68kMLA Classic Interface

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Idea: Macintosh Classic III (LC550+M1420)

Posted by: alectrona6400 on 2022-03-17 12:12:42

I have a Macintosh Performa 550 motherboard sitting around, probably hasn't been turned on since 2004 according to the person who gave it to me.
I also have a Macintosh Classic (M1420 RevB) which is probably one of my least favorite compact macs because of how it was released at the wrong time... Unfortunately it's diffcult to track down old Macintosh boards and I cannot find a Classic II board. But I also believe we can do somewhat better...
All that I would need would be an edge connector pinout for the 550 board and probably a 9" Monochrome/color CRT with an RGB input or whatever. I also need to fix the 550 board as it is battery bombed, luckily not too major.
I know this sounds like an absolutely outlandish thing to do, but why not? If I'm honest, the Classic feels like an overglorified spreadsheet machine.

Posted by: alectrona6400 on 2022-03-18 08:35:38

So I have heard from someone that the B&W compact macs have a 22KHz vsync/hsync rate? Also it appears you can just use the video on one of the RGB pins. unfortunately, still no luck finding a pinout of the color classic/Performa 5xx motherboard edge connector. this would be a very fun project to take on

Posted by: cheesestraws on 2022-03-18 09:06:27

still no luck finding a pinout of the color classic/Performa 5xx motherboard edge connector

It's in the bomarc CC LB schematics

Posted by: Daniël on 2022-03-18 11:43:11

So I have heard from someone that the B&W compact macs have a 22KHz vsync/hsync rate?

They do. However, if your Classic has a later revision analog board, it is possible to get it up to 640x480@31KHz if you're comfortable working on the analog board:

Compact Mac retina display

After a long hiatus, I'm going back to this resolution-changing project armed with a new approach. I've established (as techknight and others have found) that the flyback transformer on most of the compact Macs can't be run at VGA or higher resolutions -- no matter what external capacitor is...

68kmla.org

Posted by: alectrona6400 on 2022-03-18 11:49:06

Woooah! I might try that but I would also like to have the system in one full piece...

Posted by: max1zzz on 2022-03-18 12:59:49

Funnily me and @Trash80toHP_Mini have recently been discussing something similar only we where targteing the SE or even the Plus and we where going to make a custom logicboard based around the LCIII's

My understanding is the LCIII board should be able to drive a compact CRT / analog (As @Bolle's WIP SE/30 grayscale card is driving the SE/30's display at 12" pizzatopper resolution, allbeit with a different neck board to allow grayscale) but I haven't personally tried this yet

Posted by: mg.man on 2022-03-18 13:13:24

we where targteing the SE or even the Plus...

I know "purists" like the older (Plus, SE, etc...), but (yeah, IMO), I like the cleaner lines of the Classic and Classic II. Having the guts of an LCIII in a "Compact" with grayscale (and 640x480) would be cool. Oh, and if you need a "Classic" case and A/B to tempt you, I'm sure I can sort that out... just sayin'... 😎

Posted by: alectrona6400 on 2022-03-18 13:41:27

I know "purists" like the older (Plus, SE, etc...), but (yeah, IMO), I like the cleaner lines of the Classic and Classic II. Having the guts of an LCIII in a "Compact" with grayscale (and 640x480) would be cool. Oh, and if you need a "Classic" case and A/B to tempt you, I'm sure I can sort that out... just sayin'... 😎

Really? Might put that on my list of things to buy. Do you also have a Classic II board and FPU card somewhere?

Posted by: mg.man on 2022-03-18 13:51:13

Do you also have a Classic II board

No FPU, but I do have a Classic II 'board. I'm in the UK, though, so my comment was aimed at @max1zzz - who's also over here. I'm guessing you're in the US?

Posted by: alectrona6400 on 2022-03-18 13:51:44

Yes, unfortunately I am. Here we've got overpriced junk on eBay...

Posted by: mg.man on 2022-03-18 13:56:10

Here we've got overpriced junk on eBay...

Perhaps... but, being American myself (I just live in the UK now), I get pretty envious of the volume of vintage Mac stuff that comes up over there... much to the disgust of my elderly folks - who keep receiving random packages from eBay'rs (and MLA'rs) to caretake until I can get over, collect, and transport back here... 😉

Posted by: alectrona6400 on 2022-03-18 13:57:39

Ahhh... when do you plan to move back to the US?

Posted by: mg.man on 2022-03-18 14:00:13

Probably no time soon... been here since the late 80s... 😮

Posted by: Trash80toHP_Mini on 2022-03-20 08:45:39

Funnily me and @Trash80toHP_Mini have recently been discussing something similar only we where targteing the SE or even the Plus and we where going to make a custom logicboard based around the LCIII's

My understanding is the LCIII board should be able to drive a compact CRT / analog (As @Bolle's WIP SE/30 grayscale card is driving the SE/30's display at 12" pizzatopper resolution, allbeit with a different neck board to allow grayscale) but I haven't personally tried this yet

Well, you've let the cat out of the bag on that one. Can't wait to see how that works out when you've gotten started.

@mg.man You can do a lot better than an LCIII board in your Classic if you're ready to modify the backside. Quadra 630 or its lesser kin will tuck nicely in there and run the CRT at 512x384 in Grayscale.

