IBM XT Locking Up

[mattnb]

Hi there!

I recently got into the vintage PC game when I picked up an IBM XT and a Sharp PC-7000.

The IBM is supposed to have 320kB RAM but the actual amount is unknown. The hard drive was also removed, so it just has the two disk drives. I don't have any disks, so I'm stuck with PC BASIC for now.

The PC will POST, although sometimes it will display something like

507F 201
301

This message isn't always the same.

The main issue I'm having is intermittent and not caused by any one action. The PC will lock up and no more inputs can be made. It will do this whether I'm actively using it or not. If I leave the PC for 5-10 minutes and come back, it will usually be locked up. Other times, I've input commands and the video feed actually cuts out, almost like the PC is rebooting, but it never does.

Looking for any advice on this issue and any advice for a new collector in general. My other main question at this point is what's the best way to go about getting software for this. Perhaps a floppy emulator?

[T-Squared]

201: Your RAM may be faulty.
301: Your keyboard may be bad.

The lockup may be caused by a bad tantalum.

[modem7]

Hi there!

Welcome to these forums.

... when I picked up an IBM XT ... The PC ...

Rather than writing, "The PC", it is better to use, "The XT", otherwise some people will get confused, thinking you have an IBM PC.

The IBM is supposed to have 320kB RAM but the actual amount is unknown.

There is lots of IBM XT (IBM 5160) information at minuszerodegrees.net

The information there will enable you to identify the type of IBM XT motherboard you have, and how much RAM is fitted to the motherboard.

As for identifying any additional RAM, i.e. on card/s, working out the amount relies on us identifying the cards in your XT.
Are you able to post photos of the cards?
Once the cards are identified, and the one/s providing RAM established, reference to card user manuals, etc. will inform us as to exactly what RAM is being card-provided.

The hard drive was also removed, so it just has the two disk drives. I don't have any disks, so I'm stuck with PC BASIC for now.

If you are in Australia, I can freely post to you a DOS boot floppy (360K sized).

The PC will POST, although sometimes it will display something like
507F 201
301
This message isn't always the same.

In what you quoted, there is a 201 error and a 301 error. An explanation of those, and other on-screen errors that you may sometimes see, is at [here].

The main issue I'm having is intermittent and not caused by any one action. The PC will lock up and no more inputs can be made. It will do this whether I'm actively using it or not. If I leave the PC for 5-10 minutes and come back, it will usually be locked up. Other times, I've input commands and the video feed actually cuts out, almost like the PC is rebooting, but it never does.

Many possible causes.

Any battery leakage about? (Leakage [example] from the battery on a real-time clock card can cause headaches.)

Cables from the power supply, plug into two connectors on the motherboard. I suggest that you re-seat those connections a few times in case of poor connection.

It would be interesting to see if the symptom appears with some of the hardware removed. Try the following configuration:
* Power supply
* Motherboard
* Keyboard
* Video card + monitor (all other cards removed)
Expected at power-on is a 601 error, but press F1 so as to continue into Cassette BASIC.

As member T-Squared alluded to, you may have a capacitor (or other component for that matter) that is 'breaking down'. You may be coming back to us later with something like:
* A tantalum capacitor failed violently, and now the intermittent symptom has gone; or
* Now the XT fails to POST at all [common is a tantalum capacitor failed short-circuit, overloading the power supply].

My other main question at this point is what's the best way to go about getting software for this. Perhaps a floppy emulator?

Some methods are at [here].

For example, per [here], you have the ability to connect a 1.44M diskette drive to the IBM provided floppy controller, and then read/write 720K sized diskettes.

[Timo W.]

Since you also get a 301 error: are you sure the PC really locks up and it's not just the keyboard stop working? Because 301 means faulty keyboard anyway. Could be just a bad contact or broken wire in the keyboard cable. The DIN connector on these is also known to fall apart with age.

[modem7]

Because 301 means faulty keyboard anyway.

In an IBM 5160, the 301 error means that the keyboard test failed.
Certain failure modes of the keyboard interface circuitry on the 5160 motherboard can result in a 301 error.

[Timo W.]

While correct, chances that a 301 error has to do with a bad keyboard are quite a bit higher than having the fault on the motherboard. But the point was about whether or not the XT is really locking up. It may just seems so when the keyboard stops working while using it.

[mattnb]

I want to thank everyone for their thoughtful replies. I'll pull everything apart this week and return with photos. I definitely saw battery corrosion on at least one card, so I'll start making a list of components that need replacing.

As far as the 301 error, I think that was more of a PEBCAK thing. That said, I'll be on the lookout for error codes with each boot.

[SpidersWeb]

Not sure if it helps, but like 10 years ago-ish, I had a model F keyboard where one of the little rocker plates was kind of misaligned/not sitting right. This caused 201 (and maybe 301, I can't remember if I'm honest) errors on POST but the machine was operable and the keyboard worked, until at random times it'd start throwing garbage at the computer and would crash MS DOS, requiring a power on/off cycle to recover. Sometimes this would happen when I wasn't anywhere near the keyboard.

I've never had DOS crash from just holding down a key, but this would somehow take it down.

Stripping the keyboard down fixed the issue, as did using another keyboard.

Not saying that's what it is, just wanted to throw that in.

[modem7]

While correct, chances that a 301 error has to do with a bad keyboard are quite a bit higher than having the fault on the motherboard. But the point was about whether or not the XT is really locking up.

Yes, but you wrote, "Because 301 means faulty keyboard anyway.", an incorrect/misleading statement. If not pointed out, some readers (now and later) will learn incorrect information. And sometimes that has financial implications.

[modem7]

Not saying that's what it is, just wanted to throw that in.

Yes, various possibilities. For example, at [here] is described a 5150 that was displaying 201/301/131 errors, and the cause turned out to be a RAM card.