• Please review our updated Terms and Rules here

Troubleshooting an XT

Plugged in I am getting 4.99 volts, and the same for when the PSU is disconnected, so I guess it's good.

Is there any way to diagnose if it is the motherboard that has gone, or the 8088? Since the 8088 had been moved to the 286 card in the past, I wonder if it has been damaged...
 
later PCs and XTs were said to ignore the dip switch settings (to some degree). Remember that it's the code imbedded in rom that does the "checking", so therefore with mulitiple upgrades, the importance of those dip switch settings can vary. The first thing you should do in any instance of a seemingly dead cpu is check the voltages coming off the power connector. Unplug it from the mobo, and verify that you got +5v, +12v and whatever else present on those pins. Don't worry about how those connectors get reattached to the mobo - the black wires are always adjacent and on the "inside" (on every XT or AT power supply in existence if things were done right). A fan spinning doesn't necessarily equate to a functioning power supply.

Black is always ground. Red is +5v IIRC. Yellow is +12v. One or the other lol. You're just checking, so there's no danger (if you do it right).

O right you'll need a multimeter and learn how to use it. Radio Shlock, Home Depot, even Walmart will have something in that department. With the test probes plugged in to take a voltage measurement (NOT a current measurement), connect the "hot" (usually red lead) to the pin you're curious about, and obviously with the power supply plugged into the wall and on, touch the ground (usually black) lead to the p/s case, thereby grounding it, and providing a reference (and circuit) to measure the voltage. I know this might sound confusing at first. I can *try* to assist further if you're going to try this. I could even give my phone number lol.

If the voltages are there (and not allowing for each voltage not having sufficient current to do it's job, not all that much of a likelihood I guess) your problem is on the system board duh. You can then resort to substitution (each chip at a time) or invest in some test equipment. Logic probes can still be found around, and probably cheap (have to be able to work with at least 5mhz signals or better yet 10). It would take significant work to trace down the problem by "logical" methods. Probably the best thing to do is find a spare mobo and keep the other one for parts. They can readily be had on ebay and such practically any day of the week.

I think regardless of dip switch settings you would get some notification from the speaker within 30 seconds of hitting the switch.

Another thing to do, and it's tedious, and not necessarily even a likely problem, is to inspect the traces on the mobo. One or more could have been severed I guess. Hope some of that helps.
 
Thanks Chris, I have checked the PSU and the voltages all seem to be fine and as expected.

Unfortunately early IBM's, let alone system boards on their own are a little hard to find over here in the UK :( but it looks like that's my only option! Given that the hard drive sounds awful, I think it would be better to look for another XT if I cannot resurrect this one...

Anyone in Europe with a working XT board (or even a clone board) they want to sell or trade??? :D
 
of course like an ass I missed the whole second page of the thread. Since you know how to check voltages, try check them while the the connector is connected to the mobo, and also try when it's not connected. There maybe be more then just +5 and 12v on some of those pins. They are color coded. If you get something strange, let us know. Some computers have weird voltages, like -5 and -12v. Some components require negatives for reasons I can't recall.
Sometimes to check a pin while the p/s is connected to the mobo, you might need to utilize a paper clip or somehting, by shoving it down between the wire and the plastic of the connector. Be gentle and be careful not to short (connect to metallic points that were never meant to be). Common sense will be your guide.
If you're say reading 5vdc on a particular pin when it's not connected, but something different when it is, the problem could be the p/s. Or a short somewhere as been suggested. That would require a visual examination of the circuit board (got an eye loupe handy?). It usually doesn't take too much investingating to determine if the power is bad though. Usually.
 
now this is just my own opinion, but in nearly all cases I avoid bothering with the older hard drives. I suppose I have 1 or 2 working ones in my stash though. They're too prone to crap themselves at any point. I'd prefer to plug and IDE hard drive (usually requires an older one though) even into an XT. A better solution in my book, though nowhere near as "authentic", is to uitlize a flash card reader - but though they're out there for things like the Commodore 64, I personally am not aware of such a reader for a PC. Can anyone enlighten? Flash card are becoming real cheap.
 
This guy I know, Benjamin Heckendorn (I'm sure at least one of you have heard of him) used a Compact Flash reader in his custom-built Atari 800 laptop. They can be put in anything!

Anyways, I used to have a hard disk that sounded like that (about 5 years ago; when I was too young to diagnose it). I don't remember hwat happened, but I think I might of torn it apart out of boredom. Sounds like a head came loose in it or something... Can't be the cause though, since the BIOS controlles everything during startup. But maybe it could've generated a random code that could've reflashed the BIOS with crap! Just a thought...
 
Last edited:
Chris2005 said:
now this is just my own opinion, but in nearly all cases I avoid bothering with the older hard drives. I suppose I have 1 or 2 working ones in my stash though. They're too prone to crap themselves at any point. I'd prefer to plug and IDE hard drive (usually requires an older one though) even into an XT. A better solution in my book, though nowhere near as "authentic", is to uitlize a flash card reader - but though they're out there for things like the Commodore 64, I personally am not aware of such a reader for a PC. Can anyone enlighten? Flash card are becoming real cheap.
Click to expand...

