Resistors values by color band.

[sdancer75]

I am not sure if I can recognize correctly the colors of the attached resistors to calculate their values.

Can you share your opinion about their values?

These are removed from a cheap smps "12V 5V 2A USB to IDE/SATA Power Supply Adapter Hard Drive/HDD/CD-ROM Input Voltage AC 100-240V" like this. If you have a similar schematic




https://vi.aliexpress.com/item/1005004570475950.html?spm=a2g0n.detail.1000014.15.5ce6UBB6UBB6N7&gps-id=platformRecommendH5&scm=1007.40000.326746.0&scm_id=1007.40000.326746.0&scm-url=1007.40000.326746.0&pvid=fb78ef78-3103-4638-b2f6-8ff2e0d69839&_t=gps-id:platformRecommendH5,scm-url:1007.40000.326746.0,pvid:fb78ef78-3103-4638-b2f6-8ff2e0d69839,tpp_buckets:668%232846%238116%23907&pdp_npi=4%40dis%21EUR%214.24%212.54%21%21%214.59%212.75%21%402103847817264288235456586e33a6%2112000029665224089%21rec%21GR%21699968857%21X

Before I remove them from the pcb




R1


R2


R3

[Zipdox]

The blue one, assuming it is red-red-silver-gold is 0.22 ohm 5%. The brown one is hard to identify but I think it's brown-green-brown-gold, which is 150 ohm 5%.

But do you not have a multimeter to measure them? Also, why would you want to use these junk parts?

[sdancer75]

Hi they are all burned. They need to be replaced.

Infinite resistance is shown with multimeter

[Benta]

I see the blue one as brown-black-silver = 0.1 ohm.
The others are not readable.

[CaptDon]

There appears to be a two terminal power resistor beside the transformer with its lid blown off. Looks like one of those epoxy/ceramic substrate things. Do you want to repair this supply? You may be disappointed. Those resistors are flameproof for a very valid reason. If you are lucky it blew up due to a voltage spike on the line (not likely with the capacitor filter) more likely the transformer aquired a shorted turn or the feedback circuit failed and the unit went full tilt until it wrecked the IRF740 which then destroyed the resistors.
 

[Xena E]

There appears to be a two terminal power resistor beside the transformer with its lid blown off.

I think it's the optocoupler.

The whole thing is only fit for the trash can.

[CaptDon]

I see the opto clearly in the one picture. There must be a strange reflection on it in the other picture. I hate when everything is carefully tested, suspect components are replaced and then on power up BZZZZT...POW!!! All of the replaced parts are blown again and yet everything seemed like it was 'ready to run'. I had a 12VDC supply that kept going to 30VDC then blowing up. Every piece was tested to factory datasheet specs and yet it kept blowing up. I suspect there was an arcing or carbonized path between the top and bottom PCB layers.

[Sensorcat]

The whole thing is only fit for the trash can.

Forensic inspection of the PCB images reveals details of the case, and how much effort the OP already invested to rescue the victim. Key to the story are the timestamps in the bottom right corners. The last two pictures are the first, reflecting the state of affairs at 1:17 PM and 1:18 PM (it all happened on September 15, 2024): The presumed optocoupler lost a large fraction of the upper half of the mold, only a small corner left (black; white area is no reflection). Furthermore, D5 is soldered with leads extremely long, unlikely for the unaltered product. IRF740 has no heat sink. Q2 and Q3 are gone, visible because the flat side of the TO-92s is not flat anymore. At 2:46 PM, 2nd image, IRF740 (Q1) is missing (PCB visibly burned below!), D5 has been soldered in properly, and Q2/Q3 now look like complete TO-92s. At 8:45 PM, 1st image in the post, we see a new opto, visible from the flux and a solder blob around it, IRF740 is back and with heat sink, some resistors desoldered, together with D1 and D3. Hmm. How much magic smoke did escape in this case?

Sometimes it's better to say goodbye, CaptDon gave an example, this is another one. Telling the full story from start would also have been a good idea...

[sdancer75]

Hi to all,

Most parts of the primary power supply were destroyed, that is true. The MOSFET in the pictures is not the original, it is just the replacement part before soldering it.

The mentioned resistors, the fuse (of course), the mosfet itself, the 2 bridge diodes, the zener at the lower right side of the mosfet, and the optocoupler are all destroyed. I replaced all of them and I checked all the ceramic and electrolytic capacitors. I would like to replace the resistors to see if it would finally work. I ordered a new smps to read that values just for the f**k of it (I am sorry).