During the week, a friend dropped off a PC for me to look at. As I was now working full-time, I really didn’t have much of a chance to look at it until this evening. He had explained on the phone that it belonged to a customer that I had previously done some work with a year or two ago. The HP 110 Desktop PC is one of those that comes with a power adapter similar to those on laptops. The symptoms were that there was no display either on the VGA port or the DVI port. I suggested that maybe he could try a separate video card – however, unfortunately – this PC does not have a PCI or PCIe slot, none at all.
Anyway, I had a look – it had a bit of dust inside, not really enough to cause a problem – and sure enough, no PCI or PCIe slots. However, I did spy a wireless board plugged into a mini-PCIe slot. My diagnostic card comes with an adapter that can plug into these mini-PCIe slots. I unscrewed the single screw that was holding the wireless board, then plugged in my diagnostic card.
Since I had a power pack plugged in, the diagnostics card came to life immediately – showing me that the Reset line is active, and the 3.3V line is working. I pressed the power button, and the fans starting spinning – but the diagnostic card did not change at all. The Reset was still active – and until the Reset turns off, the PC cannot boot at all.
This is looking like a difficult repair, such that might not be worthwhile to proceed. Why? The reset line being low – could be a failure of the reset circuitry. It may also have to do with the onboard power regulators not providing the right voltages. It can also be a failure of the Northbridge chip – and can also be a processor fault. To diagnose this further, I will need to remove the motherboard out of the case, then search the internet for schematic diagrams that describe this motherboard – or a similar motherboard.
A new PC equivalent to this one together with a 20″ monitor can be bought for $429 from OfficeWorks – in fact this PC was bought from OfficeWorks a couple of years ago. Anyway, I will let my friend know and he can decide whether or not I spend any more time on this PC.
[Update] I went back to look at this again. It turns out that when the motherboard is off, it should only be the 3.3V Standby power that is on, however in this case – it is the 3.3V power and the Reset line shouldn’t be showing up at all until power is applied. Now, this is the first time I have diagnosed one of these motherboards – but even then, it should still behave like a normal motherboard. This seems to suggest that the fault is in the power circuitry – which is going to be difficult since we usually measure the voltages on the PCI slots, and now I would have to dig around on the motherboard. Anway, just wanted to update this post.