Now that is a good idea! You can buy a gadget that converts a Compact Flash to an IDE connection. I wonder if that would work? However, it seems rather hard to find an 8-bit IDE card.
 
Chris2005 said:
of course like an ass I missed the whole second page of the thread. Since you know how to check voltages, try check them while the the connector is connected to the mobo, and also try when it's not connected. There maybe be more then just +5 and 12v on some of those pins. They are color coded. If you get something strange, let us know. Some computers have weird voltages, like -5 and -12v. Some components require negatives for reasons I can't recall.
Sometimes to check a pin while the p/s is connected to the mobo, you might need to utilize a paper clip or somehting, by shoving it down between the wire and the plastic of the connector. Be gentle and be careful not to short (connect to metallic points that were never meant to be). Common sense will be your guide.
If you're say reading 5vdc on a particular pin when it's not connected, but something different when it is, the problem could be the p/s. Or a short somewhere as been suggested. That would require a visual examination of the circuit board (got an eye loupe handy?). It usually doesn't take too much investingating to determine if the power is bad though. Usually.
Click to expand...

It's a bit late here now, so I'll get on to checking those out tomorrow and report back then :D
 
Chris2005 said:
"Some computers have weird voltages, like -5 and -12v. Some components require negatives for reasons I can't recall."

From the IBM XT technical reference: "The -5 Vdc level is used for analogue circuits in the diskette adapter's phase-lock loop. the +12 Vdc and -12 Vdc are used for powering the Electronic industries Association (EIA) drivers for the communication adaptors."

The communication adaptors referred to will be synchronous/asynchronous cards (eg. RS-232, RS-422, etc.).
Click to expand...
 
dongfeng said:
'this is how the drive sounds when starting up (8mb)"

Most experienced readers will tell you that the 'rattling' sound coming from your HDD is not normal.
I have the same drive (an ST-412) in my IBM XT and so I can definately state that for an ST-412, the 'rattling' sound isn't normal.
Click to expand...
 
Although the 'power good' signal is a very reliable indication of PSU serviceability (particularly with the PSU under load), it is definately worth checking the voltages on P8/P9. For example, one of the wires out of the PSU may be broken.

You've relocated the 8088 from the "Tiny Turbo 286" board to the motherboard. I can see by your motherboard picture that it's in the correct socket and oriented correctly. Probably worth checking that none of the pins got bent on insertion.

Probably worth checking the all other socketed chips for bent pins as well (ie. you don't know the history of the board). I presume you already tried reseating all socketed chips.

If someone has earlier 'played' with the board, maybe the two ROM chips (U18/U19) were removed and accidently placed back in the wrong sockets.
 
Pointers to XT technical information were given earlier.

You may also find the attached document useful (eg. discusses the special requirement for cards plugged into slot 8).
The document specifically covers the genuine IBM XT.
 

Attachments

  • XT.zip
    33 KB · Views: 1
Motherboard plugged in only:

P8:
01 White: 5v
02 n/a
03 Yellow: 11.59v
04 Brown: -11.58v
05 Black: 0v
06 Black: 0v

P9:
07 Black: 0v
08 Black: 0v
09 Blue: -4.58v
10 Red: 5v
11 Red: 5v
12 Red: 5v

Hard Drive plugged in only:

P8:
01 White: 5v
02 n/a
03 Yellow: 10v
04 Brown: -10.25v
05 Black: 0v
06 Black: 0v

P9:
07 Black: 0v
08 Black: 0v
09 Blue: -4.03v
10 Red: 5v
11 Red: 5v
12 Red: 5v
 
I have reseated all of the chips on the motherboard, and I swapped the ram about too incase it was a faulty bank. ...but as you guessed... nothing.

The Technical Information guide is really interesting - reading it now!! Thank you :)
 
that board is a late model XT clone. It squished alot of functionality of a the original desigin (chips) onto that asic or whatever it is in the upper left quadrant (surface mounted). Terry could be right that there could be issues. In fact, I didn't study it though, it may be a different form factor altogether. Although I do own a few things with custom ic's, I tend to shy away and at one time would avoid them altogether. If I can't fix it, I may very well have no interest in keeping it around.
What you might want to do is place a (more or less) local ad in a newspaper or these little booklets they often give away (at least over here across the pond) for nuffin. There's bound to be people not too far away with old puters serving as tenements for silver fish and whatnot.
AND IF IF YOU SHOULD COME ACROSS A RESEARCH MACHINES NIMBUS PUTER PLEASE PLEASE SNIFFUL KEEP ME IN MIND. They're pretty common over there as far as things go I'm told. I'd love to see you find one. You could scrounge one of those GASP for parts, but I wouldn't advise it. Incompatible as all hell too lol, like a Tandy 2000, and n fact uses the same cpu (80186).
 
You must log in or register to reply here.
Back
Top