Me too, with the statement...I'm confused, you say "the start up resistor is 100k, the start up capacitor is 47uf, 25v" but in the schematic they are 300K and 1uF. That's a big difference
Brian.
the schematic is similar , just show for the concept not the values, in other words not the circuit i have but similar conceptI'm confused, you say "the start up resistor is 100k, the start up capacitor is 47uf, 25v" but in the schematic they are 300K and 1uF. That's a big difference in start up curve.
Brian.
the schematic is similar , just show for the concept not the values, in other words not the circuit i have but similar concept
Sure, I often implement circuits that are similar in concept to the original, but that don't work because of that.
Details make the difference in electronics.
I got it, but sorry, this way I cannot investigate the problem.Here is the real one, but sorry I don't have schematic
I don't think so , everything around this area is goodI got it, but sorry, this way I cannot investigate the problem.
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BTW, did you note the scrappy soldering close to the U14 IC ?
There may be more behind, that not only component values, but perhaps burnt parts as well.
I hope so, meanwhile...Ok, maybe other members can help and see something
There are a lot of soldering residues close to the U14. In addition to the solder guts themselves are quite irregular and oversized, giving the impression of the iron solder tip with the wrong temperature.I don't think so , everything around this area is good
This is a problem when trying to debug / repair pulsed driven devices.except the pwm ic of course as i can not test
I have oscilloscope, how you want me to use?This is a problem when trying to debug / repair pulsed driven devices.
Didn't you have any cheao handheld Oscilloscope?
You can start by checking all the expected values and waveforms on the UC3842A, as stated on their datasheet, taking extreme care when probing pins 6 and 7, which deals with quite different voltage ranges.I have oscilloscope, how you want me to use?
I have uc3845b, and the problem that it can not turn on the circuit, and not reach the Vref which should be 5vYou can start by checking all the expected values and waveforms on the UC3842A, as stated on their datasheet, taking extreme care when probing pins 6 and 7, which deals with quite different voltage ranges.
I've tried to turn on the IC with external power supply, but it can not turn on, this can be bad ic?, I make separate circuit for testing the IC outside the circuit?the UC3842A won't start until the Vcc gets to 16V - and sometimes as high as 17.5V - I note the UC3845B has lower turn on threshold about 9V
Okay, will try different one, thanksIt seems likely the IC is fried - yes
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