Run a Color Classic without an analog board or tube?

[eric]

Hey all,

I'm in a predicament - I have almost all the parts I need for a color classic - except the tube. Logic board works, analog board needs work but fixable. I don't think I'll find a local tube (which would probably be in a working/fixable CC, so I'd still be where I am today) - and shipping tubes can be successful, the one I did have shipped broke.

So sitting here pondering if I should risk another tube, wait an unknown amount of time for a local tube - I pondered this VERY high level gameplan:

1 - Use a LC style PSU to power the logic board - this has -12/+12/5v needed (and I have a spare)
2 - Tie together all the grounds on the logic board that are normally tied by the shielding (see adrian's digital basement on sound troubleshooting)
3 - (and this one is where I'll need some input) - find the appropriate points for video output to an RGB to HDMI.
4 - mount a LCD in the case non-destructively.

There could be some big show stopper here I don't know - like the analog board has some logic needed for sound or video. If no one thinks there is a deal breaker here my first step would be to wire up a harness for the LC PSU to the pins on the underside of the logic board and see if I can make it chime stand alone.

Appreciate anyone's input on if this is a fools errand or could be possible!

 

[rikerjoe]

This is another one of those times where I wish we had schematics for the CC analog board.

 

[-SE40-]

Hello Eric,

Sounds like a great project!

I may have a suggestion,….. to have a look/search for small trinitron monitors wich may fit your purpose.
Had a quick search on ebay and showed two 8 inches. (Could be 9” build format, like with the other compact Macs)

Guess if you would find a suitable candidate. that you could disassemble it and place it in your enclosure.
Just get the size/prize correct is the game.
Otherwise go -indeed- for a decent LCD replacement.

Enjoy!
Greetings, Chris

 

[jajan547]

Use a RGBtoHDMI, make sure you have a pi Zero. Next is a matter of finding a screen that fits so in this case I believe this would work. What you will be doing is taping into the video signal in the analog board to feed a video signal to the RGBtoHDMI, from here its as simple as plugging in the HDMI cable from the RGBtoHDMI into the back ports for the LCD logic board. You will need to make mounts (3D printed) this will work but you'll need to adjust the size by about an inch. Once everything is setup it's a matter of adjusting the screen settings with the RGBtoHDMI.

 

[jajan547]

Use a RGBtoHDMI, make sure you have a pi Zero. Next is a matter of finding a screen that fits so in this case I believe this would work. What you will be doing is taping into the video signal in the analog board to feed a video signal to the RGBtoHDMI, from here its as simple as plugging in the HDMI cable from the RGBtoHDMI into the back ports for the LCD logic board. You will need to make mounts (3D printed) this will work but you'll need to adjust the size by about an inch. Once everything is setup it's a matter of adjusting the screen settings with the RGBtoHDMI.

Actually don't need an analog board I think.

 

[-SE40-]

……., the one I did have shipped broke….

May I ask what the damage to this CRT is?

 

[eric]

May I ask what the damage to this CRT is?

The glass neck was cracked.

 

[-SE40-]

So, the front glass is still there and ok?

 

[eric]

So, the front glass is still there and ok?

Ya, and I've seen those mods to the glass - but not sure if I'd put the effort into that, quite the job and lots of fine dust.

----

Sound -

I toned out the sound - there is one chip on the analog board and it's just a DC amp TDA7052A for the external speaker.

Power -

Looks like the the Powercc.org tacky page has the pinouts i need... though I thought one of those was -5v.... may need to probe while a cc is on and on it's side to be 100% sure.

+12 V	P9(Yellow)
GND	P7(Brown)
GND	P5(Black)
+5 V	P3(Red)
+5 V	P1(Red)

 

[-SE40-]

Ok, sofar Ive not found any examples for that.
Its just something worth to considder, as youve got a broken tube to try it out with.

Njoy your built!

 

[Trash80toG4]

-SE40- said:
So, the front glass is still there and ok?

Ya, and I've seen those mods to the glass - but not sure if I'd put the effort into that, quite the job and lots of fine dust.

I'll assume you're talking about Dremel, a real grinder or some other dry approach to removal?

I'd suggest using a wet tile saw for that task. Got a cheap one on clearance that'll also take wood blades for fine dry cutting of small items. It's still boxed as cutting the face of the Compact tube moved way down the to do list.

Building a jig to support the tube for cutting two sides per setup is the plan. Dunno abot color CRTs, but the phosphors in a B&W CRT would be a health safety consideration IIRC?

 

[-SE40-]

Hi!
Wel, ive used a simple angle grinder and diamond disk. That worked ok. Indeed a bit dusty (safety gear needed!) Its still a work in progress…. See my url- to my Pinterest page for more if wished.

 

[eric]

Quick update on power - the pin outs were right - the -5v must be on one of the other pins.

Hooked up the LC PSU & tied the grounds together - no chime (head phones plugged in) and no scsi activity. Next step is to re-validate this board works (worked when it was pulled months ago)

 

[Trash80toG4]

See my url- to my Pinterest page for more if wished.

Can't find your link, will I be able to see it without an account?

 

[Mu0n]

Do you think a rgb2hdmi will have a color limit out of the options the cc normally offers in system 7?

 

[jajan547]

Do you think a rgb2hdmi will have a color limit out of the options the cc normally offers in system 7?

Maybe more because it goes through the raspberry pi so maybe it acts as an amplifier of sorts.

 

[Trash80toG4]

Do you think a rgb2hdmi will have a color limit out of the options the cc normally offers in system 7?

Not sure what you mean here? Color depth? That's determined by the configuration of the Mac. However it's transmitted to a display, it's still the contents of the frame buffer as limited by amount of VRAM in the system or on a VidCard.

Are you asking if there might be unsupported options? Has anyone started a thread around here about that doohickey?

 

[Mu0n]

I'm talking about the limits of the rgb2hdmi. Many people have wanted this to work for vga resolutions for classic ms-dos gaming but the threads I've read, some implicating the participation of the lead of the project, continually repeat that VGA can't be dealt with and were talking about 320x200 with 256 colors out of a few millions.

Since this is lower than the maximum ones out of a color classic, my question seems on point for this machine.

 

[Trash80toG4]

Thanks for the clarification, interesting project. Never thought it was off topic, just wondered what was up.

Looks like yet another application for the Extron Scaler. I've seen a lot of CC LCD mods, but none using the OEM board, all I recall offhand were VGA capable Logic board transplants. It's a shame it requires an external box, but it would definitely fit into the cubic vacated by CRT removal.
_______________________________________________________

That's tangential unless the OP decides to give it a try. Maybe it's time to crack the case of my box and take pics for posting a technically oriented thread about it? Comparing its hardware to the rgb2hdmi project. Got linkage that one for us folks who can't follow the geeky hub stuff?

 

[-SE40-]

Eric, I did come accross this CC example that uses a 9,7”ipad display…..I think it looks really good and authentic (asfar as I can judge that;-) Dont know if they actually did change anything to the bezel.

https://buyee.jp/item/yahoo/auction/f1051358662?conversionType=yac_item_bottom_recommend_list