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