DSO 138 Oscilloscope DIY Kit User Manual

20. Test signal ring

1. Make a small ring with a lead cut-off.
2. Solder the ring to the two holes of J2 (as shown in the photo).

21. JP3

Short JP3 with solder.

22. LCD Board

Note: Install to the side opposite to LCD panel.

• J1
• J2, J3: 2 x 20 pin
• J1: 1 x 2 pin

A. Check voltages

Note: You need a 9V DC power supply (at least 200mA capacity) to run the scope. This power supply is not included in the kit.

1. Apply 9V power to J10 (or J9).
2. Check voltage at TP22. It should be around +3.3V.
3. If voltage at TP22 is good, disconnect power. Short JP4 with solder permanently.

B. Attach LCD board

Plug LCD board into the female headers J3, J7, and J8 on the main board.

C. Verify

1. Connect power supply again. You should see the LCD lights up and the oscilloscope panel displayed.
2. Press various buttons and move switches to verify their functions.

A. Use

1. Attach probe clips to J1.
2. Touch the red clip with your finger. Do you see a signal from your finger?

No Display

• Is voltage at V+ good? ❌ Check power supply. Short JP4 if it has not been done. See Step 2 above. ✔️
• Is R36 value correct and soldered good? ❌ Fix R36 and power again. ✔️
• Do you get about 3V between J1 pin 16 & 18 on LCD board? ❌ Check J3 soldering for possible opens or shorts. Check J1 soldering on LCD board for possible opens or shorts (use Test Mode). ✔️
• Press SW8. Does LED blink? ❌ Check R36 and power again. ✔️

LCD Dark (No backlight)

• Check +3.3V voltage.
• Check Y1, C12, C13.
• Check LED installation.

No Trace

• Are the values of AV+ and AV- correct? ❌ Visit forum for detailed troubleshooting guide. ✔️
• Set CPL switch to GND and measure V1 and V2. Are they correct? ❌ Check U2B, U2C and related parts around these two amplifiers. ✔️
• Check R12 and C8.

Test Mode

What it is and how it works: Test Mode is used to find out possible opens (for all port pins) and shorts (for pins PB0-15 and PC13-15). When entered, it first checks PB and PC pins with special patterns to find out possible shorts. If found, LED will be fast blinking. Otherwise, it generates 3.3V and 0V alternatively at each port pins (PA, PB, PC and PD) in a cycle of about 4 seconds. These signals can be used to check for opens.

How to use:

1. Hold down SW4 and press RESET to enter Test Mode.
2. If you see LED fast blinking, that means there are shorts on PB or PC pins. You need to find out the shorts first.
3. If you see LED slowly blinking, use a voltmeter to check each pin related connections that are suspected open. When you don't see voltage change at a spot which is supposed being connected to a port pin, there may be an open between the spot and the port pin.

Display and Controls

• Connector for Probe
• Oscilloscope Mode
• Horizontal Position
• Trigger Level Readout
• Connectors for Power Supply
• [CPL]: Couple Selection
• [SEN1]: Sensitivity Selection 1
• [SEN2]: Sensitivity Selection 2
• [SEL]: Parameter Selection
• [+] or [-]: Parameter Adjustment
• [OK]: HOLD/RUN Selection
• Trigger Level Indicator
• Sensitivity
• Vertical (V/div)
• Timebase (s/div)
• Position
• Couple
• Indicator
• Trigger Slope
• Trigger Mode
• "Trigged" Indicator
• Reset Button

Connections

• Power Supply: Connect DC power supply to J9 or J10. The power supply voltage must be in the range of 8 - 12V.
• Probe: Connect probe to J1.

Operations

• Press on [SEL] button: Select parameter to be adjusted. The selected parameter will be highlighted.
• Press on [+] or [-] button: Adjust the parameter selected by [SEL] button.
• Press on [OK] button: Freeze waveform refresh (entering HOLD state). Press on it again will de-freeze.
• Change [CPL] switch: Set couple to DC, AC, or GND. When GND is selected, the scope input is isolated from the input signal and connected to ground (0V input).
• Change [SEN1] or [SEN2] switch: Adjust sensitivity. The product of [SEN1] and [SEN2] settings makes the actual sensitivity, which is displayed at the lower-left corner of the panel.
• Press on [Reset] button: Perform a system reset and re-boots the oscilloscope.

0V Line Alignment

Sometimes you may find the 0V line (the trace corresponding to 0V input voltage) does not match with the VPOS indicator at the screen left border. This can easily be fixed by performing the "0V line alignment" function. First, set the couple switch [CPL] to GND position. Then press on [SEL] button to make VPOS indicator highlighted and hold down [OK] button for about 2 seconds. You will set the trace aligned to VPOS indicator when you release [OK] button. You may see some residue mismatch remains at the highest sensitivity settings. This is normal.

Probe Calibration

Because there is always some capacitance between scope input and ground, the probe needs to be calibrated to achieve better measurement results for high-frequency signals. This can be done with the help of the built-in test signal. To do this, please follow the steps below.

1. Connect the red clip to the test signal terminal and leave the black clip un-connected (see photo at right).
2. Set [SEN1] switch to 0.1V and [SEN2] switch to X5. Set [CPL] switch to AC or DC.
3. Adjust timebase to 0.2ms. You should see a waveform similar to that shown in photos below. If traces are not stable, adjust trigger level (the pink triangle on the right screen border) so as you get a stable display.
4. Turn C4 (capacitor trimmer) with a small screwdriver so that the waveform displays a sharp right angle (photo C).
5. Set [SEN1] switch to 1V and [SEN2] switch to X1 while keeping all other settings unchanged. Adjust C6 so that a sharp right-angle waveform is displayed.

A - Not enough

B - Too much

C - Good

Turn On/Off Readouts

Press [SEL] so that timebase is highlighted. Hold down [OK] button for about 2 seconds. This will turn on/off measurement readouts.

Waveform Save/Recall

• Press [SEL] & [+] simultaneously: Save currently displayed waveform to non-volatile memory.
• Press [SEL] & [-] simultaneously: Recall saved waveform.

Triggers and Their Modes

Triggers are events that indicate signal voltage acrossing a set level (i.e., trigger level) along a specified direction (i.e., trigger slope, rising or falling). Oscilloscope uses triggers as reference points in time for stable waveform display and measurements.

• Auto Mode: In auto mode, oscilloscope will perform display refresh no matter if triggers happen or not. When triggers are detected, waveform display will be displayed with reference to trigger points. Otherwise, display waveform at random reference points.
• Normal Mode: In normal mode, oscilloscope will only perform display refresh when there are triggers. If no triggers happen, waveform display will stay unchanged.
• Single Mode: Single mode is the same as normal mode except that oscilloscope will enter HOLD state after a trigger has been detected and waveform display has been updated. Normal and single modes are useful for capturing sparse or single waveforms.

Specifications

• Max realtime sample rate: 1MSa/s
• Analog bandwidth: 0--200KHz
• Sensitivity range: 10mV/div - 5V/div
• Max input voltage: 50Vpk (1X probe)
• Input impedance: 1M ohm/20pF
• Resolution: 12 bits
• Record length: 1024 points
• Timebase range: 500s/Div -- 10us/Div
• Trigger modes: Auto, Normal, and Single
• Trigger position range: 50%
• Power supply: 9V DC (8-12V)
• Current consumption: ~120mA
• Dimension: 117 x 76 x 15mm
• Weight: 70 gram (without probe)