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Macintosh Portable M5120 Repair Tips

oldpcguy

Member
A friend of mine recently obtained one of these systems which initially did not work. The original power supply is dead so she researched and found a PowerBook battery can be used as a substitute. She also purchased a "rebuilt" battery as the original has long since passed. Initially it did not power up so the first thing that was suspect was the caps. She gave it to me to recap and that work has been completed (all caps, SMD and axial electrolytics). There wasn't much in the way of capacitor leakage so the board cleaned up nicely with no observable damage to anything.

After a partial reassembly I was able to coax the system to power on and eventually boot. However, the screen is not very bright (thinking I need to get the operating system up so I can set the brightness via the control panel) and now we have to disconnect the hard disk (assuming it's either bad or drawing too much power). I suspect the battery is not being recharged so as time passes and the power is consumed the system begins to exhibit more problems.

That said I now have it torn apart and would like to begin troubleshooting it. I've read a number of threads on this system as research but have not begun any troubleshooting. Power supply measurements are the first thing I want to test but I'm not sure how to go about doing this. I've read that it is not good to operate this system solely from the power supply so I am here to ask: How should I go about setting the system up to troubleshoot it? Is it OK to plug in the external power supply and attempt testing with just it? Or do I have to connect the battery (which would make troubleshooting challenging as to do that I need to have the top case connected and the wires for the connector aren't long enough to have it sufficiently out of the way)? Perhaps connecting to a bench power supply (I have an inexpensive one which does not limit current)? I have a voltmeter and DSO along with the schematics. However, I want to seek advice as to a proper set up for testing.

On another note the hybrid chip looks fine, I can detect no sign of damage and don't suspect any as the research I've done suggests the damage comes from leaking capacitors and there was little leakage from any of the caps let alone the ones in front of the hybrid chip.

Finally, on another note, I cut open the original power supply and removed all of the caps for testing with an EST meter. They all tested good with one of the 1000uf caps possibly being out of spec. No leakage or damage to any of the caps observed. I've purchased some replacement 1000uf caps but haven't purchased the others as it'll cost approximately $30 to get them. I've already spent $9.00 of the 1000uf caps and not sure if I should invest any money into the power supply. Any thoughts as to what I should do with it? Why did Apply glue this thing together?
 

SuperSVGA

Well-known member
However, the screen is not very bright
Is this the M5120 with the backlight addition, or the M5126? Only the M5126 had a backlight, though you could get a backlit display with accompanying ROM card to add a backlight to M5120

Is it OK to plug in the external power supply and attempt testing with just it? Or do I have to connect the battery (which would make troubleshooting challenging as to do that I need to have the top case connected and the wires for the connector aren't long enough to have it sufficiently out of the way)?
The system will not function properly without power via the battery connector, due to both the current requirement to spin up the hard drive as well as a line that goes directly to the hybrid that will not be connected to power without the top cover.

I would recommend a bench power supply and connecting directly to the board to test.
You can cut off the 4-pin connector from an ATX power supply, or buy an extension like this one and cut it.
If you don't have either of those as an option, you can solder a bridge across the battery input from the bottom of the logic board, and then clip on to the fuse to provide power that way.
 

oldpcguy

Member
Is this the M5120 with the backlight addition, or the M5126? Only the M5126 had a backlight, though you could get a backlit display with accompanying ROM card to add a backlight to M5120

I am not aware that it has been upgraded. Does the ROM card you mention plug into one of the slots between the modem and the memory upgrade card? There is a card there with a cable but I don't know what it is. Perhaps it's the upgrade? That would be nice as the screen was so dim I couldn't even take a picture of it once I had it powering on.

The system will not function properly without power via the battery connector, due to both the current requirement to spin up the hard drive as well as a line that goes directly to the hybrid that will not be connected to power without the top cover.

I would recommend a bench power supply and connecting directly to the board to test.
You can cut off the 4-pin connector from an ATX power supply, or buy an extension like this one and cut it.
If you don't have either of those as an option, you can solder a bridge across the battery input from the bottom of the logic board, and then clip on to the fuse to provide power that way.

