Hello there... new here...

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Hello there... new here...

Postby Refrain » Wed May 06, 2009 8:14 am


My name is Kevin and I've recently purchased a few PCjrs to cobble together a tricked-out system (and, in the process, to relive my childhood...)

I got my original PCjr, a 128K "enhanced" system, back in about '86 (I was 7 years old): my dad worked for IBM at the time and I think he got a real good deal on the system since they were discontinuing it and all... It had the better keyboard (non-chicklet), the IBM color display, 128K RAM, and the single 5.25" 360KB floppy. My favorite titles as a kid were King's Quest, Monster Math, and Gertrude's Secrets. Soon enough, however, the black power brick burnt-out or something, and in '88 or so, when I brought it to my local PC-repair shop, they laughed at the idea of repairing it (and in the process sold my mom a Leading Edge Model D, which was to become my base system for the next several years). Thus, the PCjr got pitched to the trash, though I did keep several diskettes for nostalgia's sake...

Some of which *actually worked* when I regained an interest in the PCjr about a month ago! I hadn't booted off that IBM DOS 2.11 diskette in nearly 20 years! Now *that's* a quality product! ;)

My PCjr Redux system has 128K on-board with a 512K aftermarket daughter board between the CPU socket and the 8088 (it just barely fits beneath the floppy), for a total of 640K RAM. The floppy is interesting - it's not the typical black drive with "IBM" cast into the plastic (though I have some of those too), but rather a YE-Data 360 KB floppy, grey/beige in color, with an asterisk cast into the front plate: it looks kind of like the 1.2 MB drives that came with the IBM AT (I had one of those too, once upon a time), and it has an IBM replacement part number label. I'm wondering if it wasn't an "official" IBM replacement for the original black-plastic floppy (which I'm made to understand weren't very good drives), though it could have just been installed from anywhere, I'm sure.

I have some sidecars which are intended for, but are not currently in use on, the system: (2) IBM 128 K RAM expansion sidecars, an IBM parallel port sidecar, an IBM power booster sidecar, and a Microsoft PCjrBooster w/. RAM, clock, and (bus?) mouse port (I also have the mouse, which appears to be in pristine condition).

I have a few things I want to do to this system. Firstly, a buddy of mine is handy with the soldering iron, and we just did the "Tandy mod" (to get rid of the black horizontal lines in Tandy 16-color graphics mode) to one of the spare motherboards and it worked! (Next to apply the mod to my current system, though we're going to have to get more creative with chip-placement due to the space taken up by that RAM daughterboard...)

Secondly, I really, really, really want 736K addressable by DOS. If anyone knows how to do this, advice would be greatly appreciated!

Thirdly, I want to get the PCjr on the network (I've already ordered some of the Xircom parallel port ethernet adapters) for use as a text-based terminal to access apps on some Linux boxes I've got running.

Fourthly (and finally?), I want to have a hard drive on the machine. I know there were some hard drive housings that were chassis expansions, but that these are rare as hens' teeth. Alternately, I'm imagining a parallel port hard drive, though I'd need another parallel port sidecar (they seem reasonably available) and I'm guessing it'd have to be modded to appear as LPT2 and take up another IRQ (I'm made to understand IRQs are weird on the PCjr, as compared with the PC).

So yeah, I've typed way too much, and I'll try to keep my questions to discreet topics on the forum. But that's my system. Oh - and about me? I started repairing PCs when I was 14, and did hardware and software support for 15 years. Then I decided I was tired of "IT" and am now working in the medical transcription field (but as a user ;) ). I'm an avid reader of non-fiction ancient history (studied Latin and Ancient History at college), player of Oblivion and Fallout 3, like long walks on the beach at sunset (OK, not really - I hate the beach). :D
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Re: Hello there... new here...

Postby jason » Wed May 06, 2009 2:45 pm

/wave hi Kevin :).

I got the Xircom thing a few months back and have barely tinkered with it. So my PCjr can be on the network with my other computers running gigabit and drag them all down in speed, hehe.
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Re: Hello there... new here...

Postby Brutman » Thu May 07, 2009 8:03 am

Welcome Kevin .. you have the honor of being the first non-spam registration in since I had to turn the registration system off.

The original QumeTrak 142 drives used in the Jr had a bad reputation, but I have not found them to be terrible. One of the changes in DOS 2.1 was to slow the stepping rate that DOS specified for diskette drives to accommodate the slower half-height drives like the 142 that were new in the market. A better drive would be direct drive (no belt) and not have that nasty latch mechanism that the 142 has, but overall it works. If you want to read horror stories about bad drives, look up 'Lisa' and 'Twiggy'.

Congratulations on the Tandy mod! I haven't even done that yet. Can you post the instructions?

For 736K addressable by DOS I think you can use the MS Booster unmodified - you just have to change some jumper settings. If you are going to use an IBM sidecar you have to make some minor modifications. I'll try to dig the instructions for both out and post them. Lastly, you need to use JrConfig or a memory driver that will tell DOS that more memory is installed.

The network part is easy - the Xircom PE3-10BT adapters work well. For better performance you can do the bi-directional modification, and that will greatly improve the receive rate. NCSA Telnet works great on the Jr. I'm going to be doing my own telnet client based on my TCP/IP stack in the next few weeks - it should be quite a bit smaller than NCSA Telnet.

Hard drives are a problem. I use a parallel-to-SCSI adapter and a SCSI hard drive on my daily use system. I needed to do the LPT2 modification and the bi-directional modification to make it usable. (Every parallel sidecar should at least be bi-directional.) The hard drive uses IRQ7, and the Xircom PE3-10BT on the other parallel port is told *not* to use an IRQ at all. (Otherwise, it would have to use IRQ7 too, which is a no-no. Anything else would require some cutting.) Performance is passable - it beats doing the floppy shuffle.

In the real world I'm a father of 4, a pilot (small aircraft) and a mad hacker. ;-0
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Re: Hello there... new here...

Postby Brutman » Thu May 07, 2009 10:51 am

jason wrote:I got the Xircom thing a few months back and have barely tinkered with it. So my PCjr can be on the network with my other computers running gigabit and drag them all down in speed, hehe.

For a 4.77Mhz machine it does pretty well on Ethernet. My machine (which has a NEC V20) can do about 25KB/sec using the Xircom on a bi-directional parallel port. Fact in disk I/O for something like FTP and it drops to around 18KB/sec. With a good Ethernet adapter (the bus attached WD 8003 card I have) I can send/receive over 60KB/sec. So you are in no danger of saturating a GbE network, but it isn't bad considering.

I put my older machines on their own 10Mb subnet to keep the newer machines from getting mad. :-)

Try out the mTCP stuff I'm writing - it's targeted specifically toward the Jr and other slow machines.


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Re: Hello there... new here...

Postby Jim Thomson » Sat May 09, 2009 3:34 am

You are correct the microsoft booster requires dip switches to be set correctly to get 736K mod.
There is an article in one of news letters that tells you how to do it but I remeber that Chuck Terra posted having problems with the dip switch setting recommended and posted a correction on the old site forum.

I can take a look for the original article, but I didn't keep Chucks updated info.

Just looked it up, its in the july 87 jr newsletter page 10.

it says:
switch #1 OFF
switch #2 ON
Switch #3 OFF
lets the microsoft booster add the 736K.
I think Chuck said the settings were backwards.

Jim Thomson
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Re: Hello there... new here...

Postby Arminius » Fri May 15, 2009 1:08 pm

The switch positions for the booster at 640k (to give 736k) are indeed on/off/on.
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