use-nvram? bricked Power Mac G4

[elderK]

Hey guys,

I was playing around in OpenFirmware (adding some stuff via nvedit) and I seem to have bricked my machine.

The issue happened when I entered "reset-all": I saw the usual "Erasing..." but I never saw the "Flashing...".

Since then, the machine will power on but there is no chime and the USB peripherals won't even light up.

I've tried:
- Removing the PMU battery.
- Pressing the PMU reset button on the motherboard.
- Leaving the machine without power for an age.

No love It seems whatever I wrote into nvram (with use-nvram? set to true) is unrecoverable.

I've tried the steps here, too: http://macos9lives.com/smforum/index.php?topic=2138.0

When I tried that, I do indeed hear a long beep but no matter how long I hold the button, I never hear a chime.

Does anyone know how I can resurrect the machine or is it just a brick?

~Dave

[DrNo7]

Hi elderK,

Have you tried the command+alt+P+R holding it when powering up and waiting for at least 2 chimes before letting go?

[ssp3]

1. Try fresh battery.
2. Try this ritual - http://macos9lives.com/smforum/index.php/topic,4765.msg34179.html#msg34179
3. Let it be a lesson for you.

[robespierre]

What stands out is this:

The issue happened when I entered "reset-all": I saw the usual "Erasing..." but I never saw the "Flashing...".

reset-all is supposed to initialize the nvram to the factory setup and restart the machine. OK, so whence nvram? It means "non-volatile RAM"; that is, it doesn't lose is contents when power is removed. On some machines it is contained in a SRAM chip or a "Timekeeper" powered by a battery. On Old-World PowerMacs it was part of the CUDA microcontroller.
But writing to SRAM is simple and instantaneous. It doesn't need to be erased, or flashed. So the "usual" messages point to something else. What needs erasing and flashing? a Flash ROM.
It seems that the machine implements nvram by reserving a section of the Flash ROM (the one that stores the boot firmware) for nvram. The 28F008B3 Flash chip has "Parameter Blocks to facilitate storing frequently updated small parameters (such as data traditionally stored in an EEPROM)".
So if the Flash ROM has become somehow corrupted (and I have seen it happen myself) the machine might not be recoverable by voodoo with batteries, Vulcan death pinches, chicken gizzards, etc. In that case the physical Flash chip needs to be desoldered and reprogrammed externally.

[elderK]

Hey guys,

Thanks for the responses.

Unfortunately, the solutions that require the use of the keyboard are all no good: No USB peripherals light up at all when the machine boots up so actually interacting with the machine by way of the keyboard is out of the question.

As for NVRAM, I'd assume it would be like for PC where the NVRAM itself is nonvolatile only as long as a battery supplies power. If that's not the case then robespierre probably hit it on the head: If the flash is corrupt, there isn't much I can do about it.

Still, I have a reason to hope: After digging around for awhile, I found some old Apple service manuals for the PowerMac G4 series. In that manual, they mention various "symptoms" and "solutions."

Interestingly, the one that matches my situation mentions replacing the graphics card as a second port of call after resetting the PMU.

You may have seen another post where I hosed the graphics card pretty well: I managed to reflash that again through some trickery and made things worse.

I did discover that removing the video card from the machine and attempting to boot also fails: It reports the failure by way of beep codes, the same codes that it will emit as for a "Bad RAM" situation.

So, I've ordered a new video card from eBay, mostly to see if that will correct the problem.

I am curious, however: Have any of you been able to boot a PowerMac G4 without a graphics card installed?

If you can't - and also get the same beep code - then it gives me some hope. Maybe the freeze is caused by OpenFirmware trying to probe or otherwise interact with the effectively busted video card. I imagine that would happen before USB devices were probed.

Kind regards,
Dave Ward

[peeperpc]

I am curious, however: Have any of you been able to boot a PowerMac G4 without a graphics card installed?

My MDD normally doesn't have one installed because it is used headless.

[elderK]

Thanks peeperpc, that's good to know.

Tonight I removed each stick of RAM, as well as the GPU and tried booting.

The machine gave me the expected "Ah, no memory?!" code.

I added back a stick of RAM at a time: No beep codes but USB peripherals still failed to light up.

I've tested that those peripherals haven't failed: They power and light up as you'd expect on another machine.

I'm starting to wonder if the PRAM battery is dead: It appears to be ancient.

I've found many posts online about various kinds of weird failures that can occur when a PowerMac's PRAM battery is dead. Is it possible to boot these machines without these batteries?

Could it be the reason I'm experiencing this failure?

I should note that the "Erasing..." and "Flashing..." messages I saw, when I issued "reset-all" in OpenFirmware, were probably only visible because I was connected to OpenFirmware via a Telnet connection.

I look back to hearing from you guys

I see myself going to a battery store tomorrow to acquire a new Saft LS14250 battery

~Dave

[Jubadub]

Have you tried, the very moment you replug the power cable, to press and hold the power button? I saved my DLSD PB like that from what seemed like a complete brick after a lot of OF fiddling.

I emphasize the timing is important: the MOMENT that plug goes into the socket, press and HOLD that power button. You might hear fans going crazy, and you might hear a special beep, then a boot/reboot chime, and be taken back to OF.

Works with many PowerMac models. Not sure about yours, though, so you will have to try.

[elderK]

Hey guys,

I just wanted to let you know that after replacing the PMU battery and resetting the PMU, I was able to boot the machine successfully.

Sure, the video card was still dead and stuff but I was able to boot the machine, enter OpenFirmware and start a Telnet server blind.

After a couple hours of insanity, I also managed to resurrect the video card.

It seems a little worse for wear but should, at least according to my understanding, be running the same firmware that the card was when I received the machine.

A few resolutions don't seem to work so well anymore and there's a weird "shivering" effect on the screen but hey, I can still use it!

I can't wait until the replacement card arrives from the US: It's a Geforce 4 card that has a DVI port as well as an ADC one.

That'll be great because I'll be able to more easily use it with my HDMI displays.

I have a VGA -> HDMI adapter but it doesn't seem to work very well

~Dave

[ssp3]

Looks like someone was spot on with his diagnosis. 

1. Try fresh battery.
2. ..
3. ..

[elderK]

Indeed Thanks ssp3.

~Dave

[IIO]

I'm starting to wonder if the PRAM battery is dead: It appears to be ancient.

if you have no other option to test a battery (i also belong to this group of users) you can try what happens when you leave the machine connected to the power after its been turned off, while also beeing disconnected from the internet: the clock will be wrong after next reboot.