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.

 

How are you measuring TP9? You cannot measure it with a DMM.

 

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?

 

As in most trouble shooting procedures, the first step is to check the DC voltages at the power supply.

 

All Voltages given at the Voltage Reference sheets are fine except the one in TP9/OSC. The screen turns on but stay just white.

 

As I said, you cannot test OSC with a voltmeter. OSC is a signal at 8MHz.
You really need an oscilloscope to check OSC.

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?

 

Ok i get it. Thanks for clarification. 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.

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

 

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?

 

Yes here everything is fine and all TP according to the given voltages. The soldering bridge on jp4 and jp3 is installed.

 

Yes here everything is fine and all TP according to the given voltages. The soldering bridge on jp4 and jp3 is installed.

You cannot measure DC voltage at VGEN. You need to look there with an oscilloscope.
What about TP25 and TP26? Are the voltages correct there?

 

TP26 is 0.6V and TP25 0.08V.

Thanks a lot for your Support MrChips!

 

The next step would be to examine the MCU clock signal and VGEN signal. You need an oscilloscope to do this.

 

Ok make sense but i buy this one to have one and now i need another... Thats some kind of ironic..
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?

 

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.

 

VGEN is 0.81V so its according the schematic fine. So is the MCU not fine?

 

VGEN is 0.81V so its according the schematic fine. So is the MCU not fine?

You cannot verify VGEN with a voltmeter reading.

 

Hm but why did they write these values to the manual? Is VGEN also AC?

 

Hm but why did they write these values to the manual? Is VGEN also AC?

Because they don’t know that that is wrong.
VGEN is +3.3V pulses.