Ssi_400_14a01

[ReeceyBurger123]

Re: Ssi_400_14a01

I did attempt this before, the lcd did light up however the light from the Leds was so directional that there were patches on the screen. Also leds could be more expensive than buying a replacement inverter and putting new mosfets on it. Going to see what I find tomorrow. Thanks anyway buddy

[tom66]

Re: Ssi_400_14a01

you just need a good 12v feed.

Two strips in series run fine from 24V, problem is the lack of dimmability or bl on/off often leads to distortion on the screen during start up (as the T-con has not yet initialised, the screen often flickers a little until it is ready.)

[ReeceyBurger123]

Re: Ssi_400_14a01

Luckily on this set the Tcon initializes after the Blon is turned on, this is a Vestel set btw. Remembering now I do have a set of leds left over from another failed project think its worth it ? This is also one that chains the dimming with the Tcon and the inverter so would removing the inverter cause the Tcon to not work properly or something ?

[tom66]

Re: Ssi_400_14a01

The T-con would be initialised on a normal TV before the BL ON signal fires so with a normal inverter the set would show backlight only when the screen was showing video or programmed "black" (or whatever excuse for it that it has, it is an LCD after all.)

Without the BL ON control (which you will probably not implement) the LEDs turn on as soon as the power supply is ready. In most cases this is before the T-con is ready as the T-con is usually run from the 12V supply generated by the main SMPS -and- the 12V to the T-con is switched by the main board to ensure correct power sequencing.

Exceptions, of course, always apply, this is just a typical example.

[ReeceyBurger123]

Re: Ssi_400_14a01

Yeah you are correct thinking about it the lcd/tcon will initialize before the Blon I remember on the other one I attempted to convert it to leds there was a strange distortion before any i age was brought up on the lcd.

At this point im not sure what to do this is a customers tv and doing such a mod could potentially cause them to moan or complain. I will see what I find with this inverter tomorrow. Luckily the customer is someone who has used me in the past several times and recommends me to others and doesn't mind waiting so guess that its good if I have to order things from China etc.

[stj]

Re: Ssi_400_14a01

i wouldnt do experiments on a customers tv, i thought it was yours.

[ReeceyBurger123]

Re: Ssi_400_14a01

Ahh right I said in the video I posted haha no worries, hopefully can sort this crappy inverter haha also got lots of others to fix as well haha I dont mimd though enjoy fixing tvs

[tom66]

Re: Ssi_400_14a01

I didn't tell you this but the dirty little secret no one seems to know about inverters is they are mostly interchangeable. Seriously, as long as it's got the right connectors and is for approximately the right size panel, it'll be good. I have used a completely different part number inverter before on a 37" LG, it was also for a 37" LG panel and had similar specs and matching connectors but was from a 2 year newer set. Worked perfectly, still playing strong.

[ReeceyBurger123]

Re: Ssi_400_14a01

Ahh I see, I actually already knew that just didnt say, I did the same on a 32" Vestel ages ago still going strong, as long as the lamps are the same size they use pretty much the same current meaning little potential difference to trip the protection circuit. I have been checking some SSI_400_12a01 inverters nearly the same but missing two bulb connectors which is a pain no others seem to correlate to this one they all only have 12 connectors.

[tom66]

Re: Ssi_400_14a01

Yea, 14 connectors is odd. 7 bulbs, U-shape tubes. Not easy!

[ReeceyBurger123]

Re: Ssi_400_14a01

Yep pain in the back side ! The design of this inverter as well is total crap as well in the way it drives them mosfets it pushes them quite hard no wander they fail and probably are what killed the driver with them.

[tom66]

Re: Ssi_400_14a01

[...] The design of this inverter as well is total crap as well looking at the schematic and the way it drives them mosfets it pushes them quite hard no wander they fail and probably are what killed the driver with them.

What makes you conclude that?
Schematic link?

[ReeceyBurger123]

Re: Ssi_400_14a01

No schematic of the mosfets they are being sent a higher pulse or drive voltage from the controller which I think is standard with these.

[ReeceyBurger123]

Re: Ssi_400_14a01

This is going to be difficult as the way the upper and lowwer mosfets are driven is different, going to test the upper set. The drive voltage is at 5v however seems noisy my ground point is close ??

[tom66]

Re: Ssi_400_14a01

No schematic of the mosfets they are being sent a higher pulse or drive voltage from the controller which I think is standard with these.

The top FET is p-channel so it is inverted as the source is more positive and a negative Vgs voltage turns it on or off. P channel is rare due to higher cost and poorer performance (Rdson, Qg, etc.) but driving them is easier.

It's pretty much impossible to make a FET short by abusing the gate - you can blow the gate channel open, or short gate-to-source but not drain-to-source (G-S short keeps the FET always open.) But that happens within a few seconds, normally...

[tom66]

Re: Ssi_400_14a01

This is going to be difficult as the way the upper and lowwer mosfets are driven is different, going to test the upper set. The drive voltage is at 5v however seems noisy my ground point is close ??

Best to start with lower FETs.
What probing are you using?

I don't have a photo from work (confidential prototypes, etc.) but the technique (not confidential) used there is to take the probe hook off, solder a flexible but rigid copper wire to the local ground, wrap the ground around the metal shield near the tip, and put the tip right against the SENSE POINT.

Goal being, keep ground and probe signals at the lowest inductance possible, minimising ringing.

In this case the local ground would be the SOURCE of the lower N-FET. Do NOT ground the drain of the P-FET or you will be replacing more FETs.

[ReeceyBurger123]

Re: Ssi_400_14a01

Thats what I have done Tom will get some pics. However quite certain its the controller now as its getting lots of voltage increase and drops its unstable, now also the Bl is dimming and the drive voltage is creeping up and im not even running anything on the screen just the normal back ground so I know that the tcon is not ramping the Bl dim up and down corresponding to whats being displayed.

[ReeceyBurger123]

Re: Ssi_400_14a01

What I might do it heating or cooling the Ic as when these type of Ic's fail they become heat sensitive. Will keep you posted buddy.

[tom66]

Re: Ssi_400_14a01

Thats what I have done Tom will get some pics. However quite certain its the controller now as its getting lots of voltage increase and drops its unstable, now also the Bl is dimming and the drive voltage is creeping up and im not even running anything on the screen just the normal back ground so I know that the tcon is not ramping the Bl dim up and down corresponding to whats being displayed.

Gate voltage should be constant - check the Vcc for the controller (usually a lower voltage rail, around 6V or so)

[ReeceyBurger123]

Re: Ssi_400_14a01

Pop there goes one of the fets, this time I caught the fucker ! The VCC went over 18v when they popped ! It has to be that fricking controller.