No Power In Samsung ML-4050N Laserjet Printer
This printer was sent to my partner for repair and the complaint was no power. For your information my partner Mr William doesn’t repair electronics board. If he encounters any electronics problem in printers he will ask me to troubleshoot and repair it. He is more specializing in the mechanical area/fusing/printer head of printers. He told me that it was not easy to remove the power supply board as one needs to dismantle many parts before you have the easy access to it.
Actually there are two circuit boards-one is the high voltage board and the other one is the power supply board. Since the complaint was no power so I concentrate on the power supply board. The first thing to check was the main fuse and it was tested good. There were no bulged electrolytic capacitors and while trying to search for any burn component I found a component marked as TH1 already cracked and hardly could see the whole part number. This component is a Thermistor while to some they refer to is as Thermister. Not only that, the heatsink located just behind the Thermistor had a burnt mark caused by the great spark of the Thermistor when it was exploded most probably due to the excessively high inrush current. Just to let you know that one of the main function of a Thermistor is to used as inrush current limiter.
A good Thermistor when testing it with Ohm meter it should show low Ohms reading. This particular Thermistor does not show any reading which means it is already open circuit. Please take not on this- whenever you found a burnt or open circuit Thermistor, you need to check the corresponding components as well. The main fuse did not blow does not mean other power semiconductors are good.
In my case, I did checked on the power FET, primary winding of the transformer and secondary diodes and all of these components were tested good. I’d also put special attention on the SMD power IC to see if there is any tiny burnt mark on the surface of the IC with the help of my X35 magnifying glass. Well, the SMD IC and the surrounding SMD components were in good condition too.
From the above simple scan through test I concluded that only the Thermistor having problem and I believe by replacing only the Thermistor could solve the problem. The question now is where to find the exact replacement since I could not trace the original part number datasheet? I left only two choices-either just connect a wire across it or use a replacement number. For your information if you use a wire as a replacement, then the power supply no longer have protection against inrush current. In the future if there is any excessive inrush current, many of the primary side components will be badly affected.
Since my store room has some junk Laserjet power boards, I took out a good Thermistor and used it as a replacement. My expectation was correct; the Laserjet came back to life once the AC power is applied. For your information, you need to turn On and Off the power many times to see if the replacement component is stable or not. If the replacement component has a too low spec then it may blow again. So, the best is to try On/Off the power supply many times before sending it back to your customer.
Conclusion- Not all switch mode power supplies are using Thermistor as protection against inrush current. I have seen many power supplies used low ohm wire wound resistor ranging from 2.2 to 4.7 ohm 5 to 10 watt as inrush current limiter. Some does not even have any of these components in their design. In the above case, fortunately only the Thermistor have problem. In some cases, a blown Thermistor could cause the power FET, power IC and corresponding components to blow as well and surely this will take more time and skill to troubleshoot it.
Hope you have enjoyed this repair article. Your feedback on the post is welcome. Please leave it in the comments.
Jestine Yong
Latest update: Just found the datasheet for both the Thermistors:
For more information about Varistor and Thermistor function please click on the links below:
http://en.wikipedia.org/wiki/Varistor
http://en.wikipedia.org/wiki/Thermistor
Click Here to Learn Basic Laserjet Printer Repair
Click Here To Learn Printer Head Repair
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hemant pandya
July 22, 2012 at 6:15 am
I see your mail which will be useful to many persons.
Hemant Padya
beh
July 22, 2012 at 6:23 am
HI MR YOUNG
thanks for sharing this repair .but what could be the next step?. ifyou did not find that junk laser jet power board?. in the face of varistor is written DSC 8P-9 this is enough to find a substitotion?
regards
beh
Jestine Yong
July 22, 2012 at 10:42 am
Hi Beh, Eventually I found the spec for both the Thermistor. This is a Thermistor and not Varistor. Please refer back to the blog post to see the Thermistors datasheet. I suggest that you print out the spec and show it to the electronics shop owner and get a replacement from him.
Jestine
Stageleft
July 22, 2012 at 6:32 am
Always a pleasure to learn from the masters of electronics. Many thanks for sharing!
leo bahr
July 22, 2012 at 6:40 am
Hello
Thanks for the information I'am trying to repair a small ac drive and came to a burnt component like the one you found. I thought it was either an inductor or resistor but was not sure what it did. I now know . The numbers on the thermistor are all you need to order a new one or is the number specific to the compamy buiding the drive or power supply?
