Asus M5A97 LE R2.0 powers on but does not boot

[Belushi]

My 7 year old AM3+ motherboard has broken overnight. It powers on, but does not boot (no picture, no beeps). I checked RAM, CPU (with another AM3+ board), PSU - all components works properly so it is a motherboard fault.

What I've already checked:

• no short on main power rails
• no shorted mosfets
• BIOS chip works (I could read its content with a programmer)
• RTC running (it consumes ~4µA from the battery)
• CPU and chipsets (NB / SB) are getting warm after power on motherboard
• CPU voltage (vCore) is ~0.84V and motherboard does not adjust voltage
• chipsets (NB / SB) power rails seems OK

My assumption: motherboard can't read BIOS. I tested it with a POST analyzer card, and the card showed no signs of life (0000 code and it does not changed). Unfortunately I do not have an oscilloscope, but I found that the BIOS cannot be accessed by the motherboard (checked using this brilliant method). I can't figure out which component cause this issue and I'm stuck. Could you give me any ideas? What should I do now?

OFF: I know this is an old board and may not worth to repair it, but it's not about money. It's about fun, learning electronics repairs and trying to reduce e-waste

[anikin73]

When the code is 0000 , you must check that all the main voltage must have...

[AstutePauciloquent]

Hi, I have a few similar AM3+ boards with 0000 that i am trying to diagnose. I have been unsuccessful so far but i can tell you a few things to check.

But first i must say, the motherboard will not read the Bios chip until the first cycle of the CPU is activated. Basically there is alot of power checks and signals that are passed around the motherboard before the bios can be read. If these checks fail, the CPU cannot read the bios and the board will not post.

I'm happy that Anikin73 has posted about checking all the main power supplies, I think you can also check DDR15V and any other power supplies around the board

. When you power on the motherboard look on the diagnostic card at the RESET LED, is it flashing on once then turning off forever, or is it flashing on/off repeating?
. Look up the data sheet for the Super IO and measure the voltage at the RSMRST# What is the voltage?
. Check the PS_OUT signal on Super IO, What is the voltage?

[Belushi]

Hi,

When the code is 0000 , you must check that all the main voltage must have...

What do you mean by "all the main voltage"? I checked all mosfets on motherboard and they produce proper voltage levels (according to boardview file). Majority of mosfets generates 1.5V, 3V or 5V. As I mentioned in my first post, NB and SB power rails are also present. Are there more power rails that I must check?

look on the diagnostic card at the RESET LED

Unfortunately my diagnostic card has no RESET LED. It has 3 LEDs, but they show voltage levels... i guess... they are always on (even if I put the card into my good motherboard).

Look up the data sheet for the Super IO and measure the voltage at the RSMRST#

I measured ~3.4V (in standby and full power on mode).

Check the PS_OUT signal on Super IO

It doesn't have PS_OUT pin. Maybe it is called something else in boardview file. Could you explain the role of this signal?

I found a power sequence diagram for this board (not really the same board but very close to it).



Just for curiosity, I checked the last stage which is generating ALLOW_LDTSTP signal, and I measured 1.5V. So basically it means the power sequence succeed? Or it cannot be measured with a multimeter?

To be honest, vCore voltage is very suspicious for me. It is 0.8V which is fine at the beginning of post process, but VRM doesn't change (raise) the voltage, which may not be sufficient for the CPU to work. What do you think? I measured vCore on a working AM3+ board with the same CPU, and after I switched on the computer, the VRM generated 0.8V also but then it started to communicate with CPU. At the end of post process, the vCore has been negotiated (around 1.3V). But my faulty board produces 0.8V constantly.

So now I'm wondering that the low vCore voltage is the cause or the consequence. Vcore cannot be adjusted because of something fails during post, or VRM has a fault , and it cannot raise vCore in order to operate CPU (this is less likely). Without a working CPU, nothing will happen. On the other hand, if something causes an error during post (e.g. prevent reading bios), nothing will happen again (tested with good board - I removed the bios chip and the post analyzer showed 0000 code and vCore has not been adjusted - as well as on my faulty board).

[AstutePauciloquent]

The fact that the Super IO has 3.3V (High Signal) on that RSMRST# generally means that this IC is ok. This is present before the power button is pressed, and after. It is the power good signal for +3VSB

Sorry the PS_OUT signal is sending from the PWRON pin from the Super IO. This is triggered after the power button has been pressed, and it is sent to the South Bridge/PCH. In response to this, the PCH/South Bridge sends the SLP_S5 and SLP_S3 signals back to the Super IO. Missing these signal indicates a faulty South Bridge/PCH. So check these next

But it seems like all of this will be working on your board

Unfortunately im still trying to learn the next steps to check myself, I was hoping someone with more knowledge would be able to step in and help. I have the feeling we're on our own at this stage.

As for the ALLOW_LDTSTOP signal this means ‘Lighting Data Transport' also known as Hyper-Transport or North Bridge. Its just to allow the North bridge to stop communication with the South Bridge. I'm not sure really why its on the list on this power sequence diagram. But still a nice picture to have, I will keep this for myself. The last signal of most importance is CPURST (CPU Reset) After this signal goes to the CPU the bios will be read and the motherboard will post.

But saying that, I don't believe all these signals are sent in a (step by step) sequence, but rather all sent at once, and if there is a signal loss between two IC's there is a continuous loop that happens. I've been able to detect such loops using a logic probe and or oscilloscope.

For example as i explained above I have a few faulty AM3+ boards much the same as yours that ive been trying to diagnose for some time now, mostly for fun and using as learning tools. I have found one of these loops at the SLP_S3 and SLP_S5 stage on one of the boards. Then on a different motherboard i found another such loop at the LRESET Stage also all Data pins on the PCI bus are following the loop timing. Basically this is a signal that is repeating on/off in a loop.

Trying measuring the voltage at LRESET on the Super IO chip, and watch the voltage closely if you see the voltage fluctuating like between 3.3 and 3.2 (its very subtle) you might also have this looping happening. I think what it means, is a signal loss somewhere. It's just being able to trace it is the hard part.

As for the VCORE Voltage, I don't think this voltage will go to 1.3V until after the bios has been read. But I could be wrong, it might very well be a fault with the VRM Controller IC. Then again maybe not, I don't know.