LG 1953 Dead

[smason]

Got a nice 19" LG 1953 from work, just died one day.

I figured this would be an easy recap, but looks like it might be a challenge.
That's ok, it's the only repair on my pile other than the iMac iSight PS, and I'm due for a challenging monitor.

Serious bloatage on the Samxon GFs. I replace all but a 33uf 50v that I don't have stock of, but it measures ok compared to a couple of the 1000 uf 25v that were like 2uf and 50ohms ESR

I test it, still dead.

The dual mosfets 4511GD http://html.alldatasheet.com/html-pd.../AP4511GD.html look like they've been running just a tad warm. Will check them for shorts, and test some voltages tomorrow.

[Scenic]

Re: LG 1953 Dead

you can replace the 33uF 50V with a 47uF 25/35/50V, as it's on 12V. (i've checked the max. supply voltage of the SMPS controller IC. maximum was 20V IIRC)
the PSU/Inverterboard looks identical to the LG L1952HQ that i recapped a while ago (thread is on here somewhere, including service manual)

damn those mosfets are toasty
i bet this thing was running at full brightness its whole life..

also check TH1 (below the primary cap legs).. these are supposed to be dark green.. yours is pretty much black..
http://bambooz.pytalhost.net/badcaps...u-inverter.jpg

edit: my old thread https://www.badcaps.net/forum/showthread.php?t=10078

[smason]

Re: LG 1953 Dead

you can replace the 33uF 50V with a 47uF 25/35/50V, as it's on 12V. (i've checked the max. supply voltage of the SMPS controller IC. maximum was 20V IIRC)
the PSU/Inverterboard looks identical to the LG L1952HQ that i recapped a while ago (thread is on here somewhere, including service manual)

I was considering a 47uf but wasn't sure how critical it was, until I look a bit closer and figure out what the cap is being used for.

Thanks for the link to the service manual. Love the engrish, and how they tell you to dissassemble:

1. Pull the front cover upward.
2. Then, let the all latches are separated.
3. Put the front face down.

It's just that easy. Just let all the latches are separated, then all your base are belong to us

Not sure what the heck the PWM controller is in mine it's labelled:
LAF0001
VH14
Haven't found it online yet. Wonder if it's close to the Fairchild in the parts list.

[smason]

Re: LG 1953 Dead

Update:
U303 - both FETs are shorted, measured out of circuit definitely toast
U304 - not shorted, can't test in circuit too well, will replace both. IF I can find them...

[Th3_uN1Qu3]

Re: LG 1953 Dead

Had a similar one in last year - fortunately the MOSFETs were still good but the burn marks on the board were about as obvious as yours. They received some heatsinks after replacing the caps.

[retiredcaps]

Re: LG 1953 Dead

IF I can find them...

These ones?

http://search.digikey.com/scripts/Dk...=4511%20mosfet

[smason]

Re: LG 1953 Dead

I'm considering those, I could make them work, but they're surface mount, mine are old style thru-hole 8 pin dips.

[sofTest]

Re: LG 1953 Dead

LG seem to use this MOSFET on many of the 19xx-series monitors. I recaped one a couple of years ago, and it's still going strong, after donating it to my brother. LittleDiode in the UK seem to be able to ship the MOSFET. You have to enquire for the price, though.

Is the 33uF at C103? If so, be sure to replace it also, as it has been known to create trouble.

[smason]

Re: LG 1953 Dead

LG seem to use this MOSFET on many of the 19xx-series monitors. I recaped one a couple of years ago, and it's still going strong, after donating it to my brother. LittleDiode in the UK seem to be able to ship the MOSFET. You have to enquire for the price, though.

Is the 33uF at C103? If so, be sure to replace it also, as it has been known to create trouble.

Thanks, have emailed them.

[smason]

Re: LG 1953 Dead

LittleDiode has stock, £6.99 seems a bit steep. I ordered a couple, will be here in about a month the way my luck with shipping is these days...

[smason]

Re: LG 1953 Dead

LittleDiode has stock, £6.99 seems a bit steep. I ordered a couple, will be here in about a month the way my luck with shipping is these days...

Well they just shipped them today. That's service!
I probably should have grafted in a surface mount device, or just slapped in some plain 'ol FETs. Oh well, do it right or don't do it at all, right?

[smason]

Re: LG 1953 Dead

Well they just shipped them today. That's service!

Got the parts today. Replaced both, and fired it up. Works fine.

While cycling through the "picure modes" any of the dimmer looking modes produced an arcing sound.

Subbing in my known good CCFL assy. it's one of the top lamps, or wiring to them. Actually I'm guessing wiring, as the light looks pretty even.

Maybe I'll take it to work and disassemble the panel. Too hairy and dusty at home.

[Behemot]

Re: LG 1953 Dead

I got just the LG 1953T power board from guy to repair. From what I have discovered so far, at least one Saxon GF is bulged (nothing spectacular), but also the ZD101 zener diode near power transistor seems shorted. Tester reads 0 over diode and 3 over resistor nearby. This baby needs replacement I guess.

Both APM4546 dual FETs seem fine, no short or strangely low readings. It is not darkened arround, these seem better than the 4511GD.

EDIT// unsoldered zener and it reads fine. There must be short somewhere because now both sides would be on ground.

EDIT2// it is fine I guess, resistor reads 0 but is actually 0,56 ohms so thats it