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Mac monitor to VGA adapter - sync settings?
Posted by: bigmessowires on 2013-10-20 14:20:18
I'm trying to connect a PowerMac 8500 to a modern VGA monitor, using one of those DB-15 to HD-15 adapters from eBay that's got DIP switches to configure the sync settings. But I can't seem to figure out what settings I need - no matter what I try, my VGA monitor just ignores the Mac and goes to sleep. No errors about sync out of range, or weird corrupted video, or other things I might expect to see with the wrong DIP settings.

Here's the chart that came with this adapter:

sync.jpg

Anyone else have this same adapter? Do the sync settings (modes 1-6) refer to the sync method used by the Mac, or by the VGA monitor? I'm pretty sure VGA has separate HSYNC and VSYNC signals, but what about the Mac?
Posted by: Trash80toHP_Mini on 2013-10-20 14:28:26
Does it look like any of these? Video Adapter Docs Scan Dump

Which resolutions are you trying to set?
Posted by: bigmessowires on 2013-10-20 14:56:02
It is the one posted by tecneeq in the 6th post of that thread. But my problem isn't lack of docs, it's not being able to understand the docs. 🙂 I've tried all 6 mode settings for 640x480, 1024x768, and "multiple scan 21" without getting anything on the monitor.

I'm beginning to suspect the PowerMac is toast. It was working when I last ran it about a year ago, but I'm noticing there is no startup chime, and the HD spins up but I don't hear any HD activity after that. So maybe there's a hardware problem - but shouldn't I at least see a Sad Mac or something? What kind of hardware problem might cause no chime, no video, no anything?
Posted by: bigmessowires on 2013-10-20 15:19:30
Looks like the problem was a dead PRAM battery. I removed the battery, and left the battery holder empty since I didn't have any spares. After that I started getting the startup chime again. After more experimentation with the video adapter, it seems that Mode 5 (separate sync) works. Booting OS9 now!
Posted by: Trash80toHP_Mini on 2013-10-20 18:28:36
Excellent news. Some of the adapters have counter-intuitive setting instructions. Yours looked pretty clear, but it doesn't hurt to have someone with the same adapter try it on a like machine.
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