Any reason I'd want another memory expansion card?

[Franko]

Last month I ordered a new old parallel port sidecar from eBay. I already had one from the 1980s on my PCjr, but I thought it'd be handy to have another one that I could try the bidirectional mod on and use for various purposes.

I guess I got a dodgy seller, because after placing the order I didn't hear anything for a long time. I emailed them twice, with no response. I figured they were probably out of stock and were trying to find another one to send me.

Today, a package arrived. Unfortunately they didn't send me a parallel port sidecar, but instead sent a new old PCjr 128kb memory expansion attachment in the original sealed package. My PCjr already has 128k RAM. There were a few other odd things, such as the fact that they misspelled my name and the name of my street, and got my zip code wrong, which probably sent it off-course for a couple of days.

At this point, I can try contacting the seller (keeping in mind that they never replied to my two previous emails). Possibly elevating to eBay if necessary. Or, I can just keep the 128k memory attachment and buy a parallel port sidecar from some other seller. (The price for this one was pretty cheap -- $20-ish.)

So, is there any reason I'd want or be able to use another RAM expansion card? If it were in a sidecar I could use the shell for the jrIDE I hope to eventually get, but since this is an internal card I gather it wouldn't help on that front.

[KenG]

If it is for the internal slot, it is actually a 64k care that upgrades a 64k machine to 128k. Useless to you. I would return it unless you think you will pick up another jr later.

[Trixter]

Yes, we need clarification: Is it the 64KB internal expansion to get the PCjr up to 128KB, or is it a 128KB memory sidecar? If the latter, you can open it up and mod it from 64k chips to 256k chips, turning it into a 512KB sidecar which is extremely useful.

If the former, make the seller make it right.

[Franko]

Yes, we need clarification: Is it the 64KB internal expansion to get the PCjr up to 128KB, or is it a 128KB memory sidecar?

I didn't want to open the package, since it's factory-sealed, but the box calls it "IBM PCjr 128KB Memory Expansion Attachment" and says this:

"This IBM PCjr option increases Random Access Memory (RAM) by 128KB for any IBM PCjr which has a minimum of 128KB of internal memory and a diskette drive. Highlights: Easy to install. Attaches to side of System Unit."

So actually it does sound like it's a 128KB memory sidecar. Are the 256k chips readily available to turn it into a 512k sidecar? I can see that that'd be very useful, at least until I can get a jrIDE.

One other issue -- although sealed, the box has a significant gash in the side. So I also need to figure out if the contents might be damaged in any way.

[monzamess]

Editorial: Even as-is, the unit will upgrade your jr to 256k and really improves the usability of the computer. In my experience it's harder to find & slightly more expensive than a parallel port sidecar. I'd consider this a "win" personally--assuming it's not damaged!

[Chuckphd53]

I agree, it is a great addon even if you wan to build a second system to play with,,,
LPT addons are fairly easy to find the the other add-on's can be a bit scarce at times..

I upgraded an IBM addon by upgrading the chips, they were soldered in and it took about three hours...
No reason to rush, and make sure you have the right tools, good side cutters to rmove the original chips with out damaging the PCBoard.... If you decide to give it a go, let me know and I can offer some insight.....


chuck

[Franko]

Thanks. I opened the box, the memory expansion attachment seemed undamaged, so I attached it to the PCjr and started it up. Now, instead of 128kb, the BIOS bootup reports 192KB memory. Not sure why it only recognizes 64k of the 128k additional RAM. I tried changing the DIP switches on the end of the expansion attachment, but other positions only disabled the extra RAM entirely.

Meanwhile, the PCjr's disk drive seems to have started acting wonky. I tried reading a diskette "PCjr Memory Options" that came with the memory expansion attachment. It started ok once, but a couple of other times the PCjr wouldn't read it. Worse, now when I try to boot the machine with one of my known good disks, I sometimes get errors -- reports of missing or damaged config.sys, etc. It's intermittent, though -- I just started the machine with a known good disk and it's fine and recognizing the 3.5" backpack drive. It seems as though I have to try a couple of times, and reseat the disk inside the drive, to get a good bootup read off of the disk. Maybe I'll try cleaning and lubricating the disk drive. Then, for good measure, get all of my file transfers from 5.25" to 3.5" disk completed as soon as possible just in case the 5.25" drive is gradually failing.

I upgraded an IBM addon by upgrading the chips, they were soldered in and it took about three hours...
No reason to rush, and make sure you have the right tools, good side cutters to rmove the original chips with out damaging the PCBoard.... If you decide to give it a go, let me know and I can offer some insight.

And I was wishfully hoping the chips were socketed. Ah well -- I might give that a go a little down the road.

[Brutman]

The BIOS memory test that figures out how much memory you have expects the memory to be working. It writes and then reads back memory at progressively higher addresses. If it gets a misread it assumes that bank is missing and stops. So the upper bank of your memory sidecar has a bad chip or addressing error.

Don't panic about the floppy drive. What you are describing is read errors early in in the boot process. Clean the rails and especially clean the heads. A read error early in the boot process just results in a boot failure; there is no retry logic at that part of the process.

[Franko]

The BIOS memory test that figures out how much memory you have expects the memory to be working. It writes and then reads back memory at progressively higher addresses. If it gets a misread it assumes that bank is missing and stops. So the upper bank of your memory sidecar has a bad chip or addressing error.

That makes sense. I guess I'll use it as-is for now.

Don't panic about the floppy drive. What you are describing is read errors early in in the boot process. Clean the rails and especially clean the heads. A read error early in the boot process just results in a boot failure; there is no retry logic at that part of the process.

Thanks, cleaned the rails and lubed with silicone, and that seems to have helped a lot. Now looking for the head-cleaning diskette I had my hands on only a few days ago ...

[KenG]

I have two IBM 128k sidecars that came with my first jr. Before I got my jr-IDE, I used a Quadram expansion chassis with 384k plus one of them to get to 640k. If I had more room, I would have kept the Quadram. It would be neat to have two jrs, one with modern expansions and the other only with vintage additions. When I had a Microsoft memory plus bus mouse sidecar, I could get to 768k using all vintage equipment. But I couldn’t find the mouse to go with it so I traded it to someone here who had the mouse but had damaged the sidecar.

If I was rich, this hobby could really get ugly. LOL