Mac Classic - will it ever run again!!

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Tomswork
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Re: Mac Classic - will it ever run again!!

Post by Tomswork » Wed Jan 06, 2021 7:33 pm

@rubber_jonnie

Yup if you unplug the connector from the circuit board on the back of the tube and follow it the the analog board the connector burns and cause problems

Tom

Tomswork
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Re: Mac Classic - will it ever run again!!

Post by Tomswork » Wed Jan 06, 2021 7:53 pm

@rubber_jonnie
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The board I have de capped and ultrasonic cleaning just need the caps will find a box to get a shipping cost

Tom

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rubber_jonnie
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Re: Mac Classic - will it ever run again!!

Post by rubber_jonnie » Wed Jan 06, 2021 8:10 pm

Cool, thanks @Tomswork
Collector of old Atari things:
800XL + Ultimate 1MB, 2x 1010 cassette, 1050 + Happy mod, 65XE (128k +APE Warp) & XC12, SIO2SD, 2600jr, 7800 and Lynx II
Atari 520ST (1Meg), 1040STF long button floppy, 2x 1040 STFMs + Gotek, 2x 4160STE with 32Mhz booster, ROM switcher, Mega ST1, Mega ST4, not to mention various bare ST boards for testing including a PAK 68/2 :)
Plus the rest..
Amiga stuff, Mac stuff, Sinclair stuff etc...
www.electronicnothingness.co.uk

Kai Robinson
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Re: Mac Classic - will it ever run again!!

Post by Kai Robinson » Tue Jan 12, 2021 10:06 pm

Oh hi! What you're experiencing is exactly what i'm dealing with on the Macintosh SE Reloaded project. What you're seeing on the screen is the checkerboard, but with the contents of RAM being directly displayed - hence the distortion/odd dots all over the screen.

Thing is, the Classic, is just a cost reduced version of the Classic - with some simplified logic to remove the need for a 'GLU' HAL16L8. Everything else is almost identical, same BBU, same F257/LS245 RAM control setup etc.

I stumbled across the VCFED thread about a classic exhibiting the same symptoms - turned out to be the SND IC...which oddly, also includes the Reset circuitry. It can be bypassed by lifting pin 5 on the SE's SND Chip - on the Classic - the SND Chip is a PLCC - and Pin 7 is what's responsible. Look around C71 on the underside, too, to see if there's any broken traces, or if theres indeed continuity.

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rubber_jonnie
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Re: Mac Classic - will it ever run again!!

Post by rubber_jonnie » Tue Jan 12, 2021 10:38 pm

Kai Robinson wrote:
Tue Jan 12, 2021 10:06 pm
Oh hi! What you're experiencing is exactly what i'm dealing with on the Macintosh SE Reloaded project. What you're seeing on the screen is the checkerboard, but with the contents of RAM being directly displayed - hence the distortion/odd dots all over the screen.

Thing is, the Classic, is just a cost reduced version of the Classic - with some simplified logic to remove the need for a 'GLU' HAL16L8. Everything else is almost identical, same BBU, same F257/LS245 RAM control setup etc.

I stumbled across the VCFED thread about a classic exhibiting the same symptoms - turned out to be the SND IC...which oddly, also includes the Reset circuitry. It can be bypassed by lifting pin 5 on the SE's SND Chip - on the Classic - the SND Chip is a PLCC - and Pin 7 is what's responsible. Look around C71 on the underside, too, to see if there's any broken traces, or if theres indeed continuity.
Ahh interesting, I will take a look, thanks.

I do also seem to have a problem now with the analog board too, I get no picture any more on the CRT, and in fact it looks like there is no glow from the neck of the tube. I'm working my way through the Dead Mac Scrolls to see what I can repair there, but it has been recapped and has worked before. Of concern are the voltages coming from the board, which are quite low, so 4.5V, 11.2V.

I know they can be adjusted, but they don't seem to be stable at all, even when adjusted.

Looks like I have a two pronged problem now, and need to get the AB working before I'll be able to do anything with the LB.

Are you by any chance aware of any circuitry that will allow the LB to display on a VGA display? I did find a link to some, but sadly it was dead. If I could work on the LB without needing the CRT it would make life a lot easier.
Collector of old Atari things:
800XL + Ultimate 1MB, 2x 1010 cassette, 1050 + Happy mod, 65XE (128k +APE Warp) & XC12, SIO2SD, 2600jr, 7800 and Lynx II
Atari 520ST (1Meg), 1040STF long button floppy, 2x 1040 STFMs + Gotek, 2x 4160STE with 32Mhz booster, ROM switcher, Mega ST1, Mega ST4, not to mention various bare ST boards for testing including a PAK 68/2 :)
Plus the rest..
Amiga stuff, Mac stuff, Sinclair stuff etc...
www.electronicnothingness.co.uk

Kai Robinson
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Re: Mac Classic - will it ever run again!!

Post by Kai Robinson » Wed Jan 13, 2021 6:24 pm

VGA? No. TTL? Yes - it's quite simple. The thing is, the internal CRT is a custom resolution - there's a 640x480 mod for the classic's but its very very awkward. You might have better luck running the logic board off a separate PSU for the meantime - i just built one out of a meanwell RT65 - has all the required voltage rails - just get a 14 way molex mini-fit-jr series plug and terminals, the crimp tool, the RT65 itself, some 16 gauge wire, a FPST switch, plastic box (incoming) and some mains cable.

I'm using this to fault find my Mac SE Reloaded board - can be sure i don't have to worry about a 34 year old PSU going pop, and i don't have to use the CRT, you can use the 'scope to probe the composite video signal being generated.
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