50pg20 Power Cycling When Power Applied

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

I jumped before measuring 12 and 16V... M5V doesn't seem to change upon heating of main board..

[tom66]

Re: 50pg20 Power Cycling When Power Applied

Power board should be heated not main board sorry for not being clear.

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

12V and 16V is cycling on and off but seem OK , 12.2V and 16.3V... (with warm Control/Main board)

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

Oh OK... I actually just tried heating up Power supply board near 5V regulator.. Still Cycling..

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

There is a smaller power resistor (.150 at 5W) on the top side of the board I didn't check.. only the three that you mentioned the other day..

[tom66]

Re: 50pg20 Power Cycling When Power Applied

I think M5V is the main issue. If all the heating up does not work the startup cap for the 5V may need replacing.

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

I did replace the four 3300uf caps and one 680uf cap on this board the other day... near this voltage regulator circuit... There is a 470uf, 25V near this connector I DID NOT replace...

[tom66]

Re: 50pg20 Power Cycling When Power Applied

Startup cap is on the primary side.

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

Replace four caps in middle of picture (3300uf) and one to right hand side (680uf)... NOT the one on left side (470uf).

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

I will have to pull the board out and look at the traces (NO Schematic) to find primary side of regulator at cap... I know its @19V coming in and 5V coming out..

[tom66]

Re: 50pg20 Power Cycling When Power Applied

You're looking for a 10~100uF cap on primary.

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

OK Thanks.. I will pull board and see if I can chase one down... Thanks for all the help once again! Vladas

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

I replaced the 10uf , 63 volt cap on the primary side of an adjustable high accuracy voltage regulator on this plasma. The cycling problem still continued. I went through the 5 volt standby circuit and when I ohm out the input (19v) side of this regulator (a KA431) when its on, the main board goes into standby and the TV then turns on with the main power switch.. I have to order this regulator from China, very inexpensive.... Is it possible that there is a capacitor in this circuit that is causing this voltage regulator not to bleed down when its turned off? Also, the output of this regulator is only 2.4 volts.. Its data sheet says that it's capable of regulating between 2.5 and 63 volts... could this be the problem because the voltage is lower? Thanks...

[tom66]

Re: 50pg20 Power Cycling When Power Applied

That is part of the feedback path... 2.4V is a little low (should be 2.495V or so) but probably OK. I would be considering any other startup caps. Shorting that reg is not a good idea, the PSU loses feedback control, so 5V standby will rise to excessive levels and could cause damage.

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

OK, Getting somewhere... Now the OK signal from the main board feeds this circuit I believe .. Could this capacitor actually be on this main board or would it still be on the main power supply board? I do have a small 47uf cap near the sub-micon controller chip, Page 38 of start up sequence says "The 5V (standby) voltage is routed to the Sub Micon (U701) on the SMPS and through P803 (The connection between these two boards) to the Main Board for Micon operation ( IC100). AC detect Pin 18 of P803 is generated on the SMPS by monitoring the AC input and rectifying a small sample voltage. This AC Detect Voltage is routed to the Sub Micon (U701) on the SMPS and the Micon (IC100) located on the Main Board and is used as a basic “SMPS OK”signal. AC Det actually releases “Reset” on the Main Board.

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

I'm not shorting this voltage regulator when I turn on the TV.. only causing it to go into standby mode so I can turn the TV on at its main power switch.. now, if I turn off this main switch the TV cycles again and wont go into standby.. I can operate the TV after I short it into standby and then turn the TV on.. Then I can turn the TV on and off by unplugging from the AC input..

[tom66]

Re: 50pg20 Power Cycling When Power Applied

How do you manage to "short it into standby"?

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

Hi, All I did was try to measure the voltage to ground on the 19V primary side of this voltage regulator.. I had the DMM in ohms measurement by mistake instead of DC voltage and the TV went into standby..

[Vladas]

Re: 50pg20 Power Cycling When Power Applied

I've read that this precision voltage regulator can be used as a great replacement for a zenor diode.. I may have caused a disruption in biasing..

[tom66]

Re: 50pg20 Power Cycling When Power Applied

Makes sense, you meter probably shorted the PSU, would be more worried about the meter myself, than the TV...