Jump to content

Jeramy Breckles

New Members
  • Content Count

  • Joined

  • Last visited

Community Reputation

8 Neutral

About Jeramy Breckles

  • Rank
    Combat Commando

Recent Profile Visitors

The recent visitors block is disabled and is not being shown to other users.

  1. I finally got a new multimeter and it measured 18v AC on one pin and 8v AC on the other... Seems that my previous multimeter was faulty.
  2. @HOME AUTOMATION: When I measured the voltage, I probed the connector that goes to the computer; nothing intrusive. @Ksarul: In order to get the keyboard "used" to working again, I decided to type in a BASIC game. Every keystroke (after a while) worked effortlessly. The game loaded, but ignored my inputs. I guess that there was something wrong in the code.... Until I can get some sort of media for this thing, I'll have to shelve it. I don't want to that because the whole reason for me getting a TI-99/4A in the first place was to get my 3-year-old son into a computer without a mouse and be able to feel the tactility of a real keyboard. He has trouble with the mouse pointer concept and did get used to touch screens, but I feel that there's something lost by touching a screen with flickering lights. I'll have to pinch my pennies and get a Flashrom99 and a 32k expansion card eventually. I happen to have a 2GB microSD card and an adapter to regular SD already on hand, so that's a start. At this point, I have a fully functional (as far as I can tell) TI-99/4A with late 1982 parts mixed with early 1983 parts. The keyboard I saved is an unusual one. Turns out it has Futaba sealed linear switches. No "Stackpole", no membrane.
  3. As far as the video issue, I'm trying to be patient for the F18A MK2 to come about. I know that Mr. Hagerty has been working on it, but that doesn't stop me from chomping at the bit. The dead keys on my keyboard are now working except for the period. I have to hit it a bit harder than I like for it to register, but at least I can get it into whatever I am typing on it. Now that it's working in original factory specs plus 37 years of age, it's time for upgrading the power supply. Before my multimeter died, I did measure the output of the "wall wart" and it put out 28v AC when it says 18v AC and the other rail put out 8.5v AC when the rating is 7.5v AC. The "coffee warmer" PCB from the case still put out the normal voltages to the board.
  4. I couldn't help it... I did some further investigation and found that I had accidentally bridged a connection on the 9901 chip. I took that bridge out and now the equals, semicolon, period, and "B" keys won't work. The good thing is, that's how they were in the donor unit. I did go underneath the keyboard and short across the pins on the PCB for each respective non-working key and found that they do work when shorted. Now it's just a matter of cleaning the keyboard, I think. The only other issue I have, albeit a minor one is that there is some slight artifacting/ghosting around the text. I did make my own cable out of an old audio cable and a 5-pin din, but I think I got it too hot while soldering it because the connection is hairy at best. I might look into that later unless anyone comes up with suggestions. At the very least, I have chased the original problem out of the mainboard and I couldn't be happier with that.
  5. I got up today, had my coffee break usual, and looked up this topic that I started. I went to do as you suggested Stuart, but my multimeter decided to croak somehow. (yes the battery was still good) Cheap-o unit anyway. I went ahead and turned it on without the keyboard; lo and behold it had no issues that I could tell. I.E., no more repeating semicolon. I did figure out that the cable that was soldered to the keyboard was brittle and was causing bad connections. I reached over and took the keyboard connector off of my parts board, soldered it in place, and used a short IDE cable I had laying around (same position on both ends) and tried it again. Almost everything worked... After referring to the grid diagram I found for the keyboard, it seems pin 5 has a problem. The system is slow to boot into TI Basic with the keyboard connected, but with it still powered on, I can disconnect said keyboard and it moves along like it should. After I got a flashing cursor to start typing, I reconnected the keyboard and the flashing stops. I can type the command "call clear" and that works fine. I tried to type in the obligatory "Hello World" program and once I pressed the "N" key, I heard the lower tone error beep and it just freezes. I disconnected the keyboard again and the cursor starts flashing again like normal. I did try using just a jumper wire to make the "N" type up by shorting pin 5 to pin 9, but no dice. I tried any key assigned to pin 5 with my jumper wire and nothing worked. I'm soooo close to having a working TI-99.... At this point, it looks like I'll have to wait a couple days for my new multimeter to come in and go from there.
  6. Update: I replaced the deformed resistors and tried my other clock chip (the one by the CPU) and there was no change in behavior. I've run out of ideas at this point. Any suggestions would be appreciated.
  7. I replaced the 9901... ooops.... but i also replaced the chip below it which is right next to the VDP ram. I wasn't sure if the clock chip had anything to do with keyboard input.
  8. Hello, all! Here's my story: I got a couple of TI-99's off of ebay (I know...) hoping to get a working one so that I could show my son what I used when I was a kid. The first one had a video issue and I tried to correct it by replacing the VDP ram. That actually made it worse and as an additional problem, some of the solder pads came off as I performed the swap. I tried bodge wires to no avail. At that point, I decided to give up on that board. I ordered the 2nd one and it was in much better shape internally, but the keyboard is missing about half the keys. I hooked it up anyway only to find out that the semicolon was repeating even without a keyboard connected. I grabbed the first board and robbed the 9904 chip and the 74ls156n chip off of it and installed them onto the 2nd. Nothing changed. I did poke at some resistors with my multi-meter and found that one of them didn't measure the same as the parts board (going by the same location and physical appearance). As far as the chips I changed out, I was able to test them and make sure that they were functioning normally going by what little I could decipher from the video and especially by the sound by just typing keys and hitting enter (I just went into TI Basic because I have no software atm). All sounded normal to me with the beeps I heard. As it is, I'm wondering if it's a resistor causing the repeating semicolon. I did try cleaning the board with IPA and some electronics connector cleaner from the auto parts store. As far as the resistors go, it was consistent on all of them (that connect to the keyboard) that they measured significantly less resistance than the corresponding ones found on my parts board. I at least wanted to get this out there so that anyone else who tries to Google this problem will find my topic and read it. BTW: all of the resistors in question are deformed when compared to their counterparts on my parts board. That screams to me that this poor thing and a serious surge of electricity hit it at one point. With that said, my next purchase for this computer will be a Mean Well RT-65A. Biiig "peace of mind" item there imo.
  • Create New...