"White Screen" Troubleshooting Tips for DSO138

jyephpbb
Site Admin
Posts: 8
Joined: Wed Feb 20, 2013 1:12 am

"White Screen" Troubleshooting Tips for DSO138

Post by jyephpbb »

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.
TherGuru
Posts: 8
Joined: Sat May 23, 2015 5:06 am

Re: "White Screen" Troubleshooting Tips for DSO138

Post by TherGuru »

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..
jye1
Posts: 1226
Joined: Wed Feb 20, 2013 4:58 pm

Re: "White Screen" Troubleshooting Tips for DSO138

Post by jye1 »

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.
TherGuru
Posts: 8
Joined: Sat May 23, 2015 5:06 am

Re: "White Screen" Troubleshooting Tips for DSO138

Post by TherGuru »

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
malme84
Posts: 2
Joined: Wed Jun 03, 2015 12:37 am

Re: "White Screen" Troubleshooting Tips for DSO138

Post by malme84 »

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.
zfiser
Posts: 1
Joined: Sat Jun 13, 2015 11:59 am

Re: "White Screen" Troubleshooting Tips for DSO138

Post by zfiser »

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
oricmuso
Posts: 2
Joined: Thu Jun 25, 2015 10:48 am

Re: "White Screen" Troubleshooting Tips for DSO138

Post by oricmuso »

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
Tuero
Posts: 1
Joined: Wed Jul 22, 2015 10:33 am

Re: "White Screen" Troubleshooting Tips for DSO138

Post by Tuero »

zfiser wrote: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
Hi. I have similar problem, but i dont know, how to solve her. Can you describe, how to escape that problem?
rew
Posts: 2
Joined: Thu Jul 30, 2015 5:17 am

Re: "White Screen" Troubleshooting Tips for DSO138

Post by rew »

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.
crc64Error
Posts: 1
Joined: Fri Sep 18, 2015 3:51 am

Re: "White Screen" Troubleshooting Tips for DSO138

Post by crc64Error »

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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