Switching power supply oscilloscope help

Thread Starter

imraneesa

Joined Dec 18, 2014
224
hi all,

I am trying to fix switching power supply for a sony stereo box. I generally change the whole board in TV but since this board is not available i am trying to repair it.

I have voltage coming to the main capacitor. and i have the IC ICE2QS03G is a switching IC. i want to check if it is making oscillations with my oscilloscope. i have 100w bulb in series with the main AC as a safety.
the ground pin of the IC is 8 and gate pin is 4. When i tried to touch oscilloscope ground to the IC ground i am seeing my 100w bulb glowing and i immediately took it out. i dont know what am i doing wrong. looking forward some expertise help in fixing this power supply. i am not getting standby voltage. and is this IC driving the transformer to get 13v standby. Thank you.
 

BR-549

Joined Sep 22, 2013
4,938
Is it a stereo box(not sure what that is) or a TV? Do you have a schematic? ...and some clear pictures of board?

Have you ever used a scope octopus to troubleshoot a dead, un-powered board? In many cases one can repair without analyzing the circuit.

One just verifies the separate components on board. If there is any doubt...just replace.

Compare the time taken to replace 25 parts.......to the time it takes to analyze. Can a tech replace 25 parts in an hour..........what does one hour of understanding circuit do for you?

This is how I repaired boards with no information about. Just jump down to a lower level.

Component level.
 

Thread Starter

imraneesa

Joined Dec 18, 2014
224
Is it a stereo box(not sure what that is) or a TV? Do you have a schematic? ...and some clear pictures of board?

Have you ever used a scope octopus to troubleshoot a dead, un-powered board? In many cases one can repair without analyzing the circuit.

One just verifies the separate components on board. If there is any doubt...just replace.

Compare the time taken to replace 25 parts.......to the time it takes to analyze. Can a tech replace 25 parts in an hour..........what does one hour of understanding circuit do for you?

This is how I repaired boards with no information about. Just jump down to a lower level.

Component level.

This is sony HCD-SHAKE7 stereo box. i am attaching the picture of the power supply board. i can change parts. but i am in a process of learning also. i love to learn to always go further one step ahead. while in the process if i get any doubts i seek help. i repair car amplifiers. i have just started repairing led tv. this stereo is my personal set. so i want to play with it to gain some knowledge.
 

Attachments

BR-549

Joined Sep 22, 2013
4,938
Ok....you will need a board......that you have paperwork on....to learn.

What do you expect to learn with this board?
 

BR-549

Joined Sep 22, 2013
4,938
Is that fuse at mid board, good?

You can still repair the board. One can pull and test and spec, each component.

If you have electronic knowledge, you can test many components without removing them from the board.

Do you know what a scope octopus is? They are easy to build. But it takes knowledge to be able to interpret the display. It takes a little practice too.

An octopus can show you the operating character of the caps, the inductors, resistors and the PN junctions of solid state devices on an un-powered board.

Search for scope octopus on youtube. It's not taught much......but can save a lot of time.
 

Thread Starter

imraneesa

Joined Dec 18, 2014
224
Is that fuse at mid board, good?

You can still repair the board. One can pull and test and spec, each component.

If you have electronic knowledge, you can test many components without removing them from the board.

Do you know what a scope octopus is? They are easy to build. But it takes knowledge to be able to interpret the display. It takes a little practice too.

An octopus can show you the operating character of the caps, the inductors, resistors and the PN junctions of solid state devices on an un-powered board.

Search for scope octopus on youtube. It's not taught much......but can save a lot of time.
That fuse was open and I changed it. I will check about octopus. Thank you. Yes I am good in electronics. I repair car amplifiers. Ad I use oscilloscope.
 
A light bulb in the circuit provides NO protection! If you are not familiar with high voltage circuits then it is best to leave it to someone else. That said, what you really need is an isolation transformer for the line in. That is still not a perfect solution since high voltage is still in the circuit and you can be electrocuted. Working with high voltage circuits requires a different mind set and extreme caution. Get some rubber gloves.

If your oscope has two channels, you can use them in differential mode and determine the waveform between any two points. In this instance, one probe acts as the reference point and the other is for the measured point. Make sure you keep the vertical set for a higher voltage so you don't damage the oscope inputs.
 

Thread Starter

imraneesa

Joined Dec 18, 2014
224
A light bulb in the circuit provides NO protection! If you are not familiar with high voltage circuits then it is best to leave it to someone else. That said, what you really need is an isolation transformer for the line in. That is still not a perfect solution since high voltage is still in the circuit and you can be electrocuted. Working with high voltage circuits requires a different mind set and extreme caution. Get some rubber gloves.

If your oscope has two channels, you can use them in differential mode and determine the waveform between any two points. In this instance, one probe acts as the reference point and the other is for the measured point. Make sure you keep the vertical set for a higher voltage so you don't damage the oscope inputs.
Thanks alot. i learnt this differential mode and i am very happy. it is working great. i can probe very much any two points now without any fear.
 

