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IBM 5150 Power Supply Recreation

R

RHopple

Experienced Member
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Nov 30, 2017
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55
Hello all!

I just picked up a nice early 5150 with all original components! While I am waiting for some new RAM to arrive, I decided to test the power supply, which doesn't work. :( I have another power supply, but I want to replace the early one with a modern, more efficient one. The only problem, as many of you already know, is the lack of a -5V line, used mainly by the RAM. I was thinking a simple circuit, like the one I found here http://www.larsen-b.com/Article/230.html, could make a -5V connection, but I am no engineer and don't know if this would work. I'm pretty good with a soldering iron and would feel comfortable making that simple circuit, and maybe something a little more complex.

Is this a good solution, or is there something else?
 
The -5 on the 5150 is mostly used for very low current substrate bias. Use a small 3-terminal voltage regulator such as a 79L05 off the -12 line. It's a TO-92 package and will supply 100 ma, which, IIRC, is all the original 5150 PSU was rated for on that line. Attach it to the 5150 board near the power connector and you won't have to worry about the issue ever again.
 
Chuck(G) said:
The -5 on the 5150 is mostly used for very low current substrate bias. Use a small 3-terminal voltage regulator such as a 79L05 off the -12 line. It's a TO-92 package and will supply 100 ma, which, IIRC, is all the original 5150 PSU was rated for on that line. Attach it to the 5150 board near the power connector and you won't have to worry about the issue ever again.
Click to expand...

That sounds great! I’ll order one soon. Thanks for the advice!
 
I just picked up a 5150 with the 256K motherboard. If I want to update the power supply from the stock PSU, does it need -5V? Isn't the -5V mainly for the 4116 RAM chips in the older board?
 
Mostly, yes. IIRC there were a couple of early ISA cards that needed -5 also. It's been discussed here before.

The practical problem with the -5V line is that it's very low current, so not useful for a lot of general-purpose stuff.
 
Chuck(G) said:
Mostly, yes. IIRC there were a couple of early ISA cards that needed -5 also. It's been discussed here before.

The practical problem with the -5V line is that it's very low current, so not useful for a lot of general-purpose stuff.
Click to expand...

Doesn't the XT-IDE also rely on the 5v line? A while back I was hoping to power a 3.5" IDE drive directly off of it but, sadly, unless I was looking at the wrong documentation, there wasn't even an edge connector pad for the 12v.
 
Exceter said:
Doesn't the XT-IDE also rely on the 5v line? A while back I was hoping to power a 3.5" IDE drive directly off of it but, sadly, unless I was looking at the wrong documentation, there wasn't even an edge connector pad for the 12v.
Click to expand...

Nearly all ISA cards rely on +5V, the XTIDE being one. But few ISA cards (probably name them on the fingers of one hand) use -5V, which is what was being asked about. +12 and -12 usually find their way into serial interface cards for EIA-RS232C levels. But by and large, +12V is used on the early 5150 motherboard for the 16Kb DRAM Vdd and nothing else. Its primary customers are the motors and positioners of hard and floppy drives. Most later 3.5" drives don't use +12V any longer, but most hard drives do. There are some ISA cards that use the 12V (+ and or -), but they're not the rule.
 
The 5150 I have has a Seagate ST238 HD. I have an IBM FH 10 MB drive that I'd like to use, but I've learned that the PS is too weak at 63W. I have searched for PS dimensions of the IBM 5150, 5160, and 5170 to see if I could replace mine with a more powerful IBM PS, but have not had any luck. Does anyone know?

There's a 5170 PS on ebay right now that looks tempting, but only if it will fit.
 
The 5150 and 5160 use one size of power supply (usually called "XT" form), and the 5170 uses a larger one (usually called "AT" or "desktop AT" form. The later "tower" AT power supplies lacked the big switch)

Many third parties used to make power supply upgrades for both XT and AT form power supplies.

One way to identify desktop AT power supplies is that they usually have sort of an "overhang" on the side with the power connectors, in order to fit room for full sized AT motherboards.

I've seen a lot of people get confused about that on eBay. Heck, I've seen one person call an XT power supply a "Macintosh" power supply.
 
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