If you can source a Classic II A/B you can give a CC/Takky a run for the money, if only in Grayscale by doing apm's Retina hack at 640x480. That takes your Classic into G3 territory. 😉

By using a Q630 or P6360 drawer the tail end of the drawer fits within case without problem and the drawer bezel/cover works a treat. Mini ATX aux. PSU would be required in the bucket, but with SD, cubic would be freed up for it.

Mine's a 6500/G3, with the second slot dropping down into a ZFP HDD case where the PSU is located. There's a crazy thread somewhere about this one. Tiny projector was to be used for color display, fitting within the bucket for rear screen and flipped back big screen projection use.

If anyone can get in touch with @apm please let him to know to check back in about any A/B mod that might be advisable for 512x384.

Posted by: mg.man on 2022-03-20 13:27:10

You can do a lot better than an LCIII board in your Classic if you're ready to modify the backside.

Well, sure... if you want to grab all the tools and start hacking about - pretty much anything is possible - pretty sure I've seen some Mac mini "guts" stuffed into a "compact" case over on Buyee (in the land of the Takky mod)... 😉

My thinking, however, was to avoid any case hacking... which could put a lot of ppl off. Instead, *if* the LCIII can be squeezed down to a Classic II logic board form factor, it should just slide in. Then, add the grayscale neckboard for 512x384 and you'd have a nice classic Mac games machine. It might be too quick for Arkanoid tho! 🤔

Posted by: bdurbrow on 2022-03-20 15:21:39

too quick for Arkanoid tho! 🤔

Uhh... shouldn't the frame rate be tied to the 60hz vertical blanking interrupt?

Posted by: mg.man on 2022-03-20 15:44:40

shouldn't the frame rate be tied to the 60hz vertical blanking

Dunno... I was going by @volvo242gt's post in thread 'What did you do to your Apple/Mac today?' https://68kmla.org/bb/index.php?threads/what-did-you-do-to-your-apple-mac-today.30590/post-437934
😀

Posted by: Trash80toHP_Mini on 2022-03-20 17:56:09

Well, sure... if you want to grab all the tools and start hacking about - pretty much anything is possible - pretty sure I've seen some Mac mini "guts" stuffed into a "compact" case over on Buyee (in the land of the Takky mod)... 😉

Yep, ya gotta go all out Takky on it for that kind of mod. For the life of me I can think of no earthly reason for all that empty cubic under the Classic Board? The Apple reason would be to limit cubic above the logic board that might be used for upgrades. Bend down the stops, remove that silly fan cage and a full depth, re-engineered LCIII will fit nicely in there.

By going with a two level board/daughterboard for ports on a raised platform, the full height under the chassis deck becomes available. 😉

My thinking, however, was to avoid any case hacking... which could put a lot of ppl off. Instead, *if* the LCIII can be squeezed down to a Classic II logic board form factor, it should just slide in. Then, add the grayscale neckboard for 512x384 and you'd have a nice classic Mac games machine.

Squeezing LCIII down to the Classic's size pretty much won't happen at this stage of the game I think.

I did pull the Classic out for a photo session though:

All kinds of room in there and the recessed tuschie of the Classic seems ready to to go for a minor surgery and a printed cover plate.

Posted by: volvo242gt on 2022-03-20 20:00:52

Dunno... I was going by @volvo242gt's post in thread 'What did you do to your Apple/Mac today?' https://68kmla.org/bb/index.php?threads/what-did-you-do-to-your-apple-mac-today.30590/post-437934
😀

I may also be slower in response, due to the last time I played it on anything reasonably fast (an LC 475) was almost 22 years ago. 🤣

Posted by: Trash80toHP_Mini on 2022-03-21 10:05:29

Morning musings of the day: I think I've noodled out an angle for approaching LCIII PCB reduction to Classic form factor! 🙂

Break the logic board into two sections:
Main board would be Classic form factor LCIII with every bit of memory removed, freeing up a hectare of PCB real estate.

Entire memory subsystem and PDS would be moved onto a riser card in slot located where the 72pin SIMM is located in pic:

Memory/PDS riser will be similar this 72pin SIMM Saver:

Orientation of Address/Data aligned with RA PDS slot at top of board with so card oriented toward HDD Cubic which allows my maximum size RCPII/IIsi card or LCIII PowerCache adapter to sit atop SCSI_to whatever printed cage. Humongous DIP ROM chips will be replaced by SIMM socket on riser. SIMM/VRAM/ROM sockets will be mounted to both sides of riser. Onboard RAM IC limitation excised and replaced by SIMM(s) with full CAS/RAS line implementation to increase maximum memory. Multiple RAM SIMMs will be implemented to reach theoretical memory limit.

Riser approach is designed for modification without touching the CPU/Ports PCB. Interface will be an edge card connector on riser with slot on main board. Just about anything becomes possible.

SCSI connector will align with Classic's memory expansion card slot. This will allow the cable to be plugged directly into the CPU/Connector board or a custom riser can be designed for anything wanted to be edge card slotted into its SCSI BUS with Passthru for cable connector mounted above.

Thoughts? @trag what do you think the maximum memory allotment will turn out to be in this configuration?

edit: @max1zzz whatcha think? Riser approach may also work for SE board we've been discussing?

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