: Unknown
timestamp: May 08, 2022, 09:33:07 pm
content: Quote from: tppc on May 08, 2022, 09:28:49 pmThat 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.

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 09:43:53 pm
content: Quote from: TheBay on May 08, 2022, 09:22:42 pmYes, 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.

author: free_electron
author_rank: Super Contributor
timestamp: May 08, 2022, 09:47:17 pm
content: https://www.ebay.com/itm/362087872172

author: TheBay
author_rank: Unknown
timestamp: May 08, 2022, 09:47:53 pm
content: Quote from: tppc on May 08, 2022, 09:43:53 pmDid 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.

author: Martin72
author_rank: Super Contributor
timestamp: May 08, 2022, 09:53:47 pm
content: Quote from: tppc on May 08, 2022, 09:17:11 pmDuh, that is what I would call a real OEM board...You won´t get an substitute except from lecroy itself.QuoteIs 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...

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 09:54:43 pm
content: 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

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 09:58:05 pm
content: Quote from: Martin72 on May 08, 2022, 09:53:47 pmOK, I'm going downstairs to check this too

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 10:31:18 pm
content: OK, I tested all your good ideasPS/2 Keyboard : Leds brieflly light up at power on but then no reaction to Caps lock/Num LockBIOS 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/railLooks like the damage is on the board, not the RAM nor the CPU.Next step will be to test/unsolder tantalums and ceramic caps.

author: tppc
author_rank: Regular Contributor
timestamp: May 08, 2022, 10:34:22 pm
content: Quote from: free_electron on May 08, 2022, 09:47:17 pmHi,thanks for the link, but this one misses the PC104 interface.Thanks anyway.

author: tppc
author_rank: Regular Contributor
timestamp: May 29, 2022, 08:34:58 am
content: Hi there,just an update.I lifted all tantalum caps + all mosfets on the mainboard.none of them tested badAnd 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.

author: nctnico
author_rank: Super Contributor
timestamp: May 29, 2022, 11:22:12 am
content: Did you try a different processor and RAM? Get a different board (known good) with processor and RAM so you can swap things over. I would have done that before attacking (and possibly damaging) the board!

author: tppc
author_rank: Regular Contributor
timestamp: May 29, 2022, 08:21:11 pm
content: Well, I actually have a second unit (fully working identical oscilloscope).But :- To gain access to the motherboard, you need to disassemble the whole instrument (tens of screws) + remove all other boards, which is a real pain in the butt- I did not dare swapping parts from the good unit to the bad one, because, if I burn the good parts on the bad scope, then I would lose both units.

author: nctnico
author_rank: Super Contributor
timestamp: May 29, 2022, 08:38:03 pm
content: I agree that using the parts from a working unit isn't the best idea.For such tests you have to buy a motherboard that is compatible with the processor and the memory (preferably with processor + memory so you have a working combination but also make sure to buy a processor and memory). It doesn't matter whether this motherboard fits the oscilloscope or not, the intention is to find out which part is faulty. From what you have posted so far it seems you don't know whether the motherboard, processor or memory is faulty. The first step towards a succesfull repair is to determine which part is actually faulty.

author: tppc
author_rank: Regular Contributor
timestamp: May 29, 2022, 08:54:06 pm
content: I can be wrong, but my feeling is that :a) RAM + CPU are OKb) Motherboard is defective.I removed both RAM + CPU and I still measure 8 Ohms across some unknown supply rail on the mobo.(not on any of the ATX connector pins)BTW all voltages on the ATX connector are OK.My feeling is that there is some low voltage (1, something volts) generated on the motherboard that could be defective.The problem is that there is no indication on the silkscreen that would show the low voltage rails, I don't know, 1.7 V or whatever...

author: nctnico
author_rank: Super Contributor
timestamp: May 29, 2022, 09:09:26 pm
content: Measuring 8 Ohm on a supply rail can be OK; it is not out of the ordinary. Again: first determine 100% which component (motherboard, CPU or memory) is actually faulty through elimination. Guessing leads to destroying good components.

