SMPS

[DP]

Any of you repair pcbs and switch mode power supplies using oscilloscope and other means?

 

[bernardgreen]

Yes

 

[DP]

Yes

What scope, multimeter and any mains isolation? If yes, what spec
What do you repair

 

[jurassic sparkk]

What scope, multimeter and any mains isolation? If yes, what spec
What do you repair

I use different tools everytime, whatever meter comes in front of me I use it.

 

[DP]

I use different tools everytime, whatever meter comes in front of me I use it.

Multimeter is the mainstay for voltage measurements but how do you check the waveforms
Do you use isolating transformer?

 

[jurassic sparkk]

Multimeter is the mainstay for voltage measurements but how do you check the waveforms

Oscilloscope. Mostly used for checking IC drive signals (in my case)

Do you use isolating transformer?

Always. (Well, most of the times yes. ) The isolation transformer is there to protect you just as much as your scope. It doesn't make working on mains voltage equipment entirely safe, but it does help significantly.

 

[DP]

What test leads do you use
I am new to SMPS. Understand the concept, aware of dangers.
Have been faultfinding for some 50 years. Electronic electrical, mechanical, gas boilers etc

 

[jurassic sparkk]

What test leads do you use

hantek pp200

Whenever I approach to repair a SMPS with a current output less than 5A the only thing I would likely need will be my £7 multimeter.

 

[DP]

Thank you.

You seem to be quite knowledgeable on the subject

 

[RandomGrinch]

but how do you check the waveforms
Do you use isolating transformer?

Beware, if you are testing your SMPS using an isolation transformer and a scope - when you connect up the probe ground on a traditional scope, you will lose isolation - the circuit won't be floating anymore, as the scope references to earth.
There are some interesting scope meters appearing on Amazon etc. some for less than £100 (one is on my Christmas list!). Being battery powered, you wouldn't lose isolation.
Personally, I haven't used an isolation transformer for troubleshooting, but most of the problems I've found, could be discovered with the circuit dead - i.e. the usual suspects: caps, resistors, diodes, MOSFETs, etc.

 

[jurassic sparkk]

Personally, I haven't used an isolation transformer for troubleshooting, but most of the problems I've found, could be discovered with the circuit dead - i.e. the usual suspects: caps, resistors, diodes, MOSFETs, etc.

Yeah that why I mentioned that my £7 multimeter normally finds the fault.


Don't forget to answer back on the stereo thread

 

[Gasguru]

Differential probes and electrical gloves are the only safe way...

 

[RandomGrinch]

Differential probes and electrical gloves are the only safe way...

...and the old adage of sitting on one hand!

 

[Justin Passing]

I've got a KeySight diff probe/amp which calls itself "high voltage" but it's not all that high, 100V common mode iirc. Some are rather low. I've used it for some inverters & motor drivers and some high speed serial comms where it reduces the common mode noise problem. It's around here - somewhere, haven't seen it for years.
You should be able to use differential mode on a scope with two normal single ended probes - no need to be concerned with the common mode voltage range, as long as the signal doesn't exceed the general input voltage range.

It's not really needed if you have a handheld/battery type scope though. My Fluke Scopemeter was a few quid but often one of these <£40 ones off ebay would be fine for little stuff. Remarkable for what you can get now for the price of a tank of fuel. Well, £100 - £120.

 

[DP]

Beware, if you are testing your SMPS using an isolation transformer and a scope - when you connect up the probe ground on a traditional scope, you will lose isolation - the circuit won't be floating anymore, as the scope references to earth.
There are some interesting scope meters appearing on Amazon etc. some for less than £100 (one is on my Christmas list!). Being battery powered, you wouldn't lose isolation.
Personally, I haven't used an isolation transformer for troubleshooting, but most of the problems I've found, could be discovered with the circuit dead - i.e. the usual suspects: caps, resistors, diodes, MOSFETs, etc.

To date have done repairs where cap checks showed faulty components.
Am aware about earth connection of scope and applying the scope to SMPS where input and output are isolated. For this have differential probes
Have been reading up about different component functions etc