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AwkwardPotato

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Everything posted by AwkwardPotato

  1. I got the 99/4 & its power supply repaired and sent back to its owner, but I still have the flaky 4A supply. I realized while going through my parts bin that I had some modern switching replacements for the old linear regulators that I intended to use for a Commodore project, but now I'm thinking about swapping them into the stock 4A supply along w/ new caps to try and cool it down a bit.
  2. (If this is an inappropriate place to post this, feel free to move it mods) I'm looking to buy an original 99/4 (not 4A), whether it's dead or working. I don't care too much about condition as long as it's all in one piece. If anybody has an offer, feel free to PM me. A picture(s) of the unit would be nice, if possible. EDIT: It also doesn't matter to me whether it's NTSC/PAL, and I'm just looking for the base console. Thanks!
  3. Just to be clear, you're getting static instead of video and no beep? The first thing I'd do is pull out the sound chip (should be labeled SN76489, SN94624, or similar) along with GROMs 1 & 2 (labeled CD2156 and CD2157 respectively). On your revision of the board these should all be socketed, and none of them are required to boot to the title screen. However, if any one of these fails, they can prevent the TI from starting correctly. Also, are you sure your replacement VDP is oriented in the socket correctly?
  4. Turns out this was part of the problem with the 99/4 supply! Not only was it physically broken as you described, but the transistor case was visibly deformed, a chunk had been blown out of it, and there was a small burn mark on the PCB! I don't know how I missed it the first time I looked it over
  5. I wanted to do this with my main console to cool it down a while ago, but unfortunately at the time I couldn't find a source (or at least an affordable one) for the switching/QI supply. I do agree though, getting rid of the primary source of heat in the machine would probably improve reliability a good bit.
  6. I'll could look into selling kits later if they turn out to be the issue, but I could also upload a Mouser cart later (BTW, I checked the prices and all the PSU caps + shipping comes out to around $17).
  7. This is a pretty interesting idea and I'm definitely going to look into how one could do it later. I guess you could put an appropriately rated fuse on every rail for the power supply, although I don't know how well that would protect the motherboard. To be fair though, once a protection circuit is designed, it might just be easier to replace the capacitors or whatever part(s) are failing because they're cheap and easy to replace.
  8. @Airshack - When I start working on the power supply I'll take pictures to document the repair. Luckily replacing the capacitors doesn't require any fancy desoldering equipment or skills; each capacitor only has two leads, so you can just heat one lead and pull the part out from the other side of the board. @Stuart - Thanks for the tip, I'll check on Q1 when I get home. One thing I found interesting was that Q2 (or whichever one the heatsinked transistor is) looked like it had been replaced in the past (there was a lot of flux residue around the pins).
  9. I don't know if this has been mentioned before, but here goes: Recently I've been working on three TI systems for a fellow forum member (1x 99/4 and 2x 99/4A's). Out of these three machines, two have had damage caused as a result of the internal power supply failing. On one of the 4A's, there was significant ripple on the +12V line, which kept blowing VRAM IC's until I noticed it and replaced the power supply with a spare. On the 4, the +5V line was outputting +10V, causing severe damage that I haven't had time yet to diagnose. Ouch! I'm not sure yet what's causing the power supplies to fail, although I suspect it's the electrolytic capacitors because a.) they're a common failure point in most systems from the same era, b.) these supplies are "coffee cup warmers" and c.) both of the failed supplies had a couple of capacitors where the rubber piece at the end was bulging, the typical failure symptom. I'm going to replace all the electrolytic caps on one of these supplies soon and will post any updates here.
  10. Sorry if this was answered earlier, but when this becomes available, will it be possible to purchase just the assembled motherboard by itself? BTW, this project looks absolutely amazing. Thanks in advance!
  11. Thanks for posting this! The font on those keycaps is especially weird, kinda like the one used on the Commodore machines of the same time period.
  12. Unless you're fixing some Painsticks/Mitsumis conductive paint really isn't a great option for repairing PCB traces. Running a jumper wire is a much more reliable and permanent solution.
  13. The PSU is in pretty rough shape but I wouldn't write it off as unrepairable. If the LED is on when the computer is off but plugged in, I'd definitely assume a switch issue since the anode of the diode is connected directly to the switch (and it's not surprising given the condition of the surrounding area). The corroded traces can be patched with wire. As others have stated already though, a new PSU isn't too expensive if you can't get that one fixed.
  14. Always thought these were pretty neat. Shame they're so expensive Couldn't the same be said for the TI too? Granted, a stock TI isn't going to cost you very much, but after you invest all the money into a PEB, cards, cartridges, etc. a TI still isn't going to be particularly useful in this day and age.
  15. The one time I've ever had a black screen and no sound (as opposed to the normal cacophony) was due to a power supply issue (the internal PSU, not the transformer). It was a pretty easy fix: the contacts in the switch were oxidized and needed to be sanded. When/if you're able to open the computer, check the voltages from the power supply. They're labeled on the board silkscreen.
  16. If it's not considered cheating, here's a way you can determine the manufacturer of a keyboard when buying a TI (especially if you can't look through the bottom vents):
  17. In my opinion it would be really cool to see an accelerator for the TI (I've toyed around with some ideas for one). Not necessary at all and I doubt any software would take advantage of it, but hey, why not?
  18. I'm in TN but I'll offer to work on both machines for the cost of shipping (I already have working spares of most of the chips in the TI).
  19. Ah... I didn't know Cherry made a silent switch! Would be neat to see those in a TI. I suppose that's possible. But for all the time you would spend making the keycaps by hand, along with all the time (and costs) needed to make the PCB, plate, etc. wouldn't it be easier to use a USB adapter & a USB mechanical keyboard? Personally it wouldn't be worth it for me, but I know it probably would be for others.
  20. Given that this is a thread dedicated to quieting down the TI's keyboard, I'll also note that swapping in a new switch type wouldn't help much with the noise situation. Not only are modern MX switches just as loud as the stock ones found in TI keyboards, but they also sound much more high-pitched.
  21. If you'd prefer backlit keycaps that look similar to those that come with the stock TI keyboard, chances are you could start a group buy on one of the more popular keyboard enthusiast forums to drive the cost down a bit. Otherwise, modern backlit keycaps can be found for a semi-reasonable price, although they'll probably look fairly out of place on the TI.
  22. I've built & hand-wired my own mechanical keyboard for my PC. One thing that has to be kept in mind is that the switches used in the TI's stock keyboard are much taller than any switch currently available today, so unless a workaround was devised, all of the keys would appear to have "sunk" into the case. Furthermore, you'd need new keycaps, which in my opinion at least would spoil the look of the TI.
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