AMD Geode/Video 3/Script

This is a work in progress textual description of the video.

Recount

soldering failure, and fix in video 1

video 2:

I filmed this almost of the video as a continuos 6 hour session, with 4 hours being soldering. This was not a good idea. In fact, the entire video is filled with almost entirely bad ideas.

Here's a broad listing of takeaways you should have:

Don't solder for more than an hour at a time
Take breaks when you're frustrated
Perform each action with a plan and stop if it fails

I failed almost all of these and instead tried to brute force through the process. Trying to continue a project that requires thought and attention after burning through those 15 minutes in did not work.

broke the network connector too

Mistakes

Soldering failed, but that's not very interesting: My understanding of the circuit was wrong
I thought the capacitors were inline with the circuit
Removing them successfully would not have given me signal access
I would've realized this if I checked the caps were connected to GND
Replacing the inductors weren't technically necessary either
Resistance and diode mode would show shorts or pull-downs
Would it happen on all three lines?
similary my dvref/drset schematic was wrong

Writing code

Entering test mode gives a blank screen
Datasheet seems wrong: "MBD_MSR_DIAG[18:16] = 101h" should be "MSR_DIAG_VP[18:16] = 0b101"
DAC status registers always say the DAC is below 0.35V
Mention memory mapping and how to investigate this

Editing the DVREF required source code hacking? DVREF stuff

What's interesting in the data sheet?

Measurement

I did what I should have done in the first place: Measured when the display WORKS!

The DVREF shunt looks okay and produces the correct voltage
The DVREF shunt has a 12nF cap in parallel
The DVREF shunt has 13k to the 3V3 rail
The DRSET resistor is 1.21K to GND
The VGA resistors seem fine and correct values
When external DVREF is used, the shunt drops to 800mV, the rail somehow drops to 960mV

Shorting between an existing 3.3V rail nearby caused the screen to suddenly display in full brightness.

Repair

I followed the rail and found a blown resistor, but I also wondered if the capacitor was somehow draining. So I removed both. This wasn't a completely correct fix: The bypass capacitor is in parallel to the circuit, it couldn't drop voltage like this normally. Had I measured it I could've confirmed it was 3.3V. The voltage drop here is 2.34V! So there's some in series resistor that must be dropping voltage based on current or use. The burned resistor looks like a good candidate.

Conclusion

At this point I believe the DAC is working, so the problem might be related to clocking.

I added in a fresh clock battery and it had no effect.

Things to try:

- BIOS flashing

- Fix network