Thread
Backlit Portable with broken display cable
FYI, I uploaded a quick video (using my phone) so the audio isn't great but hopefully, you can hear when it starts up.
https://youtu.be/Rd1oRmYyWbI
https://youtu.be/Rd1oRmYyWbI
I soldered a 1 Meg resistor on pin 16 and 18 (on the bottom of the PCB), but it still shows the same problem
no no no. Pin 16 and pin 18 of the LTC1040 itself. not the hybrid pins. You would have to solder direct to the pins, and fold the resistor over where it sits on top of the LTC1040 if its done correctly.
I moved the resistor to the two pins of the LTC1040, but the system still shows the same problem!
the system does that only when powered from the right side of the connector. if I plug only the left one, or both of them, it shows no signs of life.
the system does that only when powered from the right side of the connector. if I plug only the left one, or both of them, it shows no signs of life.
Well time to break out the O-Scope and see whats going on with the LTC1040CN.
Also, please verify that the RESET/NMI buttons are connected to the pull-ups, and that the pull ups are connected to VCC. And make sure the caps are connected to them as well, And make sure the two buttons also ring back to the MISC GLU.
Also, please verify that the RESET/NMI buttons are connected to the pull-ups, and that the pull ups are connected to VCC. And make sure the caps are connected to them as well, And make sure the two buttons also ring back to the MISC GLU.
Do you have a schematic for it? just to locate the two GLU pins.
also, which pins (on the LTC1040CN) should I probe?
EDIT: the switches are indeed connected to the two pull-up resistors (on the bottom of the PCB), those resistor are connected to VCC (+5V?, I checked continuity using the VCC pin on a 74-series logic chip present on the board).
The caps are connected to the switches (for debouncing?),
if I got the numbering right, reset goes to the last pin of the GLU, while NMI is on pin 26.
also, which pins (on the LTC1040CN) should I probe?
EDIT: the switches are indeed connected to the two pull-up resistors (on the bottom of the PCB), those resistor are connected to VCC (+5V?, I checked continuity using the VCC pin on a 74-series logic chip present on the board).
The caps are connected to the switches (for debouncing?),
if I got the numbering right, reset goes to the last pin of the GLU, while NMI is on pin 26.
there is no schematic for the portable, feel free to make some though and share em!!
Ok guys, I've got a great news to share with you: my portable now boots! 
Well, sort of. It's still got problems, but we've managed to get something out of it.
Ferrix has managed to get his hands on another portable that exhibits a problem quite similar to mine, so he thought he could probably get somewhere by comparing and swapping components between the two. Here are his results:
1) The portable fires up smoothly and pretty much consistently if it's overvoltaged: apparently putting 7.46V directly on the battery connector manages to keep it alive and happy, but if the voltage is lower it doesn't work.
2) The portable dislikes any additional load on the rails: in order to have a boot, he needed to disconnect both the hard drive and the internal floppy drive; even if just the floppy drive is connected, each attempt to access it results in an almost instant reboot.
Number 1+2 suggests to me there must be something wrong somewhere in the voltage regulation area / power supply circuitry.
3) If both hard drive and floppy drive are disconnected, the system boots but the display shows something like this.
Here's the cursor:
Here's the blinking floppy:
Here's the video of it booting from a zip drive: http://v8.tinypic.com/player.swf?file=nfmd5l&s=8
4) If the display is also swapped with the one coming from the other portable, we get a nice and solid picture:
All this makes me think that:
1) The logic board itself must be working ok: probably no rotten traces or anything, at least not concerning any "major" part of the system.
2) Something must be wrong with the power circuitry, since it needs an overvoltage to get going.
3) Either the video cable still has something wrong, or the display itself is fried.
So, what do you think? Where should we go from here?
Thanks!
Well, sort of. It's still got problems, but we've managed to get something out of it.
Ferrix has managed to get his hands on another portable that exhibits a problem quite similar to mine, so he thought he could probably get somewhere by comparing and swapping components between the two. Here are his results:
1) The portable fires up smoothly and pretty much consistently if it's overvoltaged: apparently putting 7.46V directly on the battery connector manages to keep it alive and happy, but if the voltage is lower it doesn't work.
