REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix

nat · 04/06/2008, 03:11 PM

It's long been known that by replacing all the capacitors in the audio circuit on the Express PCB you are able to cure all sound issues, but video issues have been a bit of a grey area. What has been unknown (until now) is just which component is directly linked to the common video problem these units are beginning to have.

Let's give a round of applause to Sinistron, the real hero in all this, for donating a TurboExpress with bad video for me to butcher on the operating table. It was a very long and tedious process, as I ended up replacing almost everything on the board by the time I was done and I had to play test after every component which meant quite a bit of assembly and disassembly.

The culprit turned out to be the smallest, most innocuous capacitor on the entire board and the only reason it wasn't the very last one I did was because there was one cap I didn't have a proper uF/voltage match for. At the very least all this paid off and finally put to rest just what causes the no-video issue. Real quick: the capacitor in question is in the power circuit, specifically, the line that supplies the mains to the LCD. This cap fails, dries out, bleeds, etc causing insufficient voltage supplied to run the LCD.

So let's get down to it.... I took photos documenting the entire process, but I'll only post the relevant ones here.

tefix1.jpg

Circled in green is the audio circuit. We already know what these caps are for, so we ignored them for this procedure.
Circled in red is the culprit for the video issue. You can barely see it, can't you ?

tefix2.jpg

Since I didn't know where the problem was specifically, I removed the shield covering the CPU, VDC, etc. The caps circled in blue are the ones that are exposed by removing the shield. It is not necessary to replace these to fix the video, but Sinistron got a freebie on this one. I included this pic so folks who might want to replace EVERYTHING can see just what's under the shield.

tefix3.jpg

Circled in red is the replacement cap I installed in place of the bad on