Jump to content

AwkwardPotato

Members
  • Posts

    159
  • Joined

  • Last visited

Everything posted by AwkwardPotato

  1. Yes, the audio coming out of the tape recorder is fed into the audio input on the sound chip. If you can find the tape recorder cable for the 4A, you can mix the audio from practically any device with a 3.5mm jack into the output of the computer. The audio input line is also present on the side I/O port of the computer; that's where the Speech Synth accessory's audio gets mixed into the computer's output.
  2. To second what Stuart said, I think you may find salvaging 4116s to not be worthwhile when they can be found inexpensively online. Removing the DRAM on these boards with solder wick/a manual vacuum tool is a right pain in the neck; the less desoldering you have to do with these, the better. The joints for the power pins especially sink a lot of heat, and it's easy to accidentally destroy the through-hole plating. An oft-recommended approach for the DRAM is clipping each of the IC legs and pulling them out one-by-one with the soldering iron.
  3. Just for the record, those green parts are film capacitors, and it is *incredibly* uncommon for those to fail in these types of applications. If any of the capacitors are going to fail, it'll be the red/black aluminum-can electrolytics (and even those generally seem to be fine in the QI power supply). Also, if the replacement capacitors are ceramics, be aware that some types of ceramics' capacitance will change significantly depending on the DC voltage applied to them. This absolutely can influence circuit operations, the film caps on the other hand are immune to this effect.
  4. Verify that all the voltages coming off the power supply are still within spec. I mention this not because I think it's the root cause of your sound issue, but because RV1 may be an adjustment for one of the power supply outputs (I don't have one ATM to verify this). The sound IC is right next to the large hole in the motherboard that one of the case standoffs protrudes through. Chances are that it's the fault, rather than the power supply.
  5. AFAIK the datasheet for the TMC0430 GROMs has never been located. If you want to verify the pull-up/pull-down circuit, probe the collector of Q500. It should swing between 0-5V and follow the DBIN# signal. If the low level is greater than a couple hundred mV, the transistor is bad, or its base resistor is open. If the high level is significantly greater than 5V, one of the diodes/R520/R521 clamping the collector voltage is open.
  6. Meant to specify, "where the larger composite tips really shine." Fine tips, some improvement. Chisel/bevel/knife, great improvement.
  7. Having used the FX-888 in school and the FX-951 at home, both with fine tips, there's for sure an improvement when using the 951's composite tip. That said, it's not a night-and-day improvement. IMO where the composite tips really shine is e.g. soldering the tabs on beefy surface-mount power transistors to copper pours with arrays of thermal vias. Just for the record, not trying to imply that the FX-888 is a bad soldering iron. My only qualm with it is that it's remained at the same ~$110 price point for years and years now -- the competition has come a long way
  8. Two models of soldering iron you'll often hear recommended for hobby work are the "classic" Weller WLC100 and Hakko FX-888D. The Weller model is power-adjustable (not the same as temperature-adjustable) unlike the old Radio Shack irons, is more than adequate for working on boards like the SAMS, and is fairly inexpensive. I used that Weller for several years, can definitely recommend, although I've upgraded again recently. The Hakko model has a leg up over the Weller, as the FX-888D is temperature adjustable. This particular Hakko isn't a great deal in 2022, though, and is outperformed by a long shot by Chinese-manufacture soldering irons like the Miniware TS100/TS80P (which are less expensive, and still reasonably well made). Also note that the market is flooded with counterfeit FX-888Ds. If you think you might get into slightly more "involved" soldering projects later, the Hakko FX-951 is pretty nice (that's what I'm using now). Unlike the WLC100/FX-888D, the FX-951 and the aforementioned Miniware models have combined heater+tip setups, and that allows the soldering iron to heat up waaayyyy faster (especially helpful when soldering to large components).
