AMD Geode/Video 1/Script

This is a textual description of the video.

Introduction

My DOS Programming playlist on YouTube scrolls down the screen.

Voice: "I've been writing a DOS program for a while now"

The DOSBox-X home page scrolls down the screen.

Voice: "I've been using DOSBox but it would be nice to use real hardware"

A picture of an IBM PC XT taken by Ruben de Rijcke is shown on the screen with big green "IBM" text on it.

Voice: "Ideally I'd use a period accurate IBM PC"

A screenshot of expensive eBay listings scrolls past. One is shown to cost $500 AUD.

Voice: "But these are really expensive"

An eBay listing titled "Vintage Advantech PCM-9375 REV. A1 SBC Single Board Computer - AMD Geode LX800" is shown. Its status is marked as "For parts or not working, sold as-is with no guarantees." It's listed as $50 AUD.

Voice: "Checking eBay I found an industrial single-board computer for $50"

The listing description is shown. It clarifies: "For sale here is an Advantech PCM-9375 REV. A1 single board computer. Previously, I was able to boot Windows 98SE from a Compact Flash card and everything worked fine. It currently refuses to output a video signal that any of my monitors can recognise, so it's being sold as-is for parts with no guarantees. For a full spec sheet, see Advantech's site."

Voice: "The very low is because the video output is broken. Without video output this computer is effectively useless."

A receipt showing payment for the board is shown. It cost $50 AUD with free shipping. It was paid on 7 November 2021 and delivered on 12 November 21.

Voice: "I decided to buy it anyway in hopes of fixing it."

A hand is shown placing the board on a table. It is an unprotected circuit board with its chips, connectors and pin headers exposed. One large heatsink covers the CPU and another smaller heatsink covers the companion chip.

Voice: "So here it is: The PCM-9375. It stars a Geode LX800 CPU and CS5536 companion chip."

A small stick of RAM is shown.

Voice: "512 megabytes of DDR1 RAM."

An empty CompactFlash connector is shown.

Voice: "CompactFlash for storage."

The side of the board is shown with four ports: A DB9 serial port, an Ethernet port, a PS/2 keyboard port and a VGA port.

Voice: "A serial port, an Ethernet port, a PS/2 port, VGA port"

A daughterboard connected to the main board is shown, with an Ethernet port on it as well as a mini USB connector. The board is unplugged already, and pliers are used to remove it entirely.

Voice: "As well as a mini USB port and a second Ethernet port. We're going to remove those for now while we troubleshoot."

Initial powering

A power supply with growing green LEDs flicker showing 0 volts and the word "off". Connected to it are two long bunched up wires that clip in to two pins on the board.

Voice: "The first thing I did was hook the board up to a current limited power supply."

A hand is shown turning the power supply on. The camera zooms closer and shows the text jumping on the display changing to 5 volts 1 amps. The amperage jumps between 0.9 amps and 1.1 amps.

Voice: "It pulled a stable load so it's not dead."

A small lapel microphone is shown next to the board's corner. A single short beep is heard.

Voice: "It made a beep! That's a good sign."

A hand is shown plugging a VGA cable in to the board.

Voice: "I connected a monitor to see what it would display."

A computer monitor is shown. Grey text appears in a box with the text "Input Not Supported" slowly moving diagonally down the screen.

Voice: "And... Input not supported."

An oscilloscope probe is shown being attached to the power wire clip followed by a rapid zoom in to an oscilloscope's view.

Voice: "So I checked the power rail with a scope."

The oscilloscope draws a flat line at 0 volts that suddenly jumps up to 5 volts and continues at 5 volts for 15 seconds.

Voice: "A major voltage drop could signal that the machine isn't booting properly. I don't see that here."

The oscilloscope draws a thin line from the bottom of the screen up to 5 volts then thickens it showing around 20 millivolts of noise.

Voice: "Likewise, no drop at all could mean the machine is dead. I don't see that here either."

The camera pans to the power supply displaying 5 volts and a steady around 1.065 amps.

Voice: "Everything looks fine power-wise."

RAM testing

A hand pulls out a stick of RAM and places another in.

Voice: "Bad memory can cause all kinds of issues so I tried another stick of RAM."

A different monitor is shown with the text "Input Not Support" appearing after a second of being blank.

Voice: "Same result. Input not support."

A hand is shown removing the RAM stick without placing another in.

Voice: "I removed the RAM to see if it was being used at all."

The video cuts to the microphone pointed at the buzzer again.

Voice: "The BIOS gave these beeps."

A set of long beeps can be heard.

The monitor is shown again with the text "No Signal" displayed.

