[Fixed] DSO Nano 201 V2.5 Battery drains while Off

Products & Technology DSO Nano
#1

Hi. I received my DSO Nano V2 few days ago. Battery was discharged on arrival. So I recharged it fully and started using it. Pretty nice basic little scope.

Then I noticed the battery would go dead over night with the Power switch turned OFF. After searching the forum, I decided to check the battery terminals. They were not shorting out. But the ground wire was hanging on with two strands which eventually broke off (pic attached.) I decided to check current draw with DVM.

DSO Switched Off: 59mA - Why???
DSO Switched On: 190mA

I also checked R27 which is 3.25K.

I also checked U10 pin 1 and 6 and getting some readings both ways, is that normal (pic attached.)

So it seems 59mA is the problem. What should I do now?

Thank you.
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#2

Here what U1 looks like.
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#3

I believe the problem could be with U1. When its charging, its too hot to touch at 65C/149F degrees which is higher than ratings in) datasheet

Update: With USB plugged in, Battery disconnected, Nano OFF; the U1 is at 55C/131F degrees. Why so hot when its not charging anything?

Update 2: I was wrong in first sentence, temp is within rating < 125C so 65C seems ok.

Update 3:
U1 Readings: USB plugged in, Battery disconnected, Nano OFF
BAT pin 3 = 4.13v
VCC pin 4 = 4.94v
PROG pin 5 = .23v

USB plugged in, Battery with 3.9v connected, Nano OFF
Battery recharges at 80mA

Any advice how to verify U1?

#4

More info.

Removing R27 had no effect. So I lifted pin 3 (Batt) of U1 and the 59mA drain disappeared. :astonished: When Nano is turned ON, now it uses 150mAh where before it was using 190mAh.

WARNING: Then LTC4054 is VERY fragile. I ripped the pin 3 off while bending it up with little force. :laughing:

So my charger was bad and now one leg short so I need to replace it. Will update once its fixed.

#5

Pic of Bad LTC4054 chager IC. This looks like possible badly cooked IC. It has many cracks. The label is hard to see. Perhaps a knockoff even though Nano came from Seeed.
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#6

I have contacted Seeed about the problem and they sent me a pair of LTH7 with a pair of 332 resistors. I could not wait for the mail man so acquired the LTH7 directly from Linear Tech.

Soldered in the IC and all is well. When battery almost dead, it recharges at 460mAh-470mAh. Battery stays charged once unplugged and turned Off. With my cheap DVM I get 0mAh drain with Nano Off, so its fixed. Also noticed with battery disconnected, USB in, U1 is cold. And once the battery is full at 4.13v, U1 is cold again. Before the bad U1 was hot in both cases.

Hope my experience helps someone.
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