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M5126 Macintosh Portable Sad Mac (0x14/0xCD36)

PacificState

Well-known member
I'm trying to rescue an M5126 portable which formerly wouldn't start up at all - and so the first thing I did was recap.

I've tried to avoid reassembling in full until I'm sure things are working, so I've carefully reconnected (with layers of insulation!) the battery holder on top of the PCB, along with the display and floppy (no keyboard or HD). After inserting a working battery - I'm now greeted with a Sad mac and an 0x14 / 0xCD36 error combo.

According to http://web.archive.org/web/20090617213904/http://support.apple.com/kb/TA46376?viewlocale=en_US, this is 'During a send, Power Manager did not start a handshake') - and, while I can (and should) go back and check the caps, I'm wondering if the power manager is toast as it seems to be a common issue. Does anyone have any more suggestions (e.g. as to whether the machine would be happier in a more complete state of assembly)? Thanks!
 

PacificState

Well-known member
Thanks! I dug a bit deeper:

- The traces actually look OK when I buzz them out ;( I've attached an image - this is right after removing the caps (see below) and I haven't cleaned the pads up yet.

- After retrying a few times, I'm getting some intermittent behaviour in terms of booting between the Sad Mac and a corrupted screen (which I *think* is actually what happened before the recap). It's honestly slightly reminiscent of https://68kmla.org/bb/index.php?threads/mac-portable-m5126-doesnt-boot-after-recap.39839/.

One error I did make initially is to use tantalum caps which were slightly too large. Given I'm a bit wary of having created a short as in the thread above, I have some more dimunitive caps on order which I'll swap in (I have hot air and a very narrow iron tip, so it's easy enough).

Any suggestions as to what to pursue, or should I wait for the correctly-sized caps and retry?
 

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techknight

Well-known member
Did you use a good battery with the system? these machines need a nice strong battery or they wont work right.
 

PacificState

Well-known member
Thanks. The new smaller caps arrived, and are installed. With a fully charged battery (verified in another Portable), I get a boot chime then either the same Sad Mac error or a blank screen. If the traces are good, is there anything else I can check?
 

PacificState

Well-known member
Progress: I hadn't swapped *all* of the caps over, only those by the power manager - with the three at the top right swapped, it now boots to the checkerboard and disk prompt! However, there's at least one issue - a vertical line just over a third of the way from the left. Separately - the backlight only came on the first time it booted, and not subsequently. Is this where I disassemble the display and check connections?
 

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techknight

Well-known member
Progress: I hadn't swapped *all* of the caps over, only those by the power manager - with the three at the top right swapped, it now boots to the checkerboard and disk prompt! However, there's at least one issue - a vertical line just over a third of the way from the left. Separately - the backlight only came on the first time it booted, and not subsequently. Is this where I disassemble the display and check connections?

Try cleaning the zebra stripes on the panel, otherwise its likely just bad. Although i think those panles use physical drive ICs, so if you can narrow down which IC it is you can replace it and see if it comes back.
 

PacificState

Well-known member
Thanks - I tried cleaning the zebra stripes, albeit only on the top side; it wasn't clear to me that they could be removed without damage. I'm away right now, but I do need to check if the IC drivers are still available...
 

techknight

Well-known member
Thanks - I tried cleaning the zebra stripes, albeit only on the top side; it wasn't clear to me that they could be removed without damage. I'm away right now, but I do need to check if the IC drivers are still available...

Probably not but thats what UTSource is for.
 

sgervasi

Member
Does anyone know how the Macintosh portable non backlit logic board generates 5V? I can't find 5V anywhere - only 12V and 6.5 and 7.5. A
fully charged 6V (reads about 6.5V) battery is connected. The board has been recapped and it won't boot at all - no video no chime
 

3lectr1cPPC

Well-known member
The Hybrid module is responsible for this - if you can't find 5V, it's probably that module at fault. That's also probably why your board won't boot, assuming no bad traces or improper repairs.
 

sgervasi

Member
How can the full Battery voltage 6.45V get to the +5 rail on a macintosh portable non-backlit? Also there is no -5 volts showing on pin 33 of the hybrid board
 

SuperSVGA

Well-known member
How can the full Battery voltage 6.45V get to the +5 rail on a macintosh portable non-backlit?
The MOSFET at Q16 isn't being properly driven, or in very rare cases is bad.

