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Help. I shorted out my 5155's power supply.

ibmapc

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I attempted to install a turbo 8088 motherboard in my 5155. The board powered up fine when hooked up externally, but I must have shorted something to ground when I mounted it in the system because the power supply fan did not start. So then I disconnected all the power leads (motherboard, disk drives, even the monitor) and flipped the switch on. Still nothing. So I then pulled out my multi-meter and found zero volts on all leads. I took the cover off and found the 3 amp fuse near the switch and removed it to test it (hoping for an easy fix) but found the fuse tested good. I can't see anything that looks burn't inside. When turned on it makes a single click that sounds like a small relay but no fan and no output. Can someone help? I'd be willing to ship it both ways if someone would be willing to look at it. Any sugestions?
 

Chuck(G)

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Maybe you already know this, but most SMPSUs won't work with no load at all. Use a hard disk drive as a dummy load (IDE is fine) and see if you get some action that way.
 

ibmapc

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Maybe you already know this, but most SMPSUs won't work with no load at all. Use a hard disk drive as a dummy load (IDE is fine) and see if you get some action that way.

OK, I tried that with two different IDE hard disks. It would not spin either one, but the one with the led blinked momentarily(less than one second).
 

Chuck(G)

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Sounds like you've got some digging to do in your PSU. It might not have been a motherboard short after all.

I'd start by checking capacitors for shorts.
 

ibmapc

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Sounds like you've got some digging to do in your PSU. It might not have been a motherboard short after all.

I'd start by checking capacitors for shorts.

I'm a little chicken around those big capacitors, especialy the ones with the "SHOCK HAZARD WARNING". Chuck, I see you're in the "Pacific Northwest". I'm in Albany, OR. How far away are you? Would you be willing to look it over for me?
 

modem7

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The 5155 PSU will start up with only it's motherboard (which is a 5160 motherboard) connected.
I know from measurements done a few years ago that a 5160 motherboard draws about 15 Watts.

I tried only an IDE drive connected to my 5155 PSU - no start (fan turns momentarily).
I tried two IDE drives - no start (fan turns momentarily).
I tried three IDE drives - no start (fan turns momentarily, and for longer than with just two drives connected).
I tried four IDE drives - PSU runs.

So your PSU may be good. Try connecting the original motherboard (or four IDE drives) and see how that goes.
 

MikeS

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Maybe even remove the MB from the case and put everything back the way it was when it worked, in case there's a short at one of the mounting screws. And of course make sure that the connectors have the black wires in the middle, i.e. next to each other. It's pretty hard to catastrophically "short out" a PC PS.
 

ibmapc

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You guy's are great! When I connected the original MB and flipped the switch, the fan came on and appears to run normal, so I turned it back off and connected the HDD with the LED and flipped the switch again and the fan came on, the LED lit and the drive spun up normally. So it would seam the PSU is fine. Just my trouble shooting methods were faulty. Glad I didn't buy that refurbished power supply from CODEMICRO!! Thanks everyone!!

Greg
 

Chuck(G)

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The 5155 PSU will start up with only it's motherboard (which is a 5160 motherboard) connected.
I know from measurements done a few years ago that a 5160 motherboard draws about 15 Watts.

I tried only an IDE drive connected to my 5155 PSU - no start (fan turns momentarily).
I tried two IDE drives - no start (fan turns momentarily).
I tried three IDE drives - no start (fan turns momentarily, and for longer than with just two drives connected).
I tried four IDE drives - PSU runs.

So your PSU may be good. Try connecting the original motherboard (or four IDE drives) and see how that goes.

I'll put it in my file that a big 5.25" hard drive may be required. :) (Many consume upwards of 30W)
 

modem7

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I'll put it in my file that a big 5.25" hard drive may be required. :) (Many consume upwards of 30W)
I didn't think one IDE drive would be enough, but it was certainly a surprise to me that four were required.
I've just done the same experiment on a 5160 PSU, and it required three IDE drives.
I guess that reflects:
1. These old switch mode PSUs require more load (minimum load) than modern switch mode PSUs, and
2. IDE drives draw less power than I thought.
 

Raven

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I got a 5170 recently with lots of documentation including that from an installed HDD upgrade. It mentions something called a "load resistor" which was placed in the casing of a 5170 without a HDD to create that minimum load, otherwise the system wouldn't function right. This resistor had to be removed when installing a HDD, which is why it was mentioned in the documentation.

I suspect that the same applies for older systems, load resistor or no, and that seems to be what you guys have come up with here.

Just sharing my two cents - a shame I didn't come across this thread sooner, as I might have saved some hassle, heh.
 

modem7

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I got a 5170 recently with lots of documentation including that from an installed HDD upgrade. It mentions something called a "load resistor" which was placed in the casing of a 5170 without a HDD to create that minimum load, otherwise the system wouldn't function right. This resistor had to be removed when installing a HDD, which is why it was mentioned in the documentation.
The load resistor you write of is mentioned (and there's a link to a picture) at the 5170 entry at our Wiki (VCWiki): http://wiki.vintage-computer.com/index.php/IBM_PC_AT_(5170)

I have a 5170 model 068 (no hard drive) in my house presently. I'm unsure why the load resistor is required, because the PSU fires up okay when I disconnect it.

I suspect that the same applies for older systems, load resistor or no, and that seems to be what you guys have come up with here.
Just sharing my two cents - a shame I didn't come across this thread sooner, as I might have saved some hassle, heh.
The issue wasn't about whether a load was present or not - it was about the amount of load required.
 

modem7

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That dummy load was a weird animal. Why the large metal cage? Maybe it acts as a heat sink.
The resistor is positioned in the cage middle, sitting on two thin metal legs (each with a cross section of about 1mm x 5mm). And so heat transfer from resistor to cage does not appear to be a major consideration.

The top plate looks to me to be a wonderful piece of over-engineering.
 

QuantumII

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Hehe, that was a cool looking dummy HDD. It's of the kind that can fool a seller into thinking "This PC has a HDD but it does not work". It could also be used as a decoration on a newer PC to give it a bit of a vintage look :)
 

Raven

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I have several 3.5" to 5.25" hdd adapters that are like that but designed to hold a HDD - like using them in modern boxes.. I even found a beige one by some streak of luck that matches my latest case's beigeness. They even have little light holes, a few of them even having a proper LED and plug for the rare IDE disk that had a header for a HDD light right on it, or you could run it to the motherboard. Most of them just had a clear colored plastic piece for a light mounted on the odd IDE disk to shine through, though.

One of them tricked me though, the first time I saw it.. It was a beige desktop case, and it looked like it had a 5.25" MFM disk. I expected some sort of cool XT or AT clone, but when I opened it it was a 486 and the HDD turned out to be an EMPTY adapter bracket, heh. The case was awesome on that machine, but unfortuantely had many broken clips making it fall apart.. I kept it so I can look out for another.
 

ibmapc

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OK, I got it working with the turbo 8088 MB. Thing is when I ran FALCON AT, I heard the what sounded like an arc and saw smoke so I powered it off immediatly and started taking things apart to see if the source of arcing could be found. I could not find any thing obvious, but the big transromer in the power supply looks funny.(see picture). Am I overloading the PSU with this 10mhz Turbo 8088 MB? Does that brown stuff on the transfomer look normal or has it been overheated? Am I risking PSU failure if I continue to use this MB?
 

Chuck(G)

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Nothing obvious that I can see. I doubt that a 10MHz 8088 board would make a big difference (are you running an 80C88 or V20 to keep the power down?). But aging components can and do make smoke. Power it up again and watch carefully. Often the component giving trouble will give itself away by the smell.
 
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