For every project I post on here where I obtain the results I was looking for, chances are there are two other projects I’ve tried that didn’t quite work out. Such is the nature of tinkering and hacking for fun.
Just because it ended in failure (and occasionally, catastrophic failure), it doesn’t mean I’ve wasted my time – here are some lessons I’ve learnt from failure over time.
Most recently, I obtained an used battery pack from a friend’s laptop. It still held a charge, but only for 15-30 minutes. I figured, “Great, I can use this to finish another project!” I have an old ThinkPad R31 with a completely dead battery pack that I already disassembled, in hopes of replacing the cells. The project was shelved while I decided how I would proceed and weighing the risks, but getting a free battery pack was all I needed to get back to it.
After taking pictures of how it was all wired, I removed the old cells, and began to replace them with the new cells. This wasn’t particularly difficult, I just had to be careful with soldering to not let the batteries get too hot (Lithium Ion battery hate heat, short circuiting, punctures… and literally, air.) This perhaps falls into the category of a dangerous hack.
Once the pack was together, I installed it into the laptop. Rather than the 0% I always got from the other pack, this one reported 92%! I though I was in the clear, and let it charge (while carefully monitoring it). Although it said it was charging, the level didn’t climb. I did some measurements, and confirmed my suspicions: the pack protection circuitry was not allowing voltage in or out of the pack. At this point, I called it a night and a failed project.
From this I learnt several things:
- A half second short circuit will shoot cell temperature right up
- These protection circuits seem to stop working when the cells discharge too low, to prevent recharging when they are too far gone
- The cells are never directly connected to the laptop, instead passing through switching circuitry
Over time I’ve amassed a collection of working LCD monitors I’ve refurbished. I’ve also collected a graveyard of LCD monitors I’ve been unable to repair – these ones do not have tell tale capacitor bulging, thus leaving me to either replace every capacitor, or look for a different source of malfunction.
Most recently, I received a 19″ widescreen LG monitor, which would have made a very suitable replacement for my 17″ fullscreen second monitor. It suffered the exact same symptoms as almost every broken monitor that makes its way into my care – backlight on for 2 seconds, then darkness. The panel still works, there is just no lighting. This happens because the protection circuitry detects an error condition: usually over- or under-voltage. I believe bad caps would lead to under-voltage. This 19″ didn’t have any bad caps, so I looked online for more ideas.
There is an IC (OZ9938GN) that controls all backlight functions, such as on/off, dimming, and error detection. Pin 7 was connected to a voltage feedback circuit. I measured this pin, and the voltage didn’t match up with the datasheet-stated values, meaning that either:
- There was an under-voltage condition
- The feedback network was not working correctly
On the Badcaps forums, someone said that they once found the feedback circuit to be the problem, and to fix this, they simply bypassed it using a 1M Ohm resistor connected from VDD to pin 7. I tried the same, but to no success.
I learnt a lot about the operation of LCD panels. From protection circuits to troubleshooting circuits based on schematics and the types of components present. Even though I didn’t manage to fix this LG (along with two other BenQs and a Cicero), I haven’t given up on them, and for every monitor I can’t fix, there has still been another one I have fixed and saved from going to the landfill.
There have been many more failures than this, however, due to their nature of being failures, no documentation exists for most of them. All that remains are the damaged circuit boards, broken cases, and blown components from a project with hours spent, ending in worse shape than when it started. Still, it takes these lessons to get better and continue expanding skills and knowledge.