Projecta Jumpstarter Power Supply Repair
I have been an electronic hobbyist for about 10 years. I remember the very first article I submitted to Jestine back in 2014 (https://jestineyong.com/pioneer-sm-700-amplifier-repaired/).
It was an amazing feeling to repair what I thought at the time was a complex repair. Looking back as well as remembering some of the comments, I would do some things differently.
Step forward many years, with renewed confidence and experience. This is not to be confused with over-confidence or arrogance. I’m sure we have all learn the hard way if we don’t take the high voltages that we deal with seriously. But that, is another story! 😉
So back to the story at hand. I am reminiscing due to what I thought was a major repair that I thought I could not diagnose. I had had several attempts to repair this power supply and failed miserably each time. For some reason, I just couldn’t sort out what was wrong. It was more annoying than sticking your tongue across a 9-volt battery!
Over the years, I have gained more experience, knowledge and confidence in my various fields – electronics, auto electrical, mechanic, college teacher, YouTuber. Yes, I probably take on too much (I’ve left out a few other jobs I have 😁). The point is, you cannot go into a field and expect to have years of knowledge automatically loaded up into your brain (unless you are in the Matrix). Especially a hobby. These activities can be fun, frustrating, devastating or satisfying. It just depends on what you are doing at the time and the results of the day.
Excuse me for waffling on.
The repair in question is a Projector Jump Starter Power Supply. I have dragged this around with me for many years. I got it from the college I used to work at in another state in Australia and brought it with me after we shifted. It sat on the shelf for many years, taunting me, knowing that I was not able to repair it.
Step forward to the new, improved, more experienced hobbyist in me. While I was sitting down watching TV the other night, I dragged out a little table that I do some repairs on when I am bored. In roughly 10 minutes I had the power supply diagnosed. Why had this been so hard? I have done many repairs in the meantime, some of them quite complex. https://jestineyong.com/hisense-50-smart-tv-struck-by-lightning-repaired/
Also, credit must be given to other contributors on this site, as well as a lot of advice given to me by Jestine. As I said in the above article, I am constantly making mistakes and learning from incorrect conclusions.
This time, this little power supply would not get the better of me.
Start with the basics.
A blown fuse. Why will a fuse blow? It has a low resistance and Ohms law tells us that if there is high current flowing though that fuse, it is designed to blow. OK, I need to find why it is drawing too much current. Usually, it is something that is shorted to ground. I started at the fuse and moved forward.
Diodes are definitely something that should be on the hit list. Testing the bridge rectifier indicated that they were shorted. Moving forward, I tested all the diodes – only some were shorted.
The questions continue. Why would the diodes short? A brief overview of the system gave me the direction toward the Mosfet – a likely culprit. Testing proved that it had indeed shorted.
Was the Mosfet the only other component that had shorted? Since the IC was a pulse width modulated controller (UC3843BN), I decided to put that on my check list. Sure enough, that was also shorted.
After removal of both the Mosfet as well as the IC controller, the diodes were resoldered back into place & found to be OK. The other shorted components have given the impression that the diodes were faulty.
Testing of the tracks without the components in place showed that there were no other faulty parts needing replacement.
With a new Mosfet and IC in place, one other test needed to be carried out. After connecting a globe in series across the fuse holder, power was applied with a load in place. The current limiting globe shone dull – a good sign that no short existed. The output globe shone brightly – a good sign that the output was being created.
Connecting a multimeter showed the required voltage was being produced – 14 Volts DC output.
And, for the final drum roll, several dummy batteries were fitted to confirm the operation of the battery charger as well as the newly repaired power supply.
Testing confirmed that the power supply was able to charge the batteries as well as the jump starter was operating correctly, both in the 12 volt, as well as the 24 volt range. A new set of batteries was all that was needed to complete the repair.
Well, this repair has been a long time in the making!
It just goes to show that you can’t instantly gain knowledge, skills and confidence overnight. It takes years! I have learned so much over the years from research, study, web sites like Jestine’s and realizing my limitations as well as my growing self-confidence in the field.
