Samsung LE40M87BDX - PSU Issue

[synaesthesia]

Hi,

Inherited a Samsung 40" as listed in title. Inverter, screen intact and good. Suspect PSU and mainboard.

I have a new mainboard on the way however have been trying to get some joy out of the PSU. On arrival it was doing the usual click repeat standby cycle. Caps all looked good but replaced anyway. Tried replacing the Eeprom on the mainboard but didn't get any joy from that.

However, keen to test the panel and inverter were OK, decided to do the jumper trick to power the panel up. It briefly flashes up but immediately turned off, and there was a noticable "hiss" very briefly coming from the part of the PSU where the inverter power comes from. This also happens with the inverter disconnected.

Voltages on the PSU don't appear too good - getting 10.6v from all 13v lines although standby voltage is perfect at 5.2v.

As well as replacing the usual suspect caps, I reflowed pretty much everything, some of the joints certainly didn't appear too sharp.

Very wary about poking around the "beefy side" of the PSU so before I do, I'd like any handy pointers at where to look at Suspecting voltage regulators but as I'm only starting out at getting this deep into things like this, I'd appreciate advice; nothing is better than getting something to work whilst learning at the same time!

[flocko]

Re: Samsung LE40M87BDX - PSU Issue

What is the power inverter board number is BN44-00165/7? this set has a balance board not to be confused with an inverter board ,that does what it says balances the output of the backlight tubes, would you care to tell us about the jumper trick and what you did? most problems on the power inverter boards would be bad caps and if replaced with low ESR replacements will get it up and running again do not forget the small start-up cap

[synaesthesia]

Re: Samsung LE40M87BDX - PSU Issue

Ah, gotcha I can't appear to find any board numbers close to that. Main power board is model IP-231135A. Balance board is SSB400HA20V; http://www.shopjimmy.com/samsung-ssb...t-inverter.htm lists some MFR part numbers. Quite likely I'm looking in the wrong place

Jumper trick was I believe from a shopjimmy video - jumpering pins 1 and 5 on CN1803 for inverter on/off and 1 & 3 on CN801 power on/off to stby 5.2v

The caps I replaced on the PSU are all low ESR with the next voltage rating up.

[zomi]

Re: Samsung LE40M87BDX - PSU Issue

If after having repaired the psu
will most likley be an issue with the main board.
bad psu can take out the main board too.

[synaesthesia]

Re: Samsung LE40M87BDX - PSU Issue

As stated, the mainboard is not connected therefore is ruled out.

[flocko]

Re: Samsung LE40M87BDX - PSU Issue

the BN44-00165 or 167 are the power inverter board part numbers what one is fitted ?so with main board unplugged from CN1801 and pin 1. PSon jumped to pin 3. 5.2v Stby , did the small voltages come up ?then when you jump B.L on (CN1803) to 5.2 Stby ,did the back light came on and stay on or then go then off ?, did you use resistors when jumping the above? did you keep the jumps in place or just flash them ?

[synaesthesia]

Re: Samsung LE40M87BDX - PSU Issue

Sorry, couldn't tell which is fitted as I can't find anything resembling those part numbers anywhere. They're directly jumped with specific jumper cables; had read about resistors but many folk appear to believe they're optional but safer.

I've taken some pictures but windows 10 decided it doesn't like my phone!

Voltages stay as they are when jumped and don't appear to fluctuate. Narrowed down the hissing to the inverter bottom left of the board.

Fairly sure it's BN44-00165A

[sordids999]

Re: Samsung LE40M87BDX - PSU Issue

look on that white serial number it should give you the BN44- number

[synaesthesia]

Re: Samsung LE40M87BDX - PSU Issue

#'£"!@!!

I must have "scrutinized" that label several times and entirely missed it!

It is indeed: BN44-00165A

[flocko]

Re: Samsung LE40M87BDX - PSU Issue

we use the resistors to replicate the logic state voltage (high or low) to turn on and off the power board or inverter in this case both needing to go high to turn these on (about 2-3v for a high state and under for low ).so with just the PSon high all small voltages are correct? but when you put BLon high as well do the backlights come on or not and do the small voltages change ?

[synaesthesia]

Re: Samsung LE40M87BDX - PSU Issue

Ah, that makes sense, thanks.

Backlight only ever comes on momentarily and all small voltages stay stable throughout the procedure.

Think I'll get another PSU, only £20. Will be the most expensive telly I've ever owned at £45 in total; the last two were damaged freebies fixed with whatever caps I've had lying around

[flocko]

Re: Samsung LE40M87BDX - PSU Issue

Without more testing your problem could be with the power inverter board / balance board or backlight tubes any one could and will cause the fault you describe, and as you tell us you already have a new main board coming. it will indeed turn out to be an expensive repair (£45.00) if its not the power board ?

[synaesthesia]

Re: Samsung LE40M87BDX - PSU Issue

The £45 is both mainboard and power board. I can't moan too much at that with the TV being free Mainboard was already gone; mostly because I was using a bad soldering iron combined with me being ham-fisted to remove a pair of IC's and took out half the traces with them. Live and learn!

[synaesthesia]

Re: Samsung LE40M87BDX - PSU Issue

Update on this issue - problem resolved Mainboard was replaced but the power issue appeared to be down to bad MOSFETS. I happened to have a couple of identical ones in my random junk/spares box, and a quick swapout later, I now have a fully working TV on the wall Also means I can sell the new PSU when it arrives!

[zomi]

Re: Samsung LE40M87BDX - PSU Issue

Thats interesting
Which ones were they ?

[synaesthesia]

Re: Samsung LE40M87BDX - PSU Issue

The two marked here, can't remember the component numbers.
I had spent some time over the last couple of days learning how to test fets and diodes with limited kit and then also stumbled across a "repair kit" for this exact PSU which was for the inverter side of the board (I had seen plenty of the kits involving the caps and the mainboard eeprom but not this one) so I concentrated on testing the diodes and fets it mentioned. Can't find the list I saved annoyingly, if I do I'll post here; there were a few diodes underneath, the two fets above and the bridge rectifier.

[budm]

Re: Samsung LE40M87BDX - PSU Issue

Those two Power MOSFETs are for the inverter transformer drivers.

[synaesthesia]

Re: Samsung LE40M87BDX - PSU Issue

Indeed, I'd read into that and certainly explains the symptoms I had. Amusingly I had ordered a replacement PSU on eBay expecting delivery on Tuesday this week; still hasn't turned up and I'm up and running anyway