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Larry, I decided to wait on the lowercase mod, but I am happy to report that I was able to successfully replace the Video RAM chip at bit 3, and everything looks normal again! Thanks for your help! Robbert

Hi Larry, Thanks for the insight! I'll follow your advice! As for the lower case mod -- I looked at what's involved in that. I'd need at least another 74 logic IC that I don't have (I have a few 21L02's on order). Not sure if I want to do that now or maybe later. Thanks! Robbert

Larry, Awesome! That one is suspiciously next to another one in a DIP socket. ;) Looks like this has been an issue before, but with another bit. I haven't pulled IC's from the Tandy circuit board yet, but I was going to try a solder wick and gently remove the solder, or try my solder "sucker"...

Larry, Thanks for the insight! I see this when the system starts: MMMORQ SAZE? RIDIG(SHICK DEVEL(II BASIC( READY ( >_(( Which IC holds Bit3 by the way? I haven't been able to find a clear diagram that shows it. Robbert

I just got another Model 1 (the other one I have has an intermittent fault when pushing on the circuit board, but no matter how much reflowing I've done, I haven't been able to locate it). This one has an interesting video issue. See link to the YouTube video. I would guess it's one of the...

Based on a very old thread on this forum and some other threads I found online, I thought it might be fun to try to get an old XT going with a ISA USB board based on the CH375 IC. I found one on Taobao in China and managed to wrestle through the Google Translator to actually make the purchase...

Hi All, I had a nice working 20MB MFM disk in one of my XTs, working off an 8-bit MFM controller (WD). I decided it would be fun to try to see if the drive would format to 30MB on an RLL controller (I remember doing that years ago, and as long as the drive is of sufficient quality, it works...

I spent most of the morning today tinkering around with the PPC-21 I have here to see if I can somehow make it emulate CGA like its bigger brother, the CorData (P)PC-400. First try was to swap out the BIOS. The PPC-21 runs 3.10, and the PPC-400 has 4.23/4.33 (at least, those images I have...

Keyboard was repaired with new foil. HDD had failed, so disconnected it, and put in a XT-IDE with CF card. Next is trying to run the newer PPC-400 BIOS (16K instead of 8K) on it when I get an ISA ROM board, and add an Intel Ethernet board to tie it to my IPX network for easy file sharing.

Does anyone know what this is? And can point me to dip settings? This came from a Corona PC-400 and appears to fill the gap from 8000H to AFFFH (yielding 704K memory on bootup). No brand name, and no part number on the board. And only 8 out of the 18 IC slots filled....

I just dumped the BIOS (2764 EPROM) from a Corona PPC-21 portable machine. It's revision 3.10. modem7 -- maybe a good addition for the minuszerodegrees site?

I think I just figured out why the keyboard isn't working ... Ugh.. Ordered foam pad replacements from Texelec... :)

I think you're right that this is an RS6000 version. I've seen that mentioned before. Haven't tried the 3C523 / 3C529 drivers, but I did try the 3C527 drivers from that same page. And those definitely don't work. The diagnostic tool says the board isn't there... Attached are a couple of pics...

Hi Everyone! I had a friend donate an old PS/2 Model 80, which had some MCA network boards in it (a 3270 emulator and Token Ring board). I would like to hook it up to my "vintage computer network", but needed an Ethernet board. Without doing a ton of research, I found an IBM 00G3368 bus master...

Hi guys, I have two of these laptops and one is behaving nicely, while the other one keeps thinking there is some kind of memory size problem. The one with the memory size problem has the standard 2MB on board and a 4MB 72-pin SIMM stick. The memory size error shows up with or without the...

And I'm happy to report that did it. Replaced one IC in bank 4 at bit 12, and the card tested perfect with the thorough memory test on Checkit. Thanks for your help!

Wow.. That worked perfectly! In about 10 minutes I was able to map the entire board! See attached map for the IC locations. When I get my next DIP socket in (tomorrow, if the Amazon Gods deliver on time), I'll swap out the C bit in bank 4 and I should be up and running! Thank you!

I bought a 2MB Micron memory expansion board off eBay. Micron PN 235-0149. I plugged it in one of my machines, and it works. Seems to fill in address space from 1M to 3M. I have a similar board which is defective (235-0140), which has dip switches. This board appears to have a ROM and no dip...

I was just reading a bit in the XT-IDE 2.0 BIOS thread, where there was an announcement that the new version can boot through a serial port. Very interesting option to run diskless systems, but that got me wondering about network boot... I know that used to be a thing with Novell boot roms etc...

After realizing there is a RAM layout / chip finder in Checkit, it came up with this. Does that seem to make sense?