author: tppc
author_rank: Regular Contributor
timestamp: May 29, 2022, 09:18:29 pm
content: Quote from: nctnico on May 29, 2022, 09:09:26 pmOK, thank you for this information, I thought it was too low.I will follow your indications and find a way to test CPU + memory.Thanks.

author: nctnico
author_rank: Super Contributor
timestamp: May 29, 2022, 09:27:54 pm
content: With a working motherboard, you can also check supply voltages around the CPU and compare with your non-working board. Don't stick the 'new' CPU into the non-working motherboard immediately; use it to collect data on the working motherboard first.

author: zhongzuocheng520
author_rank: Contributor
timestamp: December 19, 2022, 08:01:42 am
content: Hello friendI have a 44MXI-B fault that has not been resolved, but I have found a circuit diagram of the motherboard that is not customized. I hope it can be repaired. I hope this can help you

author: coromonadalix
author_rank: Super Contributor
timestamp: December 19, 2022, 11:43:46 am
content: the mainboard is supposed to be an BCM MX945GME-LC Notice the LC ending, it's because of the pc104 interface, Custom board made for LeCroy .... seen that on some threadsThe best bet would be to find a BCM MX945GME no lecroy variant and use an pci to pc104 converterlike this ??https://www.winsystems.com/product/pci-ppm/https://connecttech.com/product/pci-to-pc104-plus-adapter/Ans if the coin cell batterie dies on some scope, the modo settings are lost and when the board boot youll get many errors, if you mobo still bootAnd i think you are going too fast to check this and that, the psu is always the prime suspect, check if you can find the psu pinouts, and normally you are supposed to get an always present voltage, IE: a 5v standby or some rare instance an 12vThe best would be to get an Intel 945 motherboard and try on it your cpu and ramThis is a BCM EOL warning in 2011https://www.bcmcom.com/e-ad/eletter_07282011_MX945GME_Last_Time_Buy_notice.htmbut i think it is the normal versionyour bet will be to find a board who goes there, with an pc104 adapter and restart everything, if you dont have hidden problems elsewhere,find the drivers etc ....For a start you should clone the drive before any attemptIf you search BCM MX945 on fleabay, you have some results of normal motherboards, it could be a start and try to build something ou of themThe best and only one low priced 100$ is this :https://www.ebay.com/itm/255581180240?If you search MX945 motherboards you have more of them starting at 50$You are for the long run if the motherboad is dead, and a pci to pc104 adapter must be sold $$

author: ddrl46
author_rank: Regular Contributor
timestamp: December 19, 2022, 12:41:26 pm
content: A while ago I had a Lecroy 44Xi-A which wouldn't boot either with similar symptons to your unit. Turned out to be a bad RAM stick in that case.

author: zhongzuocheng520
author_rank: Contributor
timestamp: January 03, 2023, 10:52:19 am
content: Thank you for your advice. I also searched for the motherboard. After maintenance, I found a problem with the original motherboard. The BIOS failed. I found a replacement code and wrote it in to start it. However, many settings are different, and failures can occur again after multiple starts. I don't know whether it is a program mismatch or a BIOS problem. It is difficult to solve without the original BIOS code.

author: zhongzuocheng520
author_rank: Contributor
timestamp: January 04, 2023, 12:54:33 am
content: Hello, my motherboard was repaired last night. It's a BIOS fault. I re burned the code. This is the website providing files. I hope it can help you：https://groups.io/g/LeCroyOwnersGroup/message/5694?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3Arecentpostdate%2Fsticky%2C%2Cbios%2C20%2C2%2C20%2C82659882

author: coromonadalix
author_rank: Super Contributor
timestamp: January 04, 2023, 01:08:34 am
content: https://groups.io/g/LeCroyOwnersGroup/message/5694?file zipped attached