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Specifically the 755CD

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solidpro
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Specifically the 755CD

#1 Post by solidpro » Tue May 14, 2024 3:43 pm

Hi Everyone

I originally intended to spend the morning finishing restoring a 755CD which has been 'on the shelf' for about 2 years with an on-board 00201 memory issue. It ended up taking exactly 12 hours even after last night I'd already dismantled and resolved the issue with the memory.

The 755CD is quite different from all the other 755 machines because it is a fatter chassis - to incorporate the CD-ROM drive and, I think more so the massive video and digital sound processing hardware that accompanied this 'multimedia' expansion. Due to the battery and HDD being standard across all 755 machines, the 755CD has a plastic 'spacer on a hinge above these two bits, to keep everything in place.

All the other 755 machines came with floppy drives by default. Other things i've learned...

The 755CD was obviously the most advanced 755 machine, but it wasn't the highest specification by any means. Only the 755CX (which lacks the CD, DSP and other video enhancements) was the only 755 machine offered with an SVGA screen. This really surprised me that the 755 (out in 1994) was still defaulting to 640x480.

After much deliberation I decided to upgrade this 755CD to an SVGA panel from a CX. I always try to keep these machines 'original' but if you put it back to VGA then I guess it is.

As I said at the start, the onboard memory was duff. All 755 machines came with either 4 or 8Mb onboard, but later models had the onboard RAM removable via a little daughterboard which is only accessible by completely dismantling every. single. component. of the machine. Luckily I had a couple of spares and a replacement sorted that. Here is what it looks like:

Image

This is the spacer only found in the 755CD:

Image

And here is my 'restored' machine. It's not exactly perfect - mainly because the plastic on these machines doesn't get brittle but the coating does not fare well.

Image

Here is the difference in thickness between the 755CD on the right and a 755C on the left:

Image

Image

Image

Image

Image

Image

Image

The internals of the 755CD is made up of about 5 different boards sandwiched together with the CPU attached to a wide flat heatsink right at the bottom. Each layer above that has a variety of surface mount caps which were all a bit dodgy and I replaced with ceramics. About 20 in total, including a couple of through-hole caps on one of them.

The LCD as well had 3 surface mounted electrolytics - the type that are harder to spot initially because they're encased sideways inside a plastic box. I replaced them too because the screen was a bit flickery.

One aspect that slowed me down was that the audio board (with the rolling volume control) has about 5 surface mounted caps and one of them pulled the pad off. I managed to botch wire the missing pad but then decided to swap it with a spare audio which looks visibily the same which did not need the botch. Then after re-assembling I noticed that due to the whole chassis being taller, they'd made the whole stand which the volume wheel sits on about 5mm taller! So I then had to desolder both wheels and switch them.

Upgraded with a 16Mb IC DRAM card, giving 24Mb RAM and a clean installation of Windows 95. Drivers were a pain to get from a variety of breadcrumbs around dead links on the internet - but they are there.

I tried to use the archive.org ISO of the original restore CD (which would have brought back a dual boot OS2/Win3.1 installation on a 320Mb partition, but despite considerable resources it wouldn't work. You have the option to use the built-in CD-ROM but you are required to use a floppy boot disk - but obviously you can only have one in the ultrabay at once, and you can't hot swap. Usually this would be no problem as the 755CD does have an external FDD connector but it's unlike almost every other thinkpad I've seen. It's small and fat and I couldn't find that cable anywhere.

So the alternative was to boot using a massive Selecta Dock II, which has a built-in CD-ROM drive, which I have and I tried using but it would not detect the CD-ROM drive in the dock.

I also tried copying the files from the boot floppy to the HDD and then running those from a bootable HDD, with the built-in CD-ROM to work but no-go - the bootable floppy uses some hidden magic formula that only IBM know about so you definitely need both.

Still Windows 95 looks rather 'charming' on this machine and it would have been the obvious 'upgrade' for most owners to make. And all the drivers are there so. Yeah.

Oh and for some reason, only the right speaker works. Kinda annoying but we can't exactly allow perfection to be our enemy here.

Anyway, this is the only 755CD I've ever come across. I'm sure they aren't that rare but some of them did burn up on MIR's re-entry, so a few less.

I do have several tested 755 SVGA lids, and I probably could sell 2/3 of them if anyone else has a later 755 (has to be a later model to be ribbon-compatible) with only VGA GFX then I'd be willing to sell you a nice upgrade. You can tell the SVGA screens because the memory count is noticably smaller on boot.

