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Bruce Tomlin

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About Bruce Tomlin

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    River Patroller

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    CD C9 01
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    San Antonio, TX

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  1. Ugh, what a mess. But the top half of the legs are still there, so it can be fixed. The best pin donors are old socketed PAL chips, since you can't reprogram them. Desoldering a chip is not a simple skill. After at least 30 years of it, I'm still coming up with new tricks. Basically it's about melting ALL the solder to the other side, and sucking it all out at once. The most important thing is making sure the pin is free (with those red squeeze bulb types I gently wiggle the pin around until it can move) and adding fresh solder if it doesn't suck out properly. Ground pins are the worst because they absorb so much heat and tend to have more solder on the other side. The other trick that I recently learned is to put some extra flux on, to help it melt better. (that's probably why the fresh solder helped) And it'll be funny to see a half-broken Pokey chip being used just for the audio part.
  2. Main problems I had were an apparently slightly flaky power connector (it could have been the wire, sticking up vertically doesn't help, but it only has to disconnect just once!), and problems running from battery. It really doesn't work with NiCd/NiMH batteries because of the lower voltage, and they last almost no time. (At least it's not using a 7805, or it would be even hungrier!) That's probably why the Game Gear battery pack won't work. It really needs a 7-cell battery pack for NiMH. A lithium pack ought to be great. I suppose replacing the voltage regulator with something more efficient would be good too. And it's just so stupid chunky, like an Xbox Duke controller. I know it had to be that big back in the day, but it's still on the upper limit of acceptable.
  3. I catweaseled all my disks back in '08 or so, though I wrote my own code to decode Apple II and Commodore disks. My TRS-80 disks even had the same bad sectors where they were back in the day. The important thing is to know what format you plan to rip to. FM/MFM for TRS-80 was well supported. I never quite got what the preferred formats were for the other systems, but I never had those systems back in the day, most of my Commodore disks were a few hundred I got one day in a Sam's Club parking lot when some boomer had expected to meet someone there to give them away, and the guy didn't show up. Writing code to decode GCR taught me that Apple's GCR was better than Commodore, simply because the Apple GCR had unique extra codes that could be used as proper address/data marks. Commodore's was only straight nibbles, and you had to guess where sectors began. I also learned that for some reason Atari (8-bit) used the negative-logic version of its FDC, so all bytes are inverted, and it also ran the motor at a slower speed to get an extra sector. I even ripped a few old 5 1/4" CP/M disks for Osborne and Kaypro. It's still a "someday" project to rig up an 8" floppy drive to read the box of those that I have. (Some are RSTS-11 disks, it's amazing what you can find at thrift stores sometimes!)
  4. Also the back panel is going to be different with pre-TMSS units. If you don't see a modem port, don't even bother, the chance of it being pre-TMSS is probably zero. The modem port was completely removed after TMSS. I have two of them right now that I just looked at and tested, HRG lid with modem ports, both have an FCC ID of FJ8USASEGA. One is broken (looks like slot damage), and the other has TMSS. The broken one is missing its screws (my fault for sure), and there are chip dates of 9143 and 9149 inside. According to Wikipedia, the US Genesis was introduced in 1989, and TMSS happened in 1990, so they were making modem port units for at least a year after TMSS. They may be rare as hell now, but they were around long enough for EA to make half a dozen games that were broken by TMSS, while apparently Sega had already written their own game code in anticipation of it. As for "very late" units, somewhere I have one that had a modem port motherboard and shell, but no DB-9 plug. I had to add one myself (to use as a serial debug console), so I used a male plug because that's what I had handy. Gonna guess it was from early 1992, gotta take a look if I find it. I thought I had just found it, but I was wrong. Anyhow, that one had TMSS too. And there's always the chance that despite the FCC ID, the original motherboard died and was replaced (either as official repair or more recent history) with a TMSS motherboard. Still, it's good to know about the FCC ID thing.
  5. Still staying home and digging into the attic now that the Texas weather has finally stopped being hot. But I finally found my Gamecube (and the missing Zelda TP disc that I knew was in it), my fat PS2, and my "dev" Sega Genesis (with a DB-9 installed in the "modem" port for serial debugging at a blazing 4800 baud!). Also a big box full of Sega stuff including a floppy disc game copier. (it supports SNES but didn't have the slot adapter)
  6. If I recall correctly, IBM made some mistake when implementing their first Centronics interface, so there is a slight difference with the "original" spec, which became the only way it was done afterward. So watch out for that.
  7. 8VAC 1.5A, gonna guess you can use 9VDC of the same amps or higher if it has the same size plug.