That sounds like a plan. So if I were to supply power to through the four pin power connector I can perform testing without having to connect anything else? As an FYI I have no intention of testing with the hard drive connected (nor anything else) as I want to minimize any potential cause of issues (though I've already disconnected some of those items before taking it apart. Essentially I just want to have the logic board on the bench and performing testing without anything else connected / in the way. I suspect I'll be focusing more on power measurements and less so on digital logic signaling.
 

SuperSVGA

Well-known member
Does the ROM card you mention plug into one of the slots between the modem and the memory upgrade card? There is a card there with a cable but I don't know what it is.
Yes, the ROM slot is between the modem and RAM slots. The card has an 8 wire cable coming off for power and signaling to the backlight inverter.

So if I were to supply power to through the four pin power connector I can perform testing without having to connect anything else?
Yes, although the computer usually needs a keypress to power it on, so you may need to connect the keyboard if you want to test it past the powered off state.
 

oldpcguy

Member
Yes, the ROM slot is between the modem and RAM slots. The card has an 8 wire cable coming off for power and signaling to the backlight inverter.

It appears to be upgraded. Seven are white and the eighth is black? Unfortunately it looks as if the connector has been damaged as the black wire is hanging free.

Yes, although the computer usually needs a keypress to power it on, so you may need to connect the keyboard if you want to test it past the powered off state.

I can work with that, the keyboard is easy to attach and work with than the top cover assembly.

Thanks for the guidance.
 

oldpcguy

Member
Reviving this thread as I finally got some time to start troubleshooting this. Before doing so here are some updates:
  • I was able to obtain a working original Macintosh Portable power supply.
  • Using this I was able to somewhat charge the battery.
  • Using this somewhat charged battery I was able to boot the system and the backlight on the display turned on. A few seconds later the system went to sleep.
  • I have not been able to get the backlight to "reappear" but the system does boot to a desktop.
When reading the battery voltage from the Control Panel it is reading 6.0 volts. A meter shows it about the same. Is there a minimum voltage necessary to illuminate the backlight?

As a reminder this is an M5120 that appears to have been upgraded with the backlite display.
 

SuperSVGA

Well-known member
Do you have the Brightness control in the Control Panels? If you don't have the right system software installed, the backlight usually won't come on.

Here's System 7.1 for example:
IMG_0374.jpeg
 

oldpcguy

Member
Do you have the Brightness control in the Control Panels? If you don't have the right system software installed, the backlight usually won't come on.

Here's System 7.1 for example:
View attachment 49765
I do not as the original hard drive does not appear to function. It makes some initial noises, then attempts to spin up, and then spins back down. It repeats this process over and over.

I am currently booting it with a System 6.0.8 disk but I did not see the brightness control panel when it was booted. I am inexperienced with 6.0.8 and this Macintosh Portable. Should I be using a different system disk?
 

SuperSVGA

Well-known member
I do not as the original hard drive does not appear to function. It makes some initial noises, then attempts to spin up, and then spins back down. It repeats this process over and over.

I am currently booting it with a System 6.0.8 disk but I did not see the brightness control panel when it was booted. I am inexperienced with 6.0.8 and this Macintosh Portable. Should I be using a different system disk?
The system disk you're using is probably the bare minimum to run the computer, it doesn't have most extensions and other things you would get from the installer. You may need to use install disks and install to a floppy disk to get the proper system extensions.

What you're describing with the hard drive sounds like it's not getting enough power. At a good battery voltage (around 6.3V to 6.6V) spinning up the drive can draw around 2-3 amps. If it can't get enough current then the voltage will drop, usually causing the hard drive to reset, and sometimes the computer as well.
If your battery is too weak, even starting with the power adapter connected might not be enough to spin up the drive.
 

oldpcguy

Member
The system disk you're using is probably the bare minimum to run the computer, it doesn't have most extensions and other things you would get from the installer. You may need to use install disks and install to a floppy disk to get the proper system extensions.

I suspected that might be the case. What's odd is the backlight came on, briefly, when booted from this floppy disk. Is it possible I can copy the brightness CP to this floppy?

What you're describing with the hard drive sounds like it's not getting enough power. At a good battery voltage (around 6.3V to 6.6V) spinning up the drive can draw around 2-3 amps. If it can't get enough current then the voltage will drop, usually causing the hard drive to reset, and sometimes the computer as well.
If your battery is too weak, even starting with the power adapter connected might not be enough to spin up the drive.