I look forward to my next repair with a new sense of confidence. I would personally like to thank Jestine for his book, his guidance and web page where we can share our repairs, experiences and gain help when needed.
If you are interested in this repair, you can see a video on my channel following the link below:
This article was prepared for you by Mark Rabone from Australia.
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Note: You can check out his previous repair article on LED Light Charge Port Replacement
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Tayo
October 8, 2022 at 7:57 am
There have been many MANY devices over the years that I wish I could have had a another look at today. Unfortunately I dont have the storage space for FUTURE Tayo to do so.
To be honest, I would have probably destroyed them after years and years of tinkering with them On & Off over the years. Haha. And to tell you the truth... I HAVE!
Well Done and thanks for sharing.
Mark
October 8, 2022 at 3:24 pm
Thanks Tayo,
I'm glad I'm not alone on my learning curve
Parasuraman S
October 8, 2022 at 8:50 am
Vow! That was a never giving up attempt! Glad that you nailed the culprit at-last! Good job and very hilarious way of detailing the work done! I laughed my guts out after reading "It was more annoying than sticking your tongue across a 9-volt battery!"
Waleed Rishmawi
October 8, 2022 at 1:33 pm
thanks for sharing your life experience with electronics. we all have been there and that is such an encouragement for the electroncis begginners never to give up. have a blessed day
Mark
October 8, 2022 at 9:38 pm
Hey Waleed,
Each day I learn something new & hopefully don't make the same mistake twice!
Mark
October 8, 2022 at 3:25 pm
Thanks Parasuraman,
It heaps keep me humble. I'm always making mistakes, always learning and happy to experience new accomplishments as well.
Y. S. Rao
October 8, 2022 at 3:32 pm
I appreciate your way of writing and finding the fault. This type of problems are seen in many power supply. In some power supplies (Monitors), only IC goes bad, but others are ok. What may be the problem?
Mark
October 8, 2022 at 9:41 pm
Good question. I'm not sure. Perhaps it's the design, the amount of current passing at the time, the tolerance of the components, the age & quality of the components or the condition of other components within the circuit.
Albert van Bemmelen
October 8, 2022 at 4:56 pm
Fantastic article you made Mark! I liked your waffling as most of those remarks were spot on! (I can mirror myself in those remarks). Thanks for sharing!
Mathew Charles karonga
October 9, 2022 at 11:41 pm
Greetings
Thank you for sharing.
Well done
Mark
October 12, 2022 at 5:38 am
Thanks Mathew
Mark
October 8, 2022 at 9:46 pm
Hey Albert,
I do waffle a lot in real life (according to my wife )
I write for several magazines and organisations & it can be quite formal in the writing.
I enjoy just being able to be myself on this site and showing my successes as well as failures so that hopefully someone else can benefit from the lessons I've learnt.
Lynn Blakely
October 9, 2022 at 5:49 am
Mark:We all are either still learning or just don't want to keep trying. I thoroughly, enjoyed your dialogue very well done. I also like to read all the comments.
Mark
October 9, 2022 at 10:22 am
Thanks heaps Lynn, I appreciate your comments.
Yogesh Panchal
October 9, 2022 at 6:18 pm
Point to point fault finding Good repair! Mark
Mark
October 9, 2022 at 7:36 pm
Thanks Yogesh
Nilton Cezar Vieira
October 10, 2022 at 8:39 pm
I'm also a hobbyst who is taking the firsts steps in the repairing field and thought your words extremilly valuable. Thanks for sharing.
Mark
October 12, 2022 at 5:40 am
Good to hear Nilton!
Although it can be very frustrating at times, the satisfaction you get with a successful repair makes it all worth the effort.
Curtis Warner
October 24, 2022 at 10:00 pm
My wife complains constantly about the "projects" I've had sitting around waiting for my skills to catch up with my ambition. Recently I was able to replace and upgrade the batteries on a cordless broom ( "Swiffer"), She grudgingly agreed that this was a very useful repair.