PCE GT Burning Q900 - Backlight problem.

[pignolo]

Hi all  ,

First of all, thanks for this fantastic resource for all the Pc Engine fans!

I'm working for a few weeks on my PC Engine GT. It wasn't working when i got it. The fuse was blown.
So i cleaned and recapped totally the PCB, and the fuse was still blowing systematically. My opinion was that there was a shortcut somewhere. I then removed the T500 and T900 shielding to clean under with isopropyl alcohol, let it dry all night long.

When i switched on again the system, i could see the picture for a few seconds. Then the Q900 burned with a white smoke.
However, now the fuse is fine, and the system is working (i can hear the sound). But the backlight has gone.
I replaced twice the Q900 by a BCX56, and it's still burning...

I think it could come from a bad T900?
Does anyone knows which component is before the Q900 and could be responsible for destroying it?
Any help would be greatly appreciated!

Thanks a lot!

[Fidde_se]

Hi if install a new batch of BCX56 and don't connect the CN900 connector! Do they still burn?

[pignolo]

Hi Fidde_se,

Thanks for your message.

Yes, i tried to run only the PCB, and it burns.
I tried the entire half of the GT including the screen on another one, and the half works perfectly.
The problem comes from the PCB.

[pignolo]

Hi all,

After investigating on my GT, it appears that the component marked T900 is dead. It had a short circuit which leads to burn another component (the Q900).
I think the tiny tube is a CCFL Tube, which need an inverter to run. The T900 seems to be the transformer, transforming the 9V to higher voltage to light up the tube
I found this here, and it seems we can still find this part for service: http://www.digikey.com/Web%20Export/Supplier%20Content/Coiltronics_513/PDF/Coiltronics_4035.pdf?redirected=1

But i don't know at all the technical datas of the T900.
Does anyone here have any information on the possibility to find this part?

Thanks a lot!

[thesteve]

q900 and q901 drive the transformer, and will need to be replaced as a pair
the transformer may or may not be bad

[pignolo]

Thanks TheSteve.

The transformer is obviously dead as one cable leading to a pin was rusted and cut.
Do you know if it's possible to find one in shops?

[thesteve]

you will need to pull used
i have not been removing them with screen mods, but some may

[Fidde_se]

The PDF you refered to does not have any one with a compatible pin configuration.

it's got 9pins, 5 on one side and 3 on the other, the middle on of the 3 is NC (Not Connected)

There might be a, or should be a working transformer out there, but as we have no specifications, it's a no go.
We can however measure them to some extent.

I would like to kill a myth right here thats been circulating for some years that the Game Gear uses the same transformer.
it's spot on, except for that gamegear uses yellow tape around it for isolation and TE/GT uses a red one, and it's the same
pin configuration the the same dimensions and the same pin pitch, so what to to, just now I unsoldered one on both a GG and GT
and started measure what I could, having no henry meter around me I used a single ohm meter just trying to see what pins
goes where and compare them, one pin didn't seem to be connected the same way, but one of the best ways to tell the difference
is between Pin 2 and Pin 9, the gamegear has 42 Ohms and the TE/GT 200 Ohms (ohm can be good for measuring coils and to some extent transformers too as it's a certain ohm per length, which means a certain amount of linings).

But hey I had to try it to, it could burn the transformer or another important component, but it's a spare unit with only the backlight working so..
Of coarse it didn't work, that we could already tell from the simple ohm difference, but it had to be tried, because if it would work (might be bad in long term though) a new supply of transformers would suddenly appear, and a lot of butchered gamagears...

Another myth is that you could use the GameGears light for the CCFL tube in the TE/GT and with this I think we can rule that out too,
not necessarily but highly probable as it should use another voltage (might be off with several hundred volts) and using another frequency.
I'm not saying it wont work but that it probably shouldn't, and if it did it could blow up in everything from a few seconds to a few days use.

So if just everyone out there would take their loose CCFL transformers with 9pins and get a 200 Ohm reading between pin 2 and 9 we might just
find the equivalent some day....

Now towards what you do have...
A transformer missing a leg
it might be fixable..

Probably it isn't rust you see, it's more likely the big electrolytes fluid that has eaten the leg a little (copper with tin on it and some lead), sometimes when fixing "GameGears" it's the fluid that has corroded the via holes, and measuring both sides of the via hole you will find the dead spot, it's an easy fix really, battery acid on GBA SP sometimes does the same thing, and battery and capacitors are cousins so, the electrolyte fluid eats threw iron, unplated copper, and even gold (I thought gold was so high up in the chain nothing eats on that except Chlore)
So the leg can be easily replaced but what about the little wire that was once attached there?
if that's ok there is a chance your transformer can be fixed...