  9. The disk controller responding only to even-numbered CRU writes is normal behavior. As for why DSR access breaks with the FinalGROM, I'm not sure. While it's possible that the electrolytic caps in the video amp went bad, chances are they're not the issue at play here. Couldn't hurt to change them, but the caps on the motherboard have proven to be rock-solid compared to many other devices of the time, and you'd be hard-pressed to find reports of them failing. The audio coupling into the video signal almost sounds like a grounding issue. Happen to be able to take a photo of the inside of the DIN plug on the video cable?
  10. Would it still be possible to purchase a bare 4000B board?
  11. Oh, yeah, and on writing TI disks using a PC with a 5.25/3.5" floppy drive: I've tried three different PCs manufactured between 1991-1999, and not one of them had a floppy controller capable of writing the SD disks required by the stock TI disk controller. AFAIK standard density/FM encoding was never really a thing on the PC, as such YMMV.
  12. Rube Goldberg Approach for TI File Transfer in a Pinch (STEPS 1-5 ONLY NECESSARY THE FIRST TIME): (requires XB, RS-232 card, a "straight-through" serial cable, cassette cable, and possibly a USB-to-RS232 adapter) Download MagicFM, a file transfer program written in XB, available on WHTech and elsewhere (Note 1, see below) Use Fred Kaal's Ti99Dir to extract the LOAD and MAGICFM files from the above disk image to a directory on your PC (Note 2) Use CS1er to convert the extracted LOAD and MAGICFM files (they're in FIAD format by default) to .WAV format Connect the TI to a PC/smartphone with the cassette cable. Start the TI in XB Play back both of your converted .WAV files, one at a time, load them on the TI, then save them to a blank disk, once again as LOAD and MAGICFM. You now have an auto-booting MagicFM disk. Connect the TI to your PC via a straight-through serial cable (a null modem cable will NOT work), using the USB-to-RS232 adapter if necessary Reset the TI with the XB cartridge & MagicFM disk still in Transfer files (in TIFILES format) as needed with XMODEM mode in your PC terminal emulator of choice NOTE 1: Arcadeshopper already has a MagicFM disk in stock, which saves an incredible amount of hassle NOTE 2: Several members have reported success transferring MagicFM from an emulated TI (MAME) to a real TI over RS232, rather than using a cassette cable. I was never able to get this to work, however. NOTE 3: Getting an HDX or TIPI will save you an even greater amount of hair-pulling. The most difficult part of the above method is finding the right terminal settings to use on the PC side by trial-and-error. If you're doing this on a semi-modern Mac, be prepared for a USB-to-RS232 driver nightmare. The above mess is how I prepped my TI for file transfer when I first got my PEB. I'm drawing this from several-year-old notes, and posting it here mainly in case future passerby already have most of the above hardware and want to transfer files with the least additional expense possible.
  13. Doubt this is directly relevant to @videofx's problem, but the E/A manual does state that different 4As handle XOP 1 differently (granted I'm not familiar enough with assembly yet to know how this is significant). In other words, perhaps not all 4As with the 1981 GROMs are created equal?
  14. AFAIK bad DRAM can't cause this issue -- if it was the only fault, there wouldn't be a steady beep, and you'd likely get a corrupt title screen. I'd first suspect the 16-to-8-bit multiplexer, it's made up of the three LSTTL parts above the CPU and next to the GROMs (74LS244, '245, '373). If any of those fails (mainly thinking of the '245 here), the CPU will be unable to read from the GROMs and the system will lock up before it ever touches the VDP RAM.
  15. From what I've gathered reading around here, four of the most popular v9938/v9958-based VDP upgrades for the 99/4A are the AVPC, EVPC(2), TIM, and the Mechatronic 80-column card. Are there any differences in function/implementation among these upgrades (besides mouse support being limited to the 9938), or are they all largely software compatible with one another? Thanks!
  16. Double-checked my TI's board and yes, the damaged part on yours is a 1uF 25V tantalum capacitor. A suitable replacement can be found here on Mouser, and it appears that the same part can be found here on eBay too (not affiliated with seller). Note that this capacitor is polarized, so the rounded-off/tapered side needs to face the TIM9904 chip.
