after CPU VRM burned, CPU still good?

[kaboom]

Re: after CPU VRM burned, CPU still good?

^- Nice to hear!

Good luck with it.

[Stefan Payne]

Re: after CPU VRM burned, CPU still good?

Was able to test Windows today.
And everything seems to be working perfectly.

All 6 Cores of my E5-2630L are working, though it's only a 60W TDP CPU...

And no, you can not overclock this CPU
Tried it on two boards (my other X79 Board is a MSI X79A-GD45 PLUS with a i7-3820)...

[momaka]

Re: after CPU VRM burned, CPU still good?

Improper use of IR temp gun. Shiny surfaces (heatspreaders and cores) have low emissivity- reading will be lower than actual temp.

That's true indeed. Thermocouple would have shown a much more accurate temperature. Most likely, those Pentium 3 and 4 CPUs probably throttled down somewhere around the 60-80C mark.

What were we supposed to expect with that "test?" Even back in the day, who wouldn't know what would happen? Hey, my username resembles it!

I think I heard, that apparently it was acceptable in the older days (socket 7 and possibly earlier) to try a quick motherboard POST without installing the CPU heatsink, just to see if the system works at all (like, for example, to see if the motherboard works in the store before completing a sale). Those older CPUs, of course, didn't exactly have a very high TDP, so I think that's why it was possible to do this.

This is also why I think some motherboard manuals from the Pentium 3 and AMD Athlon era were so specific to never test the motherboard without a CPU heatsink, even for brief periods of time.

Do you know the TDP of the SB? I'm curious now and will probably look this up.

No idea, but it is an ULi M1567. NB runs very hot too, and it is a ULi M1695.

1-hi, 2-lo, per phase? Sounds like something "borrowed" from a more sensible design...

Yes.
It's very likely an (older) ASUS design. If there is one thing ASUS does fine, it it CPU VRMs. For example, the P5GC-MX has only 6 MOSFETs total, and those motherboards are actually designed for Pentium 4 and Pentium D CPUs, including the 130+ Watt TDP Pentium D mini-heaters. Go figure.

my understanding was that asrock is asus economy line.

I think that applies only to the newer stuff nowadays. The older AsRock boards really did have some interesting features (like my 939Dual-Sata2 having AGP 8x and PCI-E 16x, both being full-speed slots and also a "future_CPU_port" slots for a special add-in card to support socket AM2 CPUs and DDR2 RAM).

[kc8adu]

Re: after CPU VRM burned, CPU still good?

my understanding was that asrock is asus economy line.

[kaboom]

Re: after CPU VRM burned, CPU still good?

Me either. Though I've seen plenty of Xbox 360's survive accidental "heatsink-less" tests.

"I didn't leave gaming. Gaming left me."

Also, there this old video:
https://www.youtube.com/watch?v=06MYYB9bl70

Improper use of IR temp gun. Shiny surfaces (heatspreaders and cores) have low emissivity- reading will be lower than actual temp.

What were we supposed to expect with that "test?" Even back in the day, who wouldn't know what would happen? Hey, my username resembles it!

Nothing like a thru-hole socket with shiny leaded solder anymore, indeed. Which is why I still keep all of my Pentium II/3 and AMD stuff.

That.... and win98!

Nah, none of that nonsense. Southbridge BGA is going bad, I believe. Either Ali didn't disclose the full heat dissipation of their chips or AsRock didn't install a big enough heatsink.

Do you know the TDP of the SB? I'm curious now and will probably look this up. I take nothing for granted; whatever it is, I'll double it. I wonder if those SBs commonly fail..

Anyways, the VRM on that motherboard is the only thing that is solid - classic 3-phase design with 3 MOSFETs per phase and toroid-core inductors with medium-to-large inductance (hence, probably much lower switching frequency than modern stuff and many spots for large capacitors).

1-hi, 2-lo, per phase? Sounds like something "borrowed" from a more sensible design...

[momaka]

Re: after CPU VRM burned, CPU still good?

Sometimes, the heatsink moves as the compound heats and flows, especially with little heatsinks and lots o' heat.

With new compound, yes. But old silver compound (particularly Arctic Silver) tends to go brown and sticky rather than dry out. I wouldn't use anything with baked dry white compound, though.

