Samsung 930B re-capped, no backlight

[retiredcaps]

Re: Samsung 930B re-capped, no backlight

The voltage is steady at 163v across the big cap with the logic board unpluged

Sounds like something on the logic board is pulling down the power? I had something similar, but never managed to resolve due to a slip of the hand and shorted out some components on the power board.

I don't have any ideas. Maybe PlainBill does?

[Scenic]

Re: Samsung 930B re-capped, no backlight

r316 looks pretty toast.. doubt it has something to do with this though..

[alexanna]

Re: Samsung 930B re-capped, no backlight

The voltage is steady at 163v across the big cap with the logic board unpluged

[alexanna]

Re: Samsung 930B re-capped, no backlight

It stays at 160V to 161v the majority of the time, using the min max record it will go as low as 149v briefly at times

[retiredcaps]

Re: Samsung 930B re-capped, no backlight

Pin 1 is fluctuating between 150 and 160V D.C.

Is the DC voltage stable across the main filter capacitor?

[alexanna]

Re: Samsung 930B re-capped, no backlight

I have a 939B that is not working.
All the 10mm and smaller caps have been replaced they were obviously swollen. And have been replaced this includes the two 4MM caps.
U202 and U203 had similar damage as the OP board. And have been replaced.
I have a power supply that is starting and shutting off repeatedly, the power LED is flashing on and off
I am currently looking at the DM0565R power switch
http://pdf1.alldatasheet.com/datashe...SDM0565RB.html
I have taken some voltage measurements
Pin 1 is fluctuating between 150 and 160V D.C.
Pin 2 dose have a ground
Pin 3 is fluctuating between 9 and 15V D.C.
Pin 4 which is the feed Back is Fluctuating between .5 And 8 V D.C.
Pin 5 not used
Pin 6 is fluctuating between 32V D.C. and 159 V D.C.

I guess i should have said anybody got any ideas on what to check

[leperinc]

Re: Samsung 930B re-capped, no backlight

ebay has 10 (ten) for $7 CDN + $4 CDN for shipping. Just search for AF4502C.

<smacks head> Thanks for pointing that out! I've placed the order, so now we wait...

[jetadm123]

Re: Samsung 930B re-capped, no backlight

Fairchild shows a FDS8928A as a possible replacement. It handles less current than the AF4502C, but might be more readily available. Since they're so cheap, it would be good to order a couple extra just in case.

[retiredcaps]

Re: Samsung 930B re-capped, no backlight

but unless I can find cheaper shipping I think I'm gonna have to call it a day

ebay has 10 (ten) for $7 CDN + $4 CDN for shipping. Just search for AF4502C.

[leperinc]

Re: Samsung 930B re-capped, no backlight

On the front side between the two transformers are a whole bunch of resistors and diodes. You may want to test them all "in circuit" to see if you have a bad component.

They all look fine. No opens or shorts.

If you're not even getting a flash from the backlights when you push the power button, I would suggest you try replacing the two mosfets in question before going any further.

I wasn't able to find the original part at any of the usual places. Elsewhere in the forum here i saw a couple of people claiming success with a MMDF2C03HD from another manufacturer. A quick search shows Mouser is currently the only supplier with stock in individual chips at $1.47 each.

However, at $20 shipping, this last item is too expensive for me to continue. Getting this far has cost me $31. I'm currently not working and getting the parts from Mouser will push the total cost of this "free" monitor to just under $60. I saw the $8 USPS option but when you let them collect fees upon receipt it usually means an additional $15-20. The term "egregious" comes to mind. Well, other terms come to mind as well but...

Big thanks to both of you for helping me with this but unless I can find cheaper shipping I think I'm gonna have to call it a day

[retiredcaps]

Re: Samsung 930B re-capped, no backlight

I'd rather spend $5 in extra parts now as insurance rather than having to spend yet another $8 on shipping later.

On the front side between the two transformers are a whole bunch of resistors and diodes. You may want to test them all "in circuit" to see if you have a bad component.

As a fellow Canadian, I can relate with the $8 shipping cost.

[leperinc]

Re: Samsung 930B re-capped, no backlight

No problem, I appreciate your help with this. I'd like to hedge my bets on this one and ask what other components might be needed in case U202/3 are fine. I'd rather spend $5 in extra parts now as insurance rather than having to spend yet another $8 on shipping later.

Thanks!

[jetadm123]

Re: Samsung 930B re-capped, no backlight

If you're not even getting a flash from the backlights when you push the power button, I would suggest you try replacing the two mosfets in question before going any further.

[leperinc]

Re: Samsung 930B re-capped, no backlight

U301 is next to transformer T301. What's the part number?

Sorry about that, there are no opens or shorts no matter what pins/directions I measure.

here's the pic:

[jetadm123]

Re: Samsung 930B re-capped, no backlight

i'm going crosseyed. I can't find it. Can you point it out to me?

U301 is next to transformer T301. What's the part number?

[leperinc]

Re: Samsung 930B re-capped, no backlight

U301 is on the front side.

i'm going crosseyed. I can't find it. Can you point it out to me?

[jetadm123]

Re: Samsung 930B re-capped, no backlight

I agree with retiredcaps about the mosfets. Anything that heated up like that should be suspect. Also, they should always be replaced in pairs.

As for pin 16 connected to pin 7, since MODSEL sets the output polarity of the PWM controller, I'm assuming that connecting it to ground specifies a negative polarity.

Also, when you first power up the monitor, do you get any type of quick flash from the backlights?

[retiredcaps]

Re: Samsung 930B re-capped, no backlight

I don't see a U301

The look burned alright. Also, the plastic sheet has marks where the chips are.

U301 is on the front side.

Even though the mosfets are not shorted, the one chip looks really bad and could be malfunctioning.

[leperinc]

Re: Samsung 930B re-capped, no backlight

I figured I'd kill some time and poke around on U201 and measure everything from anywhere to anywhere in both directions. There appears to be one short between pin 7 and 16. I'm not sure if this is normal or not. On the similar model (3193) sheet pin 7 is GND and pin 16 is MODSEL. C345 (33uF/35v, replaced) is connected by traces across pin 7 (GND) and 10 (VCC)

[leperinc]

Re: Samsung 930B re-capped, no backlight

See if U301 is shorted. You can measure it in circuit. Report readings.

edit: Are you seeing 13V DC on the connector CN2?

I don't see a U301, I'll assume U201. I tried looking up the datasheet on it and can only find the BIT3193. Is this close enough, and what pins should I be paying attention to for measuring?

I see 13Volts on CN2, yes.

Hmmm, you did pick the correct location for pin 1. No shorts indicated from your readings. I'm wondering if what's on U202 is leftover residue from the soldering process. Try scratching the top of U202 with your fingernail to see if it will flake off. As for the fuse, Samsung usually puts a fuse at the 13V output, just before the inverter section. And I don't see a fuse either?! As a sanity check, try measuring for the 13V at the middle pin of heatsinked D105.

There is also 13volts on the center of D105. I've tried to clean the chips, first with my fingernail, followed by a white eraser and rubbing alcohol but it didn't change anything. I took a webcam which can be made to focus really close up and wetted the tops of the chips with alcohol. The look burned alright. Also, the plastic sheet has marks where the chips are.