Diagnosing a Classic Mac in a weird situation (Early Analog Board)

[woodapples]

Cool project, curious to know how you've connected stuff around the LM317?

I think maybe in my final build I was injecting power into the lm317 input.
I'd have to check the schematic but from memory it has soft start circuitry on the adj pin.

I haven't played with my one since I ran out of working classic/classic II logic boards (also I got a Mac plus working).

Yes, i retained the LM317, but i removed the 12v reg for efficiency's sake and combined all 12v rails into one, including the one on the heater, the 12v rails on the deflection IC and the softstart RC circuit in LM317's ADJ pin. I supplied the usb-pd's 20v to the input of LM317 and it seems to work. But i have plans to remove that chip and replace it with a better switching reg with current limiter (my measurements indicated around 17-18v with 0.4A current limit).

BTW, thanks so much for your prior project! It was quite a good stepping stone for this effort! Wouldn't have done this without that project post of yours

 

[mogs]

Yes, i retained the LM317, but i removed the 12v reg for efficiency's sake and combined all 12v rails into one, including the one on the heater, the 12v rails on the deflection IC and the softstart RC circuit in LM317's ADJ pin. I supplied the usb-pd's 20v to the input of LM317 and it seems to work. But i have plans to remove that chip and replace it with a better switching reg with current limiter (my measurements indicated around 17-18v with 0.4A current limit).

I looked at the schematic after I sent my last message and saw the other 12V reg, I don't think I'd even noticed it before.
My intention was to reduce complexity and replace it with modularity, your mods push this even further.

BTW, thanks so much for your prior project! It was quite a good stepping stone for this effort! Wouldn't have done this without that project post of yours

Oh yeah, cheers , cool to see it get picked up.

 

[woodapples]

I looked at the schematic after I sent my last message and saw the other 12V reg, I don't think I'd even noticed it before.
My intention was to reduce complexity and replace it with modularity, your mods push this even further.


Oh yeah, cheers , cool to see it get picked up.

I will list down the mods in a modified schematic of EAB later soon, hopefully folks can try it to save classic analog boards that are screwed by their broken PSU circuits

 

[woodapples]

WARNING: If you dont know how to deal with high voltage stuff, please stay away from this thread. I am not liable for any injury or damages resulting from the use of this information.

With that out of the way, this is the culmination of all my mods to make the Early Classic Analog Board run without that pesky temperamental power supply circuits. Hope this would be a useful guide for y'all!

 

[Dogmander]

WARNING: If you dont know how to deal with high voltage stuff, please stay away from this thread. I am not liable for any injury or damages resulting from the use of this information.

With that out of the way, this is the culmination of all my mods to make the Early Classic Analog Board run without that pesky temperamental power supply circuits. Hope this would be a useful guide for y'all!

I was working on the Classic analog board a while back, I was planning on replicating the PCB (and have modern schematics) so that you can repair and diagnose these machines better. Seeing how it's possible to run both the logic board and CRT power without requiring a majority of the problematic components, I wonder if it would make more sense to design a modified PCB which uses a modern power supply for the voltage lines.
The Bomarc schematic can be a bit unclear on the voltage lines, so I appreciate your work on the diagram.

 

[woodapples]

I was working on the Classic analog board a while back, I was planning on replicating the PCB (and have modern schematics) so that you can repair and diagnose these machines better. Seeing how it's possible to run both the logic board and CRT power without requiring a majority of the problematic components, I wonder if it would make more sense to design a modified PCB which uses a modern power supply for the voltage lines.
The Bomarc schematic can be a bit unclear on the voltage lines, so I appreciate your work on the diagram.

It should be possible! I mean this thing runs on a single USB-PD charger right now so integrating a better and modern power supply circuit on a brand new PCB would be really kickass!
I also think everything except the flyback and the CRT connectors can be replaced with SMD resistors and probably tantalum caps as well. It'd be exciting to find out if those components will work

It was my endgame for this project but alas I had no extra time lately for it

 

[Dogmander]

It should be possible! I mean this thing runs on a single USB-PD charger right now so integrating a better and modern power supply circuit on a brand new PCB would be really kickass!
I also think everything except the flyback and the CRT connectors can be replaced with SMD resistors and probably tantalum caps as well. It'd be exciting to find out if those components will work

It was my endgame for this project but alas I had no extra time lately for it

I think it might be preferable to use a standard barrel jack or IEC plug for power input, as you could more easily gurantee sufficent power can be delivered compared to USB-C, but USB-C is still an option as many people nowadays probably own something capable (laptop power bricks and the like).
A modern analog board solution would be neat, but seems like a lot of work. The Classic is a rather hindered (but accessible) machine compared to other Compact Mac systems.
Still an interesting idea nonetheless.

 

[davewongillies]

It should be possible! I mean this thing runs on a single USB-PD charger right now so integrating a better and modern power supply circuit on a brand new PCB would be really kickass!

There's prior art with this Mac SE & SE/30 version: https://github.com/dekuNukem/PicoRC/blob/master/mac_se_se30.md

I'd imagine it'd require some pretty light changes to make it work with the Classic & Classic II