Also still have a bunch of fully working keyboards and a few odds and ends from the CX. A lot of it will go up on ebay soon.
Last edited by solidpro on Thu May 16, 2024 12:32 am, edited 1 time in total.
http://Ret.Rocks - Rare Used & Restored Vintage Computing for Sale!
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Re: Specficially the 755CD

#2 Post by ThinkDan » Wed May 15, 2024 3:42 pm

solidpro wrote:
Tue May 14, 2024 3:43 pm
The 755CD is quite different from all the other 755 machines because it is a fatter chassis - to incorporate the CD-ROM drive and, I think more so the massive video and digital sound processing hardware that accompanied this 'multimedia' expansion. Due to the battery and HDD being standard across all 755 machines, the 755CD has a plastic 'spacer on a hinge above these two bits, to keep everything in place.
...
This is the spacer only found in the 755CD:

Image
Good work, thanks for posting the pics. :D

That one above explains it well - the chassis was deeper to accommodate the CD-ROM drive, hence the need for the keyboard support frame and other modifications. If you look at the shield over the system board(s), though, you'll see that the innards are at normal height, but for the upstand at the back increased - is that green/white bit the switch so it knows when the keyboard is lifted? That would need to be higher to touch still, like the volume wheel projecting higher.

The 486 755CD and 486 CE were released in October 1994, the Pentium CX, 486 CV and 486 CDV were released in May/July 1995, the Pentium CD, CDV and CV in Sept/Oct 1995. A Pentium 755CD with the SVGA CX screen would be the ultimate 755+ model. The 755CD & CDV were the only ones with the thick chassis.

With the 760, IBM entirely reversed this thin/thick chassis stance after the initial 760C (thin) & 760CD (thick) - all subsequent 760 models were thick chassis, except the 760L. That makes the 760C and 760L the rarities of the 760 range, and actually they look really sleek and appealing in thin chassis configuration, as I think you noted recently :wink:

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solidpro
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Re: Specifically the 755CD

#3 Post by solidpro » Thu May 16, 2024 12:38 am

The 755CD actually incorporates TWO of those little green & white switches to know when they keyboad is raised - the second one sits ontop of the first one (first one found in all the other 755CDs) keeping the first one pressed down and, my guess was replacing it at a higher level. Quite Heath Robinson, but it works.

From memory, the aluminium cage that surrounds most of the innard is different on the 755CD to all the others too. In other words, on all the other 755 machines the interposer for the LCD is just a 'dumb' looking riser, but on the 755CD it's a huge PCB, covered in big fat chips taking up the whole top of the chassis.

After the final put-back-together I realised I should have taken more pics of it disassembled but wasn't about to do it all over again...

Yeah, I like the 760C for it's thinner shape. The 760L would be an affront to an enterprise 7xx model being of L-ow cost configuration.
http://Ret.Rocks - Rare Used & Restored Vintage Computing for Sale!
Wanted: 220, 315D, 320, 350x, 355x, 500, 510, 530CS, 730TE, 750P, 755CD, Any 8xx Series, A20p, A21p, A22p, A31p, T40p
Currently For Sale (Restored): 560Z, T20, T21, T22, R61, R51, s30, 340, 755CX

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Re: Specifically the 755CD

#4 Post by ThinkDan » Thu May 16, 2024 2:40 am

solidpro wrote:
Thu May 16, 2024 12:38 am
Yeah, I like the 760C for it's thinner shape. The 760L would be an affront to an enterprise 7xx model being of L-ow cost configuration.
OK, I'll bite, you know my snobbish views on 'cost-reduced' variants :lol:

Actually, all credit to the 760 *L* models, the Mwave audio was a complex and in some regards incomplete audio/modem/DSP solution, and the non-Mwave *L* models have Crystal Semi audio (IIRC) that just works, and does SoundBlaster 16 emulation in hardware with no 'helper' drivers or TSRs needed to cludge it (like Mwave or the earlier 750/755 audio). Looking back now, when absolute horsepower is irrelevant but usability for retro computing is the appeal, the non-Mwave 760s are a better bet. There, I said it :oops:

Swap a 12" SVGA TFT lid onto a 760L and I think you have something close to my ideal 760! It's only the chunky screen bezel of the 10" TFT on the 760L that screams 'cheapness', after all :D

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solidpro
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Re: Specifically the 755CD

#5 Post by solidpro » Thu May 16, 2024 4:06 am

Having 'upgraded' the 755CD to SVGA against my innermost sacred rules, I may now end up going down a path to make the 760C SVGA too. I didn't know the 760C was VGA only just like I didn't realise that nearly all the 755 machines were VGA only (and luckily now I do, I find i'm sitting on a 'gold mine' of SVGA 755CX lids!).