  17. Hard to say whether that VDP will work or not. While the listing photo looks like it could be a genuine part, finding working VDPs on eBay seems to be extremely hit-or-miss nowadays. May be worth a shot, and perhaps other members here will be able to share seller recommendations.
  18. If the damaged component is the black one, right of center, in between the two blue wires, I *believe* it's a 1uF tantalum capacitor. Just to double-check: is the beep on your system a short tone, or one that continues as long as the system is turned on? If it's a short tone, check that your video cable is good, then try resoldering all the pins of the video connector on the motherboard. If you still don't have any video afterwards, it's likely that the VDP has failed.
  19. I missed the heyday of the TI and its contemporaries by a couple of decades so my main PEB (older push-button style) is permanently set up, noisy fan and all. No modern amenities here! It's a basic 32K, RS-232, two disk drives setup, although it may get an HRD in the future to make E/A use a little more comfortable. Also have a spare push-button PEB: cheap local pickup with 32K and disk controller, but missing the RS-232, flex, and drives. Sitting around in case I happen across a Geneve or an entire set of SNUG cards. I can dream
  20. It's a symbol found on many bottom-of-the-barrel phony TI parts. Seems that they only bother engraving one half of the TX...
  21. Do other programs accessing the 32K cause the system to lock up too? If not, it might be worthwhile to try one of the memory test programs out there.
  22. The LS257s on the 32K card are used to multiplex the row and column addresses onto the 4116 DRAMs. If any of the LS257s' outputs fails (hi-Z/floating in my case), reads and writes to certain parts of the 32K expansion will also fail. For a card like yours that locks up the TI at startup, I'd suspect one of the parts closer to the edge connector. The 74LS245 buffer comes to mind, and the voltage regulators are also worth checking just to rule out the obvious. The schematics for the 32K card can be found on Mainbyte.
  23. For sure! This PEB's disk controller was afflicted with a bad LS245 buffer several years ago.
  24. Hi all, Thought I'd share this in case anybody with a PEB 32K card (PHP1260) runs into a similar issue, since this was a bit confusing at first. It would appear that this also applies to the original PHP2200 32K sidecar, but I haven't verified that past a quick glance at the schematics. The symptoms of my card's failure: XB or EA5 programs loaded from disk either error out or crash the system, respectively Doing a rudimentary RAM test with the Minimem cart (as described by Willsy here) reports seemingly random failures Listing of an XB program looks like below, where e.g. "DSK1.SPEAK" becomes "DSK1, @EAK", and where incorrect characters change with each successive program listing In my case, the culprit was one of the two 74LS257 (U15, U16), although I accidentally removed the wrong one at first and ended up replacing both at the same time. While the 32K card is now functional, moving forward I'll look into possibly picking up a SAMS card. Been a while since I got new 4A goodies...
  25. VDPs can be finicky, but they're not delicate enough to be damaged by careful extraction. A few thoughts: The pins on TI parts of this era have a tendency to tarnish quite badly; might cause contact issues with the socket. Careful use of very fine grit sandpaper/a pencil eraser and IPA can help with this. Not sure if this applies to all boards, but all of my 99s use single-wipe DIP sockets for the VDP. This was presumably a cost-saving measure BITD and I wouldn't be surprised if the single-wipe sockets (which make less contact with the IC pins to begin with) are responsible for some reliability problems after 40 years. Standard dual-wipe sockets are perfectly suitable replacements. While the gold-plated machined types will also work fine, they're far more expensive, and intended for different applications. Kind of obvious, yes -- but it's important that the notch on the VDP faces towards the keyboard connector. Oftentimes there's a white dot painted on the VDP socket, which can be mistaken for a Pin 1 indicator. On 2 of my 3 boards, however, the dot is in the corner opposite Pin 1. Caused a bit of head scratching once... Weak color could just as easily be caused by other components between the VDP and the video connector, not that it matters if the end goal is to install an F18A. There have been reports of the crystal by the VDP drifting/failing, for instance.
×
×
  • Create New...