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Denniske1976
January 1st, 2014, 06:12 AM
Hi Guys...

First off: Best wishes to everyone for 2014! :-)

Second: I was fiddling around yesterday evening (the GF was working until 22:30 anyway) with an IBM XT (5160) that I picked up some time ago. It's from September 1985 and I was gonna fire it up after I had cleaned everything...

I switched the red lever and nothing happened :-( The fan from the PSU turns just slightly and that it, next to hearing a click. I took out the PSU and cleaned it, it looks like new now and nothing seems to be wrong with it. I connected an old Seagate ST-251 to it and it works! I had it running for about 30 minutes without any strange smells or sparks ;-) Then I put it back in the XT case, connected the old ST-412 that's in it and it still fires up... connected the full-height 360K floppy too and tried again: fires up. Then connected P8 and P9 to the mainboard and nothing again. Checked the mainboard for shorts and everything seemed fine, so I connected an old "normal" PSU (from a 486) to just the mainboard and fired it up, nothing again. After I also connected the ST-412 and fired it up again, there was a big POOF, some smoke and the top of C56 flying through the room ;-) So (as usual) it looked that's the problem and I snipped off C56 and it fired up with the AT/486 PSU. Then I connected the original XT PSU back to the ST-412, floppy drive and mainboard and tried again and it powered on as well...

So thinking all was OK now, I switched off the power and put in the cards that I had removed to check the mainboard out. Nothing fancy, just your average IBM MDA adapter, one Xebec HD controller and the standard IBM floppy controller (as seen in your local 5150 as well). Connected the floppy and HD cables, connected a keyboard and 5151 monitor and fired it up again... nothing!

So I started the whole process of removing the cards etc etc but it seems the mainboard is the culprit again. Everything works until I connect the mainboard, this happens with the XT PSU as well as the AT/486 PSU. Just a click and a minor turn of the fan and nothing. I checked the mainboard visually but all the other caps and tantalums etc seem fine: no cracks, no blackening or anything.

So, is this board dead and gone or is there anything I can do to test this with my multimeter over the 12V line or something? I think it might have something to do with C56 blowing up, but I've had that happen before and if I just remove it usually the boards seem fine then...

Can any of you help please? I'd hate to see this go to waiste :-(

Stone
January 1st, 2014, 06:45 AM
You can check the P8 & P9 board connector headers for shorts when nothing is connected to the board.

Denniske1976
January 1st, 2014, 06:47 AM
You can check the P8 & P9 board connector headers for shorts when nothing is connected to the board.

How's that done then? (sorry, I'm not that experienced with electronics)

Stone
January 1st, 2014, 07:04 AM
With the multimeter set to Ohms... the Ω setting. Probe every pin to ground and to every other pin in the header. You'll need a pinout diagram because many of the pins are repeated e.g. pins 5, 6, 7 and 8 are all ground and there are plenty of +5V pins there as well so, naturally, they would test positive for a short since they have a common source.

Here's a pinout diagram:

http://pinouts.ru/Power/MotherboardPower_pinout.shtml

billdeg
January 1st, 2014, 07:06 AM
not 100% convinced you don't have a bad card. what happens with all but the video card?

Stone
January 1st, 2014, 07:15 AM
Hey, the video card could be the culprit. :-)

Denniske1976
January 1st, 2014, 08:22 AM
Not a bad card, since they're all out... Just the mainboard and one harddrive connected to the PSU. Only the harddrive: PSU works, harddrive plus mainboard: nothing happens...

I'll try checking the PSU connector for a short and will let you know the results.

Stone
January 1st, 2014, 08:40 AM
If the drive works while the mainboard is connected there is no short -- at least not to ground. If there were, the PSU would shut down and the drive would stop spinning. So it seems the board is likely bad but not because of a short.

Denniske1976
January 1st, 2014, 08:48 AM
Well, tried some stuff with my multimeter and on the Ohm setting I don't know what I should read... I tried checking the voltages and they're weird:

The PSU connectors are correct when the mainboard is not connected, so everything that should read +5/-5 or +12/-12 reads that.

However, when I check the connectors with the mainboard connected (so P8 and P9 pin values on the mainboard) I read 0.4V on the 5V connectors, nothing on the white connector (-5) and about 1.0 on the blue connector etc.

So with P8 and P9 on the mainboard I get:

red/red/red = 0.38V
white = -0.04V
blue = 0.0V
yellow = 0.99V
red/orange = 0.39V

While without the mainboard connected everything reads fine at the PSU (so the PSU is delivering I guess)...

tezza
January 1st, 2014, 09:47 AM
Try the troubleshooting guide here.
http://www.minuszerodegrees.net/5150_5160/MDC/minimum_diag_config.htm

Tez

Denniske1976
January 3rd, 2014, 11:28 AM
Well, turned out that cap C58 was bad also... nothing to see about it but without P8 the PSU would power up (as advised on the troubleshouting guide at www.minuszerodegrees.net). Put all the cards back in and I can see the computer count up to 256K, then a message comes up that just says "Error. Press F1" and when I press F1 I get into cassette BASIC. It won't try to read from either the harddisk or the floppy drive so I guess there's something wrong with either the floppy controller too.

At least I now know that my 83-key keyboard is working, I tried it on another 5160 some time ago and it gave the 301 error... while a 101-key keyboard worked. But now this one works on this XT, so it wasn't the keyboard.