The board is shown with a chip marked 'V1.18' removed from its socket.

Voice: "I removed the BIOS chip to see if it would still beep. It didn't."

Battery testing

A screwdriver forcefully removing a coin battery is shown, making the battery jump across the board. A hand using pliers attempts to pick up the battery but it keeps slipping away.

Voice: "Next I looked at the clock battery."

A multimeter is shown with its probes touching the positive and negative sides of the battery. It displays the value 198mV.

Voice: "My multimeter showed it was around 200mV. Completely dead."

A close up of the battery being held by pliers is shown. The brand name RAYOVAC and the text "LITHIUM 3V BR1632 USA" is engraved on the chip.

Voice: "Perhaps a dead battery corrupted the BIOS settings somehow?"

The second monitor is shown again, this time with an orange plastic frog glowing on the desk near it. The monitor still says "Input Not Support"

Voice: "Running without the battery didn't help."

Keyboard testing

The board is shown powered in the background as a dusty and grimy keyboard comes in to frame and laid on the desk.

Voice: "At this point I wasn't even sure the machine was booting. I plugged in a keyboard and checked the machine's response."

A finger presses the caps lock key and the caps lock key light on the keyboard is shown to turn on and off.

Voice: "It handled toggling caps lock."

A finger rapidly presses the F1 key.

Voice: "It even made noises when I pressed keys."

The finger keeps pressing the F1 key but slower.

With each keypress heard a small beep can be heard in response from the computer.

Voice: "So it's doing something."

A ginger female cat is shown on the desk with only one eye. She makes a high pitched meow and moves towards the camera.

Voice: "Surprise cat visit!"

The cat jumps up on to the window sill behind the desk and looks out the window curiously.

Voice: "This is my brother's ginger cat. While we take a cat break let's talk about my sponsor for this video."

The cat peers out the window then jumps back down on to the desk to leave the room.

Voice: "Just kidding, I wanted to fill in time to show off the cat. Ok back to troubleshooting."

Ethernet testing

A hand plugs an Ethernet cable in to the board. After a second or two a green light on the port lights up.

Voice: "I plugged in an Ethernet cable. Maybe if the machine was booting over the network I'd see some packets."

Wireshark is shown on a computer monitor. The only incoming packets come from fe80::250:b6ff:fe1d:d419.

A terminal is shown on the monitor. It lists the machine's IP address on enp2s0f0u4 as the IP from before.

Voice: "There are packets but they're from my machine. So not very helpful."

Serial testing

A breadboard is shown with jumper wires connected to various ports on the DB9 serial port.

Voice: "I made a null modem cable on my breadboard using jumper wires."

An oscilloscope probe goes in to one of the breadboard holes.

The oscilloscope screen shows a signal at 0v raising to 5v briefly then dropping down to -5v.

Voice: "Probing it showed that the transmit line was being held properly. But it wasn't outputting any bytes."

Broken off jumper wire connectors are shown stuck attacked to the serial port. The wires they belong to are shown with their copper strands exposed at the end. Pliers come in to frame and pull them out.

Voice: "I also broke a few breadboard wires in the process. That sucks."

VGA probing

An oscilloscope probe is shown entering a hole on the VGA connector.

Voice: "Okay time to check the VGA signals."

An oscilloscope screen shows a 0v signal with shorts jump between 6.80v and -2.56v.

Voice: "First up is vertical sync. This signal pulses once every frame."

The camera zooms in to show the frequency of the signal is 60.00Hz and the period is 16.67ms.

Voice: "In this case it's 60hz."

The oscilloscope shows a a 5V wide square wave with cursors measuring the wave. The wave is around 5v, peaking at 5.57v on the leading edge and dropping down to some unknown voltage on the trailing edge. The time a pulse of the wave takes is 40 microseconds, or 24.75KHz.

Voice: "Zooming in to a single pulse we can see that's a 5v square wave lasting for around 40 microseconds."

The oscilloscope shows the leading edge of the square wave. It peaks at 6.64v and takes 228ns to settle to 4.64v.

Voice: "The pulse seems to peak around 6.6v and takes around 230 nanoseconds to settle. This all look fine to me."

An oscilloscope probe is shown entering another hole on the VGA connector.

Voice: "Next horizontal sync."

The oscilloscope shows a 0v signal with longer jumps between 6.64v and -2.40v. The camera zooms in to show frequency is 75.02KHz and the period is 13.33 microseconds.

Voice: "The signal pulses every row of pixels and this looks to be around 75KHz."

TODO:

SD card adapter

TODO

USB power adapter

TODO

USB power meter

TOD