T41 power circuit problems

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jimmy274 · #1 Post by **jimmy274** » Wed Feb 06, 2008 9:05 pm

Ok, here we go... The T41 that I bought recently had been fine on the first couple of runs... Then the battery went out (or at least I thought so)...
It turned out that battery is fine, but power circuitry might be bad - when I try to turn on the laptop while on battery alone, it's completely dead - no lights, no signs of life.
While on AC, the laptop turns on fine, detects the battery, CHARGES the battery and I have all the relevant info in battery maximiser. Nevertheless, when I pull out the mains it shuts off instantly.
After I tried it all, I tried to turn on the laptop (on AC) and the moment it turns on, I pull out the AC - it never gets to IBM splash screen, but sometimes stays on until the battery runs out, and sometimes it shuts off just before the splash screen would appear. It does, however run on the battery alone for a small fragment of time!
I'm guessing it's a fuse or a Power MOS transistor (problem that Ray had on one of the T23s). Alternative would be that the main circuit for li-ion battery went out or maybe one of the aux circuits (Maxim MAX1845 for instance) went out.
Ray, I could really use your skills here, every comment is appreciated. I've already bought an R51 (yes, turns out it's an R51, not an R50) board (2889-hg1) for possible parts, so I have all the Power MOSFETs and fusses (the packaging of the MAX1845 is different on R51, though). The R51 board is, sadly, completely dead (don't know the reason).
Guys, ideas?

#2 Post by **rkawakami** » Fri Feb 08, 2008 9:52 pm

Sorry to say that I don't have as much experience with T4x systems as I do for the T23s. From your description it sounds like the power control switching circuits are at fault. If the laptop allows the battery to be charged and correctly interrogates the battery status, then the fuse(s) to the battery are fine, along with the associated charging circuits.

Not sure if the problem is associated with the MAX 1845. That's a step-down converter/controller for providing the low voltages for the CPU, chipset and memory. I'd be more suspicious of something like a MAX1631 (Multi-Output Low Noise Power Supply Controller) that's on the T23 motherboard.

jimmy274 · #3 Post by **jimmy274** » Sat Feb 09, 2008 7:59 am

That's ok Ray, this helps too. I found MAX1631 on the board! It seems that it's on fault, judging by the datasheet. How hard do you think it is to swap it with a good one (I do have a good one on that R51 motherboard - at least I think it's good). Where can I buy one?

#4 Post by **Johan** » Sat Feb 09, 2008 2:28 pm

jimmy274 wrote:... I found MAX1631 on the board! It seems that it's on fault, judging by the datasheet. How hard do you think it is to swap it with a good one (I do have a good one on that R51 motherboard - at least I think it's good). Where can I buy one?

Maxim offer free sample(s) of their various IC's - see for yourself at MAX1630 ... MAX1635 Multi Output, Low-Noise Power Supply Controllers for Notebook Computers - check the distributors in your country/region.

Best regards,

Johan

jimmy274 · #5 Post by **jimmy274** » Sat Feb 09, 2008 4:47 pm

Great! I'll check it out, thanks.
Now, basically the MAX1631 has two input pins that are of importance - the RUN/ON3 and the TIME/ON5. I'm thinking when I press the power button, these pins should be driven to logical '1', and, if everything is ok with the circuit, the RESET signal should go low and machine would start, right? The possible problems before the circuit would make these two input pins not go to logical '1', and the problems after could appear when the RESET signal is asserted but the machine does not power up. The actual circuit is at fault if RUN/ON3 and TIME/ON5 are asserted, but the RESET signal is not...
Time for Voltmeter with fine tips... and some hot-air if the circuit is at fault.

jimmy274 · #6 Post by **jimmy274** » Sun Feb 10, 2008 7:58 am

Ok, I have a few updates. First of all, I think that the MAX1631 is fully functional, but... The main components for DC/DC converter on-board are very close to MAX1631. I can verify that when the DC is plugged in, MAX1631 operates normally, but when I plug out the DC, the whole board seems to loose voltage - everything in close proximity of MAX1631 looses power. I verified this by using voltmeter and when I plug the DC out, the voltage starts to drop out, since the whole board is full of capacitors, the voltage drop does not come instantly, but gradually. This brings me back to my first assumption - a fuse or a Power MOS are at fault.
A Power MOS has it's parasitic diode, which transfers current while the MOS is switched off - I've noticed that there are 2 MOS transistors for each battery - a PMOS and an NMOS. One is switched on while charging, while the other is switched on while discharging (using battery). The parasitic diodes are used in both when they're switched off for power transfer, since the MOS transistors are connected in parallel (Drain-to-Source)... The parasitic diode in one could be at fault...
I'll measure it up again in a couple of days and post when I'm finished.

#7 Post by **Harryc** » Mon Feb 11, 2008 9:04 pm

How do you know the battery is good? I had a bad battery that gave these exact symptoms. Charged good on AC, green status, 100% charged, etc ... machine died instantly on battery.

jimmy274 · #8 Post by **jimmy274** » Tue Feb 12, 2008 5:14 am

I've tried it in another T40, and it works...

stolar · #9 Post by **stolar** » Mon May 26, 2008 5:56 pm

Hello,

Jimmy274 could You please ensure me what should be acceptable voltmeter readings for this max1631 (especially for pins 1,4 and 15)?? How should they differ for a laptop working only on AC and one only with battery power.

T41 power circuit problems

T41 power circuit problems

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