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To close out this thread, I ended up purchasing a motherboard off eBay for the blue phosphor unit and swapped it out, and that unit now works perfectly. The only downside is that it is the unit with no floppy drives (or appropriate power supply). I'll work to add a SD card based floppy to it in...

I’ve been staring at this board for 15 min and I cannot find a trim cap anywhere. Leading me to question my sanity or basic understanding of electronic components, both of which are likely questionable even on good days. Given the horizontal RS232 I’m assuming this is a gate array model...

Here's a shot of the other unit -- despite my phone's inability to deal with the sync, the monitor perfectly displays all that random garbage... Hitting reset does not seem to change any of the characters being displayed. However, turning it off and on typically results in a very different pile...

Hi Hugo, thank you for jumping in, really appreciate it. I can turn the brightness down until the monitor is objectively dark. I've attached a few photos here, one being the monitor with the contrast turned all the way up, and the brightness turned to a point where I feel the text is about...

Hi Larry, I went through your steps last night. I did find at least two cold solder joints on the connector pins, so I reflowed the solder across all pins to be sure. Visual inspection of the rest of the power board showed everything else looks good. Unfortunately this did not change the...

Thank you Larry -- now that it's all disassembled, I will be able to take a look at this tonight. FWIW, it does boot to basic and otherwise works great. It's just this brightness/contrast issue. Cheers, Ron

@Kool65 I finally got around to checking this POT over the weekend -- it does indeed go from 0-500 (~512) ohms smoothly as I turn it. I also traced wires back to make sure there are good connections back to the monitor board and all looks okay. If you have any other suggestions for chasing this...

Thanks @Kool65 I'll take a look -- turning the pot does impact the display, but I'll get a MM on it and check the resistance range and report back. Cheers, Ron

Hey all, I’ve done a bit of searching on a monitor issue I’m having on my model 4, but haven’t come across any actionable information. This monitor was working fine and one day I powered on and got this situation. Changing the contrast and brightness has little effect on the lines but I’ve the...

Hey all, finally got around to pulling the unit apart to get some photos and videos of the drive closing mechanism: Click here to see some photos and videos. Note, depending on your connection speed it make take a moment to load the 3 videos in the middle of the table. Each image should be...

First, thank you ALL for the thoughtful and supportive replies! One of the things I love about the retro community! I've got a busy week at work this week, but I will disassemble this coming weekend and answer some of the questions posed and see if I can get a little more precise about how much...

Hey all, I've just recently started collecting some of the computers that were around in the early to mid 80's, in particular those that my young, closed mind (I was an Atari computer fanatic back then) sadly kept me away from. I have a fairly pristine 64K model 4 ( some shots here...