Switch Mode Power Supply Repair, SMPS

How to repair a switching "switch mode" power supply. See what's involved. Also a brief explanation about the difference between Linear and switch mode power supplies.

[shelacharles]

You started out with a SMPS made by Power Systems, Inc. I was the Product Safety Engineer for PSI for nearly 30 Years. I think the model shown was in the series of late PS-1600's or PS-1700's. Enjoyed watching that work again! LOVED that company and my old job! I traveled all over the world for them. BTW; that green module in the primary has a saw tooth generator and a low voltage dc reference voltage that slides up and down across the saw tooth. thereby tell the switcher to stay on for a longer or shorter period of time based on the load conditions, as felt thru the feedback loop from the sec to primary using that opto you spoke about. Wow, I am retired and its been over 10 yrs since I left America. (retired in Philippines) PSI went out of business about 8 years before that! So, the memories are wonderful! Also, the reason we used the RTV between all the caps was to add ruggedness to the supply. We used a HALT test chamber and a random vibration test at the same time we took temps up and down to find the failure points. We brought them up to about 140C before they failed, then down to -60C before they failed and found that most of our supplies lived at 30G's but would fail by 60G's. I ran that area. My people monitored about 30-50 components during the test for temperature and we monitored the input and output voltages on each channel. I also ran the RFI/EMI Testing and got them approved thru UL/CSA/TUV, etc. (I believe the standards that one met was UL/CSA60950) and often made sure they would pass the conducted and radiated emissions testing also to ISO Standards. I also sat on two technical committees in Canada helping to write the International Safety Standards for the IT industry. Later, I worked for the German TUV Agency as a Product Test Engineer. LOVED my work!

[orange]

Absolutely the finest teaching around. You have a gift, I wish my instructors would have had even 50 percent of your ability to transfer knowledge in such seamless way. Best on youtube for sure. Thank You!

[RayR]

If I haven't said this before I'll say it again.. you are a quality teacher. Some people honestly don't have the ability to teach no matter how much training they receive but you have the natural ability. Please keep up the good work!

[CharlesDAlessandro]

Your shop brings back memories of my father's shop when I was a little boy. My father was an sound engineer for the RCA corporation. Repairing sound systems all across NYC it was great fun being in the projector booths and seeing racks of AMPS in the winter you never needed heat the equipment provided it. My dad passed away just as the transistor came on the market every thing was tube operated. I miss his great wealth of know how from radio and tv repair which I saw from a very young age. He started his repair business in 1918 when he was 14 in his fathers basement. I became an electrical contractor installing alarm systems and generators building my own controls as much was not commercially available. Customers learned very quickly never say to me it can't be done I always proved them wrong. Much to there dismay and amazement. Today every one in my field is an expert or certified my father would have called them tube pullers putting wheels on miscarriages. Artificial stupidity is what I am waiting for.

[dougg]

It’s just amazing how knowledgeable and unflappable you are, I don’t think there is anything you would not be able to design or repair. Respect

[Adam_Adamsky]

Brilliant. Not that I'm too interested in electronics, but your talent and the way you can talk about complex things in a simple way, I just love.

[angel]

I love this. I was an engineer in the UK repairing Hammond Organs for many years. Retired now, but still repair things just for fun.

[rfmanchannel]

One more important comment, to regulate the output voltage, the control circuit senses the output current and increases the conduction time of the switching transistor to regulate the voltage. Love your work!!

[blokey]

Watching these SMPS videos reminds me of my time working at a power supply manufacturers. Testing units from the production line to working with design engineers building their prototypes and developing them to production status. One challenging job I had was developing a 30kV pulse supply to be used on a magnetron. I wasn't privileged enough to know what the final product was (secret stuff). Another excellent video Mr C. and I've watched quite a few of them so far.

[GoutamDAS-lswb]

The best explanation on how SMPS works with an in-depth explanation of where these are unsuitable and/or what additional devices are needed for these when running sensitive audiovisual equipment.

[JRNipper]

Paul, great video! I've been servicing SW mode PSs for many years and have found anomalies that don't make any sense and today was one of those days. Working for a college that has very limited budgets, I have taken it upon myself to repair as many electronic items as possible. The majority of these failed devices are due to a bad SW PS. With a few exceptions, all they needed were new electrolytic caps, and most of the time it is a small 10µf to 47µf cap near the control/regulator chip that needs to be replaced, although, I usually also replace the filter caps at the output for good measure.

Anyway, the sole purpose of that small cap seems to be one of obsolescence, or a timer cap. When it starts to lose its capacitance, the output amperage starts to drop and when enough capacitance is lost, the PS may make a ticking noise due to the PS starting and stopping on a continual basis, even with no load.

Now for the weird part... I pulled the "timer" cap from this no-name PS (20V @ 2A) since it was "ticking" on and off at about 2 Hz, and my cap tester showed it was well within tolerance of the 47µf value. Normally, this B&K, model 830, cap meter has always showed a greatly diminished value but not this time. I replaced the cap anyway and the PS came back up to full voltage and power output. I then analyzed the bad cap using a sensitive analog VOM and both the old and the new cap exhibited the same readings for charging time and leakage, so I'm at a complete loss as to why the PS circuit likes the new cap but not the old one. And this is not the first time this has happened.

The only possibility I can think of is that breakdown is occurring in the cap, such as its leakage is exceedingly high at its rated voltage and causing a shut down. So I put the bad cap on my lab PS and set it to 20 V, and the leakage current reading is 0.2 µA. Then ran the same test with a new cap and it had a current leakage of 1.0 µA, five times higher than the old cap. So, if the leakage current goes to low, these PS's shut down? Could this get any weirder?

If you have any insight or info about this anomaly I'd appreciate hearing from you. Thank you.

[Guitartime]

This guy's lab it unbelievable. He does a GREAT job explaining things. Like switch mode power supplies.
I watch his videos all the time. Thanks for taking the time to be so descriptive.

[Okie-Tom]

Very good explanation of the switch mode power supply, especially with your diagram you drew. If not already, you would make an excellent electronics professor. You have a very good teaching method.

[kunalblack]

after a million videos.... i finally found the proper functionality of the components.. thank you Mr. Carlson.

[VintageProjectDE]

Scope rebuild?
Yes, please!
I'd love to see you (re-)building a scope, especially if it's a Tek.

[hadibq]

Always inspiring to see a state-of-the-art repair methods and decisions. thanks Paul!

[Songwriter]

Best electronics teaching channel I found hands down. I've been repairing electronic devices nearly 40 years full time and there is always something new to learn!! Thank you. 😉

[swlee]

Carlson, you are really a good teacher! I learnt lot of electronics theory and trouble shooting skill from your video. Your speaking was so clear and very understandable, even to me a non-English speaker. Thank you very much!

[keithcoltron]

As usual the best teacher on YouTube, thank you.

[thomasrabba]

You ar e the best teacher i ever had.
Best elektronic Chanel in YouTube