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redruM69

Mac Portable troubles

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I'm currently working on a Mac Portable, backlit. Its been cleaned, recapped, fresh battery installed, w/ SCSI2SD. System 7.1 installs fine, but as soon as it booted the first time after install, I get the message:

"No battery reserve power remains. The Macintosh will go to sleep within 10 seconds to preserve the contents of memory. Good Night."

And then it sleeps. Waking it back up just gives the same message, and it cycles again.  Booting a System 6.0.8 floppy works fine, as I assume it does not monitor the battery.

The battery is charging correctly, showing ~6.2v alone, and ~7.3v if the AC adapter is connected. I have also tried a bench supply @ 6.5v to eliminate the battery being part of the equation.

I haven't torn it down again just yet.  I dug around and saw some older posts mentioning diagnosing the hybrid chip for a somewhat different, but related issue.


Is the hybrid where I should start?  Any additional tips?

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Since this is a backlit model, there is no Hybrid. 

 

You need to look at the battery meter, Even while plugged in. if it barely raises, and then unplugging it results in a hard drop, you have a broken trace between the power supply regulation area (near the buttons) and the PMU which actually reads the battery levels. 

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5 hours ago, techknight said:

Since this is a backlit model, there is no Hybrid. 

 

You need to look at the battery meter, Even while plugged in. if it barely raises, and then unplugging it results in a hard drop, you have a broken trace between the power supply regulation area (near the buttons) and the PMU which actually reads the battery levels. 

If I'm really quick, I can pull up the battery meter before it goes back to sleep.  The meter shows as completely dead.

Where is the PMU that reads the battery level?

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I tore it down today.  Something worth mentioning, is this board was particularly clean.  I dont see any signs of cap corrosion anywhere.  No discolored traces, etc

Found some pictures of the trace routing between the VREF and opamp.  Traces all test good between them, and the surrounding caps.  5V rail in that area is ~5.23v.
I tested the signal @ pin 52 of the PMU, and found 1.24v with the battery connected, and 1.02v disconnected.
Does that signal range on pin 52 seem normal?  I cant find any info on where the levels SHOULD be.
 

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Way too low. it needs to be up near 2.5V or so, otherwise the machine will go into standby all the time. 

 

Take a look at R151 and C107, and its associated connections. 

Edited by techknight

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On 2/11/2018 at 5:02 PM, techknight said:

Way too low. it needs to be up near 2.5V or so, otherwise the machine will go into standby all the time. 

 

Take a look at R151 and C107, and its associated connections. 

R151 tests 1k
C107 tests 1.15nf

 

I have continuity back to a via just to the right of C26.  The trace then heads under U2L (vref?), and I cant seem to follow it after this.  It does appear there may be some minor corrosion hiding under there.  I assume its supposed to be connected to a pin on U2L.  But, I cant seem to find a datasheet for U2L, or Mac Portable schematics that would help.
Any further insight?

20180214_184753.jpg

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After a little more poking around, I found the trace leads to the source of Q207, an N-channel mosfet.  The gate is connected to pin 16 of the opamp.  Drain is connected to pin 7 of the opamp.
I think I'm going to cross my fingers, and try replacing both the opamp, and the mosfet.

Unless you have another idea?

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Do you have 1K of resistance/continuity between the pin at Q207 and the Pin at the PMU? If so then your troubles are about to get much worse. 

 

Usually when I get into Op-Amp trouble, I have a 50/50 shot of fixing it. This circuit is very sensitive and replacing the parts sometimes wont get it working again because the capacitor goo has leaked and gotten in between the PCB layers and it screws with how the circuit operates. 

 

The next thing you can check is C26 and make sure each side of those are still good and connected in circuit. 

 

Anyways, the MOSFETs are general purpose 2N7002

Edited by techknight

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2 hours ago, techknight said:

Do you have 1K of resistance/continuity between the pin at Q207 and the Pin at the PMU? If so then your troubles are about to get much worse. 

 

Usually when I get into Op-Amp trouble, I have a 50/50 shot of fixing it. This circuit is very sensitive and replacing the parts sometimes wont get it working again because the capacitor goo has leaked and gotten in between the PCB layers and it screws with how the circuit operates. 

 

The next thing you can check is C26 and make sure each side of those are still good and connected in circuit. 

 

Anyways, the MOSFETs are general purpose 2N7002

Yes, 1k from the source on Q207 to pin 52 of the PMU.


C26 connections are OK, even though the joint isn't flowed very well.  I believe maccaps/uniserver/Charles did the recap on this board.

I'm weary of the use of ceramic caps in place of lytics.  I've seen plenty of tants used in place, as they have similar characteristics.  But AFAIK ceramics are quite different, even if the value matches.  They can cause strange resonance issues when substituted.
I'm currently waiting for a new mosfet and opamp to show.  In the mean time, I'll replace C26 with a new SMD lytic, and see if that makes a difference.  I'll update soon.
 

Thanks for your help!

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On 2/16/2018 at 6:46 AM, techknight said:

When you say C26 connections are OK, I dont know what that means. 

 

You need to test its continuity all the way back to the op-amp. 

That's what I meant.  Good continuity to pins 14 and 15 of the opamp.

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Yeap, tell me about it. 

 

the op-amp rarely fails in these boards. out of dozens of boards, I think I have changed one or two. 

 

So your likelihood is not good unless your board falls into that <1%

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Good timing.  I just now swapped the op-amp and mosfet Q207 out.  I haven't booted it yet, but I still read 1.24v @ the PMU.  So it appears unchanged as you expected.

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That was my fear. :-( 

 

I haven't had much luck with boards that have done this. its a 50/50 deal. 

 

Next thing you can do is read the resistance of that line between VCC, and between GND. Make sure that pin doesnt have an internal short to the PMGR or something along those lines. 

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Difficult to find time to work on this one.  That's the reason for the long delays in my response.
Resistance between PMGR's pin 52 and ground and VCC is about 24meg.

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Success!  It appears the opamp swap DID work after all!
Just for kicks I connected everything up, and performed a power manager reset.  It booted fine, and reported the battery nearly full, and charging.  With the machine booted, Pin 52 now measures 3.94v and climbing.

Maybe bad op-amps are a little more common than previously thought?

20180313_180810.jpg

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Congrats! Nice to see a Portable brought back to life. I'm working my way toward dragging mine out and seeing if it still works.

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1 hour ago, techknight said:

Never once have I changed an Op-Amp and it had actually fixed that. Makes me kind of hesitant. 

It makes sense to me.  If the opamp's output is way off, yet everything else checks out, then it must be toast.  I did swap Q207 at the same time, but it tested good once I had it out of circuit.
FYI, I replaced the original LT1179CS with a MAXIM unit.  $10 a pair on eBay.  Not sure what the original manufacturer was, but it was different.
I appreciate your time.  You were a huge help!

20180314_173107.jpg

20180314_172428.jpg

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Well I am just saying that I have changed a many of them for similar symptoms and never had any luck. Only time I ever fixed one was a no-output condition. You got lucky thats for sure. But I always changed them with the same part same company, linear technologies. 

Edited by techknight

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17 hours ago, techknight said:

But I always changed them with the same part same company, linear technologies. 

Hmm.. Is it possible the Maxim is a more robust unit?

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