IBM 5150 board for ... repair

[orion24]

I guess I need to start working on this before I try to power it on. This is the board:

It has a problem in the power input area and some tantalum capacitors are disconnected. If any of you experts can spot anything else, I'm all ears. Now, pretty lol question, but are the 2 missing pins in the power area really "ripped off", or does this board normally have them like this? (I've seen at least one more such board with these 2 pins missing). Then, with the tantalums, I wonder what I can replace these with. The one on the top right that has one leg disconnected is labeled : 106 +16K
To test this board, I'll also have to wait for my CGA/EGA --> VGA signal converter card to arrive, as I lack a pre-VGA monitor, I also lack an 8-bit I/O controller, but I do have an EGA video card. Final question, for now, is if I can use a typical 1.44 or 1.2 floppy with this board. I know it doesn't support HD, but will it at least accept the drives in DD mode, or will only real 720 and 360K drives work?

 

[Stone]

While it won't work with either HD floppy it will work with a 16-bit VGA card... if you have the right card.

 

[sergey]

I think an AT floppy disk controller and a 3.5" drive will work with 720 KB disks. It works on XT clones but I never tried it on an original PC/XT.

For board repair you might want to get a diagnostic ROM that would (partially) work even without display and doesn't need a floppy.

It looks like your board has (some say rare) 8088 revision ('78 ) that has the will-do-interrupt-after-ss-change bug. I don't think you'll actually ever hit it (earlier software usually had a workaround and disabled interrupts before stack changes). Just an interesting fact...

 

[dschnur]

The second port on that motherboard next to the keyboard port is for a cassette drive (for BASIC use only):

http://en.wikipedia.org/wiki/IBM_Personal_Computer#Cassette_tape

The pinouts are here:

http://en.wikipedia.org/wiki/IBM_cassette_tape

When I was in High School, a neighbor who's father got him one of those when they came out. I remember the tape drive and using it to save basic programs.

-Dan

 

[modem7]

Lots of IBM 5150 info, including IBM's manuals, at http://www.minuszerodegrees.net

Now, pretty lol question, but are the 2 missing pins in the power area really "ripped off", or does this board normally have them like this? (I've seen at least one more such board with these 2 pins missing).

I've seen a lot of the 16KB-64KB variation of the motherboard, and this is the first time that I've seen one without those pins. The two 'missing' pins are two of the three +5V ones. There are normally three to better cater for the relatively high current that may be required from the +5V line (actual current drawn depends on configuration).

Then, with the tantalums, I wonder what I can replace these with. The one on the top right that has one leg disconnected is labeled : 106 +16K

On the 16KB-64KB motherboard, the capacitors are standard two-legged 10µF/16V tantalum. See [here].

I know it doesn't support HD, but will it at least accept the drives in DD mode, or will only real 720 and 360K drives work?

If chip U33 is marked 5700671 or 1501476, then a 1.44M drive will behave as a 720K one. See [here].

 

[orion24]

For board repair you might want to get a diagnostic ROM that would (partially) work even without display and doesn't need a floppy

I've got one of these, but will not power it on now until I get the power area fixed.

On the 16KB-64KB motherboard, the capacitors are standard two-legged 10µF/16V tantalum. See [here].

I'll order some from ebay. But if possible I'm thinking of replacing them with other type 10μF/16V capacitors that are more reliable. The downside is that this would ruin the "look" of the board and make it look as one of a later era, so I'm not sure.

If chip U33 is marked 5700671 or 1501476, then a 1.44M drive will behave as a 720K one. See [here].

It looks like it is. Saves a lot of trouble, as 360/720K drives should be hard to find and expensive by now.

 

[modem7]

It looks like it is. Saves a lot of trouble, as 360/720K drives should be hard to find and expensive by now.

The web page I pointed you to earlier is under construction. I've just now modified it to alert people with a 16KB-64K 5150 motherboard to a problem that I think you will see, unless you have a RAM card to bring total RAM to at least 128 KB.