I wouldn't push my luck with "naked" S370s/462s though..

Me either. Though I've seen plenty of Xbox 360's survive accidental "heatsink-less" tests.

Also, there this old video:
https://www.youtube.com/watch?v=06MYYB9bl70
(song name is Project X by Allister Brimble, in case anyone is interested in these geeky tunes )

Along those lines, I know it's no longer possible with high-density, high-bandwidth stuff today, but I miss thru hole CPU sockets. Especially now with RoHS BGA ones.

Nothing like a thru-hole socket with shiny leaded solder anymore, indeed. Which is why I still keep all of my Pentium II/3 and AMD stuff.

Wait, it's not a classic like my A7V? Does your 939 have the "crock" of phase dropping too?

Nah, none of that nonsense. Southbridge BGA is going bad, I believe. Either Ali didn't disclose the full heat dissipation of their chips or AsRock didn't install a big enough heatsink.
Anyways, the VRM on that motherboard is the only thing that is solid - classic 3-phase design with 3 MOSFETs per phase and toroid-core inductors with medium-to-large inductance (hence, probably much lower switching frequency than modern stuff and many spots for large capacitors).

[kaboom]

Re: after CPU VRM burned, CPU still good?

As for the heatsink - you don't need any pressure at all on it. Just lay the board flat and the heatsink weight will be enough. Just make sure not to knock it down by mistake when the board is running or to have a wire push it off the CPU. I don't even add new thermal compound on my "dedicated" test heatsink - it has a thick cruddy layer on there already, which I never change or remove. Good enough for testing, though. I haven't had any CPUs overheat so far. Most CPUs will run only 5 to 10C higher that with a properly installed heatsink with fresh thermal compound.

Unless it's a 100W+ Prescott device!

Sometimes, the heatsink moves as the compound heats and flows, especially with little heatsinks and lots o' heat.

I wouldn't push my luck with "naked" S370s/462s though..

Or socket 775/1156/939/AM2/AM3 for that matter. I've seen warped boards with all of these. For AMD, it's the bracket behind the board that always warps with the board. For Intel, it's those stupid plastic push-pins... which also have the tendency to break after a few installations. I wish they brought s462/370 mounting mechanisms back - now those were a lot more legit.

Along those lines, I know it's no longer possible with high-density, high-bandwidth stuff today, but I miss thru hole CPU sockets. Especially now with RoHS BGA ones.

Well, I forgot to put a heatsink whatsoever on a 3 GHz Prescott HT (but I did have the CPU fan attached), and the PC displayed the boot screen only for a second before locking and and emitting a continuous beep. Found my mistake, corrected it, and off it went working again.

So you didn't "netbust" the netburst?

I like that name.

Well, either name is shorter than "what's the lousiest junk we can make, that at least some will buy?"

Yes, they are the same (or were at some point). Ass-Crock (there, using the new name you gave them ) is/was ASUS's "experimental" division. And indeed some of their motherboards were quite crap while some others were rather interesting. I think my 939Dual-Sata2 could fall in the latter... if it wasn't such a finicky piece of turd, though.

Wait, it's not a classic like my A7V? Does your 939 have the "crock" of phase dropping too?

[momaka]

Re: after CPU VRM burned, CPU still good?

I removed the defective MOSFET and the Board kinda works again.

Do you think it's safe to use or not?

Depends which MOSFET it is. If it's a "lower" MOSFET and the motherboard has 3 MOSFETS per phase (1 "upper" and 2 "lower"), then it is probably safe.
But if that is not the case or if you have removed an upper MOSFET, you're probably better off disabling the entire phase vs. leaving some parts of it still connected. It all depends on what MOSFET drivers the motherboard uses, though. If the drivers don't have much protection to determine that a MOSFET is gone (O/C), I think that can create problems as the other working MOSFETs are switched ON/OFF.

I don't know that I'd have it in a case yet.

Agreed.

I test plenty of motherboards without a case... usually on a plastic box about the size of the motherboard - that way, I can add cards in the slots too, if needed.

