Mac-to-VGA monitor adapter struggles

[bigmessowires]

Please help me escape DIP switch hell. I have an LC III connected to a Dell LCD with VGA input. It works fine using the pictured Griffin adapter, but with the other 10-switch adapter (Sabre brand?) I can't get any image to appear. I have the instructions for the 10-swtich adapter (pictured), but either they're wrong or I'm doing something wrong. After an hour of fiddling with DIP switches, I gave up. Do these adapters ever go bad? I would assume not since I think it's just a passive switch. Anybody have a similar adapter and can tell me what settings they're using?

 

[Phipli]

Please help me escape DIP switch hell. I have an LC III connected to a Dell LCD with VGA input. It works fine using the pictured Griffin adapter, but with the other 10-switch adapter (Sabre brand?) I can't get any image to appear. I have the instructions for the 10-swtich adapter (pictured), but either they're wrong or I'm doing something wrong. After an hour of fiddling with DIP switches, I gave up. Do these adapters ever go bad? I would assume not since I think it's just a passive switch. Anybody have a similar adapter and can tell me what settings they're using?

View attachment 62337

2356 or 23467?

I keep forgetting. I'll check mine in a while if they don't work.

 

[Melkhior]

Please help me escape DIP switch hell

I'd suggest looking at https://github.com/sfiera/mactech/blob/master/displays.rst, which I used to designed my own adapter, there's the information on the meaning of sense signals. DIP switches are only there to choose between different configurations of those, and could be wired in many different ways...

With that information you might be able to use a multimeter between various pins to figure out what the switches are doing, and if anything is broken. It's very unlikely, but if the diodes are dead or some traces are broken, you may get weird results from inaccessible configurations.

Or just use one of those your ordered from JLCPCB

 

[Phipli]

Mine is set like this :



It probably actually should be 1467. This is for 640x480 though.

 

[dramirez]

I have my 10 pin adapter with 1&5 set to ON and works OK with my LCD display. Don't remember the resolution...

 

[finkmac]

dumb question but... are you sure the LC III is even outputting video?

 

[joshc]

dumb question but... are you sure the LC III is even outputting video?

In the original post, "It works fine using the pictured Griffin adapter," so yeah, I think they've already verified it can output video,

 

[bigmessowires]

Great, please keep the suggestions coming. I'll try those combos later this morning. Yes the LCIII outputs video with the other (Griffin) adapter.

I can't remember if the Mac expects sync on green, separate h and v sync, or something else.

I'm excited for this LCIII system because it was completely assembled from separate spare parts I had lying around for 10+ years. An empty LC475 case, a fan (can't believe I actually had this), a spare LCIII mobo, another spare LC PSU, a spare SCSI HD, and a spare floppy drive. The only thing I'm missing is the audio speaker. I'm hoping to clean it up and offer it as a prize for Mactoberfest Meetup's Tetris Max competition.

 

[LaPorta]

Generally speaking, I find all such adapters work best when set to the max possible resolution. So, if the LCIII can do 1024x768 @ some Hz, shoot for that. Generally I find most adapters then work fine outputting resolutions/frequencies lower than that.

 

[LaPorta]

Man, I wish I could attend that competition!!

 

[Forrest]

I’m guessing the non-working adapter had liquid damage at some point in the past. New are available on eBay for $15.

 

[bigmessowires]

2367, you sneaky bastard!! I was one DIP switch combo away from declaring this adapter dead. Now it works.

If the manual can be trusted, 2367 is 640x480x60Hz with separate H and V sync. I tried all the combinations for 640x480x66Hz but none worked.

I should have looked up what resolutions the LCIII supports before I started - it only goes to 832x624. That would explain why none of my 1024x768 attempts worked. I tested 1367 for 832x624 and it also works, but the scaling looks ugly on the LCD monitor. 640x480 looks better.

 

[LaPorta]

That’s pretty consistent with what I’ve found. You can leave it as 832x624 and use the control panel to change between that and 640x480, but you already said you don’t want to use the former!

 

[Nixontheknight]

2367, you sneaky bastard!! I was one DIP switch combo away from declaring this adapter dead. Now it works.

If the manual can be trusted, 2367 is 640x480x60Hz with separate H and V sync. I tried all the combinations for 640x480x66Hz but none worked.

I should have looked up what resolutions the LCIII supports before I started - it only goes to 832x624. That would explain why none of my 1024x768 attempts worked. I tested 1367 for 832x624 and it also works, but the scaling looks ugly on the LCD monitor. 640x480 looks better.

2367 is actually the best mode you can use! I use it with my beige Macs, and from what I know, it can go up to 800X600 on PPC machines

 

[joevt]

Some adapter documentation at https://tinkerdifferent.com/threads/documentation-for-db15-to-vga-adapters.318/

 

[cgp]

For the record, in the DIP switch lotto on my LCIII and Acer LCD, I use 1459 .. giving 640x480x67Hz and 832x624x75Hz.

 

[Phipli]

For the record, in the DIP switch lotto on my LCIII and Acer LCD, I use 1459 .. giving 640x480x67Hz and 832x624x75Hz.

Strange, anything starting 14 should only give 640*480 at 67Hz?

Settings starting 13 are needed for 832*624 aren't they, or a multiscan option?

 

[cgp]

Strange, anything starting 14 should only give 640*480 at 67Hz?

Settings starting 13 are needed for 832*624 aren't they, or a multiscan option?

For my adapter, 1459 is multiple scan 21".

 

[Phipli]

For my adapter, 1459 is multiple scan 21".

Ah, sorry, I wasn't thinking.

 

[dougg3]

@sfiera linked me the same 6-switch adapter that Melkhior posted above...nice work creating that sfiera! That's a fantastic reference. Thought I would respond here since it's all about the adapters.

My 10 switch adapter (SABRE, looks exactly the same as BMOW's above) is similar. I spent a little bit of time tracing what the switches do. The extra switches are for various sync configs as you suggested. By default with no switches on, only grounds and red/green/blue are passed through.

• Switch 1 is DB-15 sense 0 (4)
• Switch 2 is DB-15 sense 1 (7)
• Switch 3 is DB-15 sense 2 (10)
• Switch 4 is GND
  • Switches 1-4 being on connect themselves to each other. Just like sfiera's 6 switch adapter but arranged slightly differently.
• Switch 5 connects VGA HSYNC (13) to DB-15 CSYNC (3).
• Switch 6 connects VGA HSYNC (13) to DB-15 HSYNC (15).
• Switch 7 connects VGA VSYNC (14) to DB-15 VSYNC (12).
• Switch 8 enables a diode between sense 1 and 2.
• Switch 9 enables a diode between sense 1 and 2 in the other direction.
  • For anyone in the future who cares about which diode is which, when switch 8 is on, my meter shows a 0.545 V diode drop with my common lead on pin 7 and my positive lead on pin 10.
• No idea what switch 10 does...maybe nothing at all. Instructions don't refer to it.