MS-7411 No post... help

[80sman]

Hi,
I've bought a suspect board off of ebay, mostly because I enjoy projects and repairs.

It's a MS-7411 media live diva motherboard, which is fairly unique (I have one already which works) in that it has an add-on 100W x 5 audio amplifier.

I'd like to get this one working as a second system.

I've tested it with known working components from my good motherboard.

Ok - Tested on bench with cpu + cooler, 1 stick of ram, mouse and keyboard and psu.

All plugged in, switch on by shorting the pins on the motherboard and the psu fan kicks slightly and nothing else happens, the psu fails to start.

The green led on the motherboard is on.


If I unplug the 4 pin cpu power cable from the motherboard and switch on the board, the psu powers up, although of course there is still no post.

It reacts the same whether there are components fitted to the board or not. Anyone come across this behaviour before?

My guess is that there is a short on the board which is setting off a protection circuit within the psu, and shutting it down. Removal of ac power is required to reset.

I'm not sure that this sounds like a cap problem but would love to be proved wrong.

Thanks

[kc8adu]

Re: MS-7411 No post... help

you guess correct.shorted mosfet in vrm.

[80sman]

Re: MS-7411 No post... help

Thanks for the reply.

Is there an easy way to tell which one is shorted and is it realistic for me to replace?

I had a suspicion that it was the mosfets and have examined them carefully, there's no obvious damage to them, no burn marks.

There are quite a few reports of this motherboard failing in this manner from others, do you think it's likely that msi have used a bad batch of mostfets and if this is the case am I going to be better off replacing all the the mosfets in the vrm?

Thanks

[80sman]

Re: MS-7411 No post... help

Sorry need help again.

I've tried to follow the mosfet test guideline http://www.4qdtec.com/mostest.html to check my vrm mosfets.

I have 9 mosfets in total, it's a 3 phase board. 6 of them have a high reading between the gate and source, and a low reading between drain and source.

3 of them are short circuit on all legs...... does this mean they're shorted and need replacing? I'm guessing maybe yes....

Next question,

Why would 3 mosfets have shorted simultaneously..... does this indicate a failure elsewhere and if I replace these 3 mosfets would they just fail again quickly.

Something just seems odd to me that all 3 mosfets are short in the same phase.

Hope you can help.

Thanks

[80sman]

Re: MS-7411 No post... help

bit more info:

I was being a bit dense I think, the whole circuit is shorted , so I would get a shorted reading off the three mosfets in phase. Only thing I don't know is whether it's on of the mosfets thats gone short or not. I would guess (again) that the only way is to remove them from the board and test them.

I might need a little help locating replacements. The part number on the mosfet is:

NIKOS
P70N02LDC
GN20k2R03

I've found a datasheet of a similar number, but not exactly the same, can you tell me what the differences are likely to be and what a good suitable replacement would be.

Thanks

http://pdf1.alldatasheet.net/datashe.../P70N02LS.html

[Toasty]

Re: MS-7411 No post... help

http://products.niko-sem.com/index_e...od_list&cat=24

Go to digikey.com or mouser.com and start looking up the MOSFET's and try to match the spec's on that page and the PDF datasheet.

If you have no luck with a close match, try an email to them and feed them a good story about testing or a school project. You might just get a bunch of FREE samples... (or at least be asked to cover the shipping)

Toast

[80sman]

Re: MS-7411 No post... help

Thanks for the link Toasty,

It's a G on the end not a C

P70N02LDG

Found the data. I'm based in the uk, so will try Farnells for similar.

[80sman]

Re: MS-7411 No post... help

I've found this mosfet with similar specs, can someone have a quick glance to see if there would be any problems replacing with these.
http://uk.rs-online.com/web/search/s...duct&R=6504873

The specs of my mosfets are
Original--------------------- Replacement
P/No - P70N02LDG-----------IRLR8713
Package - TO-252-----------DPAK
Config - Single
Type - N--------------------N
VDS - 25v-------------------25V
VGS MAx - 20V--------------20V
ID - 65A--------------------100A
rds(on) @ 4.5v - 15mOhms---6.3mOhms
rds(on) @ 10v - 8.5mOhms---4.8mOhms
Ciss - 1200------------------2240
Crss - 350-------------------270
Qg - 25----------------------26
QDG - 10---------------------5.8

And will I need to replace the caps in the vrm to match with the changed capacitence characteristics of the mosfets?

