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PCjr theoretical supe up strategy

PostPosted: Tue Jan 21, 2020 10:51 am
by Sharkey1331
Hello All,
Assuming the following:
1) Completely bone stock PCjr, 128k RAM, from use of memory card in memory slot. NO sidecars, 8088 CPU. Composite output into Flatpanel LCD that can read from this output.
2) Desire to play "The 8-bit guy" developed game, Planet X3, in with Tandy/PCjr sound option, and Tandy/PCjr 160x200 /16 color option.

**Main discussion question**What can be done to supe the little PCjr up a little bit, to make it a match for at least PC XT level hardware?

A) What options do you have to expand RAM? I know HotShot II cards had built-in RAM, and I used to have one, but don't have that any longer. Sidecars I've heard can add RAM, and I have a (not yet assembled) JrIDE card.. This has RAM on it I believe.. Question: could another card be designed and built to add RAM via the onboard memory slot?

And for any RAM option- can configuration of Dos -> High memory range (or other tricks) be done to avoid the video and memory refresh hit that apparently these machines have -vs- an XT?

B) For a faster CPU, can you simply swap the 8088 for an NEC V20? Or is a faster crystal needed, and/or faster RAM?

C) Anyone played this game on your Jr? Maybe it runs fine as is. Kinda neat that there is new SW developed for these old machines!

Re: PCjr theoretical supe up strategy

PostPosted: Tue Jan 21, 2020 2:37 pm
by KenG
You best memory option is the jr-IDE made by AlanH. It maximizes memory, added IDE hard drive capability and a real time clock. Unfortunately, it is not always available.

If Planet X3 supports Tandy graphics, but not PCJR, you will need that mod. Best option is the switchable board made by Chuck53. Requires desoldering a chip and soldering in machined pin headers for the board.

Yes, you can get a little speed boost using a V20. If your CPU is socketed, it is an easy mod. For a bigger speed boost, Chuck53 makes a PC-Sprint board to double the clock to the CPU. Requires a 10 MHz CPU.

Once you have more memory, there is a device driver, jrconfig, that moves memory around so that only higher speed memory is used for programs.

Browsing the hardware forum here will give you options. One other mod I like is an adapter to use a full sized keyboard.

Re: PCjr theoretical supe up strategy

PostPosted: Tue Jan 21, 2020 2:46 pm
by Brutman
Thinking in more general terms that just the one game, here is my preferred set of upgrades in priority order:

  • NEC V20: An easy to perform upgrade that is good for about a 5% performance improvement. It also adds support for some instructions that were introduced in the 80286 CPU, allowing some "286 required" real-mode software to run on a PCjr.
  • jrIDE sidecar: Besides allowing for a bootable mass storage option that is faster than comparable XT-class controllers this sidecar provides memory from 128K up to 736KB. It's static RAM so there is no DRAM refresh penalty. And we've still not done a good job of exploiting the FLASH memory on the board.
  • Bi-directional parallel port, for connecting a Zip drive or other device. I use mine with a Xircom PE3-10BT Ethernet adapter.
  • An enhanced keyboard. I like a full-sized keyboard ... there are several solutions for this.

I don't play games much so I've never bothered with the Tandy modifications. I'm happy with the PCjr as it is - a PCjr.

If you can't get a jrIDE go for a 512KB memory sidecar and another parallel printer port. The parallel printer port with a Zip drive, IDE drive, or SCSI adapter on it can provide mass storage, but obviously it's not as fast and you can't boot from it.

Re: PCjr theoretical supe up strategy

PostPosted: Sat Feb 08, 2020 8:40 pm
by Sharkey1331
Here's where I got so far:

Built the JRide kit I had in stock from a few years ago (thanks Alan H!!) Mine is a Rev. A... LOVE this device. Only thing is, I've not figured out how to get into BASIC yet- even from the ESC boot menu, it doesn't want to seem to want to go to D) BASIC.. Anyone else experience this?

I've also got JRCONFIG.sys working, and using MIPS, this got my overall system score from .55 to 1.05!
I've also got the real-time clock working, and I gotta say, it's pretty cool having it auto-set the time and date. Currently running DOS 3.22

I have an NEC V20, but have not installed it yet. The machine currently runs PlanetX3 (installed on my hard drive).. The only weird thing about that is- for some reason, the "Tandy Sound" doesn't play from the game, even though if I test the sound using CTRL-ALT-INS, the sound test passes.. The game plays music from the PC Speaker option just fine.. Obviously, the Tandy sound would be better if it was working.

I've also got a TandyMod board in stock now (thank you Chuck! I need to email you a board for you, hope to get it in the mail this weekend!

Oh- and I replaced the internal power supply and missing brick with a internal switching power supply.

