Question To Smps Masters. Smps Ticking.

[vedo35]

I have a smps belong to satellite receiver. It wasnt working. SG6841 was defective. i chanced it. After chanced i heared tic tic sounds from smps. I chanced main filter capasitor that is 100mf/400V. Again same. I controled mosfet SPA04N60C3 (Q2) its ok looking and i chanced anyway with same volts n-channel mosfet again same. Later i chanced at primer and seconder side all capasitors, resistors, diods, varistors and zeners. Again same. Later i desolder smps transformer at primer side 100mf/400v capasitor,opto-cuplor and mosfet. I controled gate enterance of mosfet between sg6841 pin-8 again i can see triggering. I chanced again SG6841 with new one. Again same.!!!

So what can be the problem?
I am sending last photo after desolder transformer,optocoupler and mosfet.
Note: only i didnt chance 220 filter transformer.

 

[Nigel Goodwin]

Usually ticking means a duff electrolytic, the power supply is failing to start up. There could also be a short on one of the outputs.

 

[vedo35]

Thanks nigel. But you are seeing no transformer no mosfet. and filter capasitors also chanced( also elektrolitic capasitor).

 

[OutToLunch]

is the output of the supply in regulation when you hear the ticking?

 

[spldart]

Shorted secondary is common cause.
OutToLunch asked an optimal question. When it's plugged in do you have stable regulated
secondary side voltages.

 

[vedo35]

no out. To pin3 must come min 250 volts. I disconnected 1M resistor. I am seeing 240 volts. Later i am soldering going to 16volts and triggering.

 

[mvs sarma]

I have a smps belong to satellite receiver. It wasnt working. SG6841 was defective. i chanced it. After chanced i heared tic tic sounds from smps. I chanced main filter capasitor that is 100mf/400V. Again same. I controled mosfet SPA04N60C3 (Q2) its ok looking and i chanced anyway with same volts n-channel mosfet again same. Later i chanced at primer and seconder side all capasitors, resistors, diods, varistors and zeners. Again same. Later i desolder smps transformer at primer side 100mf/400v capasitor,opto-cuplor and mosfet. I controled gate enterance of mosfet between sg6841 pin-8 again i can see triggering. I chanced again SG6841 with new one. Again same.!!!

So what can be the problem?
I am sending last photo after desolder transformer,optocoupler and mosfet.
Note: only i didnt chance 220 filter transformer.

A ref circuit from the datasheet is attached here. the OP may comment whether the board is approximately following this schematic? I suggest that if the TL431 device is used, better change it and then test, with all other components restored.

 

[vedo35]

Thanks i have datasheet of sg6841. I compared with application scheme, notes and test notes. To pin3 (Vin) driving via 1Mohm + 470kohm resistor. At scheme driving with two 750kohm resistors. So no problem with mine. And when i connect to vin 240 volts dieing. And no out from Sg6841 . SG6841 cant be defective because 3 times i chanced again same. Look to photos. No transformer, No optocoupler, no varistors and no mosfet. So there arent any connections with the seconder side. But Sg6841 working like heart beats.

 

[Nigel Goodwin]

Thanks i have datasheet of sg6841. I compared with application scheme, notes and test notes. To pin3 (Vin) driving via 1Mohm + 470kohm resistor. At scheme driving with two 750kohm resistors. So no problem with mine. And when i connect to vin 240 volts dieing. And no out from Sg6841 . SG6841 cant be defective because 3 times i chanced again same. Look to photos. No transformer, No optocoupler, no varistors and no mosfet. So there arent any connections with the seconder side. But Sg6841 working like heart beats.

It won't work without those components, it's powered from the transformer so can't run without it.

 

[vedo35]

thnkas for tip i will try agin Nigel. By the way , have a nice weekend.

 

[mvs sarma]

It won't work without those components, it's powered from the transformer so can't run without it.

It is correct. after giving full effort for increasing the pwm to the designed Maximum, it would hick.

the contol circuit at the output can be checked by manipulating an external supply and changing it just above or below the nominal designed output. the transistor of opto-coupler can be monitored with a dmm in Diode range.

similarly the needed lower voltage can be supplied at Vin of chip and gate output can be monitored by a HF probe or oscilloscope, as and when pi2 is grounded, it would stop output pulsing. Once these two are OK, perhaps the transformer would not go bad unless there was a 2 phase 410V across the input by accident. If so, the electrolytic would have blasted. the cap across the output rectifier or the diode itself would have shorted.

All said, we have to check the psu only while control loop is maintained and in dynamic conditions.
CAUTION: PROTECT FROM HAZARDOUS VOLTAGES.

 

[vedo35]

Guys today i checked smps on load its working !!! haa haa incradible When its working no load mode. Smps ticking. I pluged the smps cable to the pcb main board, Smps started to work. So ic was broken . I chanced but the tl431, mosfets, sckotty diods, resistors and all others were ok. Can u imagine. This smps working only on load.

 

[Nigel Goodwin]

Guys today i checked smps on load its working !!! haa haa incradible When its working no load mode. Smps ticking. I pluged the smps cable to the pcb main board, Smps started to work. So ic was broken . I chanced but the tl431, mosfets, sckotty diods, resistors and all others were ok. Can u imagine. This smps working only on load.

Most do, it would be unusual to find one that works with no load.

 

[triangle3]

Most likely the thread is dead now but I just try ... well I have continues tick-tick sound comes from my smp and it come from main I don't recognize from where it come from inductor or capacitor or from transformer and it increase as increase in load.The output voltage is continues fluctuating pls help me what is possibly damage?

 

[kazance]

I have the power of the monitor that uses SG6841S and broke down my resistance, which is marked on this scheme as the R8, how ohm resistor that? Thank you.

 

[Ian Rogers]

Just a note..

I had an Atari ST computer that did this... I removed the cheap BJT transformer driver and replaced it with a sturdy BUT11.... and surprisingly it shut up..... AudioGuru always slates the cheap eastern components... with good reason.