6500/250 Woes

[tyler5310]

Hello! I recently found a Power Macintosh 6500/250, as part of a vintage Apple collection someone local to me was clearing out. I brought it home, and found it needed a power supply. In the meantime, I discovered it had a NewerTechnologies G3 L2 upgrade card in the cache slot. Cool! Ordered and replaced the power supply, and now the machine turns on, but no chime and it will not display video. The power LED does go green after a few seconds, but nothing else. It will respond to keyboard inputs such as PRAM reset. Went ahead and recapped the board, but same results. The original caps were in good shape, but was under the suspicion that they had failed electrically. I've also replaced the PRAM battery.

Any input on what else I could do? Also, does anyone have a logic board for a 6500 for sale? Would love to get this machine up and going. Thanks!

EDIT: I've tried with all cards removed, RAM individually, as well as with no RAM. No RAM gives no power LED, so it appears it at least sees the RAM?

 

[treellama]

Pull the L2 G3, all but one stick of ram, all the PCI cards, etc. If it boots, start adding things back in to narrow down the problem.

 

[tyler5310]

Pull the L2 G3, all but one stick of ram, all the PCI cards, etc. If it boots, start adding things back in to narrow down the problem.

I've done that already, unfortunately. With no RAM, I get no power light, so it's being recognized at least it would seem.

 

[treellama]

Ah, that's a shame. Seems like a logic board is the next try, hopefully it's not some issue with the connector the logic board plugs into.

If there is no chime, how do you know it is resetting PRAM?

 

[tyler5310]

Ah, that's a shame. Seems like a logic board is the next try, hopefully it's not some issue with the connector the logic board plugs into.

If there is no chime, how do you know it is resetting PRAM?

I also reflowed all the pins of the edge connector, just to be safe. No change.

I think it is, because when I hold the key combo, the power light goes off then comes back on. So I assume it is.

 

[Fizzbinn]

Maybe try DeoxIT contact cleaner on RAM slots? I had success with that reviving a B&W G3 that couldn't boot in manner similar to what you're describing. Could also try it on the edge connector, don't think it could hurt.

 

[tyler5310]

Maybe try DeoxIT contact cleaner on RAM slots? I had success with that reviving a B&W G3 that couldn't boot in manner similar to what you're describing.

Ordered! I will give it a shot. I had my thoughts about this as well.

 

[mikes-macs]

try resetting the CUDA chip: locate the little red or white push-button switch on If your 6500 appears dead when pressing the power button, resetting the CUDA chip: locate the little red or white push-button switch on the motherboard and hold it down for one minute.

 

[tyler5310]

try resetting the CUDA chip: locate the little red or white push-button switch on If your 6500 appears dead when pressing the power button, resetting the CUDA chip: locate the little red or white push-button switch on the motherboard and hold it down for one minute.

Done that too

 

[joevt]

I think it is, because when I hold the key combo, the power light goes off then comes back on. So I assume it is.

If it works well enough to zap the PRAM, then it should be working well enough to get into Open Firmware? Connect the modem port with a printer serial cable to another Mac.

This is the code in Open Firmware (inside the _cold-init word) that checks for Command-Option-P-R and initializes nvram if it is being pressed.

_kbd-ihandle
if
	"get-key-map"
	_kbd-ihandle
	$call-method
	drop
	zapcapslock
	" "(0001 0000 1000 0120 0000 0000 0000 0000)" \ Command-Option-P-R
	comp
	0=
	if
		init-nvram
		"reset"
		_kbd-ihandle
		$call-method
	then
then

This code does not cause the restart. The restart happens when the toolbox ROM begins booting. After it draws the gray checkerboard screen with round corners, it checks if Command-Option-P-R is still being pressed and does a restart then.

Zapping the PRAM should set the modem port as the default input and output device for Open Firmware.

Press Command-Option-O-F to get into Open Firmware.

 

[Phipli]

If you want to use it some while working out what is wrong with the 6500, you could drop a 630 logic board in it. They're more common and it would give you a 33MHz 68040 to play with.

 

[Byrd]

Check the PSU voltages, any chance you've a PCI Mac video card? Might be another thing to try.

 

[Phipli]

Also, inspect around the battery area. The square batteries do leak. I've had to repair damage for two or three of them to the SCSI and video circuits.