Uni-T UT61E europeans version dead by a rechargable battery

[Rizaru]

Hello

my uni-t 61e just dead after I wanted to swap the de battery. I thought il buy those rechargeable ones from energizer at 8.7v.
didn't boot up oke I had a normal alkane one as well. but it is completely dead now 
Can someone explain how a rechargeable battery can kill a DDM? i have the schematic and only U3 is getting voltage also the Xtal is getting voltage.
now i'm whit a dead DDM that doesn't even beep when turned on. I can't wrap my head around it how it can be.
ty for you aswers!

[PKTKS]

I had a similar issue with the same profile...

When changing bat the meter refused to turn on....

I did a careful inspection and found the culprit
being a damaged MLCC capacitor just the one that
sits directly connected to the bat.

Replaced that with a tantalum and it turned on just fine.

That MLCC may get damaged by a dozen different reasons...

Schema attached
Paul

[Rizaru]

weird thing is there is voltage present on U3 and the Xtal but nothing turns on so I'm guessing the main chip :/ that is shot.

[PKTKS]

weird thing is there is voltage present on U3 and the Xtal but nothing turns on so I'm guessing the main chip :/ that is shot.

I had the same bad feeling when that happened...

Started to quote the chip... OK we can find the chip..

BUT...  A single piece is almost  the price of a new whole unit..
That is the dark side of VLSI or COB  DMMs...

If the chip is damaged you save a few bucks ordering a new one..
but last time I checked  it was not worthy

Try harder to spot a damaged cap or bad cold solder joint...

Otherwise ... the alternatives are few

Paul

[Rizaru]

Well i think i might have found it. But i don't C36 no where on schematic or i'm looking right over it.

Marijn

[radiolistener]

Can someone explain how a rechargeable battery can kill a DDM? i have the schematic and only U3 is getting voltage also the Xtal is getting voltage.

if you're using battery with DC/DC converter inside, it can fail and apply high Voltage to the battery terminals, so DMM will be damaged.

For example, if your battery has USB connector for charging, it has DC/DC inside.

[Rizaru]

it one of those
https://www.amazon.de/-/en/Energizer-rechargeable-batteries-Recharge-Power/dp/B000IWXVU6/ref=sr_1_1?crid=1BI1HDA3ZP87G&keywords=9v%2Bbatterie%2Benergizer%2Baufladen&qid=1642283084&sprefix=9v%2Bbatterie%2Benergizer%2Bre%2Caps%2C84&sr=8-1&th=1
But it charge whit the pins and a separted charger.
O well gonna see what the replacing does of c36. i hope it turn on again.

[Per Hansson]

Well i think i might have found it. But i don't C36 no where on schematic or i'm looking right over it.

It is located in the lower middle of the schematic, see attached crop where I've marked C36.

[PKTKS]

Just looking by the photo it seems really toasted...

Looks identical to the other below.. tantalum? or MLCC...

In fact you can even fit a small THT tantalum cap there...
They are bigger more robust ...

Just a bit of skill to put them there..

Paul

[theHWcave]

My 5 cents: There does not seem to be any diode protecting the meter from putting the battery the wrong way around. I know you can't clip it in with the polarity reversed but its enough to just hold the battery the wrong way around against the terminals temporarily, - realising "oh its the other way around" and then turning the battery and plugging it in. But the damage is already done. I'v nearly done this a couple of times myself. 9V batteries and their exposed terminals are dangerous, especially if is its a beefy battery (for 9V that is) that can deliver a high current.
The schematic shows a VB+ that may go somewhere without being switched. If so I have not found where but that would be a prime candidate for damage.  VC+ seems to be VB+ after being switched. If this is true then damage (blown up caps) by a temporarily reversed battery should only be possible if the meter was left on while the battery was changed.

[HB9EVI]

those 9V blocks based on Li-batteries and internal DC/DC maybe look tempting, but they are a PITA; not only the cause voltage spikes, they do generate considerable noise, what can be heard when using them in audio appliances. I struggled over that when using such a beast in my acoustic guitar. After that, I threw all of them out.
NiMH are maybe not the best solution, but as long as there are no Li 9V-blocks with clear and reliable specs, it's better to leave the fingers from them. So far I only know them from Ali & co, so you can search for a long time to find out what you get.