Help !! SMPS Repair

P.S.RAJU

Member
hello bidya
the site was having some problem,so i was not able to guide you.
first you check the 300volts dc at cl6+ with respect to cl5-which is ground of power supply primary,then check300 volt at pin 1 of ica1
check 300 volt at pin 678 of icm1 if your getting this volt then your transformer is ok, if you are not getting this 300 volt then your
transformer is open ,so you check this first .take care that you dont touch the primary side when the power is pluged.
 

Bidya

New member
hello bidya
the site was having some problem,so i was not able to guide you.
first you check the 300volts dc at cl6+ with respect to cl5-which is ground of power supply primary,then check300 volt at pin 1 of ica1
check 300 volt at pin 678 of icm1 if your getting this volt then your transformer is ok, if you are not getting this 300 volt then your
transformer is open ,so you check this first .take care that you dont touch the primary side when the power is pluged.

Thank U Sir, I will go as per your suggestion n post the result in evening.
 

Bidya

New member
Hello Friends, we tested the SMPS today as per the suggestion of KX36 n P.S.Raju. The result is, the main capacitors CL6 n CL5 have 280volts. The drain pins of ICA1 (pin 1) n ICM1 (pin 6 7 8) are getting 280volts. So, I suppose the transformers are OK. But, thereafter the ICM1 is not starting. The capacitor CM3 is OK (tried new ones also) n DM3, RM3 are also OK.
 

Bidya

New member
Another thing forgot to mention. There is only 10volts in the vcc pin of ICM1. I suppose it should be 12volts. So, what could be the reason ??
 

P.S.RAJU

Member
hell bidya
disconnect the secondary,5volt and 35volt connecter and check,5 volt if u get 5v then the fault is in the main dsp pcb,if still 5volt is not comming,after disconnecting
the,connecter,then check,all diodes at the secondary section,and also change autocoupler pcm1a 817 and diode in5239,cm3,dm3,rm3
 

Bidya

New member
hell bidya
disconnect the secondary,5volt and 35volt connecter and check,5 volt if u get 5v then the fault is in the main dsp pcb,if still 5volt is not comming,after disconnecting
the,connecter,then check,all diodes at the secondary section,and also change autocoupler pcm1a 817 and diode in5239,cm3,dm3,rm3

Hello Sir, replaced the autocoupler PCM1A , diode, CM3, DM3 RM3 n checked as per your suggestion, but there is no improvement seen. The technician showed a test with a 100 watt bulb, replaced in place of the fuse. The result is when AC power is given the bulb light up for a moment then remained light off. The technician said this indicates the SMPS is almost OK. Is it right ?? Also he then by passed the bulb from +ve of Big Capacitor (CL6) to Pin 1 of the small Transformer, the result is the bulb flashed on n off continuously. The technician said the oscillation is not having properly, it should be more vigorous with less light. We have checked all the components there except the transformers as we don't have equipment to test the same. Every component is fine but we don't know about the transformer nor can we test by replacing as it is not available anywhere. So, kindly suggest what can be done next or should leave it assuming it to be dead forever.
 
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KX36

New member
The bulb lighting initially and then going out simply shows that the input capacitors charge up and then the current draw from the mains falls as the thing isn't turning on. That tells you nothing about the problem. You can't even say that because the light doesn't stay on there's no short circuit fault, because none of the high power circuitry is turning on if the ICs aren't turning on and few parts of the primary that are actually doing something might not draw enough power to light the bulb even if something was shorted. I have less faith in your technician for hearing that he reads so much into that. This is not a simple linear supply.

Find out why ICM1 either isn't starting to switch or is being stopped by a safety feature. What voltage does capacitor CM3 get to? Does it reach ICM1's upper UVLO threashold and stay above it's lower UVLO threashold?
 
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Bidya

New member
The bulb lighting initially and then going out simply shows that the input capacitors charge up and then the current draw from the mains falls as the thing isn't turning on. That tells you nothing about the problem. You can't even say that because the light doesn't stay on there's no short circuit fault, because none of the high power circuitry is turning on if the ICs aren't turning on and few parts of the primary that are actually doing something might not draw enough power to light the bulb even if something was shorted. I have less faith in your technician for hearing that he reads so much into that. This is not a simple linear supply.

Find out why ICM1 either isn't starting to switch or is being stopped by a safety feature. What voltage does capacitor CM3 get to? Does it reach ICM1's upper UVLO threashold and stay above it's lower UVLO threashold?

Hello Sir, thanks for your views. I have already said the technician knows the basics of SMPS but don't know it in depth. Yes it is right, ICM1 is not starting. CM3 gets only 10 volts as we have checked there is only 10volts in the vcc pin of ICM1. I suppose it should be 12volts. Another thing, the main capacitors have only 280volts. Is it OK or should be 300volts. We have checked the voltage both with analog n digital multimeter.
 

KX36

New member
280V should be sufficient input voltage for it to start, your mains voltage may just be a little low. You could test and/or replace CM3. You can try adding a high value (probably 100k or more) resistor between ICM1 pins 2 and 5 to try and pull CM3 voltage up to the turn on threshold. ICM1 has an internal current source to charge that capacitor. This would just be in parallel with that for a little extra current. Most supplies have this resistor, the current source in the IC is just there to save the cost of that resistor.
 

kanon

Member
lost case ..
this smps is very simple ..
and they can not recover ...
if beginner is lost time ... repairs
better buy yourself a new dvd or you pay for your repair smps to a good technical..

is not to offend anyone but it's too ..
change this etc. ..
that happens when it's bad to repair switching power supplies .. that's all

good luck
 

Bidya

New member
hello bidya
send your smps to mumbai i will repair it

Hello Sir, Thanks for your offer. I will send the SMPS to your place n bear all the cost. In the mean time the technician has left the SMPS to me. He did everything what we have discussed here but some how could not solve the problem. He has his limitation, so no complain against him. I will be thankful to you sir if you can take the task for me.
 

Bidya

New member
Hello Friends,
Posting after more than a month. Finally, the SMPS worked with the kind help of forum member Mr.P.S.Raju from Mumbai. I had to send the SMPS to his place at Mumbai and he repaired it. Today I received the SMPS from him and it is running fine. I am really grateful to him. Surely, we couldn't have repaired it here at my place. I would also like to thank forum member Kanon, KX36 for their responses and suggestions to my SMPS related problem.
It is really wonderful that it could become possible because of this great forum where plenty of knowledge is shared, without posting my problem here I could not have find the solution.
Thanks again P.S.Raju, Kanon and KX36.
 

brewboy

New member
I realize this is a very old post, but I'm struggling with, what I think is, the same problem, Just wondering if you ever found out what was replaced on this SMPS to get it working again.
 
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