HP Compaq TC4200 not starting, at all


After not using the laptop for six months, and having left the battery in for that duration, I found that the laptop would not power up. To be fair, it had been playing up for a while prior to the six months – the sleep functionality had been intermittent for a while (it would just reboot, instead of coming out of sleep mode (I think, my memory is rather hazy)), and then there had been a bit of a refusing-to-start issue.

The first thing that comes to mind is that the CMOS/BIOS battery has expired…

The symptoms

Symptom #1a

Unplug AC adapter
Remove battery
Wait 5 seconds.
Plug in adapter and PC (no need to touch the power switch)
The charge LED goes green, for one second, and then yellow for 5 seconds, and then it goes off

Thereafter, the power button does nothing.

Symptom #1b

Unplug AC adapter
Do not remove battery
Wait 5 seconds.
Plug in adapter and PC (no need to touch the power switch)
There are no LEDs lit

Thereafter, the power button does nothing.

Symptom #2

Unplug AC adapter
Still with no AC power plugged in.
With the battery in.
Upon switching on the power switch, the power switch LED (and “On” LED) goes green for five seconds.
At the same time, charge LED flashes yellow 7 times, then the power switch LED (and “On” LED) goes off, and the charge LED green briefly (less than a second) and then yellow briefly (less than a second) and goes off

Thereafter, the power button does the same thing.

Symptom #3

Plug in the AC adapter. With the battery in, the power switch does nothing – no LEDs on the power LED nor charge LED.

Symptom #4

The AC adapter does charge the battery, the charge LED goes yellow, and a fully discharged battery is charged fully.

But once the battery is charged, there is no yellow light, on the charge LED, when the AC adapter is plugged in.

Symptom #5

When you put the battery in, no AC power, the yellow charge LED lights for about 5 seconds, and then goes out. Thereafter it will not power up.

Symptom #6

Insert fully discharged battery, plug in AC power. Yellow charge light for 5 seconds which then changes to deep orange (to signify charging)

Symptom #7

Whilst charging as in #6, switch the power button, nothing extra happens. Orange LED stays lit.

Attempt to fix

I have followed HP Notebook PCs – Computer Does Not Start and Emits an LED or Beep Code – Video

To perform a hard reset on a computer with a removable battery, use the following steps:

1. Turn off the computer.
2. Disconnect the computer from any port replicator or docking station.
3. Disconnect all external connected peripheral devices such as USB storage devices, external displays, and printers.
4. Unplug the AC adapter from the computer.
5. Remove the battery from the battery compartment.
6. Press and hold down the Power button for about 15 seconds to drain any residual electrical charge from the capacitors that protect the memory.
7. Insert the battery and plug the AC adapter back into the notebook computer, but do not connect any of the peripheral devices.
8. Press the Power button to turn on the computer.
9. …

All but to no avail. Holding the power button, for 15, 30 or 60 seconds, did not help. I have removed the hard disk, reseated the battery and held the power for 60 seconds.

Tackling the CMOS battery

The CMOS Battery is called the Real Time Clock (RTC) battery, and is located on the system board:


Related links

  1. Remove the battery and AC power from the notebook.
  2. Press and hold the power button for 20-30 seconds. This discharges the capacitors on the motherboard.
  3. Replace battery and AC power.

My tc 4200 doesn’t power up.

– on  battery  : power led blinking : 8 orange  ,1 green and 1 yellow

– on ac adapter : nothing.

The battery ‘s OK and the adapter too.


From dorivercom

Compaq TC4200 노트북 분해(Laptop disassembly)

Compaq NC4200 노트북 분해(Laptop disassembly)

My method

To replace the RTC battery, following Compaq TC4200 노트북 분해(Laptop disassembly):

  • Follow the above video, religiously, to 4:44;
  • Skip the processor flat blade bolt, that can be left as is
  • Remove, or just loosen, the black plastic square at 4:56, but leave in-situ, loose.
  • Ignore the single PCB bolt at 4:58 and 4:59, and leave in place
  • Loose the tape holding the red and black wire, @5:00, but leave in situ
  • remove the ribbon cable 5:04, but it can be left in-situ
  • 5:24 to 5:37, these two connectors (2 and 8 pin) can be left in place, if care is taken, else they can be taken out but left in-situ, loose.
  • From 5:40 to 5:46, remove the bracket
  • From 5:48 to 5:57, remove the last remaining four torx T9 bolts, which hold the motherboard in to the bottom of the case.


  • I had to remove the tape to access the bottom motherboard screw at 5:52
  • I removed the tape, at 5:30. needlessly holding the red/black lead to the furthest two pin connector

The board prior to removal:

HP TC4200 motherboard
HP TC4200 motherboard

And the location of the RTC battery, which is a Maxell CR2025

Rear of HP TC4200 motherboard showing RTC battery holder
Rear of HP TC4200 motherboard showing RTC battery holder



I used 2 x Brand New Genuine Maxell CR2025 2025 Cell Litium 3v Coin Batteries., £0.26

Non brand


Replacing the RTC did not help the situation. In fact it seems worse as no lights come on now, apart from the orange charging LED (symptom #6) and the five second yellow powerLED (symptom #5).



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