2) The portable dislikes any additional load on the rails: in order to have a boot, he needed to disconnect both the hard drive and the internal floppy drive; even if just the floppy drive is connected, each attempt to access it results in an almost instant reboot.
Number 1+2 suggests to me there must be something wrong somewhere in the voltage regulation area / power supply circuitry.
3) If both hard drive and floppy drive are disconnected, the system boots but the display shows something like this.
Here's the cursor:
Here's the blinking floppy:
Here's the video of it booting from a zip drive: http://v8.tinypic.com/player.swf?file=nfmd5l&s=8
4) If the display is also swapped with the one coming from the other portable, we get a nice and solid picture:
All this makes me think that:
1) The logic board itself must be working ok: probably no rotten traces or anything, at least not concerning any "major" part of the system.
2) Something must be wrong with the power circuitry, since it needs an overvoltage to get going.
3) Either the video cable still has something wrong, or the display itself is fried.
So, what do you think? Where should we go from here?
Thanks!
Meter the 5V rail feeding the system, while adjusting your input voltage. A variable DC Bench supply would be preferable here.
that 5V rail should be a rock solid 5.2VDC even down to 6.3V input voltage. If it is not, then something is wrong with the Hybrid, or the MOSFET itself is bad. it is a P-Channel mosfet.
the LTC1040 forms a window comparator, that when the input voltage drops below 5.9V, it will lock out the 5V regulator so it falls to 0v. The other side of the comparator is used to tell the system whether the battery is in a charge state, or a discharge state. the window comparator senses the AC adapter voltage versus the battery voltage via a sense resistor, and will latch on the next oscillator pulse (internal to the LTC1040CN), and switch on the charging circuit. or not.
There is a small 8pin op-amp in the top left corner of the hybrid, its responsible for regulating the 5V rail. its error output feeds the MOSFET itself. if the MOSFET is bad, and the R(ds) is too high, it wont bring the voltage up high enough. Likewise if there is something bad on the hybrid, the same thing happens.
From my experience, the hybrids that exhibits the most problems are the ones that look "discolored" from tons of cap goo getting into the ceramic substrate. The most common thing is, the Goo changes the cross-conduction between traces, and creates parasitic resistors that screw things up. This cannot be fixed for the most part, However, the closest thing to the caps is the resistor/capacitor network that forms the latching oscillator for the LTC1040. When the oscillator does not run, it will cause the portable to have random no-power at all symptoms, or no-charging indicator.
Anywhere from 1Meg to 100K I have been able to get the oscillator started again. But if the damage is extensive, it may have affected other circuits as well.
The only fix is to reverse-engineer the Hybrid and create a new PCB with equivalent parts.
that 5V rail should be a rock solid 5.2VDC even down to 6.3V input voltage. If it is not, then something is wrong with the Hybrid, or the MOSFET itself is bad. it is a P-Channel mosfet.
the LTC1040 forms a window comparator, that when the input voltage drops below 5.9V, it will lock out the 5V regulator so it falls to 0v. The other side of the comparator is used to tell the system whether the battery is in a charge state, or a discharge state. the window comparator senses the AC adapter voltage versus the battery voltage via a sense resistor, and will latch on the next oscillator pulse (internal to the LTC1040CN), and switch on the charging circuit. or not.
There is a small 8pin op-amp in the top left corner of the hybrid, its responsible for regulating the 5V rail. its error output feeds the MOSFET itself. if the MOSFET is bad, and the R(ds) is too high, it wont bring the voltage up high enough. Likewise if there is something bad on the hybrid, the same thing happens.
From my experience, the hybrids that exhibits the most problems are the ones that look "discolored" from tons of cap goo getting into the ceramic substrate. The most common thing is, the Goo changes the cross-conduction between traces, and creates parasitic resistors that screw things up. This cannot be fixed for the most part, However, the closest thing to the caps is the resistor/capacitor network that forms the latching oscillator for the LTC1040. When the oscillator does not run, it will cause the portable to have random no-power at all symptoms, or no-charging indicator.
Anywhere from 1Meg to 100K I have been able to get the oscillator started again. But if the damage is extensive, it may have affected other circuits as well.
The only fix is to reverse-engineer the Hybrid and create a new PCB with equivalent parts.