JYE Tech Forum

The effect of C6 is much less than C4.
On my DSO138 the corner of the trace can be varied from square to a spike about 1/4 of a division high.
As long as the corners are reasonably square the scope will work just fine.

Have you done Step 2 A? That's the one where you check the 3.3V at TP22 and short JP4 if the voltage is OK.
The 3.3V powers the microprocessor which puts pulses into R40 to drive the voltage inverter.
Your readings indicate you are missing this signal.

I'm glad to hear you now have a working scope. Out of curiosity, did you install the SMD parts or was the regulator done by JYE? Loading the 113-13801-066.rar firmware upgrade is worth the effort. read the whole thread if you want to know why. https://www.jyetech.com/forum/viewtopic.php?f=18&t=1...

There is a kit with necessary QuipQuik materials. The SMD1 removal kit cost nearly as much as the DSO138 but I'm sure you find other uses for it. https://www.digikey.com/product-detail/en/chip-quik-inc/SMD1/SMD1-ND/304148 The regulator is a LM1117IMPX-3.3/NOPB. It's in a SOT-223-4 package. https://w...

Having another oscilloscope will make troubleshooting much easier. From your description of the symptoms the problem is in U2B. You should be able to see the distortion at test point V1 to confirm this. U2, a TL084 is in a 14-SOIC (0.154", 3.90mm Width) package. https://www.digikey.com/product-...

The distortion in the photo is two divisions from the center. If I understand your post correctly that changes with the SEN2 switch setting. In that case it's unlikely the DSO138 is the problem. Check a signal from a different source. Since the frequency appears to 1000 Hz I assume you are using som...

The fourth page of the instructions has the diagram. If you didn't get this you may have a counterfeit. https://www.jyetech.com/Products/LcdScope/UserManual_138_new.pdf If you have 5V but no 3.3V U3, the 3.3V regulator is probably bad. Check for a short to ground on TP22. Before jumper JP4 is closed...

The trigger level is a control you set. Hit the SEL button to move the highlighting to the pointer on the right side of the display. Then use the + and - buttons to change the position of the pointer and the voltage reading. Holding the OK button for 2 seconds will reset it to 0. Set the trigger poi...

The range indication circuits for a three switches are the same. To the right of R19(CPL), R22(SEN1) and R25(SEN2) there are unlabeled test points. As you move the switches from left to right the resistance readings are approximately 1.5K, 4.1K and 3.6K. With power on the voltages are 0V, 1.2V and 3...

I suspect the zero volt position of the trace is not correct Verify that the the voltages at AV-, AV+, +3.3V and +5V are correct. A low battery will let the -AV drop causing the trace to be offset. With no input and the trigger mode set at auto you should see the trace in the middle of the screen. I...