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IBM Portable with AT Power Supply

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gobabushka

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Joined
Mar 29, 2011
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Palm Bay, FL
So. I finally got the IBM portable from a friend that I have been trying to get for 10 years! I also have since replaced the bad caps on the motherboard. Only problem is, the power supply is still bad. It makes a click when I flip the switch. The motherboard is good, as it fires up and POSTs when plugged into the modified AT power supply I have. What would be the best route to go for replacing the portable power supply?
 
gobabushka said:
Only problem is, the power supply is still bad. It makes a click when I flip the switch.
Click to expand...
Are you aware that the IBM 5155 power supply (PSU) needs to be adequately loaded in order for it to start?
Details at [here].

gobabushka said:
What would be the best route to go for replacing the portable power supply?
Click to expand...
One method is to swap the contents of the PSU with the contents from a different model of PSU, a PSU suitable for the purpose.
There is an earlier thread at [here] where some people have transplanted the contents of a 5150 PSU, or 5160 PSU, into the 5155 PSU.
Looking at the 5150/5160/5155 ratings at [here], I consider the 5150 PSU to be unsuitable.
 
I was running through the tutorial on how to diagnose a "dead" portable". I performed the diagnostic with just the motherboard outside the computer connected. I still heard the click, should I add more devices?
 
gobabushka said:
I was running through the tutorial on how to diagnose a "dead" portable". I performed the diagnostic with just the motherboard outside the computer connected. I still heard the click, should I add more devices?
Click to expand...
No, it should not be required. Per the 'IBM 5155 - Power Supply' web page that I pointed you to, the motherboard is known to be enough of a load. I had to ask the question because it was not clear in your first post, the situation in which your PSU "makes a click when I flip the switch."

gobabushka said:
I also have since replaced the bad caps on the motherboard.
Click to expand...
Presumeably, those were shorted tantalum capacitors. Which ones? C56 and C58? With that information, I can then add your motherboard to the list at [here].
 
I apologize for a late reply. I have been able to get my portable working again. Once I connected the SCSI hard drive and floppy, the system fired right up from the portable's power supply. I have since manufactured a null modem cable, and have been enjoying copious amounts of Wheel of Fortune! However, I have another question or two...how would I diagnose a bad bank on my AST SixPackPlus, and what would cause the floppy spindle to not actuate, but I am able to move it? And yes, I had two bad capacitors on the motherboard. Definitely add me for C56 and C68. I had a failure on both the -12v, and the -5v line. It should have been enough of a load, but the motherboard was not. Possible signs of trouble in the future? Thanks!
 
gobabushka said:
I have been able to get my portable working again. Once I connected the SCSI hard drive and floppy, the system fired right up from the portable's power supply.
Click to expand...
gobabushka said:
It should have been enough of a load, but the motherboard was not. Possible signs of trouble in the future? Thanks!
Click to expand...
Not necessarily. The table shown [here] is taken from the 5155 technical reference. I interpret that as IBM indicating that to guarantee that the power supply will start, a certain small minimum amount of +12V loading is required in addition to the +5V loading.

It is just that in practice, I (and others) have found the motherboard alone to be enough of a load. The only +12V load presented by the 5155 (5160) motherboard will be small; an uncharged capacitor on the +12V line. But the motherboard will not be presenting any load to the +12V line that is dedicated to the display unit, a load that the aforementioned table indicates is required.

So maybe your power supply and motherboard are within spec, just outside of the norm.

gobabushka said:
how would I diagnose a bad bank on my AST SixPackPlus,
Click to expand...
The first thing to do is to be quite sure that the configuration switches on the SixPakPlus are set correctly.
Next, re-seat all of the RAM chips within their sockets. That should fix any poor chip-to-socket connectivity.
If those do not rectifu the issue, then next, there are two possible methods:

1. Chip swap

Using anti-static procedures, swap RAM chips about, bank at a time. When the 5155 POST detects extra RAM, then you have just identified the faulty bank. Then, swap chip at a time to identify faulty chips.

2. CheckIt/DEBUG

This is using CheckIt diagnostic software in a particular way. If CheckIt will not run due to a lack of available RAM, then DEBUG can be used instead. Both techniques are described at [here].

gobabushka said:
and what would cause the floppy spindle to not actuate, but I am able to move it?
Click to expand...
First, is the correct type of cable in use? See [here].

gobabushka said:
And yes, I had two bad capacitors on the motherboard. Definitely add me for C56 and C68. I had a failure on both the -12v, and the -5v line.
Click to expand...
I have added your motherboard to the web page.
As evidenced by the page, a short circuit tantalum capacitor on the -5V line is uncommon.
 
If I read that page correctly, Drive A should be on the first connector. I am using the original controller and floppy drive. I should also say that I think spindle was the wrong term. I was tired when I typed that lol! The drive will read a floppy's directory, but the head does not actuate at all, yet I am able to move it freely with my hand.
 
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Ok. The floppy issue has been solved. I found a resistor pack and installed it. I then spent some time with the head armature, and now it will read and write floppies. Are there any howtos on how to disassemble the keyboard?
 
gobabushka said:
Ok. The floppy issue has been solved. I found a resistor pack and installed it. I then spent some time with the head armature, and now it will read and write floppies. Are there any howtos on how to disassemble the keyboard?
Click to expand...

I recently performed a thorough cleaning of this type of keyboard with the help of this tutorial: http://deskthority.net/keyboards-f2/ibm-5155-model-f-keyboard-t7644.html . I found it helpful to remove the key caps without damage by using two bent paperclips. And be careful you don't damage the space bar, since it can only be safely removed when you have the entire keyboard disassembled. Good luck!
 
I still need to recap my portable power supply. Does anyone have a shopping list of capacitors?

If not, I will eventually create one and share it here, likely with RS Components part numbers (will suit UK and Australian members and others with a little extra shipping involved).

Any suggested suppliers stateside, ideally offering industrial rated componants for longevity? Japanese made capacitors are also still the best, to my knowledge.

It's a pit that The portable's supply is not an easy item to remove, disassemble, recap and reininstall.
 
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