Leo
Jestine Yong
July 22, 2012 at 10:24 am
Hi LEO,
If the board marking is TH1 then you know it is a Thermistor. Some manufacturers came out with their own part number and hard to locate those spec. Try order from electronic shop to see if they have the part number you want or not.
Jestine
Mano
July 22, 2012 at 6:52 am
It is very useful information, I would like to know about how to test all kind of IC ?
Thank you,
Jestine Yong
July 22, 2012 at 10:17 am
Hi Mano,
Download the IC datasheet and understand the ic pinouts like supply voltage, input/output6 signal and type of ICs. Different IC need different ways to test it.
Jestine
Erica
July 22, 2012 at 7:06 am
very good read thank you
ARMEND
July 22, 2012 at 7:29 am
Nice and tidy repair.
Jaime napil jr.
July 22, 2012 at 7:38 am
Thank you for this information it really helps a lot.... Thumbs up 100%
Tana
July 22, 2012 at 7:45 am
Hi Jestine ,
Reading your electronic repair on the power supply was a real pleasure. The power supply and high voltage board is well disigned and look beautiful .The components are well spaced. I like to repair this type of board. You have suceccsfully repaired it. It will definitely help me when I get one to repair. Your tips and tricks are a joy and so i will remember them. Good job Jestine.
Thank you
Tana
Roberto S.
July 22, 2012 at 7:48 am
Thanks Jestine for this useful repair article!
badsss
July 22, 2012 at 8:16 am
Found article very informative aNd helpful
Antonio Marques
July 22, 2012 at 8:29 am
I'm from Portugal. Thanks for your information. It´s very simple and clear and useful for my work. Thanks again.
Eli
July 22, 2012 at 9:41 am
I think you mean to call this part an MOV or metal oxide varistor. You refer to it as a thermistor in the text, but a varistor in the images. This is also a common part that fails in surge protected power outlet strips. If you shake one and hear a rattle sound, it is a good indication that the MOV has blown and the power strip should be repaired or replaced.
Jestine Yong
July 22, 2012 at 10:19 am
Hi Eli,
It is not a varistor. It is a Thermistor and you can confirm it by reading the board marking TH1.
Jestine
Steve
July 22, 2012 at 9:47 am
Your way of explaining problems ar very clear and helpfull
Christopher Koloc
July 22, 2012 at 10:41 am
Great article, you reall explain it so even the newbies like myself can understand, thanks Jestine
I have also seen this problem in Samsung TV after a power surge.
Atanu panigrahi
July 22, 2012 at 11:23 am
too good.it help me too much.... thanks jestine
sim adm
July 22, 2012 at 11:34 am
Hi Jestine,
I came across the same case but the thermistor was not the culprit, rather, a cold solder joint was. Great post as always.
Jestine Yong
July 23, 2012 at 3:24 am
Hi Sim,
Whenever there is no power in the power supply, it can be one component, many components failure or just some dry joints.
Jestine
leonard williams
July 22, 2012 at 11:59 am
I learn a lot from your block mr young . new point in jamaica whear i live our system is ntsc now i get a pal lcd tv it just cant work in jamaica any suggision i can try thanks to you
Jestine Yong
July 23, 2012 at 10:22 pm
Hi leonard,
Do you mean your LCD TV only support Pal system? Have you try to check for the tv spec if it also support the NTSC system? Nowadays LCD tvS could support multisystem.
Jestine
beh
July 22, 2012 at 12:09 pm
HI MR YONG
yes this is thermistor and not varistor this is just miss printing sorry about that .
i will make a good print of chart and i will show to shop keepers for subtitution.
beh
zaldy
July 22, 2012 at 12:44 pm
Dear my yong
Thanks for this very useful tips troubleshooting for dead power supply unit. Yes, your'e right, The one defective component you have shown is not a Variable capacitor. It is a Thermistor resistor, Also it is found in Primary section of the Power supply board. I wondering how there's no other component to be damaged usually the rectifier and most especially the regulated components.
Anyway thanks a lot 🙂
Zahirin
July 22, 2012 at 12:44 pm
It's a great sharing...! Thank you vary much...!
S Ramachandran
July 22, 2012 at 12:45 pm
Hi Jestine ,
Thanks for the information , normally a wire wound resistors are used to (also called as surge limiting resistors ) they are of PTC component . can you correct me ,if am on the wrong side.
