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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 27th Jan 2017, 12:28 pm   #1
Argus25
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Default IBM 5155 computer - using EGA card

I'm not sure how popular these early IBM portable computers are in the UK. They came with a CGA card initially and have an internal amber color monochrome monitor.

The article here explains how to fit an EGA card while still retaining the function of the internal amber monitor:

http://worldphaco.com/uploads/FITTIN...N_IBM_5155.pdf

It also shows how a monochrome gif image can be colored and be made to appear as a good grey scale image on the vintage amber monitor.
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Old 28th Jan 2017, 12:36 pm   #2
mike_newcomb
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Default Re: IBM 5155 computer - using EGA card

Hi Argus,
I remember these, they were termed 'Luggables'
Regards - Mike
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Old 29th Jan 2017, 5:45 am   #3
Argus25
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Default Re: IBM 5155 computer - using EGA card

Yes the 5155 computer looked like a sewing machine with the keyboard on the base and the carry handle on the narrow end and they claimed it was "portable". One of the adverts for it showed a fellow riding on a bike with one. I can barely lug it across the room, its darn heavy! But one advantage of them is the small internal amber VDU that is really good to have close to the keyboard.
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Old 29th Jan 2017, 8:56 am   #4
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Default Re: IBM 5155 computer - using EGA card

The 5155 is essentally a repackaged PC/XT (5160). There's a normal PC/XT motherboard in there, so you can do the well-known mod to put all 640K on the motherboard. Standard CGA (unless you do what is suggested here) and floppy contoller cards. The technical reference manual on my bookshelf covers both the PC/XT and PortablePC.

The drives are half-height 40 cylinder (360K). Annoying not the same as the 360K drive for the PC/AT.

Just about the only unique electronic part is the power supply.

I am pretty sure the monitor (covered in the Options and Adapters Technical Reference volume 1) was made by Zenith.

One 'gotcha'. If you are working on one of these and need to get amongst the PSU/monitor area, you need a set of Bristol Spline keys. Not Torx.
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Old 29th Jan 2017, 12:23 pm   #5
Argus25
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Default Re: IBM 5155 computer - using EGA card

Quote:
Originally Posted by TonyDuell View Post
I am pretty sure the monitor (covered in the Options and Adapters Technical Reference volume 1) was made by Zenith.
The small Amber monitor in these computers has to be the best small crt monitor I have ever seen (and I've worked on and tested many in my time both vdu's and TV monitors, camera viewfinders etc). The video frequency response is flat to around 7mHz and it has no difficulty resolving that frequency in the video, much better than any monitor designed for TV work. The beam focus is sharp as a tack and perfectly uniform in the center and corners at the same focus setting.

The scan linearity is mathematically close to perfect for both the H and V scans and the raster geometry perfectly rectangular and the contrast and light output very high, without significant beam de-focus on the highlights.

It was mainly made for text rather than graphics, but with graphics & images it is fantastic too. Amber also seems better than green I find. Somebody (probably Zenith) went to a lot of trouble with this monitor design. Of course a lot of that is the CRT and yoke assembly.

But, the circuit is also more interesting than most too. The video output amplifier is a cascode configuration, much like a small medium power RF amplifier. Also, the vertical oscillator is constructed from two transistors wired up as an SCR which is an uncommon way to do the frame oscillator in the video monitor industry. So its all a bit creative.
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Old 29th Jan 2017, 11:05 pm   #6
Argus25
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Default Re: IBM 5155 computer - using EGA card

Quote:
Originally Posted by TonyDuell View Post
The 5155 is essentally a repackaged PC/XT (5160). There's a normal PC/XT motherboard in there, so you can do the well-known mod to put all 640K on the motherboard.
Yes, mine has the extra memory added, but on an add on memory card, and additional memory on a Six Pack Plus card so it has the full 640k. Also in one disc drive location I have a dual 5.25/3.5 floppy drive unit and in the other a vintage 40Mb Seagate hard drive. I get data in & out of this computer by the 3.5" drive mainly. I also have DOS 3.3, the minimal requirement to support the 3.5" drive for 1.44Mb and I have Windows V1.0 installed on the hard drive.
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Old 29th Jan 2017, 11:39 pm   #7
TonyDuell
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Default Re: IBM 5155 computer - using EGA card

Actually cascode video amplifiers are not that uncommon in computer monitors. Going through some schematics I spotted a couple of others (not Zenith designs either, one was Pericom using mostly Philips components, the other HP, but I think really Samsung)

The point of putting all the memory on the motherboard is to free up the full-length slot (and any other slots). The 5155 is tight for space inside. Pity it's not about 1/2" deeper... Doing the modification to put the memory on the motherboard is very easy (put 256K*1 DRAMs in banks 0,1, 64K*1 DRAMs in banks 2,3; then put a 74S158 or 74F158 in the empty socket pointing the same way as the chips around it; solder a jumper between pads E1 and E2).

Mine is essentially original, Original floppy drives, video card, etc. If I need a 3.5" drive I can connect it to the DC37 connector on the floppy card.
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Old 30th Jan 2017, 1:16 am   #8
Argus25
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Default Re: IBM 5155 computer - using EGA card

Quote:
Originally Posted by TonyDuell View Post
(put 256K*1 DRAMs in banks 0,1, 64K*1 DRAMs in banks 2,3; then put a 74S158 or 74F158 in the empty socket pointing the same way as the chips around it; solder a jumper between pads E1 and E2).
Thanks, I'll keep a note of this in case I decide to change it.
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Old 30th Jan 2017, 2:28 am   #9
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Default Re: IBM 5155 computer - using EGA card

Quote:
Originally Posted by Argus25 View Post
The small Amber monitor in these computers has to be the best small crt monitor I have ever seen
How did they compare to the small monitor in the HP 85? I have one of those, but it's currently dead so in the long term to-do pile, but would be interested in how it compared.
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Old 30th Jan 2017, 2:55 am   #10
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Default Re: IBM 5155 computer - using EGA card

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Originally Posted by arjoll View Post
How did they compare to the small monitor in the HP 85?
I'm not 100% ure about that particular one, but probably I would expect it would be of a high standard too.
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