Samsung LE32S73BD Flashing standby LED no backlight

[dicky96]

Hi guys
I've been looking at this Samsung LE32S73BD. Basically the Standby LED is flashing and the TV will not power up.

On the PSU all the voltage rails are coming on for a few seconds, but they read much lower than they should. For example 24V rail is going to just over 5V. Then the voltages all decay and power back up again.... ad nausium

I don't have my Isolation Transformer here yet, it is still in the UK with my variac.

Putting my scope on 10mV scale and holding the probe near to the SMPS transformer primary it is clear that the PSU is powering up for a few seconds, then stops oscillating for a second and powers back up again.

Found one bad bulging cap on the low voltage side 1000uF 10V and changed that. All the rest look OK visually. It didn't make any difference anyway.

No short circuits on any voltage rails and anyway every rail gets some voltage (lower than it should be) so there couldn't be any shorts.

I found a repair kit for this fault on ebay so it seems fairly common? The kit is one IC and one capacitor. It's obvious which IC it is, not sure which cap.

Anyone seen this fault and could suggest anyway to prove the cause of the fault before buying the repair kit (or just the IC and Cap if I know which it is)

This is definitely for my model of power supply board BN96-03775A

http://www.ebay.co.uk/itm/F9222-REPA...MAAOSwPhdU1LTi

Cheers
Rich

[dskall]

Re: Samsung LE32S73BD Flashing standby LED no backlight

Need some pictures of power board and # off ic

[vinceroger69]

Re: Samsung LE32S73BD Flashing standby LED no backlight

capactior cm802 563j 630v poly film
ic F9222L ICM801S

these are from my notes from ages ago

Edit found schematic

[budm]

Re: Samsung LE32S73BD Flashing standby LED no backlight

That repair kit is for repairing the 24V power supply section, the cap CM802, the IC ICM801S.
I would check the capacitance of that cap CM802 off the board to see if the capacitance is still within the tolerance or not.
BTW, so the standby power supply is OK, and steady, right?
Pictures provided by shopjimmy.

[dicky96]

Re: Samsung LE32S73BD Flashing standby LED no backlight

Thanks guys

@dskall will post some pics of PSU board up tomorrow but it looks just like the ones budm posted

@vinceroger69 - cheers for the PSU schematic that will help a great deal!

@budm - will check ST/BY tomorrow. I had see that small xformer between hot / cold section already and thought it was in feedback circuit of SMPS along with at least 4 opto-couplers I could see, but now the schematic shows me otherwise


@All of you
CM802 will be checked for capacitance next
Your advice is much appreciated
Rich

[attainteddragon]

Re: Samsung LE32S73BD Flashing standby LED no backlight

i would also check the ps on pin to see if if the main board is causing the ps to fluctuate.

jump the ps on without main to confirm.

[dicky96]

Re: Samsung LE32S73BD Flashing standby LED no backlight

CM802 reads good, 55.6nF.

The electrolytic which I already changed, that had leaked a little at the top, was CS852. It still read fine on ESR meter but was reading around 200uF instead of 1000uF

Voltages.

STBY is stead 6.05V
PSON is alternating 4.4V - 0.03V every few seconds. When PSON is 4.4V the power supply is running but all output voltages much lower than they should be. When the voltage is there every few seconds, it is stable although low.
during the on cycle for several seconds
24V reads 5.65V
13V reads 3.62V
12V reads 3.62V
5.4V reads 3.62V

The PSU doesn't seem 'stressed' while it is running if you know what I mean, and voltages decay slowly when powered off.

I connected my scope to have a look for ripple on the 24V rail and found it is 'ramping' between 5-6V at quite a low frequency about once every 100mS. See video

https://youtu.be/aB5_WqTySwk

The PSU is obviously not happy. It looks as though it might be detecting a 'false' over current or over voltage signal or something like that. Not having my isolation transformer isn't gonna help

I must bring it from the UK but it is soooo heavy!

[vinceroger69]

Re: Samsung LE32S73BD Flashing standby LED no backlight

are you testing this with the mainboard connected? if so maybe just test the psu by itself.

[dicky96]

Re: Samsung LE32S73BD Flashing standby LED no backlight

With the main board and the inverter connected.

I can try without. Do I have to connect a resistor between standby voltage pin on the PSU connector and PSON to get it to power up voltage? Does it need some sort of dummy load on any outputs?

[vinceroger69]

Re: Samsung LE32S73BD Flashing standby LED no backlight

im not sure about the resitor maybe try it if voltages dont come up put a 1k resistor between the two pins regarding a dummy load ive never had too use one but i have seen budm recomend car bulbs as a load.

[Andrew F. Ali]

Re: Samsung LE32S73BD Flashing standby LED no backlight

Seeing that the St-By voltage is 6.05V, I would use a pair of AA batteries in series and use that 3V to power the PS-ON to measure the 12V, 24V, etc. I would then us another lead from the batteries to power the BL-ON and see if Backlights come on.

[vinceroger69]

Re: Samsung LE32S73BD Flashing standby LED no backlight

Seeing that the St-By voltage is 6.05V, I would use a pair of AA batteries in series and use that 3V to power the PS-ON to measure the 12V, 24V, etc. I would then us another lead from the batteries to power the BL-ON and see if Backlights come on.

Yes just noticed standby was 6v so best use batteries as advised

[dicky96]

Re: Samsung LE32S73BD Flashing standby LED no backlight

I connected my bench supply via a 390R resistor to PSON. I disconnected the main board.

As a precaution I connected up a 60W light bulb as a limiter on mains input.

With 0V on the bench psu, the light bulb flashes once on mains power up then goes out. Quite normal.

