DSO-150 mini oscilloscope missing H signal line Repaired

Hi dear friends

 Welcome back to electronic repair articles after a long time  i am bringing one more very interesting topic on digital oscilloscope model  DSO-150 which is one of very useful instrument for repair technicians.

We know oscilloscope is very essential tool for debugging application but because of it's high expensive cannot own this instrument.

Here i am presenting one of the cheapest digital oscilloscopes developed by jaytech model DSO-150 which is available in the market in ideal form for around 20 dollars in Ali express online shopping.

DSO-150 Digital oscilloscope

DSO-150 Digital oscilloscope

But my story hears is an article how i damaged oscilloscope hardware and repaired an invisible horizontal signal line in the instrument.

When i brought this instrument and assembled in my bench worked excellent and i was using to trace audio signals and pwm signals in power supply circuits and also led/lcd tvs monitors really enjoyed a lot in debugging activity.

Components received from online

Really i appreciate an inventor from jaytech who developed such a wonder full handy instrument of 200khz band width with all basic function mainly employed in fast repair activity with its 2.4 inch beautiful colour display.

One of the major drawback of this instrument is it does not have battery back user need to use external dc adopter 9v . This makes uncomfortable to use effectively like handy as multimeter in my bench.

The current consumption of this instrument noted in my bench is around 90 to 100 mili amps. Made my mind to innovate battery backup by inserting 9 volts battery and tried with readily available non rechargeable battery and worked fine  but main drawback is H signal line starts coming down proportionally as the battery voltages decreases form 9 volts to 6 volts and this is failed & started to innovate to introduce rechargeable battery using mobile battery bank.

This concept is goggled in the internet and selected dc boost converter board which converts 3.7 volts to 9 volts depending up on the pot tuning on the board. I have shown the board below for your reference.

DC 3.7 Volts to 9Volts converter

I assembled the battery and charger setup for 9 volts by using above concept and powered the DSO-150 Jay-tech oscilloscope. Once the equipment powered to my bad luck i noticed noisy signal horizontal line for a movement and disappeared made many attempts by tuning the settings but not success so disappointed.

Many questions in mind what is the difference in applied boost 9 voltages to oscilloscope. Re-verified with my regulated bench power supply no results .H signal line completely disappeared and concluded i damaged my oscilloscope hardware.

Goggled an internet to find the failure cause. Thanks to the Jay-tech team for providing such a wonder full schematics and voltage test points in the web site.

https://jyetech.com/Products/LcdScope/Schematic_Shell.pdf

As per their manual started to check the voltages in there test points. Every voltage is normal expect minus 5 volts.

various test points in analogue Board

   Troubleshooted   negative five volts missing and problem is with the negative voltage generator IC5. pls go through the schematics and test points below for your understanding.

Orignal minus 5 volt circuit by JAY-TECH

Hear the heart of the circuit is U5  ICL7660 SPIC8 package. Goggled the data sheet and confirmed sensitivity level for input spikes. Ultimately i got the reason for the failure cause, IC U5 Damaged while modifying input 9v dc by using boost converter supply as stated above.

If  ICL7660 not available instead we can modify some other good negative voltage generator as in example below using IC555.This is because components are very common /low cost/available everywhere around the globe

Equivalent minus 5 volts circuit using 555

May be for compact design inventor may selected ICL7660.After replacing U5 minus five volts started to generate and re-gained the life of my mini DSO-150 Oscilloscope. I suggest the user please use proper spike free regulated dc 9 volt power supply and the voltage should not exceed the spec limit of U5(ICL7660).

minus 5voltes re-gained after replacing U5( ICL7660)

This is the best test instrument I Recommend to the technicians and has its own value for the money. If any breakdown easily can repair because spares are readily available in the market except micro-controller.

Here's the DSO150 Oscilloscope specifications:

• Number of channels: 1
• Analogue bandwidth: 0 – 200KHz
• Sensitivity: 5mV/Div – 20V/Div
• Resolution: 12-bit
• Input Impedance: 1M ohm
• Coupling: DC, AC, GND
• Time base: 10us/Div – 500s/Div
• Trigger modes: Auto, Normal, Single
• Trigger types: Rising/falling edge
• Power supply: 9V DC
• Supply current: 120mA @ 9V
• Dimension: 115mm x 75mm x 22mm
• Weight: 10

 yes, above specification is most sufficient for electronic repair work and small R&D jobs

Thank you and happy reading stay tuned for my up-coming interesting articles. 

Regards

Basavaraj BM

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