68kMLA Classic Interface

If a signal is switching between high and low the multimeter probably won't be fast enough to track it, but a steady signal like something that is staying on or off it should be able to see. Just put the negative probe on a good ground point like the shielding on the various ports or the negative leg of one of the axial capacitors, and then you can probe around with the positive probe.

SYS_PWR* for example is active low, so it's "true" when down towards 0V and "false" at 5V.

The MOSFET controlling the powered-on +5V is controlled by SYS_PWR* connected to the gate of the MOSFET. At 5V no current will flow, and near 0V current will flow allowing power to the main +5V.
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Simulation

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ok, so I went over tech by androda hybrid check and all check out except my q1. The resistance seems off. My voltage at q16 pin 2 is 5.2volts. Power manager resistance is fine. So maybe q1 is burnt out? Also, the he says the fuse should have zero resistance or no connection. I am getting 0.5ohms and continuity. Is that off?

Q1 is just for charging, so it won't really affect turning on the computer unless the battery needs charging.

0.5Ω sounds perfectly fine for the fuse. If it was more than maybe 10Ω it would be a little suspicious but that fuse sounds fine.

Since SYS_PWR* appears to be high and assuming the gate at Q11 is still connected to the power manager, it seems that the power manager is not trying to turn on the computer. Typically when the power manager is working properly it should turn on when it keyboard input, which is detected by the AKD signal going high.

One thing you could try is connecting AKD to +5V, preferably through a resistor, maybe 1kΩ, and see if that turns the computer on.

You could also try connecting SYS_PWR* to ground with a resistor. While that's grounded that should turn on the powered-on +5V and you should at least see some sign of the computer trying to start.

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So, good news. It works. So now what?? I tried the above. So anyways, not sure what needs to be done to fix it starting by keyboard??

You mean that forcing AKD high turns it on?

It seems like the 74HC133 at U13L may be bad, either that or a bad trace. If you can check pin 16 for 5V to make sure it's getting power, and check continuity between pin 9 and R189 then between R189 and AKD. R189 is on the backside so if it's too tricky you may just want to test resistance between pin 9 of U13L and AKD which should be around 10KΩ.

If all that looks good then the 74HC133 may just need to be replaced.


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You mean that forcing AKD high turns it on?

It seems like the 74HC133 at U13L may be bad, either that or a bad trace. If you can check pin 16 for 5V to make sure it's getting power, and check continuity between pin 9 and R189 then between R189 and AKD. R189 is on the backside so if it's too tricky you may just want to test resistance between pin 9 of U13L and AKD which should be around 10KΩ.

If all that looks good then the 74HC133 may just need to be replaced.


View attachment 79577View attachment 79578

You mean that forcing AKD high turns it on?

It seems like the 74HC133 at U13L may be bad, either that or a bad trace. If you can check pin 16 for 5V to make sure it's getting power, and check continuity between pin 9 and R189 then between R189 and AKD. R189 is on the backside so if it's too tricky you may just want to test resistance between pin 9 of U13L and AKD which should be around 10KΩ.

If all that looks good then the 74HC133 may just need to be replaced.


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nice crisp lcd panel too