My 486 Used to Cut Steel - DIED - Needs a New Power Supply!

[Jason Gearn]

I have a classic 1994 plasma/oxyfuel cutting system that we use to cut steel.  The picture below is 6" plate we cut using the system.  It is powered by a 486 with a floppy (now usb) system disk.  If I loose the disk (I have copies that I use regularly) or the computer, the whole system is dead.  Replacement costs are bare minimum $15,000 (probably closer to $30,000) and at least 2 months of production loss.

 

My power supply seems to have died after a power outage (not weather related).  Yes - I had it on a battery backup surge protection.  

 

I have replaced the power supply one other time at a cost of $1500 - yes you read that right.  It is 'special' with extra protections...  I still had to hot wire it (note the wire crimps to get back to my motherboard connector.

 

Currently, I have 12V and 5V on the rails, but 2 of the rails seem to be floating at around 150mV.  I am just starting to pull up pinouts and voltage levels, but I could use some help!  I am very capable, but don't have a lot of experience around this type of power supply.  

 

My first impression is use go out and buy dedicated 12V and 5V industrial grade power supplies and hook it up.  But - I'm worried that there are very particular protections on the power draw?  Enough to legitimately protect a MB if there were problems?

 

Thanks everyone!

Jason

 

 

[Dujith]

The last picture show an AT powersupply. Does that not work? or does it also have the same problems as the one in the previous pictures.

In the end its just an AT connection. And with all the retro stuff going on they are still being made  

 

Also, computers with ISA are still being made. Not that expensive even (relatively) 

[Yaxir]

This seems like a very interesting post ! 

 

I am eager to see what kind of options  the PSU experts will offer here.. 

 

That's a badass system you got right there

[CWALD]

Note that I do NOT consider myself an expert but here are my thoughts, I hope they help.

 

At that price I would just over speck a good Silverstone atx power supply and use an ATX to AT adapter. Just make sure you short the pin that tells the power supply that the computer is on if the adapter doesn't already do this (or route them to a switch if needed). jayztwocents has a few videos on how to short those pins, he primarily uses it to test cooling components before building/turning on an entire computer.

 

https://www.amazon.com/Silverstone-Technology-ET700-MG-Capacitors-SST-ET700-MG/dp/B0844JW1M6/ref=sr_1_25?crid=1K2GGH2BZN0XR&dchild=1&keywords=silverstone+technology&qid=1595598187&s=electronics&sprefix=silver%2Celectronics%2C212&sr=1-25

 

https://www.amazon.com/20-Pin-Power-Supply-Adapter-Cable/dp/B01EDGS0KI

 

Good luck.

 

[Guest]

2 hours ago, CWALD said:

 

At that price I would just over speck a good Silverstone atx power supply

 

LOL!  Why would it have to be a SilverStone PSU?  

 

It looks to be a run of the mill AT 486 motherboard.   No idea why a PSU would cost $1500.  I do see some additional wires that are NOT part of the motherboard.  Where do the brown/black wires head off to?

 

Any ways...

 

AT pinout, from top to bottom looking at your pictures, is:

 

1	orange	power good
2	red	+5 volts
3	yellow	+12 volts
4	blue	-12 volts
5	black	ground
6	black	ground
1	black	ground
2	black	ground
3	white	-5 volts
4	red	+5 volts
5	red	+5 volts
6	red	+5 volts

But it looks like you have a blue wire where there should be -5V and a white wire where there should be -12V.  So check those with a multimeter before assuming it's either standard or someone just didn't stick with the wire color standard.

 

Is it the  power good signal pin that's only coming up 150mV?

 

And yes... better PSUs have a multitude of protections.  They have what's called a "supervisor IC" and some are better than others... though not $1500 better.  Even an MCU only costs $5.

 

 

 

 

[Jason Gearn]

5 hours ago, Dujith said:

The last picture show an AT powersupply. Does that not work? or does it also have the same problems as the one in the previous pictures.

In the end its just an AT connection. And with all the retro stuff going on they are still being made  

 

Also, computers with ISA are still being made. Not that expensive even (relatively) 

Hmmm - I had forgotten about that!  I had bought that power supply a few years ago, but I got worried and bought the $1500 official replacement.  I was thinking that this power supply was already used up - but it was new.  I'm gonna try it out.

[Jason Gearn]

5 hours ago, CWALD said:

Note that I do NOT consider myself an expert but here are my thoughts, I hope they help.

 

At that price I would just over speck a good Silverstone atx power supply and use an ATX to AT adapter. Just make sure you short the pin that tells the power supply that the computer is on if the adapter doesn't already do this (or route them to a switch if needed). jayztwocents has a few videos on how to short those pins, he primarily uses it to test cooling components before building/turning on an entire computer.

 

https://www.amazon.com/Silverstone-Technology-ET700-MG-Capacitors-SST-ET700-MG/dp/B0844JW1M6/ref=sr_1_25?crid=1K2GGH2BZN0XR&dchild=1&keywords=silverstone+technology&qid=1595598187&s=electronics&sprefix=silver%2Celectronics%2C212&sr=1-25

 

https://www.amazon.com/20-Pin-Power-Supply-Adapter-Cable/dp/B01EDGS0KI

 

Good luck.

 

I really appreciate the input and the legwork on the amazon parts!  I do have a power supply switch for that purpose.  I will probably try the old AT supply I show in the picture in the meantime, then power up to new hardware with the adapter you found.

 

Thanks again!!

[Jason Gearn]

On 7/24/2020 at 11:17 AM, jonnyGURU said:

LOL!  Why would it have to be a SilverStone PSU?  

 

It looks to be a run of the mill AT 486 motherboard.   No idea why a PSU would cost $1500.  I do see some additional wires that are NOT part of the motherboard.  Where do the brown/black wires head off to?

 

Any ways...

 

AT pinout, from top to bottom looking at your pictures, is:

 

1	orange	power good
2	red	+5 volts
3	yellow	+12 volts
4	blue	-12 volts
5	black	ground
6	black	ground
1	black	ground
2	black	ground
3	white	-5 volts
4	red	+5 volts
5	red	+5 volts
6	red	+5 volts

But it looks like you have a blue wire where there should be -5V and a white wire where there should be -12V.  So check those with a multimeter before assuming it's either standard or someone just didn't stick with the wire color standard.

 

Is it the  power good signal pin that's only coming up 150mV?

 

And yes... better PSUs have a multitude of protections.  They have what's called a "supervisor IC" and some are better than others... though not $1500 better.  Even an MCU only costs $5.

 

 

 

 

Thank you for the input!  The other wire run off to power the floppy drive (now a usb floppy), and the front button panel at 5V.

The machine has now magically started working again.  I left it unplugged overnight - probably had to discharge some capacitors.  

I will work on a PSU replacement in the meantime.