No trace, voltages not correct

[Ray]

My DSO 068 has been working fine for several weeks but suddenly stopped displaying a trace the other day. Every other thing still works - all the menu functions, the frequency counter, all the switches all work as they should. The 068 is powered by a 3.7 li-po battery. The screen looks normal except there is no signal trace at all.

I went through the trouble shooting flow chart and found some bad volatges:

VBUS .012
AV- .2
V5 .5
V- .19
V4 3.5
V2 1.0
V3 1.09

All other voltages were correct. Is this a bad BOB5 board? Any other ideas?

[jye1]

Did you get correct +5V? It is most important and must be good before checking other voltages.

[Ray]

The voltages I posted are the ones that were incorrect according to the instructions that came with the 068. All other voltages were within the expected range. This includes +5v where ever the instructions said I should find +5v. Is there some specific test point you would like me to verify?

[jye1]

From your measurements AV- is not good. AV- is generated by BOB5. So please check to make sure BOB5 is soldered well. If +5V is good and no -5V output from BOB5 at V- then BOB5 might be the problem.

[Ray]

Yes, +5V is good, and there is no -5V at V- so it appears BOB5 has failed. How can I get another BOB5?

[jye1]

Please contact JYE Tech at jyetech@163.com. Thank you.

[s1292oia]

After assembly, the screen is no trace in the oscilloscope mode. When checking the voltage determined switch SW2 is broken, is not closed contacts 1, 2 and 5, 6 in position 10 mV. In other states the right contacts are closed.
The measured voltage:
+5V OK
-5V OK
AV+ 5V
AV- -4,97V
If the switch SW1 is GND:
V1 0V
V2 0V
V3 -1,2mV
V4 1,6V
VA 5V
VB 0,17V bad
VT 1,7V bad
Is this mean that the U3 is broken?
What type of SW2 is used?
Where to buy a SW2 and a U3?