LG Blue Ray /DVD player

[Radio Fixer]

Maybe 10 years old and now dead.  Wont power on at all.  Checked the fuse and OK.

Cant take PSU board out as I cant remove the plug from the connector:  any ideas on that as I dont want to break the connector ?


If I can get past that one any ideas on what would be worth changing other than caps and measuring everything possibe.  Obviouly cant do much about the ICs.

   
   

thanks for any help before I buy a replacement

Gary

[Mark Hennessy]

Hi Gary,

The white connector is fixed to the board, but the brown connector should just pull off.

Assuming there's no DC voltages at all at that connector...

As you remove the PCB, be very careful because the main smoothing capacitor might still be charged - even if it's been a while since it was last powered. Discharge with a chunky wire-wound resistor (rather than a screwdriver!) if necessary. When switched on, the DC voltage across it will be around 325V.

1. Look for high value resistors on the primary side - often they go high, preventing the thing from starting up.

2. Also check the smaller electrolytic on the primary side, as that failing can cause the same results. Generalising hugely, but startup faults were almost always caused by the resistor, but today it's perhaps more likely to be the capacitor (IME, at least). Even if it was the resistor, it's still good practice to change the cap while you're in there.

3. Those 7 pin ICs can fail, so if you can find nothing else wrong, it's worth trying that. Often, the high voltage start-up resistor is contained inside them in some form, so if you couldn't find a likely suspect for #1, that'll be why. Look up the datasheet for the IC for clues. If you can't find a service manual for the unit, the PSU might be fairly close to the example circuit shown in the datasheet.

Generally, if it hasn't gone bang, it should be fixable without too much drama. If you do get it running and the player seems to behave, it might be worth looking at the caps on the output side as a preventative measure - but if it runs but seems flaky somehow, it could be because one or more of those caps is tired. An ESR meter is useful here. Replacement caps should be low-ESR types, of course.

[Radio Fixer]

Thanks Mark

Very good info there.

Managed to get the connector apart, took a little leverage with a small screwdriver on each end. Board now out.

Looked up the Datasheet for the device: https://www.javanelec.com/stfiles/getapp...e25a07.pdf

A lot of useful stuff, block diag, typical cct diag and design data. Just need to find the likely parts and take out and measure.

Gary

[Mark Hennessy]

A good datasheet!

So yes, the start-up is within the chip, so any high value resistors are for the brown-out detection function. But that still leaves #2 and #3. Good luck!

[Radio Fixer]

Things have moved on.  I checked everything I could withunpowered measurements.  Having one of those LCR ESR testers was a big help.  All caps came out with OK values  amd ESR.

Next step was to buy some new STR A60535 chips from China.  About £11 for 5 from a recommended supplier.  Removed the original chip and fitted a 8 pin socket.  Put a chip in and powered it up.  A spectangular bang and flash which blew a hole in the chip topside.

   

The original chip had not gone bang even powered up for a fairly long time !

Not sure where to go now as from years ago experience working on SMPs when I semi goes bang it takes other things with it.  Perhaps on another day I will make unpowered  measurements again and then try another chip and bring it up on a Variac.

Gary

[Mike Watterson]

SMPSUs take excessive current at low voltage. A tungsten-halogen lamp limiter is better.

[Radio Fixer]

Good point Mike, I remember that now, thanks for reminding me.

The Data sheet actually has details of an "Anti Brown Out" addition that maybe included with the circuit.

Gary