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5150 power supply options? (Bad 12V line)

1

1200XL M.U.L.E.

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May 9, 2021
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In a past post I described how I blew up a C7 capacitor on my 5150 motherboard by installed a CHRONOGRAPH RAMPORT card.

https://www.vcfed.org/forum/forum/g...b-a-story-and-a-blown-capacitor-c7-what-is-it

I can't get the computer to boot and I starVted wondering if blowing up the C7 capacitor and the card damaged the power supply. Just now I measured the +5V and +12V lines on one of the Molex power connectors like for a drive. The 5V line reads 5V on my multimeter but the 12V line reads 24V! When my floppy tries to spin up I see the 24V reading drop to 20V and then back up to 24V. I see the head move but the drive won't spin.

With this in mind, I think I need a replacement power supply for my 5150. Am I correct here?

What are my options? I searched "ibm 5150 power supply" on eBay and the results are few. What other options do I have?

Thanks!
 
1200XL M.U.L.E. said:
In a past post I described how I blew up a C7 capacitor on my 5150 motherboard by installed a CHRONOGRAPH RAMPORT card.
Click to expand...
I think that was coincidental.

(BTW. The particular C7 that failed is the one on the -12V line - see [here].)

1200XL M.U.L.E. said:
I can't get the computer to boot and I starVted wondering if blowing up the C7 capacitor and the card damaged the power supply. Just now I measured the +5V and +12V lines on one of the Molex power connectors like for a drive. The 5V line reads 5V on my multimeter but the 12V line reads 24V! When my floppy tries to spin up I see the 24V reading drop to 20V and then back up to 24V. I see the head move but the drive won't spin.
Click to expand...
If the +12V really is at +24V, you should be worried. Components using +12V may be damaged.

If your PSU is an IBM one, then I would have expected the PSU to sense the over-voltage then shut down to protect itself and protect connected devices.
(No DC voltages out, although the fan will still turn if AC powered).

On the 64KB-256KB 5150 motherboard, there is only one component using the +12V, and that is one of the C7 capacitors - see [here]. C7 is 16V rated. 24V on that C7 would really be pushing that rating, and it could explode.

I am thinking some kind of measurement related problem. Refer to the motherboard photo/diagram below. What DC voltage do you measure between one (your choice) of the ground pins, and the +12V pin? (Pay attention to the red text in the photo/diagram.)

p8_p9_pinout.jpg



1200XL M.U.L.E. said:
With this in mind, I think I need a replacement power supply for my 5150. Am I correct here?
Click to expand...
Too early to tell. Let's see what the result of the motherboard measurement is.
 
modem7 said:
I think that was coincidental.

(BTW. The particular C7 that failed is the one on the -12V line - see [here].)


If the +12V really is at +24V, you should be worried. Components using +12V may be damaged.

If your PSU is an IBM one, then I would have expected the PSU to sense the over-voltage then shut down to protect itself and protect connected devices.
(No DC voltages out, although the fan will still turn if AC powered).

On the 64KB-256KB 5150 motherboard, there is only one component using the +12V, and that is one of the C7 capacitors - see [here]. C7 is 16V rated. 24V on that C7 would really be pushing that rating, and it could explode.

I am thinking some kind of measurement related problem. Refer to the motherboard photo/diagram below. What DC voltage do you measure between one (your choice) of the ground pins, and the +12V pin? (Pay attention to the red text in the photo/diagram.)

p8_p9_pinout.jpg




Too early to tell. Let's see what the result of the motherboard measurement is.
Click to expand...

Hi modem7 !!

Thanks for the reply. I will need to remove the motherboard from the case to measure the voltages from the bottom of the board. That will be my project tonight and tomorrow night.

Since it is easy to do, I decided to measure the open circuit voltage output of the power supply just to see what comes out. I noticed the power supply runs much quieter without the motherboard connected to it. The fan spins but like a whisper.

The +5V and +12V read as expected but my -5V is actually -4V and my -12V is actually -10V.

Anyways ... lets see how far I get tonight. :)
 
I found a thin probe lead that allows me to contact the wire crimping inside the motherboard power connector! This means I can measure the voltages from above and there is no need to remove the motherboard from the case. However, I must be careful. It makes me feel like a surgeon :)

The +5V remained at +5V.

The -5V now reads -9V! This is very different than the open circuit -4V I was reading earlier.

The -12V reads -22V.

The 12V reads 24V.

I also measured the Power Good line relative to ground. There is +5V present.

Here is a picture of the top of my power supply.

powersupply.jpg
 
1200XL M.U.L.E. said:
The +5V remained at +5V.
The -5V now reads -9V! This is very different than the open circuit -4V I was reading earlier.
The -12V reads -22V.
The 12V reads 24V.
I also measured the Power Good line relative to ground. There is +5V present.
Click to expand...
So, measurements under the load of the motherboard.
A decent power supply would have shut down when it detected the over-voltage situation.
I don't know where you live, but is the PSU's 110V/220V switch correct for your location ?
If so, it sounds like you need a new PSU.
 
sounds like that power supply needs to be thrown in the trash before you destroy your disk drives/soundcards/serial ports
 
Hi modem7 and maxtherabbit !!

Yes, my power supply input power is set to 110V for my location here in the US.

It sounds like my power supply is toast and I need a new unit. I typed in many searches into eBay and I think I may have found one. No picture is shown for this supply but the price is low.

https://www.ebay.com/itm/114325272031?hash=item1a9e5135df:g:tigAAOSwhhJfICfd

I think this is a 63W supply. Would this be adequate for running my 5150 with cards but no hard drive? I am thinking of one day getting a XT IDE and use that as my mass storage device.

