DSO138 troubleshooting - No AV- (no trace)

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

Re: DSO138 troubleshooting - No AV- (no trace)

Post by jye1 »

Can you please

1) check the firmware version at power up screen
2) post clear photos of your board(both sidea)
3) check VGEN again with LCD plugged in
redmi
Posts: 9
Joined: Sat Jul 25, 2015 7:14 pm

Re: DSO138 troubleshooting - No AV- (no trace)

Post by redmi »

Thank you for your answer:

1) As it can be seen in the next picture, the firmware is 113-13801-045
Image (https://www.dropbox.com/s/wps6dpd3baigh ... 8.jpg?dl=0)

2) The Front side: Image (https://www.dropbox.com/s/pvvj7rihr3x7t ... 0.jpg?dl=0)
The Back side (although the soldering is ugly for the several times resoldered transistors, I have checked all connections and continuities: Image (https://www.dropbox.com/s/kw292w733ir65 ... 8.jpg?dl=0)

3) VGEN is 1.01 V when the LCD is plugged in and 0V when it unplugged.

Thank you for your time.
jye1
Posts: 1226
Joined: Wed Feb 20, 2013 4:58 pm

Re: DSO138 troubleshooting - No AV- (no trace)

Post by jye1 »

Thank you for the photos. So VGEN is there although a little higher than usual. Can you please check the few voltages related to Q2 & Q1 as stated in the first post of this thread? Please measure from the back since LCD has to be plugged in.
redmi
Posts: 9
Joined: Sat Jul 25, 2015 7:14 pm

Re: DSO138 troubleshooting - No AV- (no trace)

Post by redmi »

At the end it was bad soldering on U3 (bad 3.3V signal). Now it works nice.

Thank you for all your support and patience. An oscilloscope under 30$ is pretty awesome :)
S9RKAN
Posts: 1
Joined: Wed Aug 26, 2015 1:22 pm

Re: DSO138 troubleshooting - No AV- (no trace)

Post by S9RKAN »

centurion wrote:Good day! When you start the device, there is smoke and burn the transistor Q1. Then the screen is loaded, but there is no trace. Change the transistor - again burns! What could be wrong? What settings should pay attention to?I do not have time to be measured before the transistor burns. :?
I have the same problem. Burnt out the Q1 with some smoke on it. Also L2 was too hot. Before that the oscilloscope booted up but after burning, there is only the backlight. What should I do, please could someone help me?
Heritage0343
Posts: 1
Joined: Mon Sep 21, 2015 12:49 am

Re: DSO138 troubleshooting - No AV- (no trace)

Post by Heritage0343 »

This issue seems to be fairly common and I'm not sure what the issue is. I think the engineering is good but perhaps the parts quality is poor. I have 30 years of technician experience and would consider myself to be an excellent soldering guy. Put the kit together carefully double checking component values and placement. Did the required preliminary voltage checks and assembled the LCD. Scope came on fine but had no trace so according to the provided instructions I came to this thread to troubleshoot. No AV- was the issue. Found the output of pin 46 good at +.81 vdc. base of Q2 was less that that. replaced Q2 with a suitable substitute and had -1.37vdc at Q2 base. output still bad at Q2 collector. Verified output components and soldering and replaced Q1. Had the same problem. I rechecked solder connections and component placement and eventually the scope had smoke and died all together. I removed the LCD and found U5 hot to the touch. I removed the short at jumper 4 and got u5 operating again. Some simple checks after removing capacitors at the input of the microprocessor showed an internal short so now I'm left with a dust collector! Perhaps JYEtech can explain what this common problem is and what they intend to do about it. Seems that the buyer should have some level of confidence that they are not buying a suspect item from the start. Please advise if you would...
jye1
Posts: 1226
Joined: Wed Feb 20, 2013 4:58 pm

Re: DSO138 troubleshooting - No AV- (no trace)

Post by jye1 »

Did you see any problem with AV- before the LCD was put on? No AV- could cause no trace. But no trace is not always caused by bad AV-.
Riccardo
Posts: 1
Joined: Tue Sep 22, 2015 7:09 am

Re: DSO138 troubleshooting - No AV- (no trace)

Post by Riccardo »

Hi All, I appreciate your suggestions for a lot of problems.
I suddenly have had a mafunction on my DSO138: it was well working till yesterday.
The problerm is this:
1) white screen
2) detaching screen PCB TP22 (3.3V) is only 0.7-0.8 V
3) opening JP4 3.3V reappears fine (on regulator of 3.3V), closing JP4 voltage drop down, that means short circuit or too high current flow after the 3.3V regulator .
4) In this condition JP4 closed +5V regulator becames very hot.


Any idea of which parts statistically may have had a fault.?
I cannot dissolder all active component to find breaked part.
Thank you in advance for any ideas.
ovkirillov
Posts: 2
Joined: Sun Nov 15, 2015 5:55 pm

Re: DSO138 troubleshooting - No AV- (no trace)

Post by ovkirillov »

I have a random noise, but no signal.
I've burnt my U5 and replaced it already, also failed to identify U2 pin1 and had to replace it too. :)
Now all voltages are good except AV- (TP26, -2.54V, should be -5V ) and V- (TP25, -2.02V, should be -8V). Could it be the failed D1?
jye1
Posts: 1226
Joined: Wed Feb 20, 2013 4:58 pm

Re: DSO138 troubleshooting - No AV- (no trace)

Post by jye1 »

Did you check the voltages according to the first post of this thread?
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