add images to wy-60 post, and post it.
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content/blog/wy-60-repairs/bus_architecture.png
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content/blog/wy-60-repairs/cold_joints_1.jpg
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content/blog/wy-60-repairs/socket_ram_chip.jpg
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content/blog/wy-60-repairs/the_setup.jpg
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@ -1,7 +1,8 @@
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---
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---
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title: Repairing a WY-60 Terminal
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title: Repairing a WY-60 Terminal
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date: 2025-04-28
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date: 2025-04-28
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draft: true
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tags:
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- retro
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---
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---
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# Intro
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# Intro
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@ -41,7 +42,6 @@ At this point we needed to test them out. And this is where I realized that,
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despite picking the unit with the least yellowing, mine didn't work.
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despite picking the unit with the least yellowing, mine didn't work.
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I saw the cursor, and a line for the status bar, but no characters in sight:
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I saw the cursor, and a line for the status bar, but no characters in sight:
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image here
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Thankfully, the scuffed one worked, so I was able to confirm that
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Thankfully, the scuffed one worked, so I was able to confirm that
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I could interact with it. However, the geometry was bad and there seemed
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I could interact with it. However, the geometry was bad and there seemed
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@ -59,20 +59,19 @@ This took a while, as I was still figuring out the best way to
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disassemble the unit. Testing it was initially challenging as
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disassemble the unit. Testing it was initially challenging as
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it sits on the screen face as you take it apart.
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it sits on the screen face as you take it apart.
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Eventually, I got it back together. But we were clearly not done.
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image here
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Eventually, I got it back together. But to my dismay I was still greeted with a
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blinking cursor and no status line. At this point, I needed to probe the system
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while it was running to see if any chips were being silent.
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At this point, I needed to probe the system while it was running
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I eventually came up with this setup. It's not very safe, but I coped by
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to see if any chips were being silent.
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telling myself that I would only touch the system when it was off. That rule
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didn't last long. Fortunately the low voltage digital stuff that I care about
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was close to the table and far from the spooky high voltage near the top of the
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board.
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I eventually came up with this setup. It's not very safe, but
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I coped by telling myself that I would only touch the system when it was off.
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That rule didn't last long. Fortunately the low voltage digital stuff
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that I care about was close to the table and far from the spooky high voltage near the
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top of the board.
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image here
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My next hunch was that something was wrong with the Attribute data pipeline.
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My next hunch was that something was wrong with the Attribute data pipeline.
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The attribute data is what determines if a character or line is large, blinking,
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The attribute data is what determines if a character or line is large, blinking,
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@ -80,30 +79,31 @@ reverse-color (block), or "blank". I thought that if the pin for "blank" was stu
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none of the characters would not load properly. The character attributes can either be stored
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none of the characters would not load properly. The character attributes can either be stored
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alongside the character itself, or in a separate "Attribute RAM", which is read at the same time.
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alongside the character itself, or in a separate "Attribute RAM", which is read at the same time.
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Image of functional block diagram, showing the attribute and character data pipelines.
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With my new test setup, I was able to find and probe pins from the underside of the board.
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With my new test setup, I was able to find and probe pins from the underside of the board.
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One of the challenges here is that there are multiple busses, each with potentially multiple masters.
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One of the challenges here is that there are multiple busses, each with potentially multiple masters.
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Not only do you need to probe a data line, you also need to have a probe for whatever makes the chip
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Not only do you need to probe a data line, you also need to have a probe for whatever makes the chip
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"active", be it a chip select, or an `~OE` pin on a logic buffer nearby.
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"active", be it a chip select, or an `~OE` pin on a logic buffer nearby.
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Image of the PCB schematic, showing the complex bus interconnect and 74-series chips.
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I started from the font ram, then checked U20, which was the custom chip. I kept working backwards, but couldn't
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I started from the font ram, then checked U20, which was the custom chip. I kept working backwards, but couldn't
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find anything that felt wrong.
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find anything that felt wrong.
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Things took a quick turn when I noticed this while setting up a probe:
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Things took a quick turn when I noticed this while setting up a probe:
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Image of cold solder joints.
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Uh, guys?
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Uh, guys?
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Image of more cold joints on a different chip.
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It can't possibly be this, right? U17 and U15 are part of character storage,
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It can't possibly be this, right? U17 and U15 are part of character storage,
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and I did see the font RAM output non-zero, meaning it had to have rendered
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and I did see the font RAM output non-zero, meaning it had to have rendered
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something! I quickly cleaned up the joints and powered it on. I couldn't see it
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something! I quickly cleaned up the joints and powered it on. I couldn't see it
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at first, but it worked.
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at first, but it worked. Thankfully I found this before starting to replace other chips.
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# Takeaway
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# Takeaway
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@ -120,7 +120,7 @@ seemed "off" before going further. I would have noticed the character RAM
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eventually, if I finished my testing of the Attribute RAM. In this case it was
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eventually, if I finished my testing of the Attribute RAM. In this case it was
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easy to spot visually and so I didn't need to test it any further.
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easy to spot visually and so I didn't need to test it any further.
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While I was working on this, my friend was using his unit to develop a USB
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While I was working on this, my friend was using his unit to develop the USB
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keyboard adapter. His unit was slightly more yellow and has some centering
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keyboard adapter. His unit was slightly more yellow and has some centering
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issues, but otherwise is fully functional. By the time I had mine figured out,
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issues, but otherwise is fully functional. By the time I had mine figured out,
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the firmware was mostly complete, so it was a quick flash away. I might blog
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the firmware was mostly complete, so it was a quick flash away. I might blog
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@ -128,7 +128,7 @@ about it some time, but the protocol is really simple.
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I'm typing this last portion in Vim on the terminal, using the VT100 mode.
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I'm typing this last portion in Vim on the terminal, using the VT100 mode.
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( image of editing this post with the terminal )
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# Next
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# Next
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