REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix

[Keith Courage]

I checked Pin 3 for the screens ribbon cable and it is supplying 24V.

[thesteve]

it could be the 5V or contrast pin

[Keith Courage]

So I went through the pins again for the screen today just to double check things. Turns out I must have not read something correctly yesterday. The 24V pin ends up reading almost 27V when the screen is not plugged in. As soon as the screen is plugged in the voltage drops to 15V. I know that a good working express should stay very close to 24V regardless of having the screen plugged in or not.  Does that sound like there is a short somewhere to you?

[thesteve]

that sounds more like an open cap or regulation fault on the 24V line

[mrchuck999]

Hey guys,  You know the blue cap at the back light connector? Has anyone determined the value of this cap ?   I know its a long shot but I've tried almost everything else so I would like to replace it.
Mrchuck999

[macphreak4evr]

Thank you so much, I did this and the sound fix and I am back in action!!!

[RxM]

Hi Samson, i have same issue. When i went to remove the defective cap for video, my trace also lifted.  So isit ok to solder the neg lead to the mosfet transistor? Cause i dont see any other trace. Any
Help greatly appreciated. I went to do the rest of the cap replacement and now im not getting no sound or video.  Screen light up and flicker vertical. I spent countless hours trying to figure out what else could be wrong but i have no clue.

Thank you
Regards
Alex

Thanks for the awesome repair guide.  I snagged a practically brand new TE off of Ebay for $34 and managed to fix it with a $1 part from Radio Shack.

It got a little hairy there for a bit though.  I thought I was being careful but still accidentally pulled the negative trace off the board when I removed the capacitor.  Thankfully the trace ripped pulled up far enough for me to follow it to another solder point.  The leg of the little transistor/MOSFET that sits just adjacent to the cap will work. 

If I had it to do over again I would definitely have tried to touch the soldering iron to the legs and gently pry them up rather than trying to pull the cap off cold.


Looks so innocent just sitting there.


Disaster strikes!  I did not notice the little trace that was ripped out of the surface of the board at first - I honestly thought it was just a strip of paint or glue or something.  The scratches you're seeing where the pad for the negative trace was are my desperate attempts to find what the pad had been attached to.  I was hoping that if I dug into the board I would find another solder point.  I realize at this point that was silly, but at the time I had no idea.


But that was exactly what I needed to find an alternate soldering point.


Here is the alternate soldering point magnified some more.

I decided to remote-mount the cap because the connections, while solid, were so fragile I didn't want to risk any more bending and twisting than I had to.  It may not be pretty but it works like a champ.

Thanks for the awesome repair guide.  I snagged a practically brand new TE off of Ebay for $34 and managed to fix it with a $1 part from Radio Shack.

It got a little hairy there for a bit though.  I thought I was being careful but still accidentally pulled the negative trace off the board when I removed the capacitor.  Thankfully the trace ripped pulled up far enough for me to follow it to another solder point.  The leg of the little transistor/MOSFET that sits just adjacent to the cap will work. 

If I had it to do over again I would definitely have tried to touch the soldering iron to the legs and gently pry them up rather than trying to pull the cap off cold.


Looks so innocent just sitting there.


Disaster strikes!  I did not notice the little trace that was ripped out of the surface of the board at first - I honestly thought it was just a strip of paint or glue or something.  The scratches you're seeing where the pad for the negative trace was are my desperate attempts to find what the pad had been attached to.  I was hoping that if I dug into the board I would find another solder point.  I realize at this point that was silly, but at the time I had no idea.


But that was exactly what I needed to find an alternate soldering point.


Here is the alternate soldering point magnified some more.

I decided to remote-mount the cap because the connections, while solid, were so fragile I didn't want to risk any more bending and twisting than I had to.  It may not be pretty but it works like a champ.

[thesteve]

it was the 5V regulator running at 3V due to a cracked resistor R506

[fagin]

Hi,
I seem to have the same or similar problem as Keith Courage reported above.

I had previously changed the video cap a few years back - that resolved an initial dim screen issue I had. 

Recently I tried the GT and after 10 mins the screen went very dark.  Because I also had low sound, I thought I would complete a full recap.

After the full recap I still have the same screen issues:

The backlight is working - although very dim.
You have to extremely tilt the unit to see anything - this gets worse within minutes and then backlight shuts off completely.

Any help guys?

Regards,
Shaun

[thesteve]

The backlight will shut off if not used (push a button)
Also if unable to adjust brightness properly it is a 24v supply prob if not a bad screen

Sent from my ADR6300 using Tapatalk 2

[fagin]

Thanks for the feedback.

IIRC when I measured the voltage on VR500 it was only around 10v.  I'm assuming this should be 24v.

Any pointers as to how I can perform further diagnostics and/or fix the supply problem?

(Thanks for the reply to my PM btw) - In the PM you mentioned about a possible arcing.  What should I look at to establish if this is taking place?

I've placed an order for replacement Q900 and Q901 transistors, but I'm assuming this will not fix the issue?

[thesteve]

Not sure at the pot
You should have -24V at the - pin of the 22uf cap near the pot

Sent from my ADR6300 using Tapatalk 2

[thesteve]

The pot on the side, not the one @ the top


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[thesteve]

Q900,Q901 supply the backlight transformer and are all or nothing

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[fagin]

Not sure at the pot
You should have -24V at the - pin of the 22uf cap near the pot

Sent from my ADR6300 using Tapatalk 2

11v measured at that point.