I get off the FT3 replaced the red LED & burned again. I verified all CCS connections & resistors and are all OK.
Is there a resistor in series with that LED? What kind of current does it run? If it runs a few mA then the SK117 CCS it sinks it is healthy, so the Leds maybe dodgy. If it is tens of mA or more then something is shorted and the Led rightfully burns. There is no reason a LED burns out in the Vref regarding general settings, nor it has been reported before. Troubleshoot before we try guess this and that. Use DMM and common sense.
I desoldered the trimmer to see if doesn't work also I measured the resistance near 0R, I trimmed till 838R value as per calculator, I powered & measured 7Vout aprox I used the trimmer but when goes lower than 6,68Vout the red LED lits less & if I goes lower Vout stop to lit
Between 4 & 4,5mA Idss
CCS 800mA
the trimmer shows from end to end when led is a made to a short with a blob of solder on its pads? 4,63-4.64V so I need to change Q103 and Q105 for a stronger Idss like 5V or more?
Between 4 & 4,5mA Idss
CCS 800mA
the trimmer shows from end to end when led is a made to a short with a blob of solder on its pads? 4,63-4.64V so I need to change Q103 and Q105 for a stronger Idss like 5V or more?
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you don't need to be an EE (Electronics Engineer).
Anyone that can do a bit of arithmetic can calculate.
Leave the LED shorted, does it work towards 5V? If yes, replace it with a simple diode. Cathode as in LED.
