My PCjr Setup & Collection

General discussions on the PCjr

Re: My PCjr Setup & Collection

Postby Tempest » Fri Jan 22, 2010 7:26 am

Any way to test it? I don't see an on/off switch which I thought was part of the mod.

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Re: My PCjr Setup & Collection

Postby Brutman » Fri Jan 22, 2010 9:12 am

Tempest wrote:I just got the Backpack drive today. What are all the files I'll need on a 5.25" disk to make this work? My friend is willing to transfer the files for me, but I need to know which ones I need.

Tempest


I thought I had this posted somewhere, but just in case .. the driver is BACKPACK.SYS. It should be on the CD that came with the drive - if it is not I can send it to you. All you should need is a line in config.sys to load it.


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Re: My PCjr Setup & Collection

Postby Tempest » Fri Jan 22, 2010 9:22 am

So that's the only one I need (it is on there BTW)? Great!

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Re: My PCjr Setup & Collection

Postby EHungate » Sun Jan 24, 2010 12:08 pm

Don't know exactly where to post this but I suppose this is as good as any. As I've mentioned a time or two on other forums, I have been away from the Jr for quite a few years. I thought I'd just sort of ramble on, and where I have my facts wrong or where some procedures have changed or improved, please correct me. Please understand that I don't have any of the modification instructions available to me and I'm not real anxious to do a major re-work.

OK-That said:
I have done the Thin Font numerous times. Not a biggie and as someone said, you can hide a switch inside so you don't mess up the case. You could also use the infra red hole. Trouble is, you need to beg or borrow a prom that is programmed for the thin font and borrow it to copy.

Tandy mod is also an easy one. Maybe cutting a couple of traces and a couple of adds. No switch.

Most of the memory upgrades are relatively uncomplicated, but that varies. I'm thinking that the IBM one consists of replacing the memory chips and cutting a trace. Maybe also changing some switch settings. It's your choice if you want to use the heat gun method to take the old chips out. Also you may or may not opt to use sockets. BTW, BG Micro still has the 41256 chips for a buck or so.

The Tecmar isn't as robust as the IBM so I'd be a little reluctant to use the heat gun. Originally the JRCaptain had 128 k on board. Also you could get an add-on sidecar called JR cadet. That was good for an additional 384 k. I wouldn't waste my time with a cadet. They are somewhat unreliable and consume quite a lot of power. I would just do the upgrade to the Captain. And while you're at it you can put a single jumper on the board that allows you to throw away the external power supply. That power supply causes a lot of trouble.I don't know the position of the junper but you should be able to follow the 5v in and tie it to +5 on the chips.

The Racore/Quadram are a little different. They come in two models (at least). The early ones come with 384K. They can be modified /upgraded to 640 and even 736 by stacking chips. I seem to recollect that there was some board re-work involved. I think I only did the full 736 one time and it was not terrible reliable. My daughter had a Jr modified in that fashjion in college back then, and she would get quite irate when she lost several hours because of a memory error. She finally learned to back up her work more often. Anyway, I digress. The later Racores had 512 or maybe 640 on the memory card, and you could simply upgrade from the older card to the newer card and give them a lot of money.

One more for now. The JrHotshot was a board which mounted between the 8088 chip and the system board. Neat, reliable, and no sidecar. It did have one stipulation. You engineers will know what this term means "The memory chips had to be (RAS before CAS) or maybe the other way around.

OK, I'll be quiet for a while. If this is all old uninteresting news someone plase let me know.

Later
Elmer
Last edited by EHungate on Sat Jan 30, 2010 1:09 pm, edited 1 time in total.
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Re: My PCjr Setup & Collection

Postby Brutman » Mon Jan 25, 2010 5:39 pm

I have seen a variation on the ThinFont installation from PC Enterprises where the high address line on the EPROM that is used to select between the two different fonts is connected to the output of the relay that controls the cassette interface. This allows the ThinFont to be controlled by software, and you get a satisfying click when you switch the font. It's not the way I would do it, but I thought it was a pretty novel use for a piece of hardware (the cassette interface) that was never used.

ThinFont is a interesting modification too because the original IBM CGA card was wired to do something similar. I'd have to check the ROM on the card to see if it actually has both fonts or not - I think it has it, and it was a matter of cutting a trace to get the thinner font instead of the default font.

I have not done the Tandy mod, but I know enough about it. I don't understand why it would installed with a switch - my understanding is that it gives you extra capability, without altering existing capability. So unless you needed to disable it for some reason, there is no point in making it switchable.

I agree with your assessment on the Tecmar sidecars. Putting the power supply in the sidecar was just a bad engineering decision. After you put a power supply somewhere, you need to figure out how to dissipate the heat, and that was their downfall.

The MA Prokit sidecar was another horrible piece of engineering. I inherited in the last year or two. I've not dissected it yet - the horror stories I read about it being flakey have kept me away from it.

I've found the memory boards in the Rapport/Racore/Quadram expansion chassis to be a weak link - I'm not sure if it is the quality of the chips used, the length of the traces, or the construction of the board/sidecar but if I have a bad expansion deck it is always because of memory. One of the members from the previous PCjr board (Micro-Zone) had an elegant solution - it replaced the entire board of DRAM and the refresh controllers with one or two small SRAM chips of equivalent capacity. Two SRAM chips and some address selection logic replaced the entire board, used less energy, and performed better because there were no refresh delays. That's the modification I want to do sometime.

The JrHotshots were an elegant solution, but I was always worried about heat buildup. The fan really doesn't ventilate underneath the drive tray - it is strictly to keep the floppy area cool. And energy draw on a machine with sidecars would be fairly high. But wow, what a great place to hide a major upgrade.


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Re: My PCjr Setup & Collection

Postby EHungate » Tue Jan 26, 2010 5:33 pm

Actually, the MA Prokit was my first expansion experience. $300.00 First of all they didn't use config.sys but had some software of their design. Some programs ran, some didn't. I wasn't smart enough at that time to know that there was a memory problem and it pretty much depended where a program was loaded.

Back to the Tecmar: I seem to remember that there was an interrupt conflict between the Tecmar and some other add-on but I really don't remember much more than that. It seems like it may have been correctable by moving a jumper.

With all this nostalgia going on I may have to bop over to Mike's place and get a fix <Grin>

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Re: My PCjr Setup & Collection

Postby Vorticon » Wed Feb 03, 2010 5:18 am

I did the memory upgrade to an IBM sidecar, and I can vouch that it was a delicate and very time consuming operation, specifically the desoldering of the old chips using a combination of soldering pencil, braid and vacuum pump. I ended up socketing all the new chips because I am not sure the board pads could endure another round of desoldering. It has been working very reliably since then though.

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