Samsung plasma power supply Vs and Va won't adjust???

[wadmancpu]

Hello, I have samsung model BN44-00619A that I'm trying to adjust the Va and Vs voltages on however the potentiometer screws have no effect on the output voltages. Both voltages are low and its causing a bluish ghosting on the screen. Any ideas? Thanks.

[coromonadalix]

I would check capacitors in the psu section,  and try to find the service manual before turning any pots in there or at least take their ohms values (tv powered off) before playing with them

[wadmancpu]

The values are printed on the plasma panel and the board so I know where they're supposed to be. I have removed and checked all capacitors. Neither of the adjustment pots are having an effect and I doubt they have both failed. I'm wondering if the oscillator IC isn't responding to the pots?

[andy2000]

Make sure the pots are good.  Also, check to see if they have anything in common like a reference voltage, or ground connection to one end of both pots.  Failing that, I would start looking for a board on ebay.

[Dacke]

Did you check Vs and Va with the power supply unloaded?

[shakalnokturn]

Did you check Vs and Va with the power supply unloaded?

Yes, test voltages unloaded, if closer to correct values have a quick look at the electrolytic just in case. More likely the MKP capacitor(s) (half bridge topology) on the primary will have a low value.

[wadmancpu]

Yes, I tested the board unloaded on my bench and both voltages were low. I will check the mkp caps on the primary. Thank you, I will post back my results.

[wadmancpu]

Are you saying that the mkp caps could be causing the low voltage readings even when the board is unloaded?

[shakalnokturn]

They could, although I'd expect something much closer to normal when unloaded.

[wadmancpu]

The voltage at main caps on the hot side is also about 100v low.

[Dacke]

The voltage at main caps on the hot side is also about 100v low.

If the main filter caps are 100V low then I would suspect the PFC,  also surprised that the TV would even turn on at all.  Strange as the PFC generally either works and should be 380-390V or it doesn't work and it will sit at ~160V,  either because something has failed in the circuit or the MCU isn't turning it on.

[Chris56000]

Hi!

There is a repair kit available for this PCB:–

https://www.ebay.co.uk/itm/Samsung-BN44-00619A-PN51F8500-P-Supply-Repair-Kit-For-Secondary-Drive-circuit-VS/201762463546?epid=1029304417&hash=item2ef9fadf3a:g:SzYAAOSwKfVXIWA4

Have you tried it?

Unfortunately the schematic for this pcb or chassis doesn't seem to have been uploaded to any of the usual free S.M. repositories yet, unless it's a chassis–desgination I haven't found yet!

Chris Williams

[wadmancpu]

I'm familiar with the components in the kit, it's primarily for a dead board condition but I have tested those components. I am currently leaning toward a MCU issue. The part number on that is only available from china unless I can find a compatible replacement. I have searched high and low for a schematic on this but it appears the only copy is in a vault at Samsung. Are there usually compatible parts for the MCU chips?