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electronizer

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About electronizer

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  1. Pictures of the keyboard, disk, and insert with instructions for Atari owners:
  2. I had two more pilot units—unfortunately I only had the case for these. DA000092 and the other one looks like DA000145. I gave both of these to bob1200xl.
  3. In a previous post I wrote about troubleshooting my Atari 820 printer. It’s been working solidly for more than a week now so I figured I’d post the solution. The failure mode is that the printer won’t do anything after you turn it on. The power LED comes on, but the paper advance button doesn’t work, and nothing happens when you try to print from the computer. Every once in a while, the printer may work when you turn it on, or it may work for a short time and then stop responding (no paper advance or lprint). Assuming you’ve already tried the standard “reseat the ICs” solution with no success, the fix is to replace capacitor C109, a 1uF electrolytic capacitor that forms part of the reset circuit. My guess is that this capacitor hasn’t aged well in many of the 820s out there, either losing some capacitance or developing a leakage current. Because of its small capacitance value, even a slight worsening causes the reset circuit to function poorly, and therefore the ICs in the printer may come up in an unknown (and non-functional) state. In my printer, I chose to replace the capacitor with a 2.2uF part to increase the reliability of the circuit. I tried values up to 4.7uF and the printer still powered up and came out of reset fast enough that it wasn’t noticeable. A capacitor with axial leads would be best, but I made do with the radial lead part I had. Here’s a picture of the fix: I attached the capacitor between R106 and R110. The R106 connection is a little tricky because there’s a via right next to the resistor lead and you need to be careful not to bridge the pads. I also clipped out the old capacitor in case it was passing a leakage current. You can see the empty pads at the left of the picture. The nice thing about this fix is that you don’t have to disassemble the printer, though you’ll need a small pair of precision diagonal cutters to get the old capacitor out. I laid the new capacitor on its side so that the RF shield would still fit. If anyone has an 820 that still works reliably, I’d be interested to know if it uses the exact same part for capacitor C109. Mine had a blue Nichicon rated at 50V. Let me know if your printer has a different one!
  4. Some time ago I got a Muppet Learning Keys "keyboard." This colorful flat membrane keyboard (similar to the 400's keyboard) connects to joystick port 2 and has a kid-friendly layout. For example, in one corner of the keyboard there is a chalkboard with letters in alphabetical order instead of the usual QWERTY layout. The keyboard came with a disk that had C-64 application software on one side, and an "Atari Adapter Disk" on the other side. The adapter disk isn't a game, rather, it loads drivers that map the keys on the membrane keyboard to actual keys on the Atari. It then pauses to allow you to switch disks, and will boot whatever you insert with the drivers resident so that you can use the keyboard. I used it with "Hodge Podge" as suggested in this post and it works very well! One neat feature is that there is a row of "paint pots" on the keyboard in standard colors, and pressing a paint pot will change the background color of the screen. I did some searching for an ATR of the adapter disk and couldn't find it. It may be out there somewhere, but I digitized my copy and will post it here in case anyone is looking for it. MuppetKey.atr After playing around with the ATR in an emulator, I discovered it requires an XL or XE computer, and will check to see whether you actually have a Muppet Learning Keys connected. If you know of any other games for kids that work well with this keyboard, I'd love to hear about them! Most keyboard-based games should work, but I think Hodge Podge is particularly nice since pressing a letter does something related to that letter (e.g. pressing "C" gives you a picture of a cat, "V" gives a volcano that erupts, etc.)
  5. Finally got a chance to test my theory. First I hooked up an analog voltmeter to the reset line and turned on the printer. It does stay low for a little less than a second before going high, which seems like expected behavior. However, the pointer wiggles slightly as if there is some noise before rising to 5V. Then I clipped a 10uF capacitor in parallel with the existing 1uF cap (10uF was the smallest value I had on hand that would make a difference). This time it took 4-5 seconds for the reset line to go high, but when it did, the printer worked! I was able to repeat this behavior over multiple power cycles, so my confidence that I’ve identified an issue is rising. My new theory is that there is some noise on the power line that couples to the reset line when the power is ramping on the printer, and if the chips aren’t held in reset long enough, this noise causes the chips to come up in an unknown state. I went to the parts store and picked up some smaller values to try (1, 2.2, 3.3, and 4.7). Smaller is better since larger values will mean a longer wait time after turning on the printer before I can start using it. Once I find the smallest value that seems to work reliably, I’ll solder it in and use the printer for a while to see if the issue has gone away. Doctor, to your point about other issues, I was fairly certain those weren’t the case because I had already reseated/replaced ICs. Also, I figured those parts were good because every once in a while, the printer would work fine when I turned it on. But always good to reseat ICs as a first step You mentioned a reset fix, were you referring to the tech tip?
