Power Mac 7200/90 Chime but No Video

[SawtoothG4]

I have a Power Mac 7200/90 that has been in the family since new in 1996. About 15 years ago it was put away after it stopped outputting video signal.

Recently I have gotten back into vintage Macs, and I would really like to resurrect this thing given its sentimental value. I plugged it in for the first time in many years, and found that it still does the same thing. After pressing the power button, it chimes, the power LED comes on, drive noise is heard, but no video signal is output. Additionally, when the power button is briefly pressed at any time afterward, the system immediately shuts off, leading me to believe it is not fully booting up.

So far, I have tried everything in the Service Source manual as well as various "common wisdom" troubleshooting items:

• Tried multiple tested known-working monitors and/or DB-15 to VGA adapters
• Reset PRAM
• Replaced the 3.6V battery
• Visually inspected for damaged components, leaking capacitors, corrosion, etc. (None found)
• Reset Cuda chip
• Reset the logic board as per Service Source instructions (remove battery, disconnect power cable from logic board, wait 10 minutes)
• Reseated all DRAM and VRAM modules
• Tried with one DRAM module at a time in various slots

Nothing has worked and it still exhibits the same problem. I am a lot more familiar with troubleshooting New World Macs, so I am at a bit of a stopping point.

Does anyone have any suggestions for what to try next?

 

[joevt]

Connect to another computer using serial cable to modem port. Try entering Open Firmware.

Try a PCI graphics card?

 

[SawtoothG4]

Until your post I didn’t even think these Old World Macs had OpenFirmware. I just read up on it, I ordered an 8-pin Mini DIN serial cable to try to connect it to my PowerBook 5300c. Any idea how to figure out what settings to use for data rate, etc?

I don’t have any PCI graphics cards but I will see if I can get one and test it.

 

[joevt]

Sorry for my late replay. Forums were unreachable yesterday.

All Power Macs with PCI have Open Firmware.

Default data rate is 38400 bps 8N1 (it's actually 8N2 but 8N1 seems to work). You can set it to 57600 by changing the input device and output device either from the Open Firmware command line:

" ttya:57600" io

Or by changing nvram and rebooting:

setenv input-device ttya:57600
setenv output-device ttya:57600

View current nvram settings using:

printenv

There's some notes in the first post at:
https://forums.macrumors.com/thread...ll-work-in-a-beige-power-macintosh-g3.2303689

DingusPPC has Power Mac 7200 emulation, so we can compare output from Open Firmware.

 

[SawtoothG4]

Well I seem to have resurrected it! This whole time I thought that the L2 cache slot had to be populated for the machine to boot, but it turns out the 7200 came with no L2 cache DIMM and mine had one installed as an upgrade at some point. I tried booting with the cache DIMM removed and it worked! I guess something is wrong with either the cache slot or the DIMM itself.

Thank you @joevt for the OpenFirmware info! I’m sure I will use it. Maybe I can try to troubleshoot the cache DIMM using OF over serial?

 

[joevt]

Which of these ROMs does it have?

077d.28f1.1  96cd923d  045a3b23.04a82e3e.0333e815.0400652a  02c65d54.03175e91.020d323a.027bef10.02a0f232.037e5917.0231da82.029ef77a:c241cd82bf90797a  dfebb8fdad4124e02608429d98bf349b  "1995-08 - 96CD923D - Power Mac 7200&7500&8500&9500 v1.ROM"
077d.28f2.1  9630c68b  045a3ff2.04a8169b.03334745.03ffe575  02c6b097.0317a71b.020d1a9e.027c620c.02a0a3bd.037df94c.0231514d.029e06b3:4db4a42fea3b53b3  2623a0c438045ea04d2cc67310c97743  "1995-08 - 9630C68B - Power Mac 7200&7500&8500&9500 v2, SuperMac S900.ROM"

All the Open Firmware 1.0.5 ROMs share the same Open Firmware code.

The Hammerhead memory controller has an L2_CACHE_CONFIG register. If there's a cache that is setup, then the device-tree will include a l2-cache device.
The code for setting up this device is more readable in the Apple Network Server 1.1.20.1 ROM.

: make-cpu-properties
	...
	?tnt							
	l2-cache						
	0=								
	and								
	if								
		0f80000e0 \ L2_CACHE_CONFIG
		ar-rb@						
		dup							
		h#80						
		and							
		if							
			3						
			and						
			" "(1312 1416)"
			drop					
			+						
			c@						
			1						
			swap					
			<<						
			new-device				
			" l2-cache"				
			device-name				
			" cache"				
			device-type				
			dup						
			encode-int				
			" i-cache-size"			
			property				
			dup						
			encode-int				
			" d-cache-size"			
			property				
			5						
			>>						
			dup						
			encode-int				
			" i-cache-sets"			
			property				
			encode-int				
			" d-cache-sets"			
			property				
			0						
			0						
			" cache-unified"		
			property				
			active-package			
			to l2-cache				
			finish-device			
		else						
			drop					
		then						
	then							
	l2-cache						
	?dup							
	if								
		encode-int					
		" l2-cache"					
		property					
	then							
	;

The Hammerhead ERS document describes the Hammerhead memory controller.
https://tinkerdifferent.com/threads/apple-network-server-macos-based-roms-found.4756/post-41404