Hitachi 42xt42u (17ips20) backlights

[compcycle]

Hi I have the above tv, came in with no backlights at all. Replaced 17IPS20, now I have backlights for about 3 mins. Monitered voltage to panel, I get a slight variation between 159 and 161 volts, occationaly dropping to 156 at which point the screen flickers. does this 2 or 3 times then screen goes out, voltage to 0.00
Any ideas? Not sure about the replacement board, was a pull from a smashed tv.

[ReeceyBurger123]

Re: Hitachi 42xt42u (17ips20) backlights

Sounds like your new Psu is faulty, or you have an intermittent connection in the Led strips. This uses the great VES420 panel and I have had the Leds in the screen the connections between them break down. Maybe try heating the Psu see if it shuts off faster ? Or try moving the Tv about see if it stays on longer.

[ReeceyBurger123]

Re: Hitachi 42xt42u (17ips20) backlights

Also wait what size was the smashed one ? You cant just use any old IPS20 you need the exact one for the 42" VES420 as the smaller or bigger ones have more Leds so bigger drive voltage or less Leds so less drive voltage, the Psu might not be able to supply the current for them all. You must use one from another 42" exactly.

[compcycle]

Re: Hitachi 42xt42u (17ips20) backlights

you might have hit the nail on the head, i have no idea what the ips originally came out of, but i think its only seen in tvs 40 and above, i might be wrong. ill see if i have any more. the original supply had no backlights at all, so where would i start looking at that one for faults?

[flocko]

Re: Hitachi 42xt42u (17ips20) backlights

You need to match the part numbers from you old to the new board? on the 17IPS20 there are over forty part number that cover this board look at the white bar code sticker 23XXXXXX and match that

[compcycle]

Re: Hitachi 42xt42u (17ips20) backlights

ok they dont match, so we have established that the replacement board is not suitable. So the next step is repair the existing board? What commonly fails on these to cause no backlight?

[ReeceyBurger123]

Re: Hitachi 42xt42u (17ips20) backlights

Normally the Led controller or the mosfet or the diode. Also possibly the switching transistor for the 24v rail. Quite tricky to find. Will explain more later when im home.

[flocko]

Re: Hitachi 42xt42u (17ips20) backlights

I have a repair kit (eBay item 26245489602 )to fix the no back light, replacement parts for the mosfet Q502 and four string LED driver IC U500, you would need to check for your self if these are your problem, and not an open LED in the strings ? if you are not going to return the board with the wrong part number you could change the parts on to your faulty board with the ones on there ?

[compcycle]

Re: Hitachi 42xt42u (17ips20) backlights

thanks, just ordered the repair kit from ohm supplies!
the board with the wrong part number is mine anyway, just found another one as well, this one shows splash screen then turns off, so pretty sure its not the leds.

[compcycle]

Re: Hitachi 42xt42u (17ips20) backlights

and that item number is invalid?

[flocko]

Re: Hitachi 42xt42u (17ips20) backlights

eBay item number:262454589602 missed out a 5 out , the screen can flash on with an LED open for a sec or two. but that string will show no load to the driver and the driver will shut all four strings down. Andy (ohm supplies)will be pleased with the order

[compcycle]

Re: Hitachi 42xt42u (17ips20) backlights

understand that, but on the second ips the tv was staying on for 3 to 5 minutes, surely wouldnt do that with a duff led?

[ReeceyBurger123]

Re: Hitachi 42xt42u (17ips20) backlights

understand that, but on the second ips the tv was staying on for 3 to 5 minutes, surely wouldnt do that with a duff led?

Controller possibly shutting down.

[flocko]

Re: Hitachi 42xt42u (17ips20) backlights

As I have said there are loads of versions of this board all running LED output voltages to match the number of LEDs that are fitted and the number of strings that are being driven, you could have blown what could have been good LEDs by fitting a supply that is running to high an output.

[ReeceyBurger123]

Re: Hitachi 42xt42u (17ips20) backlights

Agree Flocko when Leds get too hot and are about to burn they flicker.

[compcycle]

Re: Hitachi 42xt42u (17ips20) backlights

Thank you for the pointers, I swapped the string driver IC (U500) off the replacement board on to the original, and it seems to have done the trick, on test now for half hour so far so good

[ReeceyBurger123]

Re: Hitachi 42xt42u (17ips20) backlights

Yay, now factory reset the Tv and then set the menu to dynamic and turn the backlight to low.

[compcycle]

Re: Hitachi 42xt42u (17ips20) backlights

ok will do, reason?

[ReeceyBurger123]

Re: Hitachi 42xt42u (17ips20) backlights

Well have you not heard of the Led failure epidemic in Tv's ?

[compcycle]

Re: Hitachi 42xt42u (17ips20) backlights

yes mate, lol the obvious reason! Just wondered if it was to do with the ic change!