DVDR24HD160F Dead no standby LED

[Ruptor]

Does anybody have a circuit for the PSU board in this Wharfdale unit? Looking at the board there is no connection across the isolation line on the PCB for any supply to get across to run the standby circuit where the button and LED on the front panel are so no power means nothing to turn on the main power. Looking at the board and the switch mode device data of the STRW6252 that is the thing controlling the power it appears a signal needs to be put on one of it pins via the isolation transformer. If that is the case it is most likely faulty but I don't want to buy what looks like an obsolete part without some confirmation or if something else could be dead on the low voltage isolated side. Any suggestions would be appreciated as I am guessing and don't really grasp how the power supply gives any kind of standby voltage across the isolation line.

[R_J]

Re: DVDR24HD160F Dead no standby LED

post clear in-focus pictures of both sides of the power supply so we can see what we are dealing with. Are you getting any voltages in the power supply? It might be that there are some bad capacitors in the power supply.

[Ruptor]

Re: DVDR24HD160F Dead no standby LED

post clear in-focus pictures of both sides of the power supply so we can see what we are dealing with. Are you getting any voltages in the power supply? It might be that there are some bad capacitors in the power supply.

The only voltage is on the rectified mains side that I can see but I don't have a circuit so don't know where to measure. There should be a standby voltage to the front panel that lights the LED and allows the on switch to pass a signal back to the PSU to turn it on full but I don't know the path of that supply voltage. I can't see any blown caps or board damage.

[R_J]

Re: DVDR24HD160F Dead no standby LED

Check the value of R102 ( it is the resistor from pin#3 of the switching ic to ground) It should be a low value around 1Ω. If it is open, the ic is defective.
I see a repair kit available from this company http://www.ohmsupplies.co.uk/epages/...roducts/KIT246

[Ruptor]

Re: DVDR24HD160F Dead no standby LED

Check the value of R102 ( it is the resistor from pin#3 of the switching ic to ground) It should be a low value around 1Ω. If it is open, the ic is defective.

It measures 0.4R in circuit and 0.6R when I lifted one end. Should it be 47R since it has yellow & purple rings? Thanks for the link. Is it really a Vestel designed board? They sure know how to give electronics built in obsolescence or perhaps it is just bad design.

[R_J]

Re: DVDR24HD160F Dead no standby LED

The resistor is ok (0.47Ω), so I suspect the ic could be ok as well. If the ic's internal mosfet shorted, it would cause the resistor to go open, this does not seem to be the case.
I would check all the diodes in the secondary circuit and also check that none of the secondary supplies have a low resistance. If there is a shorted component in the secondary ciruit, the power supply ic will go into shutdown.
If you have a way to check capacitors, check C105, or try replacing it. You can also try and check what the voltage is across C105, this capacitor is in the primary (LIVE) and you must be careful checking voltages here as they do not use the chassis as ground but use hot ground, or the negative side of the large electrolytic in the primary. NOTE the primary side is connected directly to the AC mains.

[Ruptor]

Re: DVDR24HD160F Dead no standby LED

I would check all the diodes in the secondary circuit and also check that none of the secondary supplies have a low resistance. If there is a shorted component in the secondary ciruit, the power supply ic will go into shutdown.

I removed the cap and measured it at 46.5uF then I tried checking the secondary diodes that is tricky in an unknown circuit. I found two groups of 3 diodes in parallel but they measure differently so I lifted one end of the D124-6 and the middle one was dead. The diodes are 200V 3A that feed 16V caps or at worst 50V caps so a bit of overkill. Is there any reason that a 50V 5A schottky diode with TVS protection wouldn't do a better job? I can't see it being current that blew the diode because it would require a burning current that would leave evidence given the 150A peak current rating so it must have been a voltage spike. Who knows what else is dead.

[R_J]

Re: DVDR24HD160F Dead no standby LED

Sometimes parts just go bad, If the diode is shorted, just leave it disconnected and with the plug that is connected to the 16v (likely goes to main board?) removed. see if the power supply will work. The supply should operate with 2 of the 3 diodes in place just to test if it works.

[Ruptor]

Re: DVDR24HD160F Dead no standby LED

see if the power supply will work

The power supply seemed to work with sensible voltages so I connected everything back and without putting the lid on switched on. It went "preparing" opened and closed the DVD then the clock came up so all looked good. I pressed open and it did then close and it displayed both states of the draw. Next plugged up the aerial and HDMI TV turned on and everything went to pot. The DVD draw seems to open by itself at regular 4 second intervals with or without a DVD and often it ignores the open & off buttons with zero response from the other buttons. Clearly the diode wasn't the only thing to blow. Not sure where to look now.

[R_J]

Re: DVDR24HD160F Dead no standby LED

It could be that there are also bad capacitors in the power supply, If you don't have cap checker/esr meter or scope etc. to check the power supply, all you can do is start replacing parts. You didn't say what the voltages are so it's hard to say what to check.

[Ruptor]

Re: DVDR24HD160F Dead no standby LED

You didn't say what the voltages are so it's hard to say what to check.

Measuring on the diodes from the outside of the board going in there is 5.1V 3.27V & 11.42V.
Measuring the red wire on each white connector the scart connector board reads 1.5V and on the scope it is a square wave but with the plug out hence no load it is a stable 4.25V. There must be something duff on the scart board.

[Ruptor]

Re: DVDR24HD160F Dead no standby LED

I checked all the discrete components like diodes and transistors on the scart board and they seem to have sensible diode junction readings. Any suggestions for testing what else might be duff?