S Ram
Jestine Yong
July 24, 2012 at 1:25 am
Hi S RAMA,
Wire wound resistor is not a PTC component. I suggest that you visit this link for more information:
http://en.wikipedia.org/wiki/Thermistor
Jestine
jumbe mateyu
July 22, 2012 at 1:49 pm
Hi Jestine.
I always enjoy reading your articles as they carry useful information.They are easy to follow.
I thank you very much.Finally Jestine what is the difference in usage between thermistor and a line filter in a power supply circuit.
Jestine Yong
July 23, 2012 at 10:02 pm
Hi jumbe,
Thermistor is to limit the inrush current while line filer is to attenuate conducted radio frequencies (RFI), also known as electromagnetic interference (EMI).
Jestine
Waleed Rishmawi
July 22, 2012 at 3:12 pm
I thought THY is short for thyristor. is it the same as the thermistor. I never heard of thermistor before. thanks for the info.
sokhom
July 22, 2012 at 7:08 pm
Thanks Jestine for this useful repair article! thanks for sharing this repair.
amex
July 22, 2012 at 8:01 pm
very interesting ,welli am also a electronics tech and you used excellent diagnostic method great information for me too. thanks,it will be highly appreciated ifyou could advice me on how to repair motherboards for computers and laptops.best regards,amex
Jake Pomperada
July 22, 2012 at 8:20 pm
Hi Jestine,
Thank you very much for the tutorial that you always sharing with us. Indeed I learned many things from you specially in electronics which I think very essentials in todays information technology world.
Take care always and God Bless.
Regards,
Jake
razak17
July 22, 2012 at 9:03 pm
c vraiment super ...merci
Charles
July 22, 2012 at 9:56 pm
It seemed very easy to see the thermistor is cracked
Zakeer
July 22, 2012 at 11:54 pm
hi,
i am having one inverter problem with Error E9(Omron SysDrive 3G3SV inverter 1.5kw).help me out to solve this issue.
Jestine Yong
July 23, 2012 at 8:58 pm
Hi Zakeer,
Sorry i do not have info on this Inverter error code.
jestine
Dominic
July 22, 2012 at 11:57 pm
Correct me if I'm wrong but a Thermister protects against all current surges whereas an MOV protects against surges from lightning strikes?
Jestine Yong
July 23, 2012 at 3:44 am
Hi Dominic,
I suggest that you visit both the links that i have just updated. You will have a better picture of both the components function.
Jestine
ariel dulay
July 23, 2012 at 1:25 am
one of the best site...thanks Jestine.
Don Ritx
July 23, 2012 at 3:02 am
Thanks this is great.... Don Ritx from Shillong
chary
July 23, 2012 at 4:58 am
HI
Nice share i feel it would help me in sorting out the problem on smps that i was facing which i have sent along back in which the ic and the varistor are burn
kazem
July 23, 2012 at 5:10 am
thanks alot Mr. yong.it was usefull.
bluesolar
July 23, 2012 at 5:20 am
Hi Jestine...
thnx 4 sharing.... very informative & frm d master
of electronics surely its d Best... thnk u 4 answering
all our queries, u simply reply us w/ details & professional
way... All d Best for you & your family...
bluesolar8
tom walsh
July 23, 2012 at 5:28 am
Hi Mr Justine,
Just wanted to note that thermistors can have positive and negative temperature coefficients.
In the case of a degauss circuit, it will flow current until it gets hot.
In the case of your power supply, it will not flow as much current until it gest hot.
Same device type, but opposite in function.
I always enjoy and learn from reading your monthly postings.
tom
Jestine Yong
July 23, 2012 at 8:52 pm
Hi Tom,
You are right that's why this Thermistor is called as NTC and for the monitor/crt TV posistor is called as PTC.
Jestine
Froy Zurita
July 23, 2012 at 6:07 am
Thank you Jestine to share your experiences with us. Some electronics components are unknown for people
like me where I am starting testing electronic componenets.
Froy Zurita
Daniel
July 23, 2012 at 7:07 am
Thanks for sharing your experience...For me (and maybe for others less experienced too) is good way to learn and most important to understand how to do a good repair.
Richard
July 23, 2012 at 9:48 am
Hi Jestine,
Thank you for sharing this information.
etta egbe joseph
July 23, 2012 at 9:58 am
thanks so much MR YONG. I have all repair a computer power supply that had 2 exploded thermistor and a blown fused. But they were so black that i couldnt see the specifications. SO my question is that those that i replace could they cause a problem.
