Help understanding this circuit please

[punkieys17]

Trying to repair this uplighter LED array for a friend. I am suitably puzzled. Mains at 230Vac comes in via 2 fuses and I measure 211VDC at the pins of the bridge rectifier. I can then follow the circuit from the positive terminal of the bridge rectifier via 28 LEDs in series to the negative terminal of the bridge recitifier. This suggests a forward voltage of some 7.5V. I cannot find a 7.5V SMD LED. Secondly what is the function of the 3 Mosfets which are labelled D2002.....the circuit appears to be a serial string of LEDs so what are the Mosfets for? Any help greatly apprciated

 

[kellys_eye]

Quite often the LEDs are multi-die and consist of more than one LED in each package.

Have you traced the PCB tacks to determine the actual LED arrangement? It could be three lots of series all wired in parallel - one string each via the 'mosfets' that you claim are such (but probably not - likely to be simple series current regulators with the associated resistor setting the chain current)

What voltage do you measure across any one of the LEDs? and the LED you've replaced (D6)?

 

[punkieys17]

Hiya. Yes the replaced led is wrong. As i said in first post i can trace from the positive output of the bridge rectifier from led to led back to the negative on the rectifier.....so that suggests a forward voltage of 7.5v. Going to try injecting voltage to each led to check. But if it's leds in series then the additional components aren't doing anything. There are only live and neutral connections so it's not dimming or anything