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JYE Tech Forum • View topic - "White Screen" Troubleshooting Tips for DSO138

"White Screen" Troubleshooting Tips for DSO138

"White Screen" Troubleshooting Tips for DSO138

Postby jyephpbb » Sat May 23, 2015 12:56 pm

Many users reported they got a "white screen" display and AV- was found incorrect. Actually AV- has nothing to do with the "white screen" issue. AV- is the negative power supply analogue circuits while MCU and LCD depends only on +3.3V power supply. So once +3.3V is good and no any other components are found over heat you should focus yourself on making display work first. After display and all buttons are working you can proceed to taking care AV- or other analog circuit issues. That's to say, make the digital portion work first if it doesn't. Then start to troubleshoot the analog circuits if you have problem with trace display.
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Re: "White Screen" Troubleshooting Tips for DSO138

Postby TherGuru » Sun May 24, 2015 4:31 am

Hi just got yesterday assembled it , Same thing as Other complain . White Screen and no -ve voltage all other are good , How to test to find whats wrong????
need some type of flowchart to check faulty component..
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Re: "White Screen" Troubleshooting Tips for DSO138

Postby jye1 » Sun May 24, 2015 4:49 am

Generally troubleshooting can be done in two steps.

1 ) Make sure MCU is working. MCU status can be confirmed by pressing RESET button. If two blinks are observed after reset button is hit then MCU is working.

2 ) After MCU is confirmed working carefully check the connections between MCU and LCD module. These connections include 8 data lines (DB0 - DB7) and 5 control lines (labelled with "LCD_"). Make sure they have no opens or shorts. You can use the "Test Mode" to find out opens (see user manual). But Test Mode can't uncover shorts.
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Re: "White Screen" Troubleshooting Tips for DSO138

Postby TherGuru » Sun May 24, 2015 7:29 pm

Here is simple solution
If MCU is working Green LED is blinks twice then do following steps.

1) check voltage on AV+ 5v, +3.3v, +5v should be + - 0.3 OK, Don't worry about AV- for now..
2) Solder Pin on 40 Pin connector on both LCD and on board ( keep soldering tip for 3 sec on all joint one by one)
3) Check power supply voltage should above 8v or replace 9 v battery with new good one.

Try is it worked for me
Thanks
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Re: "White Screen" Troubleshooting Tips for DSO138

Postby malme84 » Wed Jun 03, 2015 12:10 pm

What should I try if the LED doesn't blink at all? I get a white screen that after 3 seconds turns to what I can only describe as "colored static". All voltages check out except av-. Putting a voltmeter on the LED shows the voltage alternating between 0 and 3.3v continuously.
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Re: "White Screen" Troubleshooting Tips for DSO138

Postby zfiser » Sat Jun 13, 2015 4:19 pm

Hello,

I had the "white screen & no blink" problem. As you can read in the forum, this problem means that the CPU doesn't work.
I had correct voltage on the CPU's power pins and the resonator (Y1,C12,C13) was OK.

In my case, the problem was invisible short-circuit to the ground on C14 capacitor which is connected to the CPU's RESET pin. Therefore, the CPU was constantly being reset and didn't work. To find out if you also have this problem, try whether both pins on the C14 capacitor are connected to the ground. If they are, you have this problem. Another place where the short could occur is on the reset switch SW8.

I hope this helps someone.
good luck
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Re: "White Screen" Troubleshooting Tips for DSO138

Postby oricmuso » Mon Jun 29, 2015 3:33 pm

My screen worked initially then I got the white screen. (mu LED blink though).
I used the connector holes that are along the top of the screen. With a continuity tester on the multimeter I checked each pin with one probe in the hole on top and the other on the soldered connector pin. (Continuity tester usually beeps then you get a good circuit. ) Testing each pin I found one that wasn't a good solder. Once it was resoldered the screen worked OK
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Re: "White Screen" Troubleshooting Tips for DSO138

Postby Tuero » Thu Jul 23, 2015 7:51 am

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Re: "White Screen" Troubleshooting Tips for DSO138

Postby rew » Thu Jul 30, 2015 10:38 am

I have the same white screen.

CPU attaches to STM32 debugger "20K ram, 0K flash". I don't know if the debugger is wrong about that or if the chip is "odd".
In the debugger I cannot read flash or RAM. Probably read protected. That could influence maybe the "reported flash size". I'm not worried.

I get the blank screen, no blinks on the led. -> CPU doesn't work, right?

Then: When I remove the screen, I get a blinking light.

But.. When I connect USB I get "device does not enumerate". I haven't read about the USB interface and what would be possible with it. Should it enumerate?

Any suggestions as to what could be wrong with my (genuine: has teardrops on almost all solder pads) DSO138?


[update:]
OK... it works! I find it difficult to solder JP4 after all the components are mounted: it turns out it didn't connect. With the hints of "it's the CPU" I checked all the grounds to the C16, C17, C18 and found them OK. Then I checked all the VCCs/3.3V's and they sounded like when you probe VCC with the other pin on GND: some capacitor, but not a connection. So when I redid JP4 it works!

Now remains the question: where do I find out what the USB connection does?

[update2: ]
USB connector does nothing. The CPU supports USB, but the firmware does not. For a next version: I would appreciate a connection option between the "VBUS" and +5V: Then although the analog side won't work, you can use the board as an usb-connected STM32F103 development board with LCD!

Where is JP2? What is it for? IIRC (I'm not where my DSO138 is right now) it is an SMD jumper on the back side. That would be a free IO. Consider connecting R31, the side that is now connected to R30, to that free IO. Then configure PB2 as input: nothing happens when you connect USB (the host does not see a device). When you want to be detected, set the pin high and as OUTPUT. Now the host will see a FULL-speed USB device.

I'm not sure if ST supports/approves of letting the CPU connect VSSA and VSS. I measure about 15 ohms and about 63 mV of differential.
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Re: "White Screen" Troubleshooting Tips for DSO138

Postby crc64Error » Fri Sep 18, 2015 4:00 pm

In my case, I have the white screen, and slow blinking led two pulses on followed by one second off, repeat. Voltages are good, except the following:

J2 Test is at 1.64
TP25, L1, D1+ are at -10.64 * I realize these are supply voltage dependent now.
D1 0.19 side is at 0.136v

Is there a way to test lcd signal without an oscilloscope? I have been thru the 40 pin connector so many times.
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