[Toasty]

Re: MS-7411 No post... help

The G means lead-free for that device per the spec sheet.

Your matches for voltage and current are fine. Your critical specs are the timing ones. Replacement should be equal or better (faster) than original. Your replacement choice does not.

Watch these parameters closely:
td(on) = Turn-On Delay
td(off) = Turn-Off Delay
tr = Rise Time
tf = Fall Time
trr = Reverse Recovery Time

All are in nanoseconds (ns)

Toast

[80sman]

Re: MS-7411 No post... help

I can't find the rest of the data for the P70N02LDG where did you get the timings from?

I checked the datasheet for the P70N02LS but the voltage figures differ. So I don't know if I can rely on the timing figures given there.

Thanks

[Toasty]

Re: MS-7411 No post... help

Well, I DID attach the PDF files but the server seems to have dropped them. Let's try this again shall we?

ARRRGH!!! Stupid file upload size limits for PDF's. Let me screw with them for a bit and get the size down.

Toast

[Toasty]

Re: MS-7411 No post... help

Link to your replacement choice: (Also found on the RS page.)

https://cdn.badcaps-static.com/pdfs/...a2dbf734a5.pdf


The NIKOS sheet:


Toast

[80sman]

Re: MS-7411 No post... help

Thanks for your help Toasty, much appreciated.

The NIKOS datasheet you linked to is the P45 not the P70.

I've found a datasheet for the P70N02LD which has slightly different specs (although I would imagine similar) to the P70N02LDG.

It's giving me a:
TD (on) 7
TD (off) 24
Tr 7
Tf 6
Trr 37

I've not been able to find anything around 65amps 25volts with better timings than this. Any suggestions?

[Toasty]

Re: MS-7411 No post... help

Yup. My bad. Google returned the P45... when I specifically typed in P70...

POS search engine. Always hated, always will.

Before you go any further, desolder the 2 legs on each of these that show shorted and confirm that they are. Then we can proceed to find something close enough to work.

Another bad board would probably do to get replacements if we are unsuccessful in finding a x-ref.

Other manufacturers such as ST Microelectronics, Fairchild, Sanyo, Advanced Power are just a few that make these devices. Somebody's got to be close to these specs.

Toast

[Toasty]

Re: MS-7411 No post... help

FYI - I have sent a sample request to NIKO and a cross reference request to Infineon (DigiKey is a distributor).

[80sman]

Re: MS-7411 No post... help

Thanks for the help

I de-soldered the legs on the 3 mosfets, the circuit is no longer short circuit. Unfortunately my soldering skills are a little rusty and I need 3 new mosfets

My soldering iron is 50w but has too small a tip on it, need to buy a bigger one I'm losing the heat out of it too quick.

Murphy's law that it had to be the last one I removed out of the 3

[Toasty]

Re: MS-7411 No post... help

The circuit is no longer shorted or the MOSFET's no longer show shorted.



TOast

[80sman]

Re: MS-7411 No post... help

Sorry the circuit is no longer shorted.

Just need 3 new mosfets

Before measuring resistance through the pins on the atx connector it was short circuit. Now it's not.

Although it was right up until I de-soldered the last mosfet.

[80sman]

Re: MS-7411 No post... help

Currently bidding on another dead board on ebay. Hopefully I'll win it and can get the mosfets off......

Another question..... this paticular revision board from msi has had many many reports of failing mosfets. Is there anything I need to have a good look at to see if there's a reason why?

My first thought (after reading some of the posts here) is that maybe the manufacturer has installed some of the capacitors backwards.

Or is it just a duff run of manufactured mosfets?

Or would a malfunctioning mosfet controller cause a mosfet to short? Some of these boards have failed within the first few hours, others have been within the first few days.

I have one of the first revision boards in my computer that's been fine for the last 6 months, it's the 2nd revision that looks to be the problem.

Thanks

edit:: Extra info, none of the boards (that I've heard of) have had the mosfets melt etc, they've all shorted to ground. Don't know if this makes a difference.

[kc8adu]

Re: MS-7411 No post... help

bad caps will kill mosfets too.
https://www.badcaps.net/forum/showthread.php?t=211