As for the heatsink - you don't need any pressure at all on it. Just lay the board flat and the heatsink weight will be enough. Just make sure not to knock it down by mistake when the board is running or to have a wire push it off the CPU. I don't even add new thermal compound on my "dedicated" test heatsink - it has a thick cruddy layer on there already, which I never change or remove. Good enough for testing, though. I haven't had any CPUs overheat so far. Most CPUs will run only 5 to 10C higher that with a properly installed heatsink with fresh thermal compound.

don't want to overtighten it and pull a "Socket 478!"

Or socket 775/1156/939/AM2/AM3 for that matter. I've seen warped boards with all of these. For AMD, it's the bracket behind the board that always warps with the board. For Intel, it's those stupid plastic push-pins... which also have the tendency to break after a few installations. I wish they brought s462/370 mounting mechanisms back - now those were a lot more legit.

Now I confess to "testing" intel's THERMTRIP by using a wee heatsink from a monitor on a 2.8G Prescott... THERMTRIP... tripped, and the CPU was undamaged.

Well, I forgot to put a heatsink whatsoever on a 3 GHz Prescott HT (but I did have the CPU fan attached), and the PC displayed the boot screen only for a second before locking and and emitting a continuous beep. Found my mistake, corrected it, and off it went working again.

left asus to start ass-crock

I like that name.

Far as I can tell, they may as well be the same- are the "backwards" capacitor silkscreens any hint?

Yes, they are the same (or were at some point). Ass-Crock (there, using the new name you gave them ) is/was ASUS's "experimental" division. And indeed some of their motherboards were quite crap while some others were rather interesting. I think my 939Dual-Sata2 could fall in the latter... if it wasn't such a finicky piece of turd, though.

[kaboom]

Re: after CPU VRM burned, CPU still good?

Update from my side:
I've found some M4 screws, so I put my Xeon E5 6Core Low Power Thingy in the socket.
Put a heatsink on and used the M4 screws. Coudn't use much force because I can't reach the screwheads with my screwdriver, so my hand had to be enough...

Installed it in a case, put a harddrive in it and used a PSU (a Hiper 680W CWT PSH thingy with that 140mm Martech blue LED fan).

But haven't booted the rig up yet :ugly:

I don't know that I'd have it in a case yet. If there's any possibility of the heatsink not making proper contact, you can always test the MB on several pieces of cardboard (to raise it up so the tails of exp slots are clear) on a table or something.

This is so you can always put gentle pressure on that heatsink to keep it in place- don't want to overtighten it and pull a "Socket 478!"

Now I confess to "testing" intel's THERMTRIP by using a wee heatsink from a monitor on a 2.8G Prescott... THERMTRIP... tripped, and the CPU was undamaged.

Boot it up already- you know you want smoke and flames!

[kaboom]

Re: after CPU VRM burned, CPU still good?

well, asrock is a company meant for engineers to try silly stuff and silly ideas on so no surprises there. going by murphy's law, 80% of the ideas they come up with will turn out to be bird brained while the remaining 20% of ideas will turn out to be truly revolutionary and will shape future mobo design to come...

no longer true- it's a myth that persists from when the "original team" left asus to start ass-crock

even then, I've got doubts. Far as I can tell, they may as well be the same- are the "backwards" capacitor silkscreens any hint?

that's a stupid fanboy excuse- "throw shit at the wall and see what sticks- you never know, it'll be the next big thing in computahhzz."

don't buy that story- don't even rent it like a cheep prostitute

[Stefan Payne]

Re: after CPU VRM burned, CPU still good?

Update from my side:
I've found some M4 screws, so I put my Xeon E5 6Core Low Power Thingy in the socket.
Put a heatsink on and used the M4 screws. Coudn't use much force because I can't reach the screwheads with my screwdriver, so my hand had to be enough...

Installed it in a case, put a harddrive in it and used a PSU (a Hiper 680W CWT PSH thingy with that 140mm Martech blue LED fan).

But haven't booted the rig up yet :ugly:

[ChaosLegionnaire]

Re: after CPU VRM burned, CPU still good?

Remember, there were some weird ASROCK boards that dropped phases as CPU activity decreased. Those didn't work too well and could be unstable, since they were 4-phase designs that actually single-phased at times. As you can imagine (look at Fig.4 diagram for reference), they tended to be less stable at part-load, especially when those Evercons aged- more ripple for a given duty cycle, as N decreases. Supposedly, they were compensated so the loop didn't oscillate, but switching-freq ripple still made it to the CPU. Silly ASROCK!

well, asrock is a company meant for engineers to try silly stuff and silly ideas on so no surprises there. going by murphy's law, 80% of the ideas they come up with will turn out to be bird brained while the remaining 20% of ideas will turn out to be truly revolutionary and will shape future mobo design to come...

