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Attemping to fix an IBM PS/2 Model 50Z

Power supply does not work when connected, function of the fuse

Power supply does not work when connected, function of the fuse

The power supply has only one connector, and that is the 50-pin in the picture in my last post. It connects to the system board, and the drives, fan, and system board receive power from this 50-pin connector. It would be nearly impossible to test the power supply if it were connected to the system board.

The power supply still does not work when connected to the system board. I tried without the drives connected, but it still does not work. It only seems to work when it's not connected to the system board.

I can only conclude something on the system board is telling the power supply not to power on. I didn't see anything unusual about the system board except I had never seen a fuse on one before (picture attached). What does this fuse do? This is the only thing I see that I can easily replace.
 

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The power supply still does not work when connected to the system board. I tried without the drives connected, but it still does not work. It only seems to work when it's not connected to the system board.
I can only conclude something on the system board is telling the power supply not to power on.
Click to expand...
You can't rule out the power supply. I've seen power supplies that fail under load.

I didn't see anything unusual about the system board except I had never seen a fuse on one before (picture attached). What does this fuse do? This is the only thing I see that I can easily replace.
Click to expand...
On some motherboards, the +5V to the keyboard connector is fused. It might be the same for the model 50Z. Someone else might know for sure.
 
Out of ideas

Out of ideas

You're correct about the fuse, it's related to the PS/2 keyboard port.

The power supply might be failing under load, or maybe the system board is bad. I've run out of ideas; I don't know what else to do. I would prefer to restore the system instead of disassembling the system for parts, but I don't really want to spend too much more time or money on it. My heart really isn't into IBM PS/2s, so I wouldn't mind giving the parts or the whole unit to anyone who can restore it.
 
Troubleshooting 101;

Remove and/or disconnect everything but the video card and see if the supply powers up

If so, it's one of the things you've disconnected, if not, remove the video card and see what the PSU does.

If it powers up, it's the video card, if not, it's the motherboard.

If it's the motherboard, remove any options (co-pro) and try it.

If it still doesn't power up, remove the ram, one bank/set at a time and try it. Save the ram in the order you took it out.

When there is no ram left, put the bank/set that you took out FIRST in (intelligent substitution) and try it.

If available, substitute any CPU that will work in it with only minimal ram.

If it STILL doesn't work, it isn't going to.
 
I tried all that

I tried all that

I appreciate the troubleshooting tips, but I tried all that, and I did it again today. The power supply tests fine if not connected to the computer, but if the power supply is connected to the system board without any the drives, fan, internal speaker, expansion cards, memory, etc. plugged in, the computer will not turn on. The lights on the power supply do not illuminate (although I can hear a humming sound as if it was on).

It sounds to me the system board is bad. If the power supply is failing under load, shouldn't it still power up with the lights on if the system board has no drives, fan, internal speaker, expansion cards, memory, etc. connected to it?

In short, it doesn't seem to matter what is connected or disconnected from the system board, except for the power supply itself.
 
Allen said:
I appreciate the troubleshooting tips, but I tried all that, and I did it again today. The power supply tests fine if not connected to the computer, but if the power supply is connected to the system board without any the drives, fan, internal speaker, expansion cards, memory, etc. plugged in, the computer will not turn on. The lights on the power supply do not illuminate (although I can hear a humming sound as if it was on).

It sounds to me the system board is bad. If the power supply is failing under load, shouldn't it still power up with the lights on if the system board has no drives, fan, internal speaker, expansion cards, memory, etc. connected to it?

In short, it doesn't seem to matter what is connected or disconnected from the system board, except for the power supply itself.
Click to expand...

I've got other 50Z planars, if you want to go down that path...
 
Allen said:
I appreciate the troubleshooting tips, but I tried all that, and I did it again today. The power supply tests fine if not connected to the computer, but if the power supply is connected to the system board without any the drives, fan, internal speaker, expansion cards, memory, etc. plugged in, the computer will not turn on. The lights on the power supply do not illuminate (although I can hear a humming sound as if it was on).

It sounds to me the system board is bad. If the power supply is failing under load, shouldn't it still power up with the lights on if the system board has no drives, fan, internal speaker, expansion cards, memory, etc. connected to it?

In short, it doesn't seem to matter what is connected or disconnected from the system board, except for the power supply itself.
Click to expand...

If you went through the list systematically and you still don't have PSU activity, then one of the chips probably has a dead short to ground.

You could probably track down which one it is by placing a fingertip on each chip on the board. The one that burns the chip logo into your finger would be the one. :)

If you aren't handy at unsoldering chips from multilayer boards, I'd take IBM up on his suggestion.
 
No to ThreadJack, but Dru - I was planning on unsoldering the CPU off of one of my Morrow MD-3 mainboards, and installing a socket.

Will this be an issue? Anything I need to know? It's a standard 40-pin DIP NEC D780C Z80 clone...


