Component identification

One of my PCs refuses to boot. I've tracked it down to a device close to the power button. The device is labelled as THC12-111B. Trouble is I don't know for sure what it is. I suspect it is a thermocouple of some description but do any of you electronic types know what it really is. And as a second question can I just bypass it if it is a thermocouple? :confused

 

Is this a desktop or a laptop?

If it is a desktop, then do you mean close to the motherboard header or the actual power button on the front of the case?

What subsystem is it part of? Motherboard, graphics card, etc?

 

Desktop.

Close to the on/off switch on the front panel of the PC. Only appears to be part of the power supply as it only has a red and black wire into it.

 

What type of desktop/motherboard?

 

if it is the front panel of the PC that would be the case that is in question not the mobo surely.
thermocouples measure a temperature difference and create voltage, so is essentially ony a temperature sensor
any chance of a photo.
a picture paints a thousand words as they say.

 

Ahh - yes, I see that now... rolleyes ...sorry...

As the machine is refusing to boot, then I can't see where bypassing would hurt anything...

 

This sounds a lot like a motherboard piezo buzzer. Can you trace the lead back to the motherboard? I bet it connects to a group of pins next to the wire from the power switch.

 

Well I've traced the wire back to the Motherboard (Asus A7V) and it connects on some pins labelled only as PANEL. But the mobo manual tells me that this is made up of:
PWR LED
SPEAKER
MSG LED
SMI (System Management Interrupt)
PWR.SW (Soft off switch)
RESET

So it can only be the speaker. I'll have to try and disconnect it and see if it makes any difference - but I still can't think of why it should stop the PC booting.

 

the SMI is a two cable switch that places the computer in suspended mode.
the pins for this are the bottom row pins 5&6.(working from the back ie left to right)
the Speaker is a 4 pin lead. whic i s teh last 4 pins on the top row, can you specify wich pins it is connected to?

 

sorry ment 4 & 5 bottom row for the SMI, was rushing to write that as i needed to get to the shops. but can not edit my last post.

 

Well the device only has two leads (red and black) coming from it. But the connector for the speaker on the mobo has 4 pins but only has the two cables running into the connector. When I've got a bit more time yomorrow I'll disconnect the speaker connector and see what happens then.

 

speakers are connected over 4 pins, with the outer 2 pins actually being connected to something.

The panel area, as you have found out, is the location of pins for the connection of case hardware such as switches and LEDs.

Another way of determining if the speaker is the problem is to actually listen to it. When you turn the computer on, does make a beep? If so, does it make a beep when the computer fails to start?

 

No it doesn't beep. I even tried removing the RAM to see if it would POST but it doesn't. It just sort of buzzes.

 

I've now tried disconnecting the speaker - that stops the horrible buzzing noise but it still won't boot.

 

you have not upgraded any of the components recently have you?
if not sounds like one has failed.
the speaker normally buzzes/beeps constantly to warn you of a fault on the board

 

No - nothing new at all. It was just powered down. Just won't come back up. I'll try removing all the peripherals next - just in case. If I get down to bare bones then I guess it's time to retire it permanently. :cry

 

Every peripheral removed and it still wont boot. Now before I rush out and buy a new mobo does anyone know if its possible that the onboard speaker which buzzes like a demented wasp is the cause of the problem? In other words I don't want to buy a new mobo only to find the thing wont work because of a duff speaker (which is an integral part of the PC case).

I personally think the speaker is picking up noise from some failed component on the mobo which is causing the speaker to buzz. Anyone else have any other thoughts?

 

Like you said, you're down to the bare bones - could there be anything power supply-wise causing this? A mislabeled or miscolored cable? I know that with many electrical circuits, if the positive and negative are switched, noise generation can occur...

Don't happen to have a spare power supply laying around, do you?

Come to think of it, though - if it's pwr supply, you'd have had this problem out of the box...

Still, a supply switch would rule out any ghosts in that part of the machine...

 

I've checked the power supply and it is providing perfect voltages. I would hope it would as it is only a couple of months old. But I had thought of what you suggested and did try using an old PSU (with a slighly iffy +5V admittedly) and the speaker still buzzed away.

 

really, the only things i can think of it being is one of the following
the RAM, HDD or the Mobo.
did it boot up fine after you replaced the PSU a couple of month ago?

 

So the speaker is constantly sounding and the computer will not boot.

This is starting to sound more and more like a faulty core component, most likely the motherboard.

Have a look at the tops of the capacitors around the processor. Are any of them burst or bulging?

Possible location of capacitors: http://www.hardwarezone.com.sg/img/data/articles/2009/3048/Capacitors.jpg

 

Yep. Booted up just fine. Can't be the HDD because I took it out and tried booting from a floppy. Can't be the RAM as I took that out too and the PC still failed to POST. So as I said it's either the mobo itself or the speaker dragging down the mobo (which I can't quite believe).

@collinsl: I think you're right. I'll have to take the mobo out and have a good look at it. Thanks for the link by the way.

 

Believe it or not I just had a capacitor on my motherboard almost blow, and at just 2 1/2 - 3 years old as well.

Must be all the heavy usage I have been giving it.

Just to help you more with this, I cannot see any damage, apart from some possibly bulging capacitors, but if they are bulging it is not by much, and a very faint burning smell.

I would suggest you look for the above - capacitors may only be bulging by 0.5MM or so.