Samsung LN32A300JID Whacked Voltages

[Sam I Am]

Hello All,
This is my newest acquisition in the Samsung line of fine products.
The symptoms are a black screen, no sound, and no backlights.
The following are things that I have checked/done:
1) 120V is present at the PS board,
2) Both known fuses show continuity,
3) All caps are original OEM showing no obvious signs of leakage/bulging (hence no ESR readings were taken),
4) All diodes are showing good,
5) Measured voltages on most of the PS input/output pins (see attached pics).
The 5V are close enough I suppose, it's the 12V, 13V, and 24V that have me scratching my head as they are way too low.
As a side note, this set appears to be brand new or has had very limited usage since the inside appears to be totally dust-free as well as super-clean.
Any and all assistance will be greatly appreciated.

[Dgtech]

Re: Samsung LN32A300JID Whacked Voltages

Hello All,
3) All caps are original OEM showing no obvious signs of leakage/bulging (hence no ESR readings were taken),
:

This statement is not true. Measure all caps, ESR and capacitance - with these symptoms that are displayed. Hell, if they were bulging, why would you need to measure ESR or anything else? Bulging always = bad....while not bulging does not mean good always.

[cadiman]

Re: Samsung LN32A300JID Whacked Voltages

If you have 5v do you have a power light lit on the front of the tv?

You can check v at output of bridge rectifier d/c ( lower right ). Make sure you have 120v a/c going into bridge. Its easy to check and the 4 pins are marked on it a/c in ( inside pins) and + - out ( outside pins ). These rarely fail, but I always check them.
This board may have around 450vdc at the big cap so be careful.

An esr meter is a must for samsung! They will all look good, but they will all be bad. Sorta like women, You can`t tell by lookin at em.

They use a different kind of esr meter.
It is called a WALLET

[Sam I Am]

Re: Samsung LN32A300JID Whacked Voltages

Huh.....
I did not initially measure the ESR due to the pristine condition (cosmetically speaking) of the set. I realize that bulging means bad as I've done more than a few cap replacements and I'm also aware of the bad cap issues with respect to many Samsung LCD products. I simply "feel" the problem is somewhere other than with the caps.
So...... to satisfy your need to point out my error, all caps are within specification with respect to ESR as well as capacitance.

If there is anything constructive that you would like to add, please feel free to do so. Otherwise,

Upon further diagnosis, the resistor looking component (RX801S) above and slightly right of the 120V connection will not show continuity. Does anyone know if this is a resistive fuse or just a plain resistor. In addition, the tiny resistor directly above ICM801 as well as RB801 will not show continuity. A resistor should show continuity.... right? Be gentle as I am still learning.

[Sam I Am]

Re: Samsung LN32A300JID Whacked Voltages

Cadiman,

The power light (LED) does light on the front.
I'll check the rectifier a little later.
Thanks for the reply.

[Sam I Am]

Re: Samsung LN32A300JID Whacked Voltages

The bridge has 120V AC on both center pins and 75V DC on both outer pins.
I had already allowed for a total recap (except the big 450V) once I got it to power up properly. Went ahead and recapped it earlier to avoid any further harassment.
I guess I must be measuring V wrong because all I'm getting at the + side of the big 450V is 75V DC.
Also noticed that the red LED at the power button stays on until you unplug it... don't have a clue as to whether this may be normal.
All other initial voltages remain unchanged.

[Dgtech]

Re: Samsung LN32A300JID Whacked Voltages

How are you measuring voltage on this cap? You should be going from one leg directly to the other leg - carefully of course. 75V is low if measured correctly.

[Dgtech]

Re: Samsung LN32A300JID Whacked Voltages

By the way, If this voltage is confirmed to be 75V, this does not point to the filter cap as a definite failure, at least not yet. Using the Negative ( - ) leg of the large filter cap, what are the DC voltages you see on the rectifier? The pic below is of the rectifier on that board.

[Sam I Am]

Re: Samsung LN32A300JID Whacked Voltages

Measuring per your instructions results in 162V DC at both bridge outputs as well as across the cap.

[Sam I Am]

Re: Samsung LN32A300JID Whacked Voltages

So.... how does this explain the incorrect voltages on the 12, 13, and 24V "rails" again?

[Dgtech]

Re: Samsung LN32A300JID Whacked Voltages

OK, I may have jumped the gun on something but I wanted to check the beginning DC. You never told us what the rail's actual voltages were measuring exactly. How low are they? (Actual voltage measurements)

[Sam I Am]

Re: Samsung LN32A300JID Whacked Voltages

See pics #3 & #4 that were initially posted.

[Sam I Am]

Re: Samsung LN32A300JID Whacked Voltages

C'mon guys.
This is probably simple stuff to most of y'all, but I'm totally bogged.
Someone please point me in the right direction.

[PlainBill]

Re: Samsung LN32A300JID Whacked Voltages

Dig through my previous posts and you will find my dissertation on the operation of a SMPS. In a nutshell, there are a very few reasons a SMPS will not have the proper output voltages. Excessive load on one output, bad input cap, defective regulation components, bad SMPS controller.

