V+ and short spot

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Joined: Sun Mar 10, 2019 5:08 pm

V+ and short spot

Post by aragon »


i encountered problem with DSO138 mini V- voltage. Are PCB layout are available ? Hereafter the description of my problem.

Analog PN :109-13801-00J
Main MB PN : 109-13800-00I

User manual Rev. 05
Step 3.1 Check voltages and controls

U2 (ICL7660)
V+=4.9V → AV+<V+=4.9V
V-=-3.6V → AV->V-=-3.5V

When SW1 is in GND position, SW2 is at 1V and SW3 is at X5.
V1=-1.4V (5-3.5)
V3=2.2V near D1=2V+/-0.2V → V4=1.1V near -1V

V1 is bad because TL084 is powered asymmetrically.
TL084 is bad powered cause V- is not the opposite of V+.

When applying Symptom 4, Solution 1 of «Troubleshooting Guide» :

Disconnect L2 and check if V- returns to normal-> V+=4.9V without any load.

If it does that means V- problem was caused by large load current. This large current is usually
created by shorts between AV- and ground. You need to uncover the short spot.

Do you have any PCB layout to help me uncover this short spot ?
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