DSO138 LCD issue (2)

Thread Starter

manuel86

Joined Mar 24, 2024
9
Hi both,

I have exactly the same issue.
0.475V on TP9==OSC. It should be 2.16V according to the manual.

Any Idea how to solve?

Moderator edit: new thread created from this.
 

Thread Starter

manuel86

Joined Mar 24, 2024
9
Hi Mr.Chips, thanks for your reply!
In the upper right corner is TP9 located in you schematic and on the pcb its labeled with OSC. In the Manuell is wtitten down the voltage on this point. It should be 2.16V. But the MCU dont give this Voltage to the Cristal.

It seams that the MCU did not boot properly because also the LED blinks only one time! Is this because the Cristal get not the right voltage? Any idea what could block the boot?
 

Thread Starter

manuel86

Joined Mar 24, 2024
9
All Voltages given at the Voltage Reference sheets are fine except the one in TP9/OSC. The screen turns on but stay just white.
:(
DSO138 voltages.jpg
 

MrChips

Joined Oct 2, 2009
30,935
As I said, you cannot test OSC with a voltmeter. OSC is a signal at 8MHz.
You really need an oscilloscope to check OSC.:D

Was your DSO138 assembled from a kit or was it pre-assembled?
Did the DSO138 ever work when you got it?
With the display not plugged in, what does the TRIGGED LED do when you apply power?
 

Thread Starter

manuel86

Joined Mar 24, 2024
9
Ok i get it. Thanks for clarification. :D i was thinking that i can measure some kind of an average voltage. My fault.

I assemble it by my self. When i remeasure everything today again i found that AV- is now 0.668V and not -5V as before. So Maybe i have made it worser by trying to fix it. The Area around L1 and V- seams causing this. I measure there now 0.115V. But i have no idea why and how to fix. In general i could not understand from where the -8.1V should come. :(1000018509.jpg

So maybe this is the end of my first soldering project...
 

MrChips

Joined Oct 2, 2009
30,935
The first thing is to check that you have +5V and +3.3V on the low voltage power supply at TP21 and TP22.
Do you have JP4 (solder bridge) installed?

DSO138 Low Voltage Power Supply.jpg
 

Thread Starter

manuel86

Joined Mar 24, 2024
9
Yes here everything is fine and all TP according to the given voltages. The soldering bridge on jp4 and jp3 is installed.
 

Thread Starter

manuel86

Joined Mar 24, 2024
9
Ok make sense but i buy this one to have one and now i need another... Thats some kind of ironic.. :D
Is it not a critical problem to dont have this -8V and -5V on this lane? How is this negative Current created and can the MCU work without?

Additionally why are there Voltages marked on the Manuell that could not be measured?
 

MrChips

Joined Oct 2, 2009
30,935
The MCU does not need negative voltage to operate. It only needs +3.3V.
VGEN is generated by the MCU. If the MCU is not operating then there will be no VGEN.
VGEN is used to drive the positive to negative voltage converter.

Hence, the first step is to verify that the MCU is running.
 
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