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GTRetro87
09-25-2014, 11:02 AM
Hey all,

If anybody knows about the Turbo Express, please chime in (broken, I know you're a PCE/Turbo guy)..

Here's the issue, I've replaced all the capacitors on my friend's Express, and after the caps were replaced, a little bit of solder somehow got stuck between some pins of one of the chips causing the screen to go out of wack.

I removed the solder and the fuse blew, so I then put a temporary replacement (1.5A SNES pico fuse) and it worked FLAWLESSLY... but it's still 0.5A higher than the recommended fuse (125v 1A fuse)..


So I got the fuse needed, replaced the 1.5A with the 1A.. and now the backlight doesn't turn on.........:blow_top:



I tested a few points on the board and I'm stumped.. I've checked the legs on the blue ballast cap, one side gets voltage and the other doesnt.. so I thought replacing it would work... nope, same symptom


Now I'm thinking that it's the transformer, but I'm not sure how to diagnose a transformer (at the moment)..

I've checked Q900/Q901 and whatever could possibly drive the transformer, everything looks good...


I did notice that one of the traces on the board goes to one leg of the ballast cap, and connects to the transformer.. that pin on the transformer is dead...

My guess, it's not a ground..




If anybody can chime in, PLEASE DO!!!

GTRetro87
09-26-2014, 04:16 PM
ok maybe not... Alright well, for those watching and wondering.. I've found out that transistors placed at Q900 and Q901 are what drive the Backlight. These transistors are listed as 2SD1898, and a suitable replacement is a pair of BCX56 transistors.

These are known to be 90% of the back light problems that many face with a TG Express. I guess we shall see!

jesesfbi
09-26-2014, 07:03 PM
You sure you didn't damage the 1uH inductor at the very top of the board near the backlight transformer? I had bought one before that that damaged and no backlight would come on lol. Well either way good luck.
If you do end up tracking it to the transformer in that upper corner a replacement I found that worked well was a Sega game gear one lol.

GTRetro87
09-27-2014, 11:25 AM
I wouldn't think so, I swapped all the caps cleanly, never touched the inductor. I'll check it even though it's still covered in that white silicone or whatever they used from the factory.

I ordered some transistors to see what would happen. But good point, I'll definitely keep the game gear inductor in mind lol.

ScoreAddict
12-24-2014, 02:17 PM
Hi!

Sorry to revive this old thread, but I have a very similar problem!

My Turbo Express has been recapped by the previous owner and would not turn on.

After opening I discovered that the fuse was burned out. And that most of the new caps had been marked with colour to indicate testing.

I replaced all of the capacitators and put in a new fuse. No problems encountered there.

So I tested it with a game and power supply at 6V.

The Turbo Express would turn on for once and the sound would play, but only a white display would show. Which started to flicker and then the TE went out - fuse burned. And Q900 or Q901 - not sure which - got very hot! (Touched it accidentally.)

Next I put in a new fuse and tested the lower half of the Turbo Express without the upper (which works just fine btw.) and it would burn out the fuse again and Q900 (or Q901) got very hot very quickly!

Could it be that one or both of the transistors are shot? Or is there a short somewhere else?

ScoreAddict
12-30-2014, 02:58 AM
Bumpedi Bump!

I'm going to replace the transistors in position Q900 and Q901. Let's see if that fixes the issue...

ScoreAddict
01-29-2015, 06:54 AM
It's fixed! :)

The replacement 2SD189s arrived today.

Important info:

- Capacitators AND transistors (on the backlight-circuit) may both fail and have to be replaced!

- The transistors on Q900/Q901 may NOT be replaced with 2SB1260/BCX56!!! PNP- and NPN-transistors are not interchangable!

GohanX
01-29-2015, 09:51 AM
Nice! I probably would have never tried changing the transistors.

BladeDancer314
01-29-2015, 11:20 AM
Good job.

Now just LCD mod that express.

fremen
01-29-2015, 12:16 PM
Hi dudes,

I have de same problem
http://www.neo-geo.com/forums/showthread.php?255880-PC-Engine-GT-problems

I will try to do the same substitution

I think there is a mistake and the correct specification is 2SD1898

Thank you

ScoreAddict
01-29-2015, 08:03 PM
I have de same problem
http://www.neo-geo.com/forums/showthread.php?255880-PC-Engine-GT-problems

Seems to be a common issue. Well, no wonder since most of the voltage is running over this circuit.


I will try to do the same substitution

Good luck! :)


I think there is a mistake and the correct specification is 2SD1898

Exactly! Only substitute the original transistors with 2sd1898!

fremen
01-30-2015, 02:30 AM
Hi,

Thank you man, I have another question about yours 2SD1898, are they P, Q or R??

Un saludo

ScoreAddict
01-30-2015, 07:40 PM
Actually... I have no idea! ;)

But I ordered them from here:

http://www.aliexpress.com/item/Electronic-Components-2SD1898-2SD1898-T100R-SOT-89-Mark-DF-RN-NPN-Silicon-Epitaxial-Transistor-Original-new/32256090859.html

fremen
01-31-2015, 07:39 AM
Thank you mate for the link, yours 2SD are R according to the linkk information.

Could you sell me 20 units??

Un saludo

GTRetro87
05-05-2015, 04:30 PM
Hey all!

Back again to revive this thread - so far I still can't get the Express to work. I've tried NUMEROUS transistors (2SD1898's and the other BCX5's).. still no go..

Actually, when I first used the BCX, it worked! but then... after a few minutes it just cut out all together. I can't see how RE-replacing all the already new caps would make a difference. The link you guys posted for the 2SD1898's, I ordered those and still have a roll of them - but even those didn't work!!!

I replaced Q900, Q901 and Q500 - the backlight comes on no problem, but no actual picture...

So I've decided... to do the LCD mod. If I can't get the original screen to work, I'll just build the circuit needed to send composite video signal to a small 3.5" TFT LCD screen and just let that be that finally - or a 2.5" TFT LCD just for the sake of not cutting up the case (I have 2 projects now).



So, that's that. I have no means of using the original screens anymore. I hate these things, they're so temperamental!! One false move and you get a REALLY sour taste in your mouth.


Actually, I've got a third project. I'm going to turn a TurboGrafx-16 console --> handheld!! I have a TFT screen ready to go, and it's much easier to work with a lot more room - so I can add all the buttons, D-pad and turbo adjustments to the case, and then still keep the video output so it can be connected to a TV - controller as well... I may have to reinforce the case with a thin layer of fiberglass just for extra strength, but I feel this might not only be absurd, but A LOT easier to repair... seriously..

when was the last time anybody had to change capacitors on a turbografx-16.. seriously

BladeDancer314
05-10-2015, 10:04 AM
Do you think it might be a faulty stock screen?

Needless to say, I have a few laying around.

GTRetro87
06-23-2015, 09:24 AM
I'm sure you saw my post on another thread about this but yes it was the screen. I did an LCD mod as a last attempt and it ended up working - my only issue was finding the right seller on ebay who had an LCD that would accept the Express's resolution and display it with sharp quality (and no scrolling either).

So, it works now! All I have to do is cutout the plastic to show the entire 3.5" screen and hot glue everything down.. then it's all fixed!