Xbox flashing red and green

Softmod on 1.6 is definitely possible! It's tsop flashing that doesn't work with 1.6

If you have access to a pc with IDE connection on the mobo, then rebuild the hard drive (slayers disk) and lock it with the key once you've extracted it from your eeprom.

 

There was a misunderstanding with the term "FRAG"
While it's indeed a short writing for "flashing red and green", most people only use the term when the xbox is not showing any video. In such case, the xbox will try to reboot 2 or 3 times and will give up after that with a red and green flashing power button. The 1.0 - 1.5 xbox revisions will leave the power on in such occasion. The 1.6 and 1.6b xboxes will turn the power off.
So, if your xbox boots into an error 5 screen, it's not a frag. You will likely not see the typical reboot attempts (blowers slowing down for a second or 2) It's what they call "My xbox boots into error screen x...."

I can confirm as well that softmodding a 1.6(b) is possible.

You can't measure the D0 with a multimeter since it's a data line that is most of the time tristate (floating) and only occasionally driven by the bios rom or the mcpx. It's not a stable voltage (unless it's grounded)

You should never measure ohms on a system under tension (which is maybe what you were attempting to do?)

So basically, it's still a bit unclear what your xbox is doing.

Without modchip error 5
With modchip and D0 disconnected error 5 ??
With modchip, D0 connected and modchip disabled with dipswitches error 5 ??
With modchip, D0 connected and modchip enabled ???
With modchip, D0 grounded ???

Do you know if it ever worked with that modchip?
Maybe the harddisk became unlocked accidentally and the modchip was installed in an attempt to fix that issue?
Maybe, the system was used with that modchip and the harddisk isn't locked since it's not needed with most modchip biosses?

 

The good thing about a softmod is they don't care what ram type ( 1.6b ) or opcodes are used as they don't touch or need to know any of this information as the kernel does all this on boot.

All a softmod is is a kernel patcher ( NKPatcher ) well it's an exploit to run unsigned code then it's a patcher ( second stage after the NDURE exploit is NKPatcher )

So all know kernels are supported, only way a Xbox wouldn't be supported is if there was a new kernel released. ( and that's never going to happen )

Also Error 5 Unlocked HDD, you need to lock it to the eeprom key. But do what I said, extract it and use liveinfo beta 3 to convert it to 1.6 ( or create a new one from scratch ) and set its HDD key to 32 zeros ( 00000000000000000000000000000000 ) That way you don't need the eeprom ever again to lock or unlock the drive via a PC. ( you will still need to reflash the updated eeprom back to the Xbox )

Note:
On 1.6+ Xbox when you try to read the eeprom via the LPC it will frag twice ( reboot ) quickly and then give you about 3 seconds to read the eeprom before turning off completely. ( may take a few try's to read it, do it twice and compare the files )

 

Thank you all for your help.

I had a breakthrough, I got the Xbox and the modchip working. It turns out some human error is to blame for this.
When I first got the Xbox, as I mentioned earlier in this thread, I was using the wrong component input on my receiver. While trying to get a picture I was playing around with the three switches on the modchip switch-panel (Enabled/Disabled, Unprotected/Protected, Bank1/Bank2).

Later I discovered the input issue (doh...) and started using the correct input on my receiver. At this time I only played around with the Enable/Disable and Bank1/Bank2 switches. I figured Protected was the way to go, as I didnt want to risk anything. This is probably a well known fact for old school modders, but it turns out Enabled alone does not equal "modchip ON".
In my case, modchip ON is set like this: Enabled, Unprotected, Bank2
Modchip OFF: Disabled, Protected (Bank-switch could be either 1 or 2).

@obcd you are probably correct that the previous owner did not bother to lock the hard drive - thus explaining the Error Code 05 when modchip is disabled.

Next on the list for this old Xbox is to refurbish the DVD belt as it is not ejecting.

Again, thanks to everyone who replied!

 

Glad you were able to get it working.

I'd thought protected only prevented you from flashing the modchip with a different bios. I'd not seen one that you had to set it to unprotected to enable the modchip.

Although, there are chips that you can enable/disable modchip depending upon pressing power or eject button on startup and some had control via a short or long button press.

Different teams used different methods in their designs.

 

A small side note to this. Today I discovered that if I apply pressure underneath the modchip's switch board I would also get the flashing red/green + no video error. When I was initially testing the Xbox, I had it on top of a soft base, and I would get the error, but on a solid base (table/floor) all would be fine and dandy. Probably something on the switch board is making a connection (or breaking a connection) when applied pressure to, so should be a simple fix.

 

All is well and ends well. I love it when a plan comes together....Dah dah da daa.....dun dun dun!!!