Tandy 2000 Restoration

 

August 5, 2007

Ok, so I haven't been so good in keeping up with the log. I've had other projects get in the way, and finding a CM-1 monitor proved to be a huge challenge. Here's what I've accomplished so far:

• Completed making disk images of all software. Discovered that two of the five Wordstar disks are shot. Other programs which imaged fine include MS-DOS, Lotus 1-2-3, Microsoft Multiplan, pfs:file, and pfs:report. For archival purposes, here is a ZIP file containing the MS-DOS disks from my system.
• Purchased a second T2K in better physical condition (still white; not a shread of dust anywhere). This unit also suffers from a failed hard drive. According to some stuff I've read, the Tandon TM502 drives are not known for their long-term reliability. Better search for a new drive...
• Finally located and purchased a CM-1 color monitor. No cable unfortunately.
• Built replacement HiRes Color cable. This requires a standard DE9M on one side and an EIAJ 8-pin rectangular connector on the other. I used a serial extension cable with one end cut off, and purchased an EIAJ connector from AV Supply Store. Part E8M is the connector and shell. The pinout for the CM-1 monitor is here (from the Tandy FaxBack archive at Oldskool.org). The HiRes Color Card pinout is in the Tandy 2000 FAQ (local copy here). Wiring is obvious. Works perfectly.
• Purchased Seagate ST-225 (20mb) MFM hard drive to replace the TM502 in one machine. Turns out that the HD controller on one of my T2Ks is bad, so now I'm in Frankenstein mode to get a single working machine. Installed and formatted drive using "HFORMAT c: /s /p". The "/p" switch causes the formatting program to prompt for the drive geometry (613 tracks, 4 heads, interleave=5).

After all of this, I now have a very solid 640k 2000HD system that I also upgraded to dual floppy drives (taking the other from my other machine).

Other things I've discovered:

• Any MFM drive less than 32mb should work with the 2000HD. The 32mb limit is a limitation within DOS 2.xx. I found a Seagate ST-225 on eBay for $20 and it fit the bill perfectly.
• If you have a hard drive controller with the external port, the external port will work with any MFM drive so long as the cables are straight-through, the external drive is jumpered for drive 1, and the drive is terminated. Be aware that Pin 7 on the 20-pin data cable carries 12v. This pin is listed as "reserved" for all MFM drives so it shouldn't be a problem. Tandy used this as a power-on signal for the external hard drive enclosure power supply.
• Poor long-term quality of the Tandon drives. At least for me, the failure mode is the same -- the head positioner servo doesn't move. You do feel back-EMF if you try to move it with the power on, but it doesn't respond to commands. It's a shame too -- both of these drives had software on the for which I don't have disks.

Now that this is done, I have to pull together all of the disk images into one place. Then, I have to scan the Technical Reference Manual. That one is going to be a pain because it's spiral bound. I also want to connect the failed hard drives to an MFM controller in a regular old PC and see if maybe I can waken them.

November 21, 2006

I've made images of most of the disks using Teledisk. Some of the disks, for whatever reason, were not readable. Fortunately, the programs exist on the hard drive so I should be able to regenerate the bad disks from the copies on the hard drive.

The bad news is that the hard drive has become flaky. It worked fine initially but now it spins but doesn't go "ready" so I keep getting "bad unit" errors. Oh well.

I have another MFM drive and I'm hopeful I can get the old drive working one more time so I can copy everything to a new drive.

November 12, 2006

I'm getting closer to powering up the T2k for the first time tonight. The first thing I did was to make copies of the BIOS EPROMs. Indeed, they are TMS2532JL-35 EPROMs. U47 (high/odd) contains a label with "474600" on it. U48 (low/even) contains a label with "484A00". I presume that these are checksums but right now I have no way to tell.

Here is a zip file containing the binary ROM dumps for burning replacements.

After cleaning the keyboard I plugged everything in and gave it a whirl. The machine powered-up without a problem! It reports MS-DOS version 2.11.03 and a BIOS revision of 02.02.00. Perfect!

Next thing for me to do is to make images of all of the disks.

November 11, 2006

I started cleaning the Tandy 2000HD system unit I received (26-5104 serial M5405732). A quick system inventory reveals that it has only one floppy drive in addition to the 10mb hard drive. The expansion card cage contains, from top to bottom, the following cards:

• Hard Disk Controller (no number)
• 128k/256k Memory Board (26-5161)
• 128k/256k Memory Board (26-5161) with 26-5162 memory option
• {empty - for the color board I have on order}

This configuration would imply a system with 640k of memory. Not too bad, and more than my first PC had (128k I think).

The system is in good physical shape but the case is severely yellowed and smells musty. I opened the unit and using compressed air and a brush, blew out the dust. I opened the power supply and looked for any obvious signs of previous trouble (none), and then I blew out the dust. Two screws that attach the front fascia to the case were missing so I replaced them.

I gave the outside a quick cleaning with Simple Green just to de-grime it. At this point I turned the system over so I could get to the planar cage. I removed the four screws holding the cage to the case and the two screws that hold the cage to the riser connector and with a little tug to unseat the Euro connector, it hinged upwards. Again, another quick dusting.

The first thing on tap for tomorrow is to remove the two BIOS ROMs and make copies. Interestingly, the ROMs weren't even mask programmed ROMs -- they were TI 2532 EPROMs with a label upon which is printed what appears to be a checksum. According to what I've read, the BIOS version is 02.00.00 but that somehow doesn't reconcile to the fact that they used EPROMs (and it also implies that there were earlier revisions). Tandy made, what, 10,000 or 12,000 of these machines -- each with two EPROMs. It had to be more cost effective to run 20,000 masked ROMs than buy and gang program the same number of EPROMs. Maybe someone can shed some light on this for me.

That's it for now.

 

 

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Last updated 2010-06-06 08:08 -0400