Ssi_400_14a01

[ReeceyBurger123]

Re: Ssi_400_14a01

Ok replaced the Mosfets again and all is up and working, drive voltages are fine and all other input voltages now to wait and see.

[ReeceyBurger123]

Re: Ssi_400_14a01

This is getting strange, the mosfets have blown out again but not the ones I replaced, now its the ones at the bottom of the board and its not the ones that drive the transformer that I swapped over but the one above it Wtf ? Im really starting to suspect that the driver Ic is messing up somewhere and is killing the mosfets but annoying thing is the drive voltage was fine until they popped now its 0 and this time the fuse blew for em mosfets. Now time to try and find a SEM2017 from some where that ships to the Uk. What a nightmare this thing is better keep on checking things.

[CapLeaker]

Re: Ssi_400_14a01

Those Mosfets where not any Chinese fake crap ones by any chance? Maybe upgrade the Mosfets with ones that have better specs?

[ReeceyBurger123]

Re: Ssi_400_14a01

They are genuine parts same brand as originals, the ones that have now failed were the originals so I now know the lamps and transformers are not at fault here, I have a feeling its the controller.

[stj]

Re: Ssi_400_14a01

controller is probably turning all the fets on together.
it's a terrible design.

[ReeceyBurger123]

Re: Ssi_400_14a01

Your right its total crap, going to take it to my uncles and get it on a scope so can see what that controller is doing. I have a suspicion its pulsing them on and off too fast causing them to over conduct then fail.

[tom66]

Re: Ssi_400_14a01

Your right its total crap, going to take it to my uncles and get it on a scope so can see what that controller is doing. I have a suspicion its pulsing them on and off too fast causing them to over conduct then fail.

You would want to use two channels: check the upper and lower gate for each pair, and see that there is no overlap. If there is overlap, this will cause cross conduction and heating of the FETs.
Also check how hot the FETs get - could still be counterfeits if from eBay, etc.

[stj]

Re: Ssi_400_14a01

it's not overlap, you need a gap for the gates to discharge.
also known as a "deadzone"
that's why circuits that use an invertor between the channels piss me off.

[tom66]

Re: Ssi_400_14a01

it's not overlap, you need a gap for the gates to discharge.
also known as a "deadzone"
that's why circuits that use an invertor between the channels piss me off.

Depends on the FET - modern FETs can work with effectively zero dead time as they are off within a few tens of ns - and it takes at least that time to discharge the gate capacitance. Does depend on the FET of course, PFETs are worse.

Still not sure how dead time would change due to a fault, unless some cap or resistor reference has drifted...

[ReeceyBurger123]

Re: Ssi_400_14a01

I will try overlap I think it will be for this type of fet, good job is I wont have to order a whole set of fets as have two left over that are good. Will update you tomorrow on what we find too bad his scope is analogue so cant set it to trigger on a wave form if anything messes up from what it normally was, but if they fail as fast as these did then wont have to stare at it for long. This is going to be hard as cant get the probe leads on the fet leg so will have to solder a wire lol. Cheers guys

[tom66]

Re: Ssi_400_14a01

Make sure to get your ground as close as possible to reference ground. Use a short lead - don't use the probe hook, either. Otherwise, you'll get ringing and you won't get the right result.

[ReeceyBurger123]

Re: Ssi_400_14a01

Yeah will do I know the game..... well sort of still learning about how to use a scope hopefully getting one this christmas which will be the best as hate having to keep transporting things. Luckily the customer doesn't mind waiting if I do have to order a chip from China.

[ReeceyBurger123]

Re: Ssi_400_14a01

Im actually looking forward to getting a scope, especially to see the sustaining wave forms generated by a PDP thats what im dying to see and other things, I will be getting a Rigol one like you have Tom soon with in next two months

[tom66]

Re: Ssi_400_14a01

Im actually looking forward to getting a scope, especially to see the sustaining wave forms generated by a PDP thats what im dying to see and other things, I will be getting a Rigol one like you have Tom soon with in next two months

They really are quite beautiful - I especially like watching them vary as the panel picture changes. The controller software adapts so much due to panel temperature, image brightness and power saving, it's crazy. KURO sustain is completely different - if you ever open up your 428, I'd be interested to see how it compares to a 5090.

[stj]

Re: Ssi_400_14a01

if you bypass the safety, you can probably scope the controller without putting new fets on first.
just a thought.

[ReeceyBurger123]

Re: Ssi_400_14a01

Thats why I love Plasma just amazing devices I have opened my Pdp428xd to clean when I got it this time last year so when I get my scope will surely be taking it back apart to see the sustaining wave forms. Everything about Plasma fascinates me

[ReeceyBurger123]

Re: Ssi_400_14a01

if you bypass the safety, you can probably scope the controller without putting new fets on first.
just a thought.

Yeah im going to remove a fet and turn off that protection circuit so that it will run. Yes the other will be stressed but they are all going to be replaced.

[stj]

Re: Ssi_400_14a01

what size tv is it btw, and how many tubes?

[ReeceyBurger123]

Re: Ssi_400_14a01

40" Ccfl with 14 lamps.

[stj]

Re: Ssi_400_14a01

maybe just say "fuck it" and put led strips in the back?

a friend of mine tried it a few times with the led strips you get on a 5m roll with good results.
you just need a good 12v feed.