  6. Thanks hunmanik! ”We are not aware of any service problem...” I was hoping there was a service problem with a suggested fix. My printer won’t work even when it’s been off for a long time before I turn it on. I’ll still try increasing the capacitance in the reset circuit to see if that makes a difference.
  7. Still no luck finding the tech tip. Here's the reset circuit: If I understand this correctly, C109 and R106 form an RC time delay circuit of around 1 second. The charging current flowing through C109 and R106 causes Q102 to initially turn on, pulling pin 1 of the 6507 and pin 34 of the PIA low (grounded through R134) to hold them in reset. After C109 is charged, Q102 turns off and pins 1 and 34 go high (+5V through R108, 4700ohm resistor). This also causes Q103 to turn on, and a current flows through R110, Q103, and R134 to ground. This raises the voltage on the emitter of Q102, causing it to go further into cutoff and ensuring it is no longer trying to pull the reset pins low. The next thing I'd like to do is look at the +5V supply and reset pins on an oscilloscope; the +5 supply should be stable before the reset pins go high. If it isn't, I imagine that using a larger capacitor (maybe 2.2 or 4.7uF?) to increase the time delay would give the supply enough time to stabilize.
  8. Thanks for the offer! I did a close inspection of the print head and discovered it was just dirty. I was eventually able to get it working again. I can also update on the platen tape—I talked to Brad at Best Electronics and he thought it was probably teflon tape. He sent me a piece and it worked very well to replace the old peeling tape. The printer now works fine! Now if I could only find the Macrotronics interface that works with this printer (uses joystick ports 3 and 4, mentioned briefly in Analog #2, page 42). Since my original post I also acquired a Trendcom 200 (80 column thermal printer). Macrotronics published some screen printer software that works with the 200 and it would be fun to try doing some screen dumps. From what I read, these would have been some of the earliest printers available to Atari users.
  9. Got the regulators soldered in place, installed the boards and cables, turned on the drive and inserted a disk. Turned on the computer and it booted on the first try! The Doctor said it well...the Grass Valley upgrade is the debug Now the only thing wrong is the power LED—it doesn’t light up. I followed the debug flowchart and it led me to CR107. On closer inspection, there’s a capacitor there when it’s supposed to be a 5V zener diode. Makes me wonder if there are other errors on the side board, but I guess if the drive reads disks ok it must be fine. I’ll put the correct part in and if the LED starts working, I’ll call it good. Now I have two working 810s—no more swapping when I want to duplicate disks
  10. Ready to go. Good thing the local Atari Service Center is well stocked
  11. Found two analog boards. One of the boards had test results printed: Last tested on April 27, 1983 and...as of a few minutes ago! Verified working on my known good 810 analog drive. The other analog board worked too. Guess these are just more reliable than the old design. Time to perform the upgrade; the only thing I haven’t tested is the power supply board. Off to find a 12V regulator...
  12. For comparison since I happened to have all three: On the left is rev 1 of the Grass Valley power supply, the middle is rev 2. On the right is rev 8 of the older rear board. I will probably install the rev 2 Grass Valley board. Apparently it last worked on Oct 6, 1982...coming up on 37 years!
  13. Thanks for the additional advice Doctor! I confirmed the mechanism is fine by swapping it into a known good drive (the newer analog drive, incidentally). It does have the felt pad. So, the only possible place left for the problem to be hiding is the rear board. I’ve already reseated and then replaced all the chips. I suppose it’s possible that one or more of the rear board headers are faulty... I do have a couple of newer power supply boards and an analog board; at this point it’s so far disassembled that I’m thinking about just doing the Grass Valley upgrade. Though it would be fun to have working examples of each version, if the old version is so unreliable I wonder if it’s worth it to debug the issue...
  14. Good find Allan! I’ll have to compare some of the other pages when I get a chance...
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