IBM 5170  -  Known Problems/Issues

Floppy disk drive - Pin 34

In the earlier IBM 5150, 5155 and 5160, the supplied IBM floppy controller (photo) does not 'care' about pin 34 - because the controller does not monitor pin 34 of the cable connector.
However, in the IBM 5170, the pin 34 situation is much different. The controller supplied in the IBM 5170 monitors pin 34.

1.2M floppy drives in an IBM 5170 are required to generate a DISK CHANGED signal on pin 34, a requirement of the IBM 5170's BIOS. Failure to observe the requirement can result in corrupted floppy disks.

360K floppy drives in an IBM 5170 are not required to generate a DISK CHANGED signal on pin 34, possibly because the BIOS authors knew that most 360K drives cannot generate such a signal. However, some 360K drives generate a READY signal on pin 34. A READY signal is a problem for the 5170. If you intend to connect a 360K drive, the simple rule is, disconnect pin 34. Some 360K drives have a jumper that can be removed to achieve that (e.g. the JU-455-7 has an 'RY' jumper).

More information about this subject is in the 'Diskette Changeline' section on pages 781 and 782 (PDF pages 814 and 815) of the document here.  In the first sentence of that section, 'standard PC floppy controller' should have instead been 'standard AT floppy controller' to avoid confusion.

Deteriorated lubrication in floppy disk drive

It is often found that in 5.25" floppy drives that have not been used in many many years, that the lubrication in the drive has deteriorated to the point where it 'gums up' and stops the drive from functioning properly.

This is commonly seen on the rails that the head carriage slides up and down on. Deteriorated lubrication there results in the inability of the head carriage to move properly, or in extreme cases, not move at all. By hand (and with power off), you should be able to freely move the head carriage along its rails. You will experience some slight resistance presented by the stepper motor.

What is required is to clean the rails of the old lubricant, then followed by application of new lubricant. Myself and others have found a silicone based lubricant to be satisfactory. I sometimes use silicone spray, but there is a tendency for the spray to get to areas where it should not go. Otherwise, I use 'silicone dielectric compound', a particular type of silicone grease that I also use to get rid of any squeak sound from the drive's front panel latch.

If in any doubt, clean/relubricate the rails. The clean/relube is a worthwhile maintenance activity even if it doesn't fix a faulty drive.

Some cards designed for the 5150 and 5160 do not work in a 5170

Yes, it happens. One of the reasons is that the timing used in the 5170 slots is different to that used in the 5150/5160. Some cards can tolerate it and other cards cannot.

Some cards designed for the 6 MHz 5170 do not work in an 8 MHz 5170

Details of an example is in the document at here.

"I cannot fit a third half-height drive into the right cage."

That is because IBM did not design the 5170 for that. IBM designed the right cage for:
1. Two half-height floppy drives, or
2. One half-height floppy drive with a full-height hard drive (the 5170's optional second hard drive) underneath.

Nil or unreliable operation when using an XT-class power supply

Powering a 5170 motherboard using an XT-class power supply can sometimes cause problems.
Some possible symptoms:

* Type 1 motherboard with 01/10/84 BIOS does not start at all, with a POST card revealing failure of the 'Verify shutdown byte' test.  It is discovered that upgrading the BIOS to either the 06/10/85 or 11/15/85 revisions (where the test gets done later) is a workaround.  Of course, the proper solution is to use an AT-class power supply.

* Intermittent start-up of motherboard.

* Intermittent loss of CMOS SETUP configuration.

An AT-class power supply has a wire on pin 2 on plug P8; an XT-class power supply does not.  Diagram at here.  That is not the only difference.

Loss of time

SYMPTOM: Upon powering on the 5170, it is discovered that the clock has lost some time during the period that the 5170 was off. If left untreated, the rate of time loss gets greater and greater.

CAUSE: Low battery voltage.

NOTE: A 3.6 volt battery may be unsuitable for some 5170 motherboards (technical info)

On the 5170 motherboard, the real time clock (RTC) circuitry is essentially two blocks: an RTC chip and an oscillator that feeds (ticks) the RTC chip.
Of the two blocks, the oscillator is more sensitive to battery voltage.
When the battery voltage drops below a certain point, oscillator operation becomes intermittent - most of the time operating (ticking) but sometimes not.
As the battery voltage drops lower and lower, the percentage of time that the oscillator operates becomes lower and lower.

RAM failure in motherboard bank 0

Vintage RAM chips have a relatively high failure rate.
The failure of any chip in the 5170's first bank of RAM (bank 0) results in what appears to be a 'dead' motherboard.

Note that rather than a RAM chip actually failing, what might have instead happened is that a RAM chip has developed poor electrical contact with its socket.
And so the first thing to try is to simply to reseat all of the chips in bank 0 (wiggle each chip in its socket).

For the 5170, one way of diagosing a faulty RAM chip in bank 0 is by the use of a POST card (set to port 80h). If there is a failure in bank 0, the POST code of DD will be shown on the POST card. A breakdown of POST code DD is shown here.

If your 5170 motherboard is of type 1, then it has two banks of RAM, and therefore what you could try is swapping the bank 0 and bank 1 chips. If the motherboard then 'comes to life' and generates a 201 error on-screen, then a faulty bank 0 chip was the problem.
If your 5170 motherboard is of type 2 or 3, then it has only one bank of RAM. Swapping chips within the bank will not identify a faulty chip (though the removal/insertion of chips may fix a poor electrical contact problem).

CPU gets very hot

It is normal for the 80286 CPU on the 5170 motherboard to get quite hot, beyond what you may think is acceptable.
So that you can guage what I am writing of, look at the following table.

  Approx. temperature
on chip top
How long I can hold my
finger on the chip
80286-6  (6 MHz) 38 degrees Celsuis About 30 seconds
80286-8  (8 MHz) 50 degrees Celsuis About 5 seconds

The measurements were made about 30 minutes after power on (from cold), and during those 30 minutes, the 5170 was sitting idle at a DOS prompt. Ambient room temperature was about 20 degrees Celsuis.
It was interesting to see that the temperature ratio of 38:50 degrees matched well with the speed ratio of 6:8 MHz.
Of course, the finger measurement technique is very subjective, and therefore is not to be relied on as an accurate way of determining temperature.

POST error of 601

With the second (06/10/85) and third (11/15/85) BIOS revisions (BIOS info here), removing the IBM Fixed Disk and Diskette Drive Adapter and substituting a third-party floppy controller results in a 601 error during POST (Power On Self Test).
There is something in those revisions that expects the IBM Fixed Disk and Diskette Drive Adapter.
The first BIOS revision (01/10/84) does not have the problem.

Incompatibility with the XTIDE Universal BIOS

See the 2010 dated post on the Vintage Computer Forums that is at here.

In 2014, the same issue appeared to be seen by someone else. The post about that is at here.

More ...

More issues are listed in the 'Some known issues' section in the Vintage Computer Forums' wiki entry for the 5170.