750P Restoration Blog

[whizkid]

My first PC was a 750P. Awesome machine at the time. I sold it to someone a couple years ago for about 3% of what I paid for it. I got it back today for nothing. It's got no battery and I think the hard disk is the original 170MB drive. It's got a 16MB card to go with the original 4MB RAM. (Somebody seemed to imply he would mail me a 32MB card, but I haven't heard anything more about that.... j^h ahem.')

I know it was working fine when I sold it to him. He said he thinks he never even turned it on, and he's probably right.

I attempted to power up with AC and got errors 161 (battery dead), 163 (no time or date set) and the killer I9990303 (bad bank 2 EPROM checksum).

I can rig up a CMOS battery, but if the BIOS is really cooked, there's no way to continue except by replacing the system board.

This machine is just for fun... so I think my first step is to try a new CMOS battery and see what happens.

Both of you who are interested are welcome to follow the tale as it ... unravels.

Consider this thread my personal blog on restoring my 750P to something that works, if not to something actually useful.

I would appreciate comments if anyone is interested in the topic. Maybe I can put some pictures somewhere.

[JHEM]

(Somebody seemed to imply he would mail me a 32MB card, but I haven't heard anything more about that.... j^h ahem.')

I sent you a PM on 15NOV asking for your address.

I still await your reply.

Regards,

James

[whizkid]

I bought a CMOS battery. Most places wanted $18 to $20 for a cell with leads ready to go, or about $3.50 for just the cell. I went to a local Batteries Plus, and bought the cell for $3.59. The clerk offered to spot weld my existing leads onto the new cell for $1. What a deal! I'll consider this for all my ThinkPads.

Anyway, the 750P still has the bad checksum error, of course, and the new CMOS battery was of no help. I bought a parts 750C off eBay for $5. It arrived today. I put the new CMOS battery in it, and it powered right up. Nice TFT screen. Too bad it's only 640x480. The case is badly marred and cracked.

Now I'm not sure if I want to spiff up the old 750P using the 750C system board to make it work again, or have the cool color screen. What a choice.

Time for a BIOS upgrad (I think I have that floppy... yep), and install DOS, or maybe Win3.1 or Win95!

[whizkid]

The BIOS upgrade went perfectly.

I booted on the original 170MB(!) hard drive, and Win95 came up. Hey, no Internet Explorer? Isn't that something. I haven't seen my PC Card modem in a long time, and I don't have a NIC for it either. Not too useful at the moment.

Since the case on the 750C is in rough shape, I'm going to restore the 750P first. If I miss color (on the whopping 256 color VGA screen), or just having a TFT, I'll put the color screen on it.

I used the HMM (tpvol2... very hard to find) to remove nearly everything. The case just reeks of smoke. You know the old stale smoke like it's been sitting in a room for six years next to a smoker.

Everything up to the main system board came off pretty easily. I imagine it would have been easier if I had used the part in the HMM meant for this machine! Oh well, next time.

Anyway, there are four screws that anchor the hinges, just like on the 600 series. One was missing, two came out easily enough, but the third one is still in there. It's a soft brass screw, so I've stripped the head badly. None of my cross-headed screw drivers will work in it, and none of my flat-blade ones have enough torque to move it.

I think the next step is to take it to a machine shop to see if they can cut the screw or get it out. Criminy.

[whizkid]

750P Restoration budget so far:

Getting the 750P: Zero. Donation.
750C for parts: $5, $25 shipping.
CMOS battery: $4.59.

Total: $34.59

[whizkid]

I tried a 12GB drive in the 750C. The machine didn't even recognize a drive was present.

How large a drive can work in this machine without some hard disk BIOS patch?

How large WITH a patch?

Does anyone have an old 2 to 4GB drive you're willing to part with? PM me with an offer.

[AlphaKilo470]

Not sure what the limit is on hard drive size is, but I do have some spare laptop drives laying around. I have a spare 1.2gb drive and a spare 2.1gb drive. If you would like, we could work out a trade. The 1.2gb drive also has a caddy still attached, it's from a 760 series but will also work with a 755 and I'm not sure but maybe a 750.

[leoblob]

How large a drive can work in this machine without some hard disk BIOS patch?

How large WITH a patch?

I don't know the exact answer to your question, but common BIOS limits occur at 528MB, 2.1GB, 8.4GB, and 137GB. Without a patch, a 2.1 or slightly smaller, would probably work.

Using a program like Western Digital's Easy Drive, there's virtually no limit how large of a drive you can use. I ran a 5GB drive in an old 486 desktop with the 528MB limitation, and it worked perfectly, with no "visible" partitions... just one nice big 5GB "C: drive"... still using the original 1993 BIOS that came with the machine.

If you're using an older OS, like the first release of WIN95 or earlier, then there may be OS limitations that require partitions. But Easy Drive handles this, too. I believe a similar program is available from Maxtor, and probably the other drive manufacturers.

[whizkid]

Thanks for the replies. I swapped the system board from the 750C into the 750P and it worked! I suppose I shouldn't be surprised.

I used the Maintenance diskette to program in the serial number. Woohoo. That diskette allowed me to test the audio system. It failed. I thought it odd.

Anyway, on I went to try to get the 12GB hard drive to work. No luck. I used Hitachi's Feature Tool to limit the drive size to 8GB, then 4GB, then 800MB and neither PC-DOS 6.1 nor FreeDOS saw any drive at all. Fdisk said there were no fixed disks.

The EasySetup grays out HDD-1 in the test section (who said the 755 was first with EasySetup?), so it looks like the machine can't see the drive at all, but the Feature Tool saw it easily.