Check the highlighted points at each end:
Screenshot 2023-04-03 at 3.19.05 AM.png
Screenshot 2023-04-03 at 3.18.48 AM.png

You can check that there is voltage making it from the hybrid to pin 1 on Q16. If there's no or very low voltage on both ends then there's likely a problem with the OpAmp circuit on the hybrid.


Screenshot 2023-04-03 at 3.28.17 AM.png
On V+ (yellow highlight) you should see near battery voltage, or at least 5V. If you don't then the comparator isn't supplying power to the OpAmp.
You should see 1.2V at IN- (green highlight).
IN+ (red highlight) is the feedback which should normally be around 1.2V as well, but since you have 6.45V on the 5V it will likely be higher than 1.2V.


How can the full Battery voltage 6.45V get to the +5 rail on a macintosh portable non-backlit? Also there is no -5 volts showing on pin 33 of the hybrid board
This is normal, the -5V is only enabled when when the computer requests serial or modem usage (for example turning on AppleTalk).
 

sgervasi

Member
Thank you for taking the time to give so much detail!
I checked the voltages and at Q16 pin 1, and at pin 8 on the hybrid I get .10 volts (pins 2 and 3 on Q16 read 7.36V)
I see 0 volts on the yellow highlighted pin on the op amp in the last picture
The green highlighted pin shows .18V, the red highlighted pin is at 1.7V
 

SuperSVGA

Well-known member
Thank you for taking the time to give so much detail!
I checked the voltages and at Q16 pin 1, and at pin 8 on the hybrid I get .10 volts (pins 2 and 3 on Q16 read 7.36V)
I see 0 volts on the yellow highlighted pin on the op amp in the last picture
The green highlighted pin shows .18V, the red highlighted pin is at 1.7V
So it sounds like the comparator isn't turning on power to the rest of the hybrid, and for some reason the 1.2V reference isn't working either.


Screenshot 2023-04-03 at 1.20.30 PM.png

On the comparator, check the V+ pin marked in yellow, it should be around the same voltage as the battery.
The green mark is the same 1.2V reference, connected to the -IN on that side of the comparator.
The red is the +IN and should be higher than the -IN for the comparator to supply power. If the 1.2V reference is really that low then it shouldn't be that hard.
If the red pin is a lower voltage than the green pin however, check the blue highlighted pins to see if you see battery voltage there. If you don't then you'll need to verify both power pins on the 4-pin battery connector on the board are receiving power.
 

sgervasi

Member
The V+ (yellow) shows 7.51V with the power supply connected and battery voltage 6.44 when it's not
on the comparator the red pin shows 0V, the green .09V - the blue highlighted pin is at .02V
when I connected the 9V battery to the left side + and - pins on the molex the voltages change -
red .09V green 1.22V and the blue shows the 8.3 from the 9V battery

I also noticed that with the 9V battery connected the op amp (OP20H?) you showed in the earlier picture reads 1.22V on pin 2 (green), and 1.49V on pin 3 (red)
 

sgervasi

Member
I should mention this board doesn't turn on at all - no chime, no video. After I recapped it I could get a sad mac intermittently by doing different things - unplug/re-plug the keyboard, then it quit all together just like before I recapped it.
 

SuperSVGA

Well-known member
The V+ (yellow) shows 7.51V with the power supply connected and battery voltage 6.44 when it's not
on the comparator the red pin shows 0V, the green .09V - the blue highlighted pin is at .02V
when I connected the 9V battery to the left side + and - pins on the molex the voltages change -
red .09V green 1.22V and the blue shows the 8.3 from the 9V battery

I also noticed that with the 9V battery connected the op amp (OP20H?) you showed in the earlier picture reads 1.22V on pin 2 (green), and 1.49V on pin 3 (red)
It sounds like you may have a bad battery cover switch or bad connection somewhere. Power from the main battery is only making it to one of the two battery inputs on the 4-pin connector.
 

sgervasi

Member
The board is on the table with only the battery connected to one side of the molex connector. Does the 6V battery need to connect to both positives in that connector?
 
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