Kahenraz wrote on 2025-02-16, 06:55:
Props to your repair work on the Toshiba. Not gonna lie, though. That key cap arrangement would drive me insane.
Yeah it does require looking at the area every time I want to press Ctrl or Caps Lock. It's the same for most of the beige Toshiba T series laptops like the T19xx and the whole T4xxx series.
I'm pretty stoked right now, in my last post I said that I was having terrible luck with mainboards for the T4400C and T4400SXC laptops I'd recently bought, where I had killed one by running it before recapping the PSU. That first one is still dead giving a black screen even though it's reading the BIOS there are no POST codes. That mainboard got further than the one I got the other day in a T4400SXC which was seemingly totally dead, it wouldn't even spin up the hard drive and the HDD led would stick on.
The T4400 is really tough to test since it's got the separate power board and lots of flex cables going everywhere, but eventually I set up another recapped PSU on the bench and started probing and checking things with the thermal camera. Thermal camera shows nothing of note except that the RAMDAC on the video card area is getting rather warm - it's got its own clock.
I had thought the gate array that makes up the chipset on this thing was toast, or the keyboard controller was toast since that handles the LED indicators and idk maybe it all falls over
It took me some time to work out how the rest of the mainboard gets its clock, there's a 25mhz oscillator at X2 that I couldn't figure out how it works, what drives it? It's just connected to that little R57 resistor and goes off into a via to elsewhere. The pads on the crystal oscillator go to 1:nowhere, 2:Ground, 3:clock signal 4:5V VCC. Eventually found out that's a thing called an SPXO and they all seem to use the same pinout - when it's working and powered by 5v (which it does on the no POST codes motherboard) - it gives out 0 to 5v DC clock frequency rather than an AC type signal.
I can't find the original part or even the form factor (this one is 4pin SOJ with 7.5mm pitch between pins lengthwise and 5mm pitch widthways.
My theory now is that when the DC-DC power supply board messed up its regulation because of bad caps, the 5v went too high and sometimes it destroys the CPU, sometimes other things but on two of these boards it broke the clock generator, must be a pretty common fault with these I think.
So I pulled off the non functioning SPXO oscillator and used my mini scope the owon hds2102s's signal generator function hooking up ground and the clock signal on the red lead. Power it all up while it looks like this with the frequency being fed in externally and it POSTS!
Wow, I actually have enough working mainboards to put all the T4400s back together, at last! Looks like I'm going to need to figure out a proper replacement for the clock generator though, perhaps overclocking to 33mhz is an option too 😁
