17IPS20 No Led Voltage Solved With Video :)

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Ok thanks.

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Sorry BudM got to be away on business for a couple of weeks so post will be silent until my return.

[budm]

Re: 17IPS20 No Led Voltage Solved With Video

OK. I am pretty busy helping solving problems in the other threads too.

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

Hi Budm
Finally back home and yesterday fitted the replacement Q502 and U500.
Fired the PSU up with LEDs connected and measured the voltages on U500:
Pin 1 COMP 2.55v
Pin 2 EN 3.2v
Pin 3 DBRT 0.16v
Pin 4 GND 0.0v
Pin 5 OSC 0.0v
Pin 6 ISET 1.5v
Pin 7 BOSC 6.5v
Pin 8 LED4 7.0v
Pin 9 LED3 7.0v
Pin 10 LED2 7.0v
Pin 11 LED1 7.0v
Pin 12 OVP 0.6v
Pin 13 ISENSE 0.0v
Pin 14 GATE 0.0v
Pin 15 VIN 11.8v
Pin 16 VCC 5.9v

LED+ 156v
LED- 7.0v
On startup LED+ went to 190v then fell to 156v and remained there.
Most individual LEDs were dimly lit but occasionally and suddenly all LEDS will light to full strength and LED- will fall to 0v-1v ie as would be expected. This will only last a few seconds then back to dim LEDs and 7.0v on LED- connector.
It looks to me that the board is now able to function and constantly now has 6v on Vcc
but pins 8,9,10 and 11 on U500 have a constant 7.0v ( the same as LED- has) whilst the LEDs remain dim so I suspect a possible dry joint or disturbed joint given this board has now had so much work done on it.
Any thoughts on the above would be much appreciated.
John

[johnboy183]

Re: 17IPS20 No Led Voltage Solved With Video

A further finding if you read the above. Testing voltages while the leds flash or remain constant for a few seconds shows on Q511 (FQD6N25 6N25 TO-252):
LEDs dim G = 11.9v
D = 7.0v
S = 7.0v

LEDs lit G = 11.9v
D = anywhere from 56.0v to 0v
S = 0-1v
Also when power is switched on or off and running up to standby the Gate on this fet = rapidly changing voltages between 4 and 60v
Maybe this is normal - do you reckon?

[ReeceyBurger123]

Re: 17IPS20 No Led Voltage Solved With Video

Controller Ics fail on these often, if you think you’ve narrowed the circuit down to the control Ic turning the mosfet on and off weirdly replace it, the mosfets also die too.