Samsung 930B re-capped, no backlight

[jetadm123]

Re: Samsung 930B re-capped, no backlight

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.

[retiredcaps]

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?

[leperinc]

Re: Samsung 930B re-capped, no backlight

U202 and U203 look in pretty bad shape and are probably burned out. They look to be AF4502C dual mosfets.

[...]

With you meter set on resistance:

Measure across the following for shorts:

S1-G1
G1-D1
S1-D1

Do the same test S2-G2, etc

Thanks for the reply.


I put the black lead on the first point mentionned and the red lead on the second i.e. black to S1 and red to G1, etc. It's hard to see so I've included a pic pointing to what I think is pin 1. Hupefully I've gotten it correctly

I've checked both U202 and U203 and they read identical.

S1 --> G1 = 2.5K ohms
G1 --> D1 = 30K ohms
S1 --> D1 = 700 ohms
S2 --> G2 = 400 ohms
G2 --> D2 = 100 ohms
S2 --> D2 = 350 ohms

No shorts or opens.

I also forgot to mention the inverter fuse might be between the large cluster of caps and the heatsink. It might be underneath the white adhesive. It might be green and stands upright.

I still can't find it. I've been looking where you said from before but this time I cleaned off the component and it appears to be a 1 watt(?) resistor. it's light pink. There's noting green in there. I've attached updated pics of the area.

thanks!

[jetadm123]

Re: Samsung 930B re-capped, no backlight

I also forgot to mention the inverter fuse might be between the large cluster of caps and the heatsink. It might be underneath the white adhesive. It might be green and stands upright.

[jetadm123]

Re: Samsung 930B re-capped, no backlight

A while ago I was given a dead Samsung 930B and made an attempt at fixing it by replacing the obviously damaged electrolytic caps. On my first attempt i replaced:

cap# orig uf/v ---> new uf/v
-------------------------------------------------
301 820/25 820/25 nichicon pw
111 820/25 820/25 nichicon pw
112 820/25 820/25 nichicon pw
109 1000/10 1000/25 nichicon pw
110 1000/10 1000/25 nichicon pw

When I pressed the power button the green LED stayed on followed by a high pitched screeching noise coming from everywhere on the board. I replaced the rest of the electrolytics inluding the large one. Here's the rest of the list showing what I replaced:

cap# orig uf/v ---> new uf/v
-------------------------------------------------
113 330/10 330/16 nichicon pw
123 10/50 10/50 nichicon pw
107 47/50 47/50 nichicon pw
105 100/450 100/450 chemicon kxg
345 33/25 33/35 nichicon pw

Now the screeching is gone, it's all nice and quiet. When pressing the power button the LED is green and steady. It appears fine but there's no backlight whatsoever. I can faintly see a 'no input' message moving around the screen when I shine a light at it.

Attached are some pics of the board. After reading other threads in here I've checked my work again and i can't find anything wrong. I've checked the high voltage transformers both primaries read 0K ohm (my $cheap meter only has a R * 1K setting so i can't tell something like 10 ohms from a true short) and the secondaries read 1.3K ohms. There is no continuity between the primaries and secondaries.

I am unable to find any fuses (mentionned in another thread for a 930b) apart from F101 which is good. U202 and U203 look rather suspicious though. I can't read all the numbers on them and am not sure how to test them. Anyone?

U202 and U203 look in pretty bad shape and are probably burned out. They look to be AF4502C dual mosfets. Datasheet below:


http://pdf1.alldatasheet.com/datashe...P/AF4502C.html


With you meter set on resistance:

Measure across the following for shorts:

S1-G1
G1-D1
S1-D1

Do the same test S2-G2, etc

[leperinc]

A while ago I was given a dead Samsung 930B and made an attempt at fixing it by replacing the obviously damaged electrolytic caps. On my first attempt i replaced:

cap# orig uf/v ---> new uf/v
-------------------------------------------------
301 820/25 820/25 nichicon pw
111 820/25 820/25 nichicon pw
112 820/25 820/25 nichicon pw
109 1000/10 1000/25 nichicon pw
110 1000/10 1000/25 nichicon pw

When I pressed the power button the green LED stayed on followed by a high pitched screeching noise coming from everywhere on the board. I replaced the rest of the electrolytics inluding the large one. Here's the rest of the list showing what I replaced:

cap# orig uf/v ---> new uf/v
-------------------------------------------------
113 330/10 330/16 nichicon pw
123 10/50 10/50 nichicon pw
107 47/50 47/50 nichicon pw
105 100/450 100/450 chemicon kxg
345 33/25 33/35 nichicon pw

Now the screeching is gone, it's all nice and quiet. When pressing the power button the LED is green and steady. It appears fine but there's no backlight whatsoever. I can faintly see a 'no input' message moving around the screen when I shine a light at it.

Attached are some pics of the board. After reading other threads in here I've checked my work again and i can't find anything wrong. I've checked the high voltage transformers both primaries read 0K ohm (my $cheap meter only has a R * 1K setting so i can't tell something like 10 ohms from a true short) and the secondaries read 1.3K ohms. There is no continuity between the primaries and secondaries.

I am unable to find any fuses (mentionned in another thread for a 930b) apart from F101 which is good. U202 and U203 look rather suspicious though. I can't read all the numbers on them and am not sure how to test them. Anyone?