Color Classic analog board re-design, needs community feedback.

[ArjenCNX]

Ladies and Gentlemen, ​

I have spent quite allot of time fixing Color Classic computers, and always there was that one Major issue: the analog board PCB quality.

Since it is a single sided FR-1 board with a super thin copper layer, populated with leaking capacitors this has presented myself, and probably you if you are reading this post, lots of issues over time.

Thus, I have found a company that specializes in PCB design and had them re-create the original board, then I altered their single layer design in to a two layer design, to be made from FR-4 2 ounce copper PCB boards, selected all SMD parts, had them populated by JLCPCB so we have a fair shot of getting another 10 years out of our beloved Color Classics.

Work done so far: ​

- Created the layout of the PCB (Rev1.0)
- Created the Schematic of the analog board (Rev1.0)
- Created Bill of materials for all the components (the ones available, that is)
- Ordered PCB's with SMD parts (Rev1.0)

All this is done in the Free and opensource KiCAD software package, so anyone can chime in. The files recieved were in Altium, since I do not want to use closed-source software for this, I have converted this to KiCAD, this did introduce some discrepancies, not all of those are resolved at the moment.

My To-Do's:​

- Populate PCB with through-hole parts
- Testing
- Sharing current design
- Getting your feedback
- Create next revision of PCB
- General clean-up of the schematic

Community affords:​

I initially thought, ill just finish everything and test it and order new revisions, and get it all done before posting, but then I thought, that's just my ego talking, I should share it, ask you if your interested to help check the design, perhaps suggest improvements, make your own revisions, and so on because after all, that is what Tinkerdifferent is for!

So, I suggest we get to Rev.final together, most of the tedious stuff is done now and I would like your input on the current revision as I'm sure together we will be able to get a better end result if we can work together.

Community to-do's:​

- Check current PCB design for mistakes
- Check current schematics for mistakes
- Check bill of materials
- Suggest improvements
- Build your own and test
- Hopefully someone will fork this and find alternate components that can still be bought, That's a long shot I know but it will be possible now.

Currently every part that is available has an LCSC part number, manufacturing part number.

So Happy tinkering everyone, hope you can chime in and for those willing and able, please help!

Arjen.

 

[Mark_W]

Great work Arjen and congratulations on finally releasing the project.

Took a quick look at it and noticed CP12 and CP15 are swapped, 100V capacitor should be on VE (+B, 60V) rail:

Also some random thoughts:

• Can we use modular power supply instead of relying on original design? Most parts on switching power supply can still be bought (TDA4605, IRFBC40, CNY17, etc.) but the Astec power transformers can only be salvaged from donor boards. Logic board power supply is easy as it only outputs +12V, +5V and -12V, but crt power supply can be a bit tricky as it outputs +60V, +24V and +8.3V. Already checked meanwell modular power supply catalog, they only offer power supply modules up to 54V:
  
  
  
  
  
  Maybe other manufacturers offer higher voltage options? Ideally we would want something close to 70V or even 84V if we want to do the VGA mod.
  
  
• Maybe we can use linear DC-DC voltage regulators instead of zener diodes to generate 18V and 8.2V? It's not a great design to begin with
  
  
  
  
  
• Most CRT driver chips (v-deflection ic, rgb output amplifier and HOT, etc.) can still be bought from china even though major distributors no longer sell them. However the motorola jungle/deflection ic can't be sourced anywhere and need to come from donor boards. Note LC 520/550/575 analog boards also use this chip and can be bought relatively cheap on ebay unlike CC boards..

 

[bakkus]

FYI there was a previous effort to recreate the CC Analog Board, but it seems to have stalled.
There are probably some useful information in there, nonetheless: https://github.com/pferronato/MacCCAB
edit: And it's forked and slightly improved at https://github.com/maekawa-mugi/MacCCAB

 

[qubitz]

This is really great! I’ll take a look and see how I can help. I’m currently debugging my board and have been really worrying about the future for keeping these machines going.

 

[ArjenCNX]

Great work Arjen and congratulations on finally releasing the project.

Took a quick look at it and noticed CP12 and CP15 are swapped, 100V capacitor should be on VE (+B, 60V) rail:
View attachment 28084

Also some random thoughts:

• Can we use modular power supply instead of relying on original design? Most parts on switching power supply can still be bought (TDA4605, IRFBC40, CNY17, etc.) but the Astec power transformers can only be salvaged from donor boards. Logic board power supply is easy as it only outputs +12V, +5V and -12V, but crt power supply can be a bit tricky as it outputs +60V, +24V and +8.3V. Already checked meanwell modular power supply catalog, they only offer power supply modules up to 54V:
  
  View attachment 28085
  
  Maybe other manufacturers offer higher voltage options? Ideally we would want something close to 70V or even 84V if we want to do the VGA mod.
  
  
• Maybe we can use linear DC-DC voltage regulators instead of zener diodes to generate 18V and 8.2V? It's not a great design to begin with
  View attachment 28087
  
  
• Most CRT driver chips (v-deflection ic, rgb output amplifier and HOT, etc.) can still be bought from china even though major distributors no longer sell them. However the motorola jungle/deflection ic can't be sourced anywhere and need to come from donor boards. Note LC 520/550/575 analog boards also use this chip and can be bought relatively cheap on ebay unlike CC boards..

Thanks for the heads up on the capacitors, ill swap that round to correct the issue.

On the power supply section and other issues with parts that do not have a replacement:

the real problem here is that there is no work-around to not needing donor boards, the Motorola Jungle chip is probably the biggest challenge here as it controls quite allot of complex stuff.

On the power supply design, as is is powerful enough to run the computer, especially in the absence of a mechanical hard drive. personally i have had little issue with the power supply section of the analog board, I have re-built maybe 20 units over the years, and this seems quite stable if the load is not too high. The transformers can be made, I can have them copied in China, if we can get enough orders in to get a small batch. It is possible to re-design the power supply and use say a nice Power integrated chipset but it will always require custom transformers.

On the 8.3/18V zener solution, here I agree, it's probably best to use a DC-DC converter there to significantly increase the stability and efficiency, ill be looking in to this, and select a suitable DC-DC converter that we can hopefully fit somewhere on the board.

ill look at some small boards as well, there are some small modular replacements that are adjustable, 3 pin LDO replacements, we can do an LDO swap but it's just as inefficient.

 

[ArjenCNX]

FYI there was a previous effort to recreate the CC Analog Board, but it seems to have stalled.
There are probably some useful information in there, nonetheless: https://github.com/pferronato/MacCCAB
edit: And it's forked and slightly improved at https://github.com/maekawa-mugi/MacCCAB

I've looked at that, but it is still very incomplete, less then 25% of the schematic is there. at least now we have the whole schematic, i have the PCB's in, so once some time becomes available i will add all the donor components and do some de-bugging if needed and see if it runs. i think it will take 2 or 3 revisions to get it where we want it to be.

 

[ArjenCNX]

This is really great! I’ll take a look and see how I can help. I’m currently debugging my board and have been really worrying about the future for keeping these machines going.

my biggest concern with these really was the PCB itself, cracked traces, electrolyte damage, loose pads, so many hard to spot issues creep in over time, making even the most experienced guys wonder if they should spend days on end getting it running again. my goal is to avoid that, and make a re-build something that can be done in say 3-4 hours. I hope we will be there soon!

 

[ArjenCNX]

Here for those that do not use KiCAD, the current schematic in PDF form. Ideal to have for repair work. also the BOM in HTML format for easy reading and part locating. 95% of the parts have the LCSC order number, or if not available the Digikey order number, and also the datasheet link.