  8. The MC-10 was Tandy's ZX-81. Except even Tandy couldn't bring themselves to make something crappy enough to compete with Sinclair.
  9. SSN might imply a military family. Back in the 70s a lot of my family's stuff had my dad's SSN on it.
  10. Don't forget the clock cap in the original Xbox! Most of them are PowerStor caps (black wrapper) and they will slowly leak and mess up your board. (There are also some gold ones which are Nichicon and supposed to be okay.) If you find one and don't have time to take the board out, wiggle it until its legs break and fix it later. Better to have to set the clock than to let the board get any worse. One of my two "good" units had a Nichicon and the other had a PowerStor. As I was removing the PowerStor, an SOT-23 diode fell off the board, probably related to the charge circuit, but I was able to save it, get the board pads re-tinned (not easy!), and put it back. Then I put a header in the wider pair of holes (0.2" apart) and connected it by a wire to a larger PowerStor that was scrap from a place I used to work. (We had a few of those leak too!) Then I then snugged it into a place away from the board. But yeah, the biggest problem with electrolytic capacitors is from the early '00s, when China stole a formula for a "better" electrolyte, but they didn't get it right.
  11. This was apparently $10 off last week, so I ordered it and got it today. Now I need to come up with something to mount it in. At least I've got plenty of scrap lumber bits in the garage.
  12. I see we have forums here going up to Dreamcast, and in Modern Gaming starting with PS3 / XB360 / Wii. But no forum for PS2 or original Xbox? These things are 20 years ago now! And I just noticed there's not even one for the original PSX either, which is older than Dreamcast! I care much more about those systems than the PS3 / PS4 / PS5 / XboneSZseriesQ++. Maybe there could be a new category between "Classic" and "Modern"? Apparently there was a PS2 thread once, but it fell off two years ago:
  13. Some people just stack pages onto a sheet feed scanner and don't even check for pages that got stuck together or dogeared. I've seen that with magazine scans too.
  14. The way I hear it, what they wanted was a 16-bit CPU with more than 16 bits of address bus, and 8-bit data bus. The extra address bits were needed to go past 64K without fiddly bank switching, and a 8-bit data bus meant that you need half as many RAM chips for the minimum configuration. It's important to keep in mind that DRAM was getting cheaper, but still very price sensitive. So they were talking to Intel about the 8088 and apparently also to Motorola about the 68008. That they specifically wanted the 68008 is less certain, but it fits with the time frame. There is a lot of speculation here, but this was a time when the sales guys at Motorola really only wanted to sell the 68000 in hundreds and thousands quantity for use in expensive Unix systems. (Read DTACK Grounded for more about Motorola's attitude. Before 1983 or so they really didn't want the 68000 to be used for home computers or embedded applications.) IBM had a date by which the chip would have to be ready, and Motorola refused to make a commitment to that date. I guess it wasn't a big priority at Motorola, and they were just making the 68008 to fill out their product line. Apparently it was actually ready by IBM's deadline (Wikipedia says "introduced in 1982"), but IBM had already gone with the 8088. That Wikipedia article about the 8088 mentions something that was also important: the bus interface. The 68000 had a synchronous bus by default, because the higher clock speed meant it needed wait states depending on what it was talking to, letting them use existing 6800 peripheral chips made for 2MHz clocks. The difference was adding two lines: DTACK and BERR*. Motorola's idea was that every address would send back a signal (DTACK) when the memory or I/O device was ready, then you could mix and match different speed devices. But if you grounded it (hence "DTACK Grounded"), it would run at full speed, becoming a 6800-style bus, assuming everything you had could keep up with the faster clock. There were already minor differences between the 8080-style bus and the 6800-style bus, but this was an extra pain in the ass if you wanted a simple system. (*BERR would tell the CPU that the requested address was invalid. If neither DTACK nor BERR ever happened, the 68000 would wait forever for it. This is why reading certain address ranges on the Sega Genesis will lock up the console. You could probably implement it with a 4040 counter and a gate or two, but it wasn't useful for finished games.)
  15. Recursion is dangerous on a system with limited RAM, because it pushes more than the state you're keeping track of, so you could easily be using twice the RAM just from return addresses. What you need is to make a list of just the things you're keeping track of, add to it every time you have a new one to explore, then when you finish each one, pick the last one on the list and do that next. Technically it's a stack, it's just not the CPU stack. And it's easier to know when the list is full and abort. Something may get missed, but at least you won't crash. As for negative numbers, you do know how 2s-complement math works, right? Numbers can't be just anything, they're words, bytes, whatever, and you have to know how big they are. You don't just have "a set of" "numbers". It's meaningless without knowing how many bits they are.
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