Next up would be these two units.

https://www.ebay.com/itm/194221282588

https://www.ebay.com/itm/153434293436

One of them says it can supply 200W of power, which should more than enough.

Would any of these fit the 5150 case cut-outs and holes?

Thanks!
 
1200XL M.U.L.E. said:
No picture is shown for this supply but the price is low.
https://www.ebay.com/itm/11432527203...gAAOSwhhJfICfd
I think this is a 63W supply.
Click to expand...
IBM part number 6447195 is showing in multiple places as 63W (63.5W)

1200XL M.U.L.E. said:
Would this be adequate for running my 5150 with cards but no hard drive? I am thinking of one day getting a XT IDE and use that as my mass storage device.
Click to expand...
Should be.

1200XL M.U.L.E. said:
Next up would be these two units.
https://www.ebay.com/itm/194221282588
https://www.ebay.com/itm/153434293436
Would any of these fit the 5150 case cut-outs and holes?
Click to expand...
Not my area of expertise. Someone else here may comment.
 
1200XL M.U.L.E. said:
Hi modem7 and maxtherabbit !!

Next up would be these two units.

https://www.ebay.com/itm/194221282588

https://www.ebay.com/itm/153434293436

One of them says it can supply 200W of power, which should more than enough.

Would any of these fit the 5150 case cut-outs and holes?

Thanks!
Click to expand...
Judging from the pics, yes they would both fit the chassis.

Not sure about that one-piece motherboard harness plug on the 'ROC' unit though. Also both of them are priced rather extremely
 
I ended up buying the CPI unit. It's the one with the two separate power connectors. That supply was also only a little bit more than the IBM 63W supply.

Finger crossed, let's hope it works! :) I'll keep the forum posted.

Thanks!
 
I received the CPI labeled power supply from Recycled Goods on eBay and installed it inside my 5150.

It seems to work!

First, I tested the open circuit voltage levels on the device power connectors. +5V measured to +5V but +12V measured a bit low at +11V or so. The motherboard power connectors did not register anything when not connected to the motherboard.

Then, I connected the power supply to the motherboard and to the original full height floppy drive. Upon turning on the supply, I heard a nasty click-click-click coming from the power supply. I shut down quickly. My first thought was to disconnect the full height floppy drive and I did so. When powering up again the monitor showed a cursor! Hooray! :) I saw the 301 error code since I still do not have a proper keyboard. Then the computer went to IBM basic! Hooray again! :)

So it looks like the full height floppy drive burned out from the original power supply. Now I need to go hunting for a floppy drive replacement. Again. Such is life. ;)

Oh, before I forget! This CPI power supply uses some sort of larger screw for attaching to the case. I happen to have one of these larger screws but I need three more. What kind of thread is it?
 
Last edited:
Hi jafir !!

I apologize for not replying sooner to your post with your recommendation.

I replaced the the C36 and C37 capacitors, reconnected the drive, and powered on the computer. The power supply spun up and I saw a cursor on my screen! Hooray! :)

I tried to trace the capacitors and it looks like they they simple filtering caps between power and ground to smooth out ripples. Is that right? I tried to verify this using the SAMS Computerfacts Service Manual for the TandonTM100-2/2A but I could not find these devices on the schematic. See sheet 11.

https://www.manualslib.com/manual/1020775/Tandon-Tm100-2.html#product-TM100-2A

If these really are simple filtering capacitors then I am going to guess that they failed to a short-circuit state when my previous power supply failed.

Going further, the drive had a really hard time booting a MS-DOS 3.30 disk I formatted in my Epson Equity 1+. The drive was filthy so I decided to clean it. Yuck, there was all sorts of oil and grime everywhere. The head rails were bone dry too. After the cleaning the drive wouldn't boot at all. :-( I kept seeing "Disk Boot Failure" messages. :-( Maybe I didn't let all the alcohol dry before powering up the drive. I kept pressing the space bar to repeat booting. After 20-something retries I heard the head move. Then after 5 more tries I heard the head move twice and then thrice. I tilted the drive on its side to check the speed. The strobe bars for 60Hz were stable. I set the drive back down but I set it down such that the spindle wheel was touching the case!! :rolleyes: You can guess what happened next. I pressed the space bar and the drive flew off and nearly fell onto my motherboard! :nervous:

But .. guess what happened after that? The drive booted. Well ... sort of. :huh: I got a weird messaging saying I had a bad command line interpreter. Then I soft reset the computer and rebooted from the beginning. This time the computer booted to a DOS prompt! :)

I tested the general functionality of the drive by formatting a disk on it, writing to it, and reading it back on my Epson. Then I did the reverse by writing on the Epson and reading it back on the 5150.

I also copied half of the disk (180kB worth of files) to the unused portion of the disk in order to fill it up. This tested the reading of the original 180kB. Then I read it all back on the Epson.

The only other big boo-boo I made here is the value of the capacitors I installed. I understand they were suppose to be 4.7uF. When I reexamined what I installed I think I put in 47uF capacitors! My eyesight is bad and I didn't notice. How much trouble do you think I am risking here?

(And to think ... all this started with a wonky power supply!)
 
I don’t know enough about electronics to answer your questions.

Was this faulty floppy drive connected to your old power supply when you were measuring 20+ volts on the 12 volt? I’m curious what it would measure without a short. Perhaps instead of shutting down like it should, it somehow misbehaves and that why you got 20 volts? Do you have anything you don’t value that could supply a bit of load to try and see how the old power supply behaves? Maybe a more modern ide hdd that isn’t worth much. (Perhaps what I’m suggesting is impossible, so if that’s the case, ignore me, as I said I don’t know much about electronics right now)
 
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