[kaboom]

Re: after CPU VRM burned, CPU still good?

No, I just haven't tested much.
Mostly because I don't have another heatsink for a LGA2011 CPU...

Got any spare/junk 478/775, or other heatsinks you could either cut down or hold in place? All you want to test is POSTing, and maybe a Memtest CD. If you could clamp a substitute heatsink down with zipties thru the holes near the socket, it might get you by for testing.

I thought I should ask here before trying to do anything else..

As for the VRM thing:
I kinda ripped the traces off the PCB, so soldering a replacement on it could be a little bit challenging (but not impossible).

Seems like I shouldn't touch that board until I'm able to afford a scope and scope it, right?

If there's any question about step-load overshoot, you might consider going into the BIOS setup and lowering VCore several steps below the default VID- again, just for testing and to check viability of the board/CPU. Since there were 12 phases, the output capacitance is rather small- no "huge" capacitors like in other boards. Do you know the TDP and Vcore of the highest-spec CPU that board could take? And if so, what's the TDP and VCore of your current CPU?

Ripple/overshoot may not be a problem if you're far enough away from the maximum demand of that VRM. You're "ripple bumpiness" with varying duty cycle will not be as pronounced as the diagram I referred to earlier; you've still got 11 phases. While there will be a suckout during the missing phase's period, if your CPU doesn't pull VCore too low during this time and the loop remains stable, you just might get away with it.

Remember, there were some weird ASROCK boards that dropped phases as CPU activity decreased. Those didn't work too well and could be unstable, since they were 4-phase designs that actually single-phased at times. As you can imagine (look at Fig.4 diagram for reference), they tended to be less stable at part-load, especially when those Evercons aged- more ripple for a given duty cycle, as N decreases. Supposedly, they were compensated so the loop didn't oscillate, but switching-freq ripple still made it to the CPU. Silly ASROCK!

As for the board:
it's this one and advertised to have 12 phases...

Again, such tiny caps for VCore...

Edit: Nevermind, looks like VCore caps are missing in those pix! Found a -UD3 board with the usual compliment of polies in VCore:
http://www.amazon.com/GIGABYTE-GA-X7.../dp/B0064Z6YD2

If your -UD5 has the same VRM as that -UD3, it'll probably be fine as long as your CPU is 11/12, maybe 10/12, the TDP of top-spec for that board. All those polies in parallel make a nice, low-z supply. Is it perfect? No, but it's what ya have to work with...

[Stefan Payne]

Re: after CPU VRM burned, CPU still good?

I don't know what you mean by "the board kinda works." I presume this means POSTs, but not stable enough to finish booting. Or perhaps crashes once device drivers come up to speed, and start "pushing" the system.

No, I just haven't tested much.
Mostly because I don't have another heatsink for a LGA2011 CPU...

I thought I should ask here before trying to do anything else..

As for the VRM thing:
I kinda ripped the traces off the PCB, so soldering a replacement on it could be a little bit challenging (but not impossible).

Seems like I shouldn't touch that board until I'm able to afford a scope and scope it, right?

As for the board:
it's this one and advertised to have 12 phases...

[kaboom]

Re: after CPU VRM burned, CPU still good?

I removed the defective MOSFET and the Board kinda works again.

Do you think it's safe to use or not?

That was the bad one on the high side, right? I'd x-ref a sub and replace it if that's the case. That regulator was compensated for its original complement of phases. Remove a leg and you'll suffer poor ripple and step-load response, as well as worse ripple performance overall with fewer phases. (see link)

It could be enough to make your CPU cranky- a bit like a marginal O'C.

I don't know what you mean by "the board kinda works." I presume this means POSTs, but not stable enough to finish booting. Or perhaps crashes once device drivers come up to speed, and start "pushing" the system.

See Fig.4 on page 4- for a given duty cycle, ripple is worse as n decreases, with higher phase count giving smaller ripple-peaks.
https://cdn.badcaps-static.com/pdfs/...398f5d4066.pdf

If you can at least boot to a Memtest CD, replace that one MOSFET! Don't condemn the CPU or MB 'til you "feed the beast" properly.