Hopefully I can then list them on ebay for four figure sums like some of us seem to be benfitting from.

I get your point about the Mwave. Although back in the 1990s, if I saw my computer had 'Crystal' audio, I would spit on the floor. Owned by Cirrus Logic, I think, always sounded a bit naff compared to proper soundblaster.
http://Ret.Rocks - Rare Used & Restored Vintage Computing for Sale!
Wanted: 220, 315D, 320, 350x, 355x, 500, 510, 530CS, 730TE, 750P, 755CD, Any 8xx Series, A20p, A21p, A22p, A31p, T40p
Currently For Sale (Restored): 560Z, T20, T21, T22, R61, R51, s30, 340, 755CX

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Re: Specifically the 755CD

#6 Post by ThinkDan » Thu May 16, 2024 5:27 am

The 760C will already be 10" or 12" SVGA TFT from memory, the 760L is a 10" VGA TFT

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solidpro
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Re: Specifically the 755CD

#7 Post by solidpro » Thu May 16, 2024 5:53 am

Ah, I see. 12" always better than 10".
http://Ret.Rocks - Rare Used & Restored Vintage Computing for Sale!
Wanted: 220, 315D, 320, 350x, 355x, 500, 510, 530CS, 730TE, 750P, 755CD, Any 8xx Series, A20p, A21p, A22p, A31p, T40p
Currently For Sale (Restored): 560Z, T20, T21, T22, R61, R51, s30, 340, 755CX

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Re: Specifically the 755CD

#8 Post by ThinkDan » Thu May 16, 2024 7:17 am

solidpro wrote:
Thu May 16, 2024 5:53 am
Ah, I see. 12" always better than 10".
Remember that's a diagonal though, so it exaggerates both length and width. Typical engineers.

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Re: Specifically the 755CD

#9 Post by astral » Thu May 16, 2024 9:38 am

If you're listing on eBay, a VGA screen will always be more desirable than SVGA. Most people purchase these for DOS gaming, where an SVGA screen is not desirable due to crappy scaling/black borders.
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Re: Specifically the 755CD

#10 Post by ThinkDan » Thu May 16, 2024 12:02 pm

astral wrote:
Thu May 16, 2024 9:38 am
If you're listing on eBay, a VGA screen will always be more desirable than SVGA. Most people purchase these for DOS gaming, where an SVGA screen is not desirable due to crappy scaling/black borders.
Good point, I hadn't thought of it like that, I'm still stuck in the 'more desktop real estate' mode of trying to use it for the interest of using an old environment and applications.

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Re: Specifically the 755CD

#11 Post by solidpro » Fri May 17, 2024 4:21 am

Real estate me too. I think all the VGA players have died now and we're onto SVGA players having maximum disposable income combined with long weekends infront of ebay.
http://Ret.Rocks - Rare Used & Restored Vintage Computing for Sale!
Wanted: 220, 315D, 320, 350x, 355x, 500, 510, 530CS, 730TE, 750P, 755CD, Any 8xx Series, A20p, A21p, A22p, A31p, T40p
Currently For Sale (Restored): 560Z, T20, T21, T22, R61, R51, s30, 340, 755CX

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Re: Specifically the 755CD

#12 Post by astral » Fri May 17, 2024 10:31 am

solidpro wrote:
Fri May 17, 2024 4:21 am
Real estate me too. I think all the VGA players have died now and we're onto SVGA players having maximum disposable income combined with long weekends infront of ebay.
Not sure exactly what you mean - not many people buy old laptops to play early Windows games. Look at how much people pay up the nose for Toshiba Satellite Pro 400CDTs and Compaq LTE 5000s - they want VGA so their DOS games don't stretch. Any laptop made before 3D accelerated graphics breaks the aspect ratio when scaling up to 800x600, or 1024x768, and there are only a couple laptops with 3D accelerated graphics that have DOS compatible sound.
Then again, not many are gonna buy a 755CD for DOS because of the mwave.
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Re: Specifically the 755CD

#13 Post by evening_hunger » Thu Jun 06, 2024 8:25 am

So that means I cannot e.g. replace my 755CE lid with this svga lid from the 755CD? (CE is older)
T14amdR7-4750U/32GB/500gb.ssd/debian_testing (main driver)
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T30Pentium-M 4 1.8Ghz 512MB RAM - under restoration
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755CE, 486DX, approx 28MB RAM (Win95 JP)

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