LG RT42PZ45V internal electrical interference

[maxvalutech]

This old plasma had a power board problem so replaced it and set started up showing menu and no signal message all good. Owned by a friend who was a poker machine tech so left it for him to replace back on etc. When connected to signal source however being set top box and DVD the screen shows what I think is electrical interference probably from power board capacitor/s. As said menu screen etc is perfect. Any thoughts or experience with this problem?

[maxvalutech]

Re: LG RT42PZ45V internal electrical interference

pics hereunder

[happyade123]

Re: LG RT42PZ45V internal electrical interference

I had similar on a Samsung Plasma, and it turned out to be the control board.Very easy to prove just do the bypass mainboard test. If the resulting screen still shows the lines(interference) chances are its the control board.I would first check the Vs and Va Voltages are close to printed value.

[maxvalutech]

Re: LG RT42PZ45V internal electrical interference

Thanks and will do. Should have said did check Va Vs very touchy to set but got them to within 0.5v.

[maxvalutech]

Re: LG RT42PZ45V internal electrical interference

Have now got this set onto my workbench and checked all voltages OK except 3.4 comes up as 3.05. Led LD740 which is bottom one of a line of 4 is blinking red on main board so probably means something. There are 3 lit green LEDs on control board and 1 blinking green at about 1sec. The screen lines move around usually running at about 30deg angle to horizontal sometimes l to r then vice versa and at odd times almost vertical and there are small blue snow dots most of the time all over screen when looked at closely. I think we used to call the striping "venetian blind effect". Th e low buzz sound is also only heard when a signal is used and not when menu or no signal message is the only thing on screen. No circuit and an old complex plasma. Anyone have anything ? Pics to follow later.

[maxvalutech]

Re: LG RT42PZ45V internal electrical interference

Havent had any luck with this set. Difficult to take apart and get any boards out except powerboard. Now have full 3.4V after finding an adjustment point and all other voltages are spot on. Note perfect screen with menu etc and problem only occurs with signal input from antenna or other in this case dvd on av. Looks like "ringing" of some kind. Does anyone have any experience of this problem?

[maxvalutech]

Re: LG RT42PZ45V internal electrical interference

Still trying to find problem with this set. History is set was turned off and an hour or so later would not turn on - standby ok and after tests another powerboard obtained and fitted. Started up and menu came up good. However when signal applied via set top box and also DVD the interference problem showed up. I note the following on main board RHS the stby led on red. LD740 5V blinking red on LHS - power on 4 x leds RHS light up and all voltages ok- on LHS 4 x leds but only LD740 lit and blinking. On control board 4 x green leds light at power on one of which blinks approx each second - 1 x led has 3V marked at test point but this only measures 1.85V. Another led on the board does not light. Cant find a circuit for that board although I have service manual it does not show.
Fans x 2 do not start - they have 3 leads and 5V is present - maybe heat sensitive switch?? A domed large main cap on y-sus replaced by me but no difference. LD740 is connected with the others and goes to 5VST-PCF and IC743 (74HCT574) other side.
My thoughts are 1. Picture is good under the interference lines and was perfect when menu/no signal displayed (some coloured pixelation evident now) so Y and X sides all ok. 2. No previous problem evident so interference may well be from the powerboard now fitted - if so coils or ??? it seems to pulsate at around about once per second. 3. Am I right about the fans. 4. do the leds tell me anything - the main board ones are green/red and circuit shows G 10MCD R 6MCD but does not say what should be on/off or whatever. 5. As can be seen by not very clear pics the boards are full of stuff and hidden behind screens heatsinks and each other in case of control and associated small ones which to get at means pulling almost the wholeof the hardware fittings off!! 6. the set is really too old now to muck with although picture is bright and its my mates favourite from his den. Any suggestions welcome and thanks in advance.

[maxvalutech]

Re: LG RT42PZ45V internal electrical interference

Have now got onto another powerboard dirt cheap so will wait and try it when if no go will remove control board and follow it testing as best I can - do note that previously saw 5 green LEDs thereon with 2 blinking but now only see 4 and 1 the other showing nothing.