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What's going on? XT turns off.

L

Luke

Experienced Member
Joined
Apr 3, 2006
Messages
418
Location
Poland
After about a year i got my IBM XT out of basement. It seemed to work ok and I finally managed to put it on the internet. I was chatting on IRC when it turned off. Only PSU fan was working. I turned power switch down and after a while I turned XT on again and it loaded with no errors. It happend to me second time now when I was transferring data trough RS-232 between XT and my main comp.
What could be faulty?

Luke
 
Digged out another PSU from XT clone. 7120AT Maxtor would start and calibrate. Lower voltage is exactly 5V perfect! Not. Higher voltage is 11.2V more than 5% and neither 5.25" NEC nor Seagate medalist would start. When two disks are connected "yellow" voltage is 11-11.3V depends on disks connected. Is there anything that can be done to fix it? Faulty cap?
It's really hard to get across XT power supply in Poland. Getting genuine IBM one is nearly impossible.

Luke
 
Just take it apart and look carefully around the base of the caps for any signs of leakage, or swelling of the body.

Otherwise find yourself a Baby AT power supply (has the same type of connectors on the DC side) and transplant the internals to your XT PS case.
 
I think it's the best way to resolve the problem. A bit of soldering and Im back to vintage computers :)

Good to see you again dongfeng!

Luke
 
I transplanted the guts from an AT supply into an XT one. You need to make some legs for it to stand on as the AT supply board is smaller (I made some from wood glued into place). You also need to wire the power switch.

It's relatively straightforward, but took some head-scratching and about 3 hours!
 
Transplation was succesful, everything is working except fan. At first I connected it to 12V but it wouldn't spin up. I realized that this is 230V beast. Because it's riveted to PSU case I would like to keep it.
Specs of the fan: 230V, .070/.060 Amps, 50/60 Hz. Can it be connected to regular 230 from power socket? I think amperes are different..

Luke
 
You are working with 230 VAC and so of course, be very careful.

Yep, you can connect it just as long as the power source is capable of supplying the AMP rating
Click to expand...
If the fan is to be connected to the 230 VAC power connector inside the power supply, then the current is sourced directly from the house wiring, and the house wiring is quite capable of supplying the required current for a fan.

you might put a resistor there if it gets hot
Click to expand...
A 230 VAC fan supplied with 230 VAC will be operating as intended and as such, if the fan gets hot, then that is either normal for that fan or the fan is faulty (turns but is overheating).
If I had a 230 VAC fan that was faulty as I described (turns but is overheating), I would consider it a fire risk and replace it.
 
I had the PSU done waiting under my desktop to be installed for a long time but I got myself to install it today. Before I tested it with hard disks and motherboard, voltages were okay. XT was working with no problem for about one hour then the same thing as with the old PSU happened - everything turned off. I turned PSU off and on again but only fan started. The next time I tried to start the computer something exploded and it seems it's C58 cap (the one near power connector).

PSU is still working with proper voltages so I doubt if it was the cause of damage. Is it possible that the cap was causing turning off the system along with hard disk?
Anyone have specifications of C58 cap?
 
I don't recommend this=, but if you remove a card or change a dip switch while the power is on, sometimes the powersupply will switch off in response. I believe IBM had some kind of autoswitch for bad power situations. I have caused this myself (oops). I *think* that in the ref guide someplace there is a reference to this.

In other words, your power supply may be doing what it's supposed to be doing. There is a problem where one of your cards is not inserted properly, and it does not have full contact.

Try removing all cards including the display card, update the switch settings to match (so it matches the condition of no monitor and no drives), and then power on the system. Let it run for an hour or two. Repeat, adding one card at a time starting with the monitor, drives, extra memory, etc.

If I think of where I read that the power supply has an autokill built in, I will scan. Anyone else hear of this, or am I mistaken?
 
Psu

Psu

Well, some switchers do shut off on overcurrent, short, or non-good voltage conditions. Can't remember if the stock XT PSU does or not.

billdeg's idea is great, I would just add to unhook the PSU from the mainboard, and just leave a floppy drive hooked up to it. It's enough of a load to get it going, and it'll be easier on you rmainboard.

patscc
 
Actually the PSU that came with my XT when I bought it about two years ago wasn't IBM one. I tought that turnig off was caused by bad PSU so I put AT PSU in XT PSU case. AT one was working in my 386 for many years and I had no troubles with it.
Different power supplies - same problem. I think there's something wrong with motherboard or one of cards.

Now I have to replace blown cap C58 to do anything, what specifications does it have?
 
C58

C58

Luke said:
PSU is still working with proper voltages so I doubt if it was the cause of damage. Is it possible that the cap was causing turning off the system along with hard disk?
Click to expand...
Yes.

Luke said:
Now I have to replace blown cap C58 to do anything, what specifications does it have?
Click to expand...
C58 filters the -12V. The -12V is not used by motherboard components. It is routed to the expansion connectors for possible use by expansion cards.

You can run the motherboard without C58 in place, so use wire cutters to remove whatever is left of C58. Do you need to replace C58? I'm sure different readers of these forums will give different answers. Myself, I wouldn't be fussed about the -12V line.

C58 is a triple-lead 10uF 16V tantalum.
If you are seeking a close replacement (possibly different maker) then replacement details are are at: http://www.vintage-computer.com/vcforum/showpost.php?p=72153&postcount=38
Tantalum caps have polarity, but the three lead configuration means that this part can be inserted either way.

You could use a standard 2 lead 10uF 16V tantalum (rated at 16V or greater actually) if you wanted to, but you would need to observe polarity:
Inner hole = + lead of cap
Either outer hole = - lead of cap
 
It seems that the problem is gone now. I cut off the C58 cap and XT is working fine.
It's been running for about 4 hours today - transferring zipped 8088 corruption via COM took 3 hours :D.
Before the machine would turn off after 30 minutes.
 
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