I was thinking this too. The battery I am using is a manufactured one purchased off of Ebay (this is not my system and I did not buy the battery so I don't have the details). Reading the volage from the CP it showed 6.0 volts and that's what I measure with the meter. I have always suspected it may not be a good battery.

I do have a bench power supply and I get the impression some people have used one to power up their Portable. However I have been reluctant to do so because:
  • This power supply does not provide a means to limit the current. Given people say not to use a Portable with a PowerBook battery because it can supply, even slightly, more amps than the genuine power supply this would be the concern would it not?
  • Typically when connecting a source which is not rechargeable to something which does charge one needs to place a diode in the path to prevent the charge current from being applied to the source. Is this true of the Portable?
Thanks for all your help.
 

SuperSVGA

Well-known member
I suspected that might be the case. What's odd is the backlight came on, briefly, when booted from this floppy disk. Is it possible I can copy the brightness CP to this floppy?
You could likely copy it, I'm not certain if it needs some sort of extension as well, I'll have to look later. It may vary based on what system version you copy it from, try the one named "Portable" or something as well.

This power supply does not provide a means to limit the current. Given people say not to use a Portable with a PowerBook battery because it can supply, even slightly, more amps than the genuine power supply this would be the concern would it not?
You shouldn't use a PowerBook charger with it, as it may supply too much power to the charging circuit. It will run fine with a bench power supply pretending to be a battery, as long as it can supply enough current. Current limiting is a good idea when you don't know what condition a circuit is in. The battery can happily supply in the tens of Amps, however on the portable it passes through a 7 Amp fuse.

Typically when connecting a source which is not rechargeable to something which does charge one needs to place a diode in the path to prevent the charge current from being applied to the source. Is this true of the Portable?
I wouldn't recommend having the charger attached while supplying power to the battery terminals using a bench supply anyway, there's just no reason, but in most cases I don't think anything bad will happen since the bench supply is not a battery and can't really be overcharged. That diode would be more for cases where you're replacing a rechargeable clock battery with a lithium coin cell which cannot be recharged.
 

oldpcguy

Member
You shouldn't use a PowerBook charger with it, as it may supply too much power to the charging circuit. It will run fine with a bench power supply pretending to be a battery, as long as it can supply enough current. Current limiting is a good idea when you don't know what condition a circuit is in. The battery can happily supply in the tens of Amps, however on the portable it passes through a 7 Amp fuse.
This is the concern I have with using the bench power supply. Or is it different as I'd be connecting the bench power supply to the battery terminals instead of the charger port? Mind you I only want to do this as a test, by using the bench power supply I would know there is sufficient power available (unlike the battery which is, atm, suspect.

The plan is:
  • Disconnect the power adapter
  • Connect the bench power supply to the battery "fingers"
  • Ensure the cover switch that selects power from the battery or the 9 volt battery is set to select the battery.
Should I disconnect the 9 volt battery? What is the correct voltage I should set the bench power supply at?
 

SuperSVGA

Well-known member
This is the concern I have with using the bench power supply. Or is it different as I'd be connecting the bench power supply to the battery terminals instead of the charger port? Mind you I only want to do this as a test, by using the bench power supply I would know there is sufficient power available (unlike the battery which is, atm, suspect.

The plan is:
  • Disconnect the power adapter
  • Connect the bench power supply to the battery "fingers"
  • Ensure the cover switch that selects power from the battery or the 9 volt battery is set to select the battery.
Should I disconnect the 9 volt battery? What is the correct voltage I should set the bench power supply at?

Yes, connect the bench power supply to the battery terminals or the 4-pin connector on the board.
If you connect to the battery terminals you will need to have that switch pressed down. If your wiring allows there's a few different gaps where you can have the wires come out while the battery cover is on.

You don't need the 9V battery connected to test.

As for voltage, I usually do 6.4V but it doesn't have to be exact. Unless you're specifically testing the battery meter or cutoff I wouldn't go below 6V, and around 7.5V is the absolute upper limit.
 

oldpcguy

Member
Yes, connect the bench power supply to the battery terminals or the 4-pin connector on the board.
If you connect to the battery terminals you will need to have that switch pressed down. If your wiring allows there's a few different gaps where you can have the wires come out while the battery cover is on.

You don't need the 9V battery connected to test.