I'm guessing I need to do the bi-directional mod on the parallel sidecar (I tested, and it is still stock PCjr) to get it to work with the XircomPE3/IRCjr setup?

Re: PCjr theoretical supe up strategy

PostPosted: Sun Feb 09, 2020 5:24 am
by Chuckphd53
Jason, there is a write up on Mikes pages for the bi-dir mod, if you have questions let me know...
Also stick the V20 in it gives a nice pop in speed.
I have not experienced the Basic issue on boot up, but it may be better to just go into Basica or GWbasic and get more features.
I also have the PS2 dongles if you are looking to use a standard keyboard, its a nice addition..

Email me and I will send you a couple pics of my set up showing the Tandy and PCSprint switches , you may want to put them on yours also so you can toggle
Tandy and PCSprint modes on and off, also the Sprint brd has a reset, VERY useful , no more power switching if the system hangs..


Re: PCjr theoretical supe up strategy

PostPosted: Sat Feb 15, 2020 9:46 am
by Sharkey1331
Here's where I am so far...

-Started with an eBay IBM PCjr 4860, in "un-tested" condition. Missing power supply, side cover, and keyboard. No sidecars. No cables. Turns out original drive was toast- carriage was locked.
-Found an NOS, real keys (not the chicklet) keyboard on eBay.. Not too expensive as it was missing the box.
-Found an NOS parallel port sidecar- sealed in the box! Yeah! (expensive though at $100.00?)
-Found an NOS motherboard at BGmicro. Socketed 8088.
-Found an NEC v20-8 on eBay. Swapped it into the NOS motherboard.
-Had an extra PCjr floppy drive from another PCjr! Thank goodness for saving clutter (I mean, carefully managing stock!)
-Got a reproduction PCjr keyboard cable (uses phone cable) from eBay- 10 bucks.
-Made a new internal power supply using open source boards from OshPark (got the gerber files here, bought parts from ... y-Adapter/
-Got a MiniBox PSU/80 switching power supply- fits on the board listed above, and is completely internal to the PCjr case.
-found my jrIDE kit from AlanH from a few years ago. It is RevA, had never previously assembled it. Put it together- nice design! Awesome product!
-picked up a Maxtor 92048D8, 20GB, 3.5" IDE HDD. Thanks for the "known working" specs on your page, Mike- it works great!

So, I completely dis-assembled the PCjr, cleaned it with simple green and scrub brush. I epoxied the left-side motherboard clips- which were both broken. I got all new screws for the motherboard->case as I was missing all but one.
I cleaned the drive fan, cleaned the floppy drive head and rails, and lubed the rails. Plugged in the NEC V20, and assembled the whole computer.

I started with IBM PC-DOS 3.3, but now I'm on IBM PC-DOS 5.0 (thanks to this forum, and another great Mike post- I used debug to patch the boot sector).
It's fully working now, and pretty clean looking. Check it out:

I'm still getting the software loaded on to it, but so far it's working, and able to play PlanetX3, which was an initial goal of mine!
Thanks for letting me blather on about this neat little machine- I really like this one!
**For info towards the original post purpose: MIPS now shows overall system performance as 1.41 of an original IBM PC... Yeah! :lol:
-Get a C compiler going on it,
-fix/patch? EDIT and QBASIC so that they work,
-upgrade to the 2020 version of mTCP package
-get this dude online using the Xircom PE-3 I've got from my previous PCjr
-Need new rubber feet
-Need to fix the IR keyboard receiver, which is not working
-better monitor solution? Do the PCjr monitors come with the monitor cable built in?
-get a joystick maybe...


Re: PCjr theoretical supe up strategy

PostPosted: Sun Feb 16, 2020 11:16 am
by KenG
Yes the PCJR monitor has the cable built in. There are also various solutions, browse this forum, to convert CGA to VGA and use a modern monitor.

Re: PCjr theoretical supe up strategy

PostPosted: Wed Mar 25, 2020 11:27 am
by ZiggyTheHamster
Planet X3 requires you to run a tool like TSOUND (search this forum) to enable the SN76489, then it works perfectly. It also runs with a stock jr CPU just fine.

EDIT and QBASIC can be made to work with NOBEEP (again, search this forum). I found I had to use the non-SYS version and pipe its output to NUL: for it to work properly without writing garbage to the screen in IBM DOS 5.

If you want to install a V20, you should also install Chuckphd53's PC-SPRINT board. He's selling them for cost somewhere on here. I bought some oscillators to see what the limit is with higher speed V20-family clock chips plus a V20. He ships it with an oscillator that will go as fast as possible using the stock clock chips, which is I think 7 MHz. The NEC clock chips + a V20 anecdotally do 15 MHz but that could be under perfect conditions only.