Lynx tablet

[cbee]

Hi all. If I replace the useless 3.7 volt battery in the Lynx 8 tablet with a dc 3.7 volt supply, will the lynx tablet start. To put it another way, should the Lynx tablet start? I have done this and I can get nothing out of the tablet. I have supplied the tablet with 3.7 volts DC and the power supply will give at least 8 watts if required (probably more). The supply goes directly to the battery terminals (I have thrown the battery away as it is crap). Am I doing something wrong. Any info would be helpful. Even guesses might help. Thank you. PS. As you may know, there is a circuit which forms part of the battery. I have included this circuit and I have connected directly to where the battery terminals would have been. As far as I can see, I have observed correct polarity. Do you think i may have destroyed anything with the heat of my soldering iron? Is there some other reason why this does not or won't work? Once again, thanks for any help.

 

[Hopup]

That battery protection circuit is probably the cause of it not starting, if your power supply really gives the required voltage and current out.

 

[Alec_t]

there is a circuit which forms part of the battery

Yes, the BMS circuit for protecting the battery. It may have detected that the switch-on/off characteristics of the 3.7V supply don't match a battery presence and gone into shut-down mode. If the Lynx queries the BMS it would then fail to start up. Just a guess.
Since battery failure is no longer a threat the BMS is redundant. Perhaps you could try disconnecting it.
With or without the BMS you may have to give a dummy response to any BMS query.

 

[cbee]

Thank you, Hopup and Alec_t. Since I have little to lose, I will bypass the battery protection circuit and see if that helps. would you please explain the dummy response. The voltage and current are as I said. I am using a 12volt dc power supply, which can supply 1 amp. I am passing this through a buck converter and this adjusted to 3.7 volts dc. There are at least 2 (and more) amps available

 

[BobK]

Why not just run 5V into the charging input?

Bob

 

[Alec_t]

would you please explain the dummy response.

If the Lynx queries the BMS (and we don't know if it does) it must expect some response; either a voltage or code or .... who knows? If it doesn't get the expected response it will sulk.

 

[cbee]

Thanks BobK for your input. Because the battery won't hold a charge, if I try to charge in the normal manner, there is a delay of about fifteen minutes before the tablet will switch on. This makes the tablet just about useless. This is what caused me to try something else.

 

[cbee]

Thanks Alec_t. I'll bypass the battery protection circuit and see what happens. If I can't provide any response, maybe I can do nothing else. Some people online are calling these tablets throw away when the battery packs up. When I bought this about a year ago (if that), I paid over £100. Hardly throw away money.

 

[Alec_t]

Since you already have 3.7V connected into the battery terminals, if you also apply 5V to the charging input, as Bob suggested, what happens?

 

[cbee]

The answer to that, Alec_t is that I don't know. Sounds like a good suggestion. In the next day or so, I'll give that a try.

 

[cbee]

Here’s an update on my lynx tablet problems. Thanks for all your input. I supplied the tablet with 3.7 volts DC straight to the battery terminals, (in place of the battery which was useless after about a year from new). As suggested on this forum, I also connected the usb charger. Then I switched the tablet on. To my slight surprise, the lynx switched on. That was about as good as it got. When I put a multimeter on the battery terminals, the voltage which was originally adjusted at 3.7 volts, was fluctuating wildly between 3.7 and 4.2 volts. Although the lynx switched on, the internet connection kept dropping out and I couldn’t get it stay in. The tablet was quite erratic in everything I tried to do. It also got quite warm to the touch. Eventually it switched off completely and would not come back on. I assumed that something had fried and a few days later I tried one last time to switch on before giving up. Again to my surprise, it switched on but with the same erratic behaviour as before. The tablet started to warm up and then switched off and would not switch on again (just as before). It looks as though this tablet is destined for the dustbin (trash).