All I need to do is put about 1V out on the bench supply and the 60W light bulb comes on about half brightness or so, and now I have 5.6V continuous on the 24 volt rail. I didn't bother to measure the other rails. I did increase the bench supply to 4.4V as that is what I was seeing from the main board on PSON but it makes no difference to the light bulb brightness.

I then tried disconnecting the inverter board and I then have around 12V continuous on the 24V rail with the light bulb at the same half brightness or so.

So with no load I get more voltage output but it seems a bit strange the limiter light bulb is at the same constant brightness regardless of whether the SMPS has a load or not.

I then disconnected the bench PSU and reconnected the main board. I left the inverter board disconnected.

I now have the original 5.6V on the 24V rail, cycling on and of every couple of seconds with the 60W bulb flashing on and off at the same rate.

I'm really not sure why, with the inverter disconnected, I get about 12V on 24V rail when I trigger PSON with the bench supply, but I only see 5.6V when PSON is driven by the main board. Unless the extra load of the main board itself is dragging down voltages further.

I'm also puzzled why the SMPS seems to be dissipating 30W or so (guessing from the brightness of the bulb) with no load. But nothing goes pop even without the limiter.

I could I guess leave it running for a few mins with no load using the bench supply to enable and then switch off and see if anything is warming up on the SMPS? The energy must be going somewhere

Rich

[dicky96]

Re: Samsung LE32S73BD Flashing standby LED no backlight

Actually I tried that - had the SMPS running continuous for about a minute. I did notice that the 12V on the 24V rail (inverter disconnected) is not actually completely stable. It starts at about 12.5V and gradually reduces at a decreasing rate to about 10.5V after a minute or more then seems to settle

After powering down nothing was warm that I could find but I could have missed something of course - or it was something large that would take longer to heat.

Rich

[budm]

Re: Samsung LE32S73BD Flashing standby LED no backlight

"CM802 reads good, 55.6nF.' What is the value as printed on that cap? 563 as shown in the schematic?
BTW, what is the PFC boosted Voltage as measured between the two legs of the main filter cap?

[dicky96]

Re: Samsung LE32S73BD Flashing standby LED no backlight

"CM802 reads good, 55.6nF.' What is the value as printed on that cap? 563 as shown in the schematic?
BTW, what is the PFC boosted Voltage as measured between the two legs of the main filter cap?

Will measure the PFC boost voltage tomorrow

563 = 56000 = 56nF. 55.6nF is pretty damn close

[dicky96]

Re: Samsung LE32S73BD Flashing standby LED no backlight

Right... this is really interesting.

Firstly CM802 is marked 563J on the component bud.

I measured the boost voltage across the main electrolytic as suggested.

With the 60W bulb limiter, no load on the SMPS and no voltage applied to PSON I get a steady 319V boost on the cap with AC input reading 220VAC and the bulb is off

Once I apply PSON from bench PSU the 60W bulb lights, the boost voltage is 309V and the AC input drops to an unbelievable 9.8VAC! But the power supply still runs with about 12V on the 24V rail. I hardly believed my eyes, or my DMM, but tested several times and i really do see 9.8VAC input as soon as I apply PSON voltage!

I went and got a 105W bulb. Using this, the lamp gives a quick dim flash on power on, it doesn't light at all with PSON present and the boost voltage is 389V. I still only have about 12V on 24V slowly rising over 10-20secs to 14V.

Just as a reminder with main board attached, current limiter bypassed, inverter disconnected I get the cycling on and off every couple of seconds and about 5.6V on 24V rail

It seems to me the PFC circuit is working, unbelievably so in fact, if it manages to produce a 309V DC potential on the main electrolytic with 9.8VAC in! I suspect it isn't good for the SMPS though so will stick using the 105W bulb

Still no nearer to fixing this one yet though, any other suggestions... or next I will be pulling all the electrolytics on the PSU board that look OK physically to test for ESR and capacitance

Rich

[vinceroger69]

Re: Samsung LE32S73BD Flashing standby LED no backlight

could the ic F9222L ICM801S be faulty as it does the 24 v line

[budm]

Re: Samsung LE32S73BD Flashing standby LED no backlight

309V is not even close to PFC being running, at 220VAC input , the Voltage on the cap will be 220VAC x 1.414 = 311V with 60W lamp is limiting the PFC circuit to start up, so you have to maintain the PFC boost Voltage.

"if it manages to produce a 309V DC potential on the main electrolytic with 9.8VAC in" That is impossible! How and where did you measure the ACV feeding the bridge? Where did you put the probes?
If you can manage to feed this TV with only 9.8VAC and able to get 309 VDC on the the cap , you better patent this invention and you will be very rich.

[vinceroger69]

Re: Samsung LE32S73BD Flashing standby LED no backlight

309V is not even close to PFC being running, at 220VAC input , the Voltage on the cap will be 220VAC x 1.414 = 311V with 60W lamp is limiting the PFC circuit to start up, so you have to maintain the PFC boost Voltage.

"if it manages to produce a 309V DC potential on the main electrolytic with 9.8VAC in" That is impossible! How and where did you measure the ACV feeding the bridge? Where did you put the probes?
If you can manage to feed this TV with only 9.8VAC and able to get 309 VDC on the the cap , you better patent this invention and you will be very rich.

Budm I thought the pfc voltage was low too but then i saw this sentance in a above post so was confused

I went and got a 105W bulb. Using this, the lamp gives a quick dim flash on power on, it doesn't light at all with PSON present and the boost voltage is 389V. I still only have about 12V on 24V slowly rising over 10-20secs to 14V.