Power Mac 7100 only one resolution to choose from

[Greystash]

I know this is a stretch since it's a first gen PPC, but has anyone come across this before?

I finally got my hands on a Power Mac 7100 with a CPU upgrade but can't screen change resolutions. I have tried two LCD monitors (one with a native resolution of 1024x768), and a ViewSonic CRT with a native resolution of 1600x1200.

I have tried several NUBUS cards and at the moment am sticking with the SuperMac Thunder/24 since the CPU upgrade uses the PDS slot. I have also tried three PDS cards. I'm using a DB15 > VGA adapter but this doesn't seem to be the problem as I've also tried a different one and get the same results.


I've tried changing resolutions within the Monitors control panel, Control Strip, and with SwitchRes - and I am only given one resolution to choose from (1152x870 which seems to be the max the card supports) and can choose all color depths. This is the same with all video cards, monitors and System 7 - System 9.0. I am using the SuperVideo 3.1 drivers, but performance is terrible and it doesn't appear to change anything after installation.

 
Does anybody know why I would be getting this sort of behavior? I've never experienced this before with any Mac.. I know for a fact that there is nothing wrong with the PDS cards, they work fine in my 7200.

 

[rvense]

I think the adapter can be the problem. Some of them have DIP switches to let you select the resolution. I have both a simple cable and an adapter with switches that I use with my Quadras, and I can only use the higher resolution if I use the one with the DIP switches set correctly.

[Angel]

I think the adapter can be the problem. Some of them have DIP switches to let you select the resolution. I have both a simple cable and an adapter with switches that I use with my Quadras, and I can only use the higher resolution if I use the one with the DIP switches set correctly.

I can confirm. I have too this type of adapter: in normal applications it's all ok then in games it's impossible set the resolution in full screen (it it's lower than what is manually set, the rectangle will be placed in top left)

[Greystash]

Thanks rvense and Angel. One of the adapters I have has dip switches so I spent a good 2hrs last night going through every configuration and got a little closer. Switch changes wouldn't do anything unless I rebooted and reset the PRAM.

On both the Thunder/24 (NuBus) and Radius Precision Color 24 (NuBus) I can successfully switch between 640x480 and 832x632. Even though the adapter, and graphics cards both support resolutions up to 1152x870. None of the modes past 832x632 work. When I configure the adapter to anything above 832x632 the Precision Color card goes into secondary mode as if there's another video card in the machine. On the Thunder/24 it just defaults to 1152x870.

Maybe I need to try another adapter? Any thoughts on why it's so difficult to use a VGA monitor? I found it strange that even with a VGA CRT screen I got the same behavior and couldn't get a list of resolutions with a dip switch adapter, or the one without.

[ssp3]

VGA has always been tricky on older Macs. IIRC, only few resolutions were available with non Mac monitors.
There was also something about using Monitors control panel instead of Monitors and Sound in some specific case. What it was I can not remember. As an alternative, you can also try Griffin Super Res control panel to set/change the resolutions.