Hey, let's try the Drive Fitness Test... The drive is recognized with the capacity set by the Feature tool. But it just quits to DOS when I start the test if the drive is limited to 4GB. Trying with the limit removed... does the same thing. It looks like this machine really doesn't like this drive. Bah. I had a Fujitsu 2GB in this machine way back when, but parted it out when I sold the machine.

Hitachi's tool said the drive appeared as the slave drive. I wonder if that's an issue... and how to fix it. Anyone know for sure?

HGST no longer provides their drive overlay software Disk Manager. Can anyone provide a copy or point me to IBM's site?

I put back in the OLD 170MB disk and booted Win95. Or started to, anyway. The process stopped when the audio driver was loading. Looks like I'll have to take it apart again. At least I have two audio cards to try.

[whizkid]

I found an OLD post by our host and moderator, Mr. Morrow. Bill, you said that 6.4GB drives work fine in the 750 series. Do you suppose an 8GB drive might work?

Then again, 6.4 would be really nice too.

[leoblob]

Hitachi's tool said the drive appeared as the slave drive. I wonder if that's an issue... and how to fix it. Anyone know for sure?

My experience with DESKTOP computers tells me that problems with master/slave settings can mess things up big time! There may be jumpers on the back of the drive (where the main connector is). I'd check them (or their absence) for the proper setting for Master. There should be a label somewhere on the drive telling you where the jumpers belong.

[whizkid]

I bent over a pin on my 12GB drive, popped it in my 750P and voila! It works and appears as an 8GB drive. Good enough for me.

Now to install some OSen on it.

Since Windows really won't run well, and I want to help with the FreeDOS effort, I plan to install Linux, FreeDOS and probably PC-DOS 6.1 to test it against for functionality and performance.

Most excellent.

[whizkid]

I have PC-DOS 6.1 on the 750P now. It seems fine... but really old. I made a partition for FreeDOS, which really is quite a bit nicer in many ways, but I have yet to install it.

As I mentioned before, the BIOS sees my 12GB drive as 8GB. At least it boots. Any OS that uses the BIOS for hard disk access (such as DOS) will also be limited to that 8GB.

However, Linux (and Windows since 3.1) does not use the BIOS to access the drive. As long as my /boot is below the 8GB limit, Linux can and does use the entire drive!

I got a LinkSys PCMPC100 16-bit 10/100 NIC for cheap and it works great in the machine with DOS, W95 and Linux. Maybe some rainy Sunday when I'm REALLY bored, I'll try to get it working with Win3.0.

So now I have a 2GB PC-DOS partition, a 2GB FreeDOS partition, a little /boot, a little Linux swap, and a 7GB root partition for Linux, and it appears to be working just fine... so far.

I'm installing Debian because they still support a floppy/network installation mode. Other distributions can be forced to work that way, but I'm not in a forcing mood. I only wish I hadn't selected so many packages, because installation has been going for nearly two days. Every few hours in complains about some package that didn't install properly and I have to poke it. I can hardly wait (and wait and wait) to bring up the windowing system.

I wonder if I can get WiFi to work with this thing! Ah, but then I'd have to buy a battery to be useful.

[whizkid]

X Windows runs at 320x200. Neat. I suppose it's time to head over to the Linux section.

[slagmi]

Fun read!

Strange thing for me is, once I'm done fixing up and old, mostly usless computer, once everything is working, it's then of little interest to me. Is that weird?

[Bob Collins]

Fun read!

Strange thing for me is, once I'm done fixing up and old, mostly usless computer, once everything is working, it's then of little interest to me. Is that weird?

Same here. I think it is the challenge that lays ahead that is more important than using the item once the problem has been solved.

[AlphaKilo470]

Yeah, I also noticed the same thing. I spent about 8 or so hours getting Windows installed, getting the patches and drivers installed then installing all my software on my old 760E then spent about an hour or 2 replacing the 120mhz CPU with a 133mhz CPU and after all of that was done, the very next day, I lent the computer to a friend who has been using it for school since then (this was about a month or so ago.)

The same, however, doesn't apply to my 380ED, that, I still use on a daily basis and probably won't take oput of service until A: I get my 600E fixed, B: I get a new laptop (not likely with my budget) or C: the thing dies.

[whizkid]

Debian Linux is running, but not well. It's using swap most of the time, so more RAM is in order.

I bought a 32MB card at a local shop today. It looked factory sealed and new. It's a Kingston KTM-TP750/32, and the little instruction booklet is copyrighted in 1997!

It says the card works in the 750 and 755. The BIOS saw it when the shop guy let me test the card before purchase. The BIOS memory test passed. I'm now running memtest86, but it looks like it's stuck at 16% in test 1. It's been stuck less than half and hour, so I'll let it keep going. I know that memory tester can be very slow on fast machines, and this is a sloth.

Add to refurbishing budget: $15 for 32MB memory.

If anyone is interested, the shop is Midwest Electronics, they have a site here: https://secure.midwest-electronics.com/intro.asp and they have a bunch more of these parts. Fire up those 755's people!

[whizkid]

I read some of the fine documentation over at XFree86.org and found out some interesting things.

First, the WD 90C24 video chip in the 750 series is not supported in the latest versions. No one has bothered to port the old driver to the new driver module format. No one even maintains the package any more.

Second, VGA should work, and does, but at the bit depth I chose (8 bits per pixel), the VGA driver will use only 64K and give a resolution of... 320x200. Most excellent.

I'm trying 4 bits per pixel right now, and... no good. The video timings are out of range. bah.

All in al, the 32MB part is working fine. Large hard disks can work if you're persistent. The machine is basically working. I think that's the end of this blog, unless I go crazy with my tax refund and get a battery and WiFi!

If I do any more work on getting video and audio working with Linux, I think I'll put it over at http://www.thinkwiki.org. Audio should be easier because at least there's a driver. I just don't think it works with the weird IO address that IBM put it at.