Thanx for all the help guys, I guess up next it figuring out why it won't read the floppy drive...

modem7
January 3rd, 2014, 12:27 PM
I have added this motherboard failure to the list at http://www.minuszerodegrees.net/vcf_motherboard_failure_history.htm

Denniske1976
January 4th, 2014, 04:57 AM
I have added this motherboard failure to the list at http://www.minuszerodegrees.net/vcf_motherboard_failure_history.htm

Your site is awesome!! If you ever need a mirror of that just let me know... BTW: maybe it's a good idea to include the remedy with the problem, as mine is listed as "bad C56 and C58", maybe include that removal of both solved the problem as with framers' from AUG13??

Denniske1976
January 4th, 2014, 07:13 AM
OK, the 601 error is gone now... I had the floppy drive connected to the first connector on the cable, turns out it's supposed to go at the second (last) connector of the cable. Didn't think about trying that and when I got it it was connected to the first one so I just put it back where it was ;-)

I now have a normal booting XT, just need to put in a boot floppy and see what's on the harddisk (since it won't boot from that maybe I need to LLF that).

modem7
January 4th, 2014, 12:18 PM
If you ever need a mirror of that just let me know...
In case I 'drop off the radar', I know of at least two forum members who are making periodical backups.


BTW: maybe it's a good idea to include the remedy with the problem, as mine is listed as "bad C56 and C58", maybe include that removal of both solved the problem as with framers' from AUG13??
In your case, both C56 and C58 were bad.
In Framer's case, all I know is that he removed both. So, there is the possibility that one of those caps was good.

Denniske1976
January 7th, 2014, 11:57 PM
Well, went ahead and the system boots fine from my DOS 2.10 floppy... only problem is that DIR C: gives me "invalid drive letter". Seems the hard disk is kaput? So I took out my IBM Advanced Diagnostics disc (version 2.02) and tried a low level format, that takes a few hours on a 10MB hard disk! Not good either right?

After the LLF finally finishes, and I do notice the disc actually formatting because of all the squeaking noise, activity LED burning/flashing and the actuator moving around... when I exit the LLF I get "1701 FIXED DISK ERROR". But not actually any explanation or reason. The disk doesn't really make any scary grinding noises or ticking sounds either. Trying FDISK from a DOS floppy just gives me "Error reading fixed disk" on every option (Create Primary Partition, Display Partition Information etc).

Anything else I can do here? Or is this one a goner? If it's a goner, any other drives compatible with this one and the Xebex #2 controller (I guess an ST-225 won't work, I have a few of those but I think I need Xebec #3 controller for that?).

modem7
January 8th, 2014, 12:30 AM
So I took out my IBM Advanced Diagnostics disc (version 2.02) and tried a low level format, that takes a few hours on a 10MB hard disk! Not good either right?
Not good. The low level format of a 10MB on a Xebec #2 should take just a few minutes, at the most. In the past, people reporting "hours" usually end up finding a setup problem (cable, jumpers, etc.)


After the LLF finally finishes, and I do notice the disc actually formatting because of all the squeaking noise,
Squeaking! That's not good. (Not accidentally formatting the mouse are you? :) )


when I exit the LLF I get "1701 FIXED DISK ERROR". But not actually any explanation or reason. The disk doesn't really make any scary grinding noises or ticking sounds either. Trying FDISK from a DOS floppy just gives me "Error reading fixed disk" on every option (Create Primary Partition, Display Partition Information etc).
If the low level format is taking more than minutes, then something is wrong at that stage, and it is my opinion, useless to proceed further.


Anything else I can do here? Or is this one a goner? If it's a goner, any other drives compatible with this one and the Xebex #2 controller (I guess an ST-225 won't work, I have a few of those but I think I need Xebec #3 controller for that?).
You can connect an ST-225 to the Xebex #2 controller, but only 10 MB of it will be used (specifically, the first 306 of its 615 cylinders). During the low level format, you will only see the stepper damper/flag/interrupter rotate half of full travel.

Denniske1976
January 8th, 2014, 01:42 AM
Squeaking! That's not good. (Not accidentally formatting the mouse are you? :) )

If the low level format is taking more than minutes, then something is wrong at that stage, and it is my opinion, useless to proceed further.

You can connect an ST-225 to the Xebex #2 controller, but only 10 MB of it will be used (specifically, the first 306 of its 615 cylinders). During the low level format, you will only see the stepper damper/flag/interrupter rotate half of full travel.

Well, with squeaking noise I mean that I can hear the disk do stuff... it kinda makes the same noise as the WD-325q in my PS/2 Model 30 but just a bit more silent and less audible because of the rotating noise (man are those ST-412 disks noisy!). Good to know I can actually connect that ST-225 so at least I have another solution... I might even have an original one with IBM full height faceplate and some kind of bracket so it fits in an XT, an old ST-225 with "Manufactured for IBM Corporation" sticker on it. I have that in storage somewhere probably and I guess I should be having a Xebec #3 controller as well somewhere since that came in a newer 5160 (a model with 20MB HDD, one FH floppy drive and that Model M keyboard with the LEDs missing for NUM, CAPS and SCROLL LOCK).

So I guess I'll just play around a bit with this old ST-412 and see what happens, when I have some more time I'll dig up that other ST-225... I think I have 3 or 4 of those actually and one being "Manufactured for IBM Corporation" that I saved because of the weird "half-height drive fits in full-height slot" bracket around it, and maybe the other controller as well...

So it's no use trying to oil it or maybe opening up and see if anything is stuck? Since it hadn't been used for about 15 years according to the guy I got it from...