T
 
also any one think his fdd may be bad? when the one went on my p70 nothing would happen except the power supply would hum. I thought the power supply had went, but like Allen's would also test good off system. it may be your drive is shorted or something. try running the computer with floppy drive disconnected. floppy disk drive being bad would also explain the reference disk problem. the drive i replaced in my second p70 would act like it was accessing. but wasn't and would some times give me an error and kick over into ibm basic.

btw sorry for lack of grammar its late i'm tired and i went to a charter school with questionable grammar teaching methods LOL.
 
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linemanduke said:
also any one think his fdd is bad when the one went on my p70 nothing would happen except the power supply would hum i thought the power supply had went but would also work off system may be your drive is shorted or something try with floppy disconected. would also explain the reference disk problem my previous p70 drive would look like it was accessing but was not and would some times give me an error aand kick over into ibm basic.
Click to expand...

???:roll:

--T
 
linemanduke said:
also any one think his fdd is bad when the one went on my p70 nothing would happen except the power supply would hum i thought the power supply had went but would also work off system may be your drive is shorted or something try with floppy disconected. would also explain the reference disk problem my previous p70 drive would look like it was accessing but was not and would some times give me an error aand kick over into ibm basic.
Click to expand...

Windage & elevation, d00d! No, wait...fall back and regroup...make that gramm'rage & punctuation!

--T
 
I won't try to fix the system board

I won't try to fix the system board

The unit will not power on even if just the floppy drive is disconnected. Thank you linemanduke for the offer, but since the original owner said it was not absolutely necessary to retrieve the data, I won't spend any unnecessary time and money to read the disk. I might be able to find another compatible PS/2 in my area to connect the hard disk. Otherwise, it's not a big deal.

Since I'm not an expert in electronics and have no experience in soldering and unsoldering connections, I will not attempt to fix the system board. I just want to be sure the real problem is the system board and not the power supply. I didn't know a system board can stop a power supply from working (or tell it not to power on properly). This appears to be the case.
 
Sharkonwheels said:
No to ThreadJack, but Dru - I was planning on unsoldering the CPU off of one of my Morrow MD-3 mainboards, and installing a socket.

Will this be an issue? Anything I need to know? It's a standard 40-pin DIP NEC D780C Z80 clone...


T
Click to expand...

Several.

You will have to apply heat to the pin longer than with, say, a double sided board to get the solder to melt all the way up the tube (via) and any given pin may be attached to several lands (I hate to say this) via the via.

Too little heat and it won't melt all the way and you won't extract all the solder. Too much heat and the pad you are working on will lift.

When you think the tube is clears, put the soldering tip against the pin (don't touch the pad) and push it one way then the other several times until it wiggles easily and the top side pad of the pin shows no solder. Then that pin is free. Repeat for all the other pins.

Power and ground are a bitch, but, you can keep the tip in contact for longer without damaging the pads as they are usually much bigger.

If the tube doesn't completely clear on the first attempt, don't keep re-heating and trying to remove the solder. Let it cool, re-solder it, let it cool and try the de-soldering again.

When you THINK you have all the tubes clear, gently pry up one end of the chip and then the other, but, not too far or too hard. If you do, you'll rip the the plating right out of the hole and you'll be screwed.

Rock the chip end to end while observing the pins. Any that aren't moving should be re-soldered and desoldered again.

And, finally, if you don't HAVE to remove a chip from a ML board, don't.

You guys thought this stuff was easy, didn't ya :)
 
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Allen said:
I didn't know a system board can stop a power supply from working (or tell it not to power on properly). This appears to be the case.
Click to expand...

Most switching power supplies contain what is called a "crowbar circuit". The purpose of this is to "crowbar" the PSU into shutdown if the draw on any of the voltages is abnormally high, as in the case of a dead short or high resistance short to ground, to keep the supply from going nova.

This is normal protective operation for a switching supply and reacts much more quickly than a fuse could. Waiting for the fuse reaction time would have you digging shrapnel out of walls, ceiling and body.
 
I actually fixed it

I actually fixed it

Allen said:
I thank everyone for the help and useful information--I learned quite a lot. I don't want to spend any more time and money trying to restore the system, so I will give away the PS/2 50Z's parts and options to anyone who would like them...
Click to expand...

I originally wanted to give up on this IBM PS/2 Model 50Z, but I had a change of heart. As I was disassembling it to give some of the parts away (in early May), I just felt it needed a second chance at life. At the very least it needed a new system board and diskette drive, but I wasn't sure if the hard drive was good or not. It would not have been worth spending any more money and time on it if the hard disk was bad, but I decided to take a chance.

I acquired a working system board back in May or June and recently found a working floppy drive. As a result, I now have a working IBM PS/2 Model 50Z with the original hard disk functioning and booting the system. I was able to retrieve the files for the original owner.

I acknowledge the encouragement and help from those of you who replied, including the offline encouragement and help from IBMMuseum, johnorun, linemanduke, and Lou - N2MIY. Thanks very much--I couldn't have done it without all of you.
 
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