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High DPI LCD replacement for CRT


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Saw this on Adrian's Digital Basement:  https://www.youtube.com/watch?v=pvjsXbz1xlk&ab_channel=Adrian'sDigitalBasementAdrian'sDigitalBasement

 

So if you can go direct from the motherboard to HDMI, then use one of these with an iPad 2 screen, and you could theoretically replace the CRT with a high res DPI LCD and have pretty much a perfect screen with no interpolation artifacts.

 

Any thoughts?

 

Edit:  Well, maybe not an iPad 2, but you get the idea.  Maybe an iPad 3 screen or something.

 

Edited by olePigeon
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I so badly want to get ahold of one of these now. I've got a Mobius accelerator for my Classic that supports a second display. I'd love to take advantage of that, and it's not like Mobius displays show up very often (or at an affordable price point).

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This is excellent – really innovative and cool stuff!

 

I have a feeling that this will become more and more important over the next couple of years. We had a discussion here recently surrounding the inevitable demise of the remaining functional flyback transformers (and what to do when that happens) and replacing CRTs with LCDs (or even OLEDs!) sure seems easier to me than reverse engineering dozens of different flybacks. We could probably even crowd-fund custom glass pieces to recreate the original appearance of the tubes. 

 

There are some sticking points that would need to be addressed. For example: I'm fairly sure that all AIO Performas need the tube connected in order for the power supply to not instantly kill itself when you power it on. I discovered that the hard way with my 5400. I'm not sure how compact Macs behave without the tubes hooked up. This likely just requires a voltage sink of some form to trick the PSU but it'll still take some fairly serious engineering to do right. 

 

@olePigeon thanks for sharing this. It's great food for thought. 

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1 hour ago, PowerMac_G4 said:

This is excellent – really innovative and cool stuff!

 

I have a feeling that this will become more and more important over the next couple of years. We had a discussion here recently surrounding the inevitable demise of the remaining functional flyback transformers (and what to do when that happens) and replacing CRTs with LCDs (or even OLEDs!) sure seems easier to me than reverse engineering dozens of different flybacks. We could probably even crowd-fund custom glass pieces to recreate the original appearance of the tubes. 

 

There are some sticking points that would need to be addressed. For example: I'm fairly sure that all AIO Performas need the tube connected in order for the power supply to not instantly kill itself when you power it on. I discovered that the hard way with my 5400. I'm not sure how compact Macs behave without the tubes hooked up. This likely just requires a voltage sink of some form to trick the PSU but it'll still take some fairly serious engineering to do right. 

 

@olePigeon thanks for sharing this. It's great food for thought. 

I think it would be far easier to just design a replacement power supply board, even if the compacts will run without the tube connected you wouldn't really want to (it would be hard to safely secure and insulate the HV lead), your going to get the the point where you are having to modify the analogue board to disable the HV circuitry at which point you might as well just use a different PSU.

 

 

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20 minutes ago, max1zzz said:

I think it would be far easier to just design a replacement power supply board

 

You're most definitely correct. The power draw for compact Mac logic boards is so low that you could probably use a picoPSU or similar. 

 

With respect to the AIO Performas: retrofitting a modern screen might actually end up being a significant upgrade. The 5000 series machines get awfully hot and this is largely due to the inefficient PSU and the complete lack of space around the CRT. Removing all that bulk would surely make a huge difference to the thermal performance. There's also the weird issue of my 5400 supporting 1024x768 but the tube itself does not. An LCD would surely be able to run at that resolution with no problems. 

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Yes this is really nice! If we could somehow remove the CRT/Flyback components and put this into a different cabinet....many different ideas.

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Posted (edited)

I have 29 of these RGBtoHDMI Version 12 Issue 4 boards for sale $1 each. Here's the mouser cart I used to populate my board (which works fine). I have been using mine on a Mac Plus. It's worth noting Adrian's profile won't work on a Mac Plus.