THANKS SO MUCH cus your post are really a great help to me.
I have another problem. thats i really want to read those books your are selling but i dont have the means to buy them. in my country CAMEROON my dont have credit cards so that is really a big problem to me.
Daud Asi
July 23, 2012 at 10:21 am
Offcourse. sometimes a little thing does a big job.
ishtiaque
July 23, 2012 at 10:48 am
hi..
really informative..........great work ......
Apurba Krishna Buragohain
July 23, 2012 at 11:42 am
Dear sir Jestine,
I like your repairing technique and description of the repairing procedure. It helps me lot. Thank you very much for it. Please keep on informing the case histories.
With regards
Apurba Krishna Buragohain
Tura, Meghalaya, India.
Henry
July 23, 2012 at 3:27 pm
Hi Jestine,
I'm busy servicing the Canon iR2200 Photocopier machine. Now it is delivering paper which is folded or Wrapped 2rds towards the end. I have checked the Developer unit, Fuser unit but cant see anything wrong with the units. Vertical delivery and other mechanism appear to be working ok. Where could I find information to help me overcome this problem?
Jestine Yong
July 23, 2012 at 10:26 pm
Hi henry,
Check to see if there is any photocopier machine forum in the internet. My side here don't repair photocopies thus I do not have info on this.
Jestine
Sanjay
July 23, 2012 at 3:33 pm
Hi, Mr. Young.....
Thank You very much for the tutorial on the laser printer.
I have a HP laserjet Model 2200 for repair. The problem of the printer is the paper lifting cam is not working. I have find that their is a relay for lifting the paper. How could I check this one? The letters on the relay are STC-F15E-B04-RH7-5275-01.
This relay is for one step lifting of paper and to prevent continuity.
Please tell me how to check the relay ?
Jestine Yong
July 24, 2012 at 1:43 am
Hi Sanjay,
Could you take some photos and send it to me at jestineyong(at)electronicrepairguide.com By the way you are referring to the relay or the solenoid?
Jestine
WALEED
July 23, 2012 at 3:46 pm
DEAR JESTINE,
HOW ARE YOU I HOPE YOU ARE WELL, I FACING ONE PROBLEM WHICH NEW TO ME IN HP LASERJET 2420 THE MACHINE HAVING USUAL PROBLEM WITH THE MICRO SWITCH BUT WHILE WE ARE DISSEMBLING THE MACHINE & RE-ASSEMBLING THE MACHINE THE MACHINE WILL RUN AND THAN WILL STOP RUNNING AT ALL WE THOUGH ITS FROM POWER SUPPLY BUT WE CANT TEST, ANY ADVICE.
THANK YOU,
WALEED
Jestine Yong
July 27, 2012 at 10:25 pm
Hi WALEED,
Sorry i don't get your meaning. Is the power supply working? If it is working then it could be some sensor problem. Try check on all the sensor.
Jestine
Leon Enloe
July 23, 2012 at 4:25 pm
Hello Jestine,
I thought you had a good prospective in this resolution of trying a component from another similiar power supply by giving us the advise to turn it off and on before returning to the customer. That gave me some helpful advice when not sure about which component to use.
Thank you,
Leon Enloe
n'guessan yapo ferdinand
July 24, 2012 at 4:13 am
am one of your admirer and I would like to learn near you. but my problem is that am Ivory Coast and I do not know how to get access to your training
Jestine Yong
July 24, 2012 at 7:49 am
Hi Yapo,
Do you mean you want to come to my country to learn or just to buy my products to learn on your won?
Jestine
Jorge Monroy
July 24, 2012 at 9:28 am
In order to identificate the right thermistor to replace, I Think is useful to visit the folowing link:
http://www.nscn.com.cn/new_pdf/dip/remin/D%E5%9E%8B%E6%8A%91%E5%88%B6%E6%B5%AA%E6%B6%8C%E7%94%B5%E6%B5%81NTC%E8%B4%9F%E6%B8%A9%E5%BA%A6%E7%B3%BB%E6%95%B0%E7%83%AD%E6%95%8F%E7%94%B5%E9%98%BB%E5%99%A8%E8%A7%84%E6%A0%BC%E4%B9%A6.pdf
Best Regards