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#61 |
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![]() Check for a shorted D7988, or defective PC7903, something is killing the feedback voltage. I suspect the voltage needs to be above 1 volt and maybe around 3~5 volts, but needs to be lower than 8 volts
Last edited by R_J; 05-19-2022 at 12:40 PM.. |
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#62 |
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#63 |
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![]() What do you think?
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#64 |
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![]() I think something is causing the voltage to be too low. If you look at the datasheet for the ic (page 11) you will see FB/OLP pin is supplied by approximately 7 volts, this line is controlled externally, so I suspect either the diode D7908 is bad or the optocoupler is bad.
170Ω and 90Ω does seem to be low. lift one end of the diode and check again to see what the resistance is. Last edited by R_J; 05-19-2022 at 04:48 PM.. |
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#65 | |
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#66 | |
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![]() Quote:
You should be able to leave the zener diode out of circuit for testing. |
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#67 |
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#68 |
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#69 |
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![]() I checked diode D7908 57Omh and infinity , PC7904, PC7903 desolder and check all fine(
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#70 |
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![]() If the optocoupler and the diode are good, then it only leaves the ic that is bad.
If you look at the datasheet page 11, you will see that without anything connected to the FB pin, that pin should be at 7 volts. Normally the optocoupler controls this voltage and varies it around 3~4 volts to control the ic. You measured almost 0 volts on the FB pin. So something is keeping the voltage low or the ic is bad. |
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#71 | |
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![]() Quote:
How i can check my ic? Thanks |
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#72 |
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![]() and I also suspect the C7900, but I don’t understand how to check it with a multimeter. Like a regular cap, it does not show voltage after charging.
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#73 |
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![]() What is your ohm reading on R7900?
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#74 |
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#75 |
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![]() C7900 is likely good, If it was open circuit it will not stop the circuit from working. This cap is not your problem.
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#76 |
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![]() I no longer know what to do, maybe IC7903 is defective ? I also read on another forum that the voltage on large caps should be 380V with a working ic7801, and I have 300
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#77 |
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![]() You need the #$%%^ standby circuit working BEFORE the pfc circuit OR the main supply circuit will work.
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#78 |
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#79 |
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![]() Check the transformer winding between pins 4 and 5, it should be almost 0Ω, then check the resistors R7908,R7909,R7913, if they are good, check the diode D7904, also check the zener diode D7909
If these are all good, Disconnect D7908 and pins 3&4 of the optocoupler PC7903 and see if the voltage on pin 4 of ic7903 comes up to about 7 volts. If it does not, I suspect the ic is bad. It is a simple circuit, and should not be that hard to diagnose. If you look at the schematic for the dps-262, you will see the pfc ic ic7801 pin8 gets it's VCC_ON voltage from the emitter of Q7902, The collector voltage is supplied via D7906/C7918. This voltage is only there when the standby circuit is working. Last edited by R_J; 05-20-2022 at 03:26 PM.. |
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