Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

[tom66]

I'd have immediately said that this was an LVDS cable or panel setting wrong, but here's a panel which is showing a solarised picture where the transitions aren't particularly smooth, and the gamma IC is the cause. So looks like I was wrong on that one... it is possible.

Interestingly, a certain band of colours does appear OK - it's only the darkest or lightest which go all crazy. For example on Jake Sully's face, the mid-blue details are accurate; but the darker and lighter colours aren't.

Has an AUO 37 inch 720p panel in it.

VGAMA voltages, only some are available for test but we can still see it is bad:
1. 14.91V (should be near AVDD)
2. 14.55V
6. 10.36V
7. 9.56V
8. 9.42V
10. 7.63V
11. 7.42V (midpoint - should be 1/2AVDD so this is OK)
12. 10.77V (notably bad)
13. 10.35V ^^
15. 7.53V ^^
16. 7.07V ^^
17. 6.22V
21. 6.02V ^^ (should be nearer to 0V by now)
22. 0.37V (seems OK, should be about AVDD-VGAMA1)

I compared REF voltages and they match, so it seems like that's not a reliable test: what appears to be happening is the input bias of the device is failing, and this is causing it to malfunction, but it sure is an odd failure. The references are derived with a long resistive divider, with 1% resistors.

A quick check: device was running 55C which is hot, in a 21C room. Calculated rise of temperature at 67C/W T(j-a) as specified in datasheet puts it at 480mW... according to the datasheet the quiescent power should be 130mW so we can see that the IC is dissipating 3x more power than it should, probably due to an internal short.

It's an AS15-U gamma IC, but this is identical to AS15-F, AS15-G, etc.

My first gamma IC failure! woot.

[budm]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

From what have been seeing so far, testing the voltages is the best way to find out if it is the GAMMA Voltage problem or not, and with the help of your spreadsheet, that sure comes in handy.

[audiofreak19]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

Wow that's crazy. Tom ur knowledge blows my mind. I'm actually gonna go to school in the fall for a electronics degree. Anyway. How can you fix a gamma ic

[budm]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

BTW, is this the same T-CON as this one?
https://www.badcaps.net/forum/showth...ng+LN37A550P3F

https://www.badcaps.net/forum/attach...7&d=1392518014

[tom66]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

Mines slightly different; I'll get a picture later.

[audiofreak19]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

How did you check for these voltages. And how do u repair this.

[tom66]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

Check the array of points marked "GAMMA" or test points marked GAMA#, VGAMA#, VGMA#, VGM#, VG#, GMA#, GM#, etc. There are usually from 12 to 22 points.

A quick check which detects 99% of failures is that the curve goes in one direction only, for example 1V, 2V, 3V, 4V is OK, 4V, 3V, 2V, 1V is OK, and 1V, 3V, 2V, 4V is NOT OK.

I also have an Excel/OO.org Calc spreadsheet available for general t-con tests including gamma tests.

Fix is to replace AS15-U IC with a new IC, 44 pins TQFP SMD chip, takes a little practice but isn't too hard.

[audiofreak19]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

Ah ok. Good info here. Thanks.

[splitcrete]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

I have replaced 9 of AS15-F same chip as toms . If you never did a unsolder and solder On a IC practice on a junk board. The pads are very delicate, and will pull off if heat is to high. Will tear if wiped across the pads with an alcohol swab. It takes two hands to solder one on using 60/40 solder and lots of flux so have magnification you don't have to hold. Last thing have a steady hand ,and good luck.

[splitcrete]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

better picture

[ecking767]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

I have replaced 9 of AS15-F same chip as toms . If you never did a unsolder and solder On a IC practice on a junk board. The pads are very delicate, and will pull off if heat is to high. Will tear if wiped across the pads with an alcohol swab. It takes two hands to solder one on using 60/40 solder and lots of flux so have magnification you don't have to hold. Last thing have a steady hand ,and good luck.

some Chip Quik will make it easy to remove that chip without damaging any solder pads.

[audiofreak19]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

What technique do u usually use the drag method with flux across it to remove it and solder back on. I'm not certified in soldering yet but it have been learning online about the different methods and techniques.

[ecking767]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

What technique do u usually use the drag method with flux across it to remove it and solder back on. I'm not certified in soldering yet but it have been learning online about the different methods and techniques.

I will apply the flux made by Chip Qiuk on the chip leads, and then I solder all leads of the chip with the special Chip Quik solder, and then I used the solder iron and heat up all four side of the chip, until the chip move off it pads. if there is a heat sink pad on the bottom of the chip then I will use a heat gun using very low heat, about 350 degree

[audiofreak19]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

Ok thanks.

[splitcrete]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

I take them off with chip quik, but I solder one pin at a time with my smallest tip. I tried dragging the first one i did, and a pad slid under the pin next to it. Now its one pin at a time takes a while because I go from side to side not to over heat the IC I know it sounds silly , but I'm retired and have a lot of time on my hands.

[tom66]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

I've done a lot of QFPs and my favourite method is to take them off with ordinary solder and wick, and put them back on using ordinary solder, tack the corners and flood the pins, wick away the excess. A bit wasteful of solder but I have quite a lot left over from my last job (got all the leaded stuff they couldn't use anymore .) If the device has a thermal pad, I'll use hot air to take it off.

[budm]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

Tom, that is what I do also.

[audiofreak19]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

Yea I saw that method online. Good tips to know

[SlickClick]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

@tom66 Ive recently seen an IR heat wave machine on ebay for about $200 thinking of getting one... makes doing board IC swaps super easy...

Tom likes chip level repairs where most would have just swapped t-cons out...

Electronics Degree or Electronics Engineer degree..?
Id look into the value of the "degree" in the long run... the class itself is good to take; but a degree is a long term financial expense/debt... Consider a trade school course in micro electronics maybe; same info less cost/debt...

I once applied for an IT job and was told that a Masters degree could be used for/as ONE of 2 years experience they were seeking... I had the experience but when I saw a masters degree in IT was only worth 1 year experience in the real world I found out fast that pursuing a degree in IT was NOT worth the debt... be wise as to what you choose to indebt your future too and for...

[tom66]

Re: Sony KDL-37U4000 solarised picture due to Gamma IC AS15-U faulty

Electronics & Electrical Engineering Master's Degree. I'm fine with my career path. TV stuff is a hobby, only.