Asus TX300CA "pulses" - periodically interrupts power when connected to DC supply?

Question

I've got an Asus TX300CA, and as if I wasn't unlucky with it already, now I have this problem.

The TX300CA has a tablet part, and a keyboard/dock part. When the tablet part is docked to the keyboard part, only a 40-pin connector is (or seems) to be used. In addition, both the keyboard part and the tablet part, have a DC input which matches the original power supply (although, the tablet part seems to have more pins on it? However, I've tested that occasionally when the system was working, and it worked correctly)

Anyway, when the tablet part is docked to the keyboard part, the hinge is very fragile - and even when the whole system was working, whenever I'd hit the desk by accident, even gently, the rocking action of the tablet part in the hinge was enough to temporarily disconnect the tablet from the keyboard dock - and this was followed by change of brightness of screen (I use Ubuntu 14.04, MATE desktop); a notification that battery was discharging (i.e. no DC power supply input detected); a "thk" or "khk" short sound from the speakers; and temporary disconnect of the hard disk drive in the keyboard dock, which is registered as connected through USB (the tablet part also has SSD drive, which is where I have Ubuntu installed).

Since the original working condition:

• One of the handles on the hinge broke (but the system was working the same as before)
• The disk drive in the keyboard dock silently died
• And now this:

This problem occurred several days after "the disk drive in the keyboard dock silently died"; basically, now whenever the DC power supply is connected -- either through the keyboard dock, or through directly through the tablet DC input -- Ubuntu will first register power supply and increase the brightness, then after a second or two, it will notify that the DC input is disconnected (battery is discharging), and brightness will be lowered; then after a second or two, again charging is detected and brightness increased; then again it turns off -- and so, it loops, or "pulses" between these two states (and also, the "khk" sound is heard whenever it switches state). I have posted a small video of this here:

https://streamable.com/bb85y

Here is only the tablet part, and the DC supply is plugged directly into it; but the same happens when the tablet part is docked in the keyboard, and the DC supply is plugged in the keyboard dock (note that when docked, the hinge only has a 40-pin connector connection with the tabled, there is no matching connector for the tablet DC input on the hinge). EDIT: the video shows tail -f /var/log/syslog, and it shows anacron process restarting each time the "pulse" happens.

Also, when I plug the power supply in the keyboard dock without a tablet, a small LED light on the left side shines orange or green (not sure if this indicates the state of a standalone battery inside the keyboard dock, separate from the battery on the laptop). However, this light is still continuous, which tells me the adapter itself should still be fine (or at least, not the cause of this "pulsing"). However, if I now dock the tablet, in turned off state, this small LED on the left stops shining - and instead, I get pulsing from the Windows logo on the bottom of the tablet (which shines white). I've noticed (from when it was properly operating), that this white Windows log light turns on only if the tablet part is running, but is undocked (when docked, it turns off).

For reference, here are the largest images I could find of this machine's ports and adapter (click for larger image):

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Would anyone know why does this happen - and is it possible for me to fix it?

As a workaround, I could live with charging the tablet part separately, and then using it strictly on battery - however, as I mentioned, this pulsing occurs also when the tablet is running and the DC adapter is plugged into it directly; unfortunately, when the tablet is turned off (and the DC adapter is still plugged into it directly), the battery does not seem to charge... Anything else on the dock-tablet connection still seems to work (i.e. I can use USB keyboard, mouse even when this pulsing occurs).

EDIT: It seems the tablet battery does charge, when tablet is turned off and docked to keyboard, and the Windows logo on the tablet pulses white - in the hour or so I was preparing this post, the charge went from 35% to 51%, though I imagine it goes a lot slower than usual... Still, I'd love to know if a proper fix is possible without a trip to the shop (maybe some "reset factory defaults", if it is something like a firmware problem?)

Answer 1

Leds on a left side of this laptop indicates states of charge. Blinking orange idicated depleted battery
Solid orange - charging.
Solid green - full charge.

First of all - buy a non OEM hinge replacement. The aftermaket chinese ones are way more durable than asus ones. I had original, tablet was loose inside of it and often get disconnected from HDD, then the metal support thing broke, got RMA repair, got a replacement hinge which was faulty as well and broke even worse than the first one.

I bought non ASUS-made hinge which was higher, more sturdy and lives for this day (5 years and counting).

Second of all - Check if your cable in a charging plug is not broken. Mine got broken and needed resolidering - easy part. More difficult was when cable got broke on a brick side. I made an ASUS-Maglock <-> 3mm DC <-> USB-C adapter with PD-Trigger board set to 20V so I can charge it with USB-C 100W charger/powerbanks. I repaired my powerbrick at the end but it's very convenient to be able to charge it with powerbanks and PD ready monitors.

I hope you still have your transformer book and I could help.