If you scope VCore with that MOSFET missing, be aware that it will look nasty until all phases are working correctly.

Good luck...

[Stefan Payne]

Re: after CPU VRM burned, CPU still good?

I removed the defective MOSFET and the Board kinda works again.

Do you think it's safe to use or not?

[ben7]

Re: after CPU VRM burned, CPU still good?

As I said, this is a best case scenario. You've still got a large amount of bulk capacitance (PSU, probably at least 2200uF, plus motherboard and others) that will dump a lot of energy into the processor through the upper FET. And, you're assuming that the IRF devices (controller included) implement this function. As I said many controllers don't implement it because it complicates the control loop during transient response.

How about the capacitance on the output of the VRM? It takes time to charge that through a resistance and an inductance.

[momaka]

Re: after CPU VRM burned, CPU still good?

Some of those substitute devices may not be optimal. While there are dedicated gate drivers, you've got to watch gate charge, gate capacitance, and feedthrough capacitance. If any trash couples via D-G capacitance, the drive waveform could get distorted, depending on the layout and capabilities of the driver IC(s).

What were the existing ones, and what did you use to replace them with?

Original MOSFETs: FDD8780 and FDD8796 for upper and lower MOSFETs respectively. VRM is 3-phase, with 1 upper and 2 lower MOSFETs per phase (so 3 and 6 total).

I used 85N02 from ON-semi (Xbox 360 pulls). Yes, the 85N02 have considerably higher capacitance, but I figured it shouldn't be a problem, since the drivers are ADP3120A - which are similar to what the Xbox 360 uses sometimes: ADP3118 (at least I don't see much difference between the two). And those 85N02, along with 60N02 are often used in Xbox 360 VRMs.
The PCB around the MOSFETs on that board did look a bit overheated/dark. The copper pads on which the MOSFETs were soldered on were quite tiny compared to what I have seen on other motherboards, so I though maybe that was the problem, and the 85N02 would do better with their lower Rds_on resistance compared to the originals.

Do you think one of the low side MOSFETs was leaky, and taking out the high side ones?

It is entirely possible, granted I had to change two upper MOSFETs before a lower one blew.

Just because I'm curious, was it also squealing w/o the CPU?

I can't tell you, because the board is designed so that it won't turn ON if there is no CPU in the socket. But now that I mention that, I didn't think of trying to short the PSU's PS_ON wire to ground to see if I can force-start it. So, I might just try that next (when I get home from college, that is... bleh).

But with the CPU in there and my replaced MOSFETs, *and* the coil for the VRM phase that had the shorted lower MOSFET removed, the CPU VRM voltage does come up to about 0.6-0.8V - albeit with a lot of squealing.

I honestly doubt most manufacturers care to be honest - it's simply a case of getting lucky. Why would they care about saving the CPU, when the VRM burns, the average guy is just going to throw away their console.

I suspect it's not the manufacturers of the board that care, but rather the manufacturers of the PWM controller and/or drivers. They probably try to add those fail-safe features for marketing purposes. Whether they are implemented improperly (or messed up unintentionally) in the design by the board manufacturer is another story.

[kaboom]

Re: after CPU VRM burned, CPU still good?

This is good to know! I've often wondered about video cards implementing "protect the load no matter what." Of course, all cards don't use the same PWM controllers, but at least for you, all turned out OK.

This only assumes the PWM uses synchronous rectification. If the upper MOSFET shorts, and the lowside is a plain rectifier diode, the load sees gross overvoltage.

[tom66]

Re: after CPU VRM burned, CPU still good?

I honestly doubt most manufacturers care to be honest - it's simply a case of getting lucky. Why would they care about saving the CPU, when the VRM burns, the average guy is just going to throw away their console. Sad, but that's the way it is. Certainly, this is how the company I work for does it. Our video decode CPUs run at ~0.85V, from a 12V VRM, one test involves simulating the upper FET shorting, the CPU dies every time, and that's fine, all we care about is that the FET doesn't melt or distort the plastic casing/cause a fire etc. (We're only talking about a 12V, 5A plug-top in most cases so it's not a major concern.)