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| • | There were different models of the IBM 5150 (IBM PC). Do not assume that what applies to one model also applies to the others. This is mostly due to the different types of IBM 5150 motherboard, and the different motherboard BIOS'. |
| • | About five seconds after power-on, there is a small flashing cursor in the top-left corner of the display. You will not see a RAM count as you do with IBM's later personal computers. |
| • | This is a slow computer. BE PATIENT. After turn-on, it can be minutes before an error message is displayed (e.g. some hard disk drive controllers wait 2 minutes before displaying an error message.). |
| • | An AT-class keyboard will not work. More information at here. |
| • | Make sure that the keyboard gets plugged into the keyboard port, not the cassette port. (If accidentally done, no damage results.) |
| • | The IBM supplied floppy controller and 5.25" floppy drive are double density. They will not read high density 5.25" floppies, such as 1.2M (2SHD) ones. |
| • | Just in case tried on a different computer, formatting or writing to a double density 5.25" floppy using a high density 5.25" drive is unreliable. See here. |
| • | There is no 'CMOS SETUP'. All motherboard configuration is done via switches/jumpers. |
| • | There is no real-time clock (RTC) on the motherboard or on IBM-supplied expansion cards. Some examples of third-party solutions are at here. |
| • | After turning off the 5150's power supply, wait at least 5 seconds if you are planning to turn it back on. Any shorter; the 5150 may not start. See here. |
| • | All four RAM banks on the 5150 motherboard are permanently enabled. Therefore, you need to populate all four banks before adding a RAM card (which would be used to complement motherboard RAM). Note that, per here, removing the RAM chips from a bank will not disable the bank. |
| • | If the motherboard has the final BIOS revision (10/27/82), then bugs in the power-on self test (POST) of that BIOS result in the requirement for all four banks of motherboard RAM to be populated (and SW1/SW2 set appropriately). If you do not meet this requirement, the POST will miscalculate the amount of fitted RAM. |
| • | The 5150 motherboard does not have a keyboard controller chip. Instead, it uses discrete components - see here. |
| • | The power-on self test (POST) of an IBM 5150 motherboard is a confidence test only. It only partially tests things. |
| • | The power-on self test (POST) of an IBM 5150 motherboard does not access floppy drive B: (if fitted). |
| • | The power-on self test (POST) of an IBM 5150 motherboard does not output POST codes. Any numbers that you may see displayed by a POST card are not POST codes; they will be the result of something else. |
| • | The BASIC that is built into the motherboard, Cassette BASIC, cannot write/read BASIC programs to/from floppy disks (or hard disk drives). It supports the cassette port only. |
| • | The "Bytes free" figure that Cassette BASIC displays, is not representative of the amount of RAM fitted. |
| • | Not all ISA expansion cards will work in an IBM 5150. Ensure that any card you acquire is IBM 5150 compatible, and that it does not conflict with any existing card. |
| • | If you connect a 1.44M diskette drive to the stock IBM floppy controller, you will discover that you can read 720K sized diskettes. More information is at here. |
| • | On the motherboard, the BIOS ROM and BASIC ROM's have a special pinout, and can only be replaced by 27xxx series EPROM's if an adapter is used. More information is at here. |
| • | When upgrading the BIOS on a 16KB-64KB motherboard to the 10/27/82 one, the setting of switch 5 on motherboard switch block SW2 needs to be changed in most cases. More information is at here. |
| • | Aged tantalum capacitors are known to explode. That has happened to me many times, in the vast majority of cases, when I have acquired something that has not been powered on in years. If the motherboard, or expansion cards, are exposed to your face when you power them on, then consider wearing glasses of some sort. More information at here. |
| • | If the 5150's IBM power supply (PSU) becomes overloaded or underloaded, it will shut itself down, in order to protect itself. If that occurs, the PSU will not generate any of the output DC voltages. Note that the PSU's cooling fan will still turn if the PSU powers it via AC mains voltage (rather than by DC voltage). PSU overloading: Typically caused by a short circuit in one of the many devices (motherboard, keyboard, expansion card, hard drive, floppy drive) that use power from the PSU. In the IBM PC family, a tantalum capacitor is usually the culprit. If you believe that you are that situtation, try the diagnostic procedure at here. PSU underloading: The 5150's IBM PSU requires a minimum amount of loading in order to operate. The 5150 motherboard alone is usually enough of a load. |