 

If you use my mouser cart, make these updates:

  1. swap out the stand offs for these.
  2. Remove the 10k resistor (MFR PN: CR0805-JW-103ELF)
  3. Remove the 2x 5-pin 4.7k Ohm resistor net (MFR PN: 4605X-101-472LF)
  4. Remove the 10 Pin straight header (MFR PN: 929850-01-10-RA)

 

Takes about 60 minutes to assemble. If you're comfortable working with SMD components this won't be challenging. Only frustration I experienced was two SMD caps that insisted on tombstoning as the evening got late and my patience grew thin :)

 

image.thumb.png.fc92e7989270e472b8b82c8bfa3844e5.png

 

I have my settings dialed in now (with the exception of the inverted BW) but I thought this was a sort of fun GIF I made from early in the config.

1910864423_RGBtoHDMIprogress.gif.452153ba2e2a92b905635425ef37a229.gif

Edited by Stephen
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I've mulled this over a fair bit today and my ultimate fantasy idea involved pairing a modern flexible LCD with a curved piece of custom-made glass. It would be ludicrously expensive and over the top but it would probably look almost flawless if you got the scaling right. 

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I’ve been working on an LCD adapter plate for the CRT curvature of compact macs. Started the project, worked on it off and on since 2015, and finished the design about 2 weeks ago. Very timely.

 

I’ll share the design files as open source on Thingiverse for 3D printing once I finish the back mount for the LCD. 

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I am working on putting a LCD into a compact Mac. It displays at 1024x684, pixel doubled using a 1024x768 panel. It is FPGA based. Remaining issues are to reconstruct the CPU clock from the video signal (so as not to rely on a clock from the PDS connector) and to generate LVDS signal to drive the LCD direct from the FPGA, making the whole thing a little cheaper than using a separate driver chip. It works now but isn’t finished. The object has always been to make this work with no soldering or case modification. If you have a working Mac you could just put the analog board and CRT away safely to restore at some future time.
 

For those compact Macs with a bad CRT or flyback it means they can live again… it also means greater flexibility with power supply; a replacement analog board subsystem could mount many varieties and of course removing all the hot stuff means no fan would be necessary!

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21 hours ago, aeberbach said:

The object has always been to make this work with no soldering or case modification. If you have a working Mac you could just put the analog board and CRT away safely to restore at some future time.

 

I am really glad you are working on this.  When it is finished, I'll be in the queue...

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Posted (edited)
On 6/6/2021 at 1:38 PM, Stephen said:

I have my settings dialed in now (with the exception of the inverted BW)

For anyone who has a RGBtoHDMI, here are the settings from my Mac Plus:

sampling=1,1,1,1,1,1,1,0,0,0,5,0,0,0,0,0,0,1,0,0,100,256,100,256,100,256,0,256
geometry=172,22,512,342,512,342,2,2,0,1,15667200,704,5000,370,1,0,0
palette=Tea1002

 

You can save this in a text file

/Profiles/6-12_BIT_RGB/Mac_Plus.txt

 

The B/W is inverted, I don't think the software supports inversion yet. If you want it "reverted" you will have to use an IC on your video line for now.

 

Page 10 of this doc will give you the V-Sync, H-Sync, and Video lines from the Mac Plus.

Edited by Stephen
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I'd like to give this project a try, but it looks like the CPLD that this project requires is backordered for months and months. Maybe it's a spike in demand from this project, but I think it's more likely a Covid-related supply chain problem. Does anyone happen to have a spare CPLD chip for sale?

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1 hour ago, davidg5678 said:

I'd like to give this project a try, but it looks like the CPLD that this project requires is backordered for months and months. Maybe it's a spike in demand from this project, but I think it's more likely a Covid-related supply chain problem. Does anyone happen to have a spare CPLD chip for sale?

 

Digi-Key told me they would restock on the 28th. In the meantime, I ordered five XC9572XLs from AliExpress (this seller) – although they have cleared customs in Canada surprisingly quickly, they haven't arrived in my mailbox yet, and so I haven't been able to verify them.

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17 minutes ago, ravuya said:

Digi-Key told me they would restock on the 28th

It looked like they were backordered almost everywhere, so I just ordered mine from Mouser last week and got into line with everyone else.  Its not like I don't have plenty of other projects to keep me busy for three or four weeks, while I wait.

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