One common feature of TV power supplies is a dual supply. There is a 5 volt standby supply that is always on. There is the main supply that is switched on only when the TV is on.

Another common feature is a PFC front end that is enabled only when the the main supply is on.

I took a look at this several times, and while you have pretty good pictures, I had a hard time figuring out where the 5 Volts comes from. Sure enough, it's the small transformer at the top of the first picture.

How about checking the input voltage to the main SMPS, and identifying the part number of the main SMPS controller?

PlainBill

[Sam I Am]

Re: Samsung LN32A300JID Whacked Voltages

I must be stupid or something as I seem to be having difficulty finding your "dissertation" concerning SMPS operation.
You have a substantial amount of posts so a link would be much appreciated.
Otherwise, I'll be searching for hours.
In addition, which components are the main SMPS and it's corresponding controller?

[Sam I Am]

Re: Samsung LN32A300JID Whacked Voltages

Okay, I'll take a stab at it.
The component at the lower left corner of the first pic is showing 52V DC on all 5 pins. Looks like a transformer to me but what do I know.
As far as a controller goes..... beats me!
I can consistently ID capacitors, diodes, fuses, resistors, heat-sinks, bridges (as of yesterday), and inductors.
Anything else..... well... hand me some dice and we can play craps.
Sheesh.... how many times do I have to say this, I am inexperienced when it comes to electronics. That's why I'm here.
To learn from those with considerable more experience.

[PlainBill]

Re: Samsung LN32A300JID Whacked Voltages

I must be stupid or something as I seem to be having difficulty finding your "dissertation" concerning SMPS operation.
You have a substantial amount of posts so a link would be much appreciated.
Otherwise, I'll be searching for hours.
In addition, which components are the main SMPS and it's corresponding controller?

It's late, I'm tired. On the picture of the top side of the board there are two ICs. The 8 pin one (ICB801S??) is almost certainly the controller for the standby supply. The 16 pin one (ICM801) seems to be the controller for the main SMPS.

On teh picture of the bottom side of the board there is an 8 pin IC in the upper right corner. I believe that is the PFC . I would like the numbers of those ICs, please.

One additional comment. 50 years ago it was possible to repair more than 80% of all TV problems with little more than a screwdriver, a tube tester, and a caddy full of tubes. Things are different now. I'm not telling you you shouldn't try to fix this TV, I'm just pointing out that if your primary goal is to get this TV working, it should be taken to a professional. If your goal is to learn some electronics troubleshooting and hopefully get a working TV out of it, you should continue.

PlainBill

[PowerAmpFreak]

Re: Samsung LN32A300JID Whacked Voltages

Okay, I'll take a stab at it.
The component at the lower left corner of the first pic is showing 52V DC on all 5 pins. Looks like a transformer to me but what do I know.
As far as a controller goes..... beats me!
I can consistently ID capacitors, diodes, fuses, resistors, heat-sinks, bridges (as of yesterday), and inductors.
Anything else..... well... hand me some dice and we can play craps.
Sheesh.... how many times do I have to say this, I am inexperienced when it comes to electronics. That's why I'm here.
To learn from those with considerable more experience.

Where do you put the negative pin of your voltmeter? not to chassis i hope, since this is connected to secondary side of the powersupply. You should stick the voltmeter to the negative side of the bulk mains capacitor, that's primary. And beware of the primary side if you're not used to repairing switchmode power supplies, because you would regret touching the wrong stuff.

[PlainBill]

Re: Samsung LN32A300JID Whacked Voltages

Where do you put the negative pin of your voltmeter? not to chassis i hope, since this is connected to secondary side of the powersupply. You should stick the voltmeter to the negative side of the bulk mains capacitor, that's primary. And beware of the primary side if you're not used to repairing switchmode power supplies, because you would regret touching the wrong stuff.

Or worse yet, not live to regret....

PlainBill

[Sam I Am]

Re: Samsung LN32A300JID Whacked Voltages

Thanks for the boost PlainBill....
This is what I have found so far, the 16-pin is a MC330167P found at http://pdf1.alldatasheet.com/datashe.../MC33067P.html
The V at Vcc is 15v with Vref showing 5V.
The 8-pin is a Q0165R which I believe is found at http://77.221.132.234/datasheet/FSQ0165R.pdf
There is not a FS is front of the number on the chip but this is all I could find that made any sense. The V at Vcc is 16.3V, Vfb = 800mv, Vsync = 1.7V, Vstr = 160V, and the drains are showing 163V.
On the back is a FAN7530 found at http://www.fairchildsemi.com/ds/FA/FAN7530.pdf
I'm scratching my head where to go on this one.
All readings were taken with the ground clip at the neg. leg of the big cap.
Also the correct readings for the transformer at the lower right corner is 162V at the 2 top right corner pins, 0V at the pin by designator LP801 and 0V on the 2 lower pins at the bottom edge.
Did notice something while probing around taking V readings on various components. The V on the DP802 diode (directly below + leg of big cap) is 162V on stripe side and 130V on the opposite side. DP804 (raised diode directly below big cap) is 162V on both sides. There are also a couple of more diodes on this board showing voltage on both sides. I thought diodes had voltage in one direction only or am I missing something....