Plamen

Joined Mar 29, 2015
98
hi all,

I am trying to fix switching power supply for a sony stereo box. I generally change the whole board in TV but since this board is not available i am trying to repair it.

I have voltage coming to the main capacitor. and i have the IC ICE2QS03G is a switching IC. i want to check if it is making oscillations with my oscilloscope. i have 100w bulb in series with the main AC as a safety.
the ground pin of the IC is 8 and gate pin is 4. When i tried to touch oscilloscope ground to the IC ground i am seeing my 100w bulb glowing and i immediately took it out. i dont know what am i doing wrong. looking forward some expertise help in fixing this power supply. i am not getting standby voltage. and is this IC driving the transformer to get 13v standby. Thank you.
Petkan:
Using a ballast bulb as protection is fine...but you also need isolation transformer. The front end of the switching mode power supplies is essentially 4 diode bridge rectifier. This makes both + and - dc ends untouchable by grounded scope. Assuming you have no scope with isolated inputs - your best option is to use isolation transformer. In absence of suitable (120vac/120Vac or 240Vac/240Vac) transformer I use two back to back 120Vac to 6V transformers. Another option is to use a lab power supply and force feed the dc side. Moreover you can trace the Vcc pin of the controller chip and force feed it from a lab power supply too. Study its data sheet first and adjust the voltage and current limit accordingly.
 
Something around 100 to 200mA is the lethal range of current, give or take a little. This range of current through your heart can cause fibrillation. Higher currents can still be lethal and can cause severe burns and unconsciousness. If you expect a 100 watt light bulb to provide protection from electrocution then you may have a very shocking and lethal surprise. Use a GFCI device. Even better, don't work with high voltage!

An isolation transformer can enable you to establish a ground reference point at the output of a line connected bridge rectifier but it doesn't remove the lethal high voltage. An isolation transformer nullifies the action of a GFCI. If you are highly skilled and capable individual in high voltage circuits you may be able to use an isolation transformer safely. Otherwise avoid all contact with high voltage circuits. Lethal voltages are generally defined as above 42.5 volts but even lower voltages have killed people. After all, it is not the voltage that kills, it is the current.

And don't try to use 120VAC to 6V back to back transformers as a substitute isolation transformer. A simple understanding of transformer action will show you it won't work for anything except a trivial, low power application. (calculate the current flow required in the 6 volt circuit) In any power application this would give you lots of heat, smoke, insulation breakdown, probably fire and all sorts of undesirable effects.

There are no second chances at life, protect the one you have.
 

Plamen

Joined Mar 29, 2015
98
Something around 100 to 200mA is the lethal range of current, give or take a little. This range of current through your heart can cause fibrillation. Higher currents can still be lethal and can cause severe burns and unconsciousness. If you expect a 100 watt light bulb to provide protection from electrocution then you may have a very shocking and lethal surprise. Use a GFCI device. Even better, don't work with high voltage!

An isolation transformer can enable you to establish a ground reference point at the output of a line connected bridge rectifier but it doesn't remove the lethal high voltage. An isolation transformer nullifies the action of a GFCI. If you are highly skilled and capable individual in high voltage circuits you may be able to use an isolation transformer safely. Otherwise avoid all contact with high voltage circuits. Lethal voltages are generally defined as above 42.5 volts but even lower voltages have killed people. After all, it is not the voltage that kills, it is the current.


Petkan: The isolation transformer is supposed to be real transformer, not auto-transformer i.e. to provide completely floating secondary. Even if you touch either end if the DC High Voltage, there is no path to GND and you are safe (no reason to claim that the ground fault protection is eliminated. In fact in some medical offices they use fully floating power)
And don't try to use 120VAC to 6V back to back transformers as a substitute isolation transformer. A simple understanding of transformer action will show you it won't work for anything except a trivial, low power application. (calculate the current flow required in the 6 volt circuit) In any power application this would give you lots of heat, smoke, insulation breakdown, probably fire and all sorts of undesirable effects.

There are no second chances at life, protect the one you have.
 

Dodgydave

Joined Jun 22, 2012
8,878
This is sony HCD-SHAKE7 stereo box. i am attaching the picture of the power supply board. i can change parts. but i am in a process of learning also. i love to learn to always go further one step ahead. while in the process if i get any doubts i seek help. i repair car amplifiers. i have just started repairing led tv. this stereo is my personal set. so i want to play with it to gain some knowledge.

Here is the data sheet for the switch mode chip, it uses a tl431 zener and opto coupler for feedback regulation.. Looking at your PCB it has 2 chips and 5 optos, so it may have dual outputs and current sensing..

It will help you with the psu repair..
NOTE THIS CIRCUIT USES LIVE MAINS PRIMARY SIDE, !!!

https://www.infineon.com/dgdl/Infineon-ICE2QS03G-DS-v02_03-en.pdf?fileId=db3a304324fc7f9a01250689233a7046&ved=2ahUKEwicrbbl7b3iAhXKQxUIHZmrAfAQFjAAegQIBRAB&usg=AOvVaw1GDP67oMape63S8roazUIO





ICE2QS03G-6.png
 
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