As for voltage, I usually do 6.4V but it doesn't have to be exact. Unless you're specifically testing the battery meter or cutoff I wouldn't go below 6V, and around 7.5V is the absolute upper limit.
Thanks for this information. As I had previously purchased an ATX connector and with it I was able to plug directly into the Mac Portable instead of using the battery compartment "fingers". With it I was able to boot the system from floppy but not the hard drive (see picture).

The power supply has an amp meter which was pegged above 1A when the hard drive attempted to spin up. Unfortunately this is an inexpensive power supply and is limited to 1A for its power output. I assume this is insufficient to power up the hard drive (the system appears to operate on 1/2A when just sitting there and floppy access causes it to move up to 3/4A)?

Here is some light testing I performed:

  • I set the bench power supply to 6.7V and the system, using the floppy disk, booted fine. It was this setup for which I took the pic. I also checked the battery level in the CP and it read full at this level. Adjusting it down to about 6.2V and the battery level in the CP showed a corresponding decrease in "charge".
  • I measured the battery terminals, unloaded, and they measured 6.26V.
  • With the battery out and the Portable power supply plugged in I measured the battery compartment "fingers" and read 5.22V.
Is the 5.22V read at the "fingers" the voltage I would expect to see in a properly functioning charge circuit?

Desktop Pics.JPG

In order to take this picture I had to have my bench lamp illuminating the screen, otherwise it's barely readable. Is this normal?
 

LaPorta

Well-known member
That means that the contrast is also likely down (adjusted by that very same control panel). I am sure someone can furnish an image (I can if you give me enough time).

Also…has this been recapped?
 

oldpcguy

Member
This is a pic of the battery which I have been using. The battery was purchased from Ebay as a replacement for the Macintosh Portable. It appears the seller may have 3-D printed a case and installed this battery and wired as appropriate. Reviewing the specifications it looks as if this is a 6V, 4.5Ah battery. Would this be sufficient to operate the system?

Internal Batterys.JPG
 

oldpcguy

Member
That means that the contrast is also likely down (adjusted by that very same control panel). I am sure someone can furnish an image (I can if you give me enough time).

Also…has this been recapped?
Yes, I recapped it. Initially it didn't work until I had done so. There was some slight leakage but nothing severe nor was anything damaged. Here's a pic with the Control Panel open and the Portable icon selected along with the battery status. Again I had to use the bench light in order to see it this well. Actually, with good lighting this may be sufficient (but I can see why they updated it to a backlite model).

Desktop with CPs Pics.JPG
 
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LaPorta

Well-known member
I’d definitely slide contrast all the way up. But yes, you need direct overhead light to be able to see it. Sunlight works too.
 

oldpcguy

Member
I’d definitely slide contrast all the way up. But yes, you need direct overhead light to be able to see it. Sunlight works too.
I ran it through the full range and it didn't really, nor did I expect it to, change the brightness of the display to make it easier to read in lower light. I wonder if the backlit display without the backlight on is darker than the non-backlit display. For the brief period I saw the backlight it looked very nice. Can't wait to get it that way again. Might be time to invest in a quality bench power supply.
 

SuperSVGA

Well-known member
The power supply has an amp meter which was pegged above 1A when the hard drive attempted to spin up. Unfortunately this is an inexpensive power supply and is limited to 1A for its power output. I assume this is insufficient to power up the hard drive (the system appears to operate on 1/2A when just sitting there and floppy access causes it to move up to 3/4A)?
All of that sounds normal. 1 Amp is typically good enough to run without the hard drive, but I typically see the total draw of the system around 2.5 Amps when the hard drive first spins up.
Is the 5.22V read at the "fingers" the voltage I would expect to see in a properly functioning charge circuit?
Was the computer running? There's quite a few different variables here, so it's hard to say which is at fault. The charger is limited to 1.5A, so the voltage will drop if the computer draws more than this. This is normal as the Portable is not designed to run off charger alone. It's possible the charger is bad as well and can't even provide that much current.
In order to take this picture I had to have my bench lamp illuminating the screen, otherwise it's barely readable. Is this normal?
I've noticed the backlit Portable's display is much harder to see with the backlight off compared to the non-backlit version. Likely just the difference in screen reflectivity due to the addition of the backlight.
 
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