Author Topic: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix  (Read 19216 times)

thesteve

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #150 on: May 30, 2011, 09:02:18 AM »
found the cause of the top left part of the screen too bright.
the 100uF 16V cap by the fuse was bad

farankoshan

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #151 on: August 29, 2011, 06:02:44 PM »
Right now, my friend and I (more him actually) have checked the board and the 4.7uF 35v contacts are all right. And testing it with a multimeter shows proper current to and from it, through the board. The thing is, now he's trying to nail down a problem with the LCD. He's tested the power circuit that routes power to the LCD. (forgive my caveman terms) It's one of the cables you stick into the red port on the board. He keeps saying that the contacts at 4.7uF 35v are all fine, but the multimeter shows no power going through that red "teethy" port, hence the LCD isn't getting the power it needs. We turn on the TE and the audio works fine, even the start buttons (with the help of sound cues) get us past the start screen, but still no video coming out of that LCD. So he may be right.

Any ideas? Are we on the right track?
« Last Edit: August 29, 2011, 06:05:24 PM by farankoshan »
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thesteve

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #152 on: August 29, 2011, 09:17:33 PM »
the lcd has a florescent backlight.
is the backlight working?

farankoshan

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #153 on: August 29, 2011, 10:55:06 PM »
the lcd has a florescent backlight.
is the backlight working?
How can you check that?

Right now, we're pretty stumped on our problem. Still not getting any successful video out of the TurboExpress. Will be taking photos of both sides of the boards & will attempt to translate (he's not very fluent in English) what my fix-it friend needs to know from this forum. I hope you guys will be able to help. :)

He's been able to test & is almost positively sure that both the 4.7uF 35v cap itself and the traces on the board around that cap work out just fine, so it's not that problem.

Off the bat though, he was wondering if anyone here has a diagram of the board and the leads that go around it. He's tried to isolate where the problem is, and it seems that the "red teethy port" I mentioned earlier is not giving power to the screen. Does this make sense?

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farankoshan

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #154 on: August 29, 2011, 11:29:31 PM »
Ok, still no video and I've included 4 pictures for reference.


Board (cap side)


Board (back)


My best closeup of the 4.7uF 35v cap, in case any of you spot something we don't.


Closeup of our problem spot
(Everything that's within the yellow border is our problem, front and back. help.. :pray:)

Ok, of what I have been able to glean from my fix-it friend, is that if you look at the last photo, the "red teethy port" is not giving any power to the screen. He's tested the light blue cap that it's connected to on the other side, and he says that the current is just fine, so it should be working.
Also, I've highlighted (in a pink rectangle) 5 studs that he wanted me to point out to you guys. I'm not sure why, but he seems to say that there's a problem he can't isolate around these 5 studs. Please meet me halfway in trying to understand what he's saying. He's pretty brilliant, if you ask me, he just doesn't think in English, so let's all try to see how we can make it easier for me to translate what you guys say to him.

Ok, from what I was able to gather from the "dead end" that he's hit, he's asking 2 questions:

1. (See the last photo, pink arrow) What is feeding this port it's power? Where is this port supposed to draw its power from? I think he needs to know the route and source so he can isolate where the problem is.

2. What's the voltage requirement of this red port? He figures if he knows that much, and he can't properly route power to it, he can find a way to cheat and get power there another way. Now whether this is a good idea or not, I hope you all understand that we've tried to test every cap the whole day and nothing is helping.

Any help would be MOST appreciated. :)

« Last Edit: August 29, 2011, 11:38:55 PM by farankoshan »
"MISSION INCOMPLETE: I cannot f*ck up for this."
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thesteve

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #155 on: August 30, 2011, 05:14:32 AM »
that port provides high voltage AC to a flourescent lamp.
the purple hilighted studs appear to be the transformer/balast for the lamp.
the two 100uf 16V caps next to the transformer provide the power for 2 transistors that drive the transformer.

farankoshan

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #156 on: August 30, 2011, 07:41:31 AM »
big help! thanks thesteve! whats the voltage requirement for that port?
"MISSION INCOMPLETE: I cannot f*ck up for this."
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thesteve

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #157 on: August 30, 2011, 10:05:31 AM »
not sure on voltage, likely 600V+ with no load, dropping to around 30V once lamp starts.
the only way to test it is with a lamp.

Charlie

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #158 on: August 30, 2011, 10:27:40 AM »
He is checking for AC, right?  Not DC?  And the value can be anywhere between 100V and 300V; typically 225V.

Charlie

farankoshan

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #159 on: August 30, 2011, 02:58:06 PM »
Thanks guys! I forward the info to him and...well, we'll see what he can whip up. Anything you guys have been able to gather from the photos? Or if you need specific photos of my board?
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farankoshan

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #160 on: August 30, 2011, 08:33:44 PM »
Ok, with your help & some more tinkering, he was able to locate the source of the problem!
When we first opened up the TurboExpress, we noticed a massive amount of leakage all over the board. It was really wet. We thought to simply clean it up and hoped none of the leaks affected any of the other components. While everything still seems alright, he's finally deduced that the transformer for the lamp (the one we've been talking about above) seems to have shorted out. All the traces and components leading up to it, and after it seems fine, but that transformer is what's dead.

Does anyone know where I can source this from? I have a feeling that if we can replace this one piece, my Turbo Express will be back up and running. :)

Any ideas? Anyone here have the part?
"MISSION INCOMPLETE: I cannot f*ck up for this."
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BlueBMW

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #161 on: August 31, 2011, 12:30:23 AM »
Is that transformer just for the flourescent tube for back light?  Worst case maybe you could rig up an LED array as a replacement backlight.
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thesteve

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #162 on: August 31, 2011, 05:12:20 AM »
yes its just for the backlight.
yes an LED array would work.
id be surprised if its a bad transformer

farankoshan

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #163 on: August 31, 2011, 05:42:00 AM »
I'm really stumped at this point.
But if the backlight lamp was the only problem, wouldn't I be able to see graphics on the screen? Kind of like how the non-backlit Game Boy Color used to look like?
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BlueBMW

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Re: REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix
« Reply #164 on: August 31, 2011, 06:24:13 AM »
Its very hard to see without a backlight because there isn't much behind the screen to reflect light back at you.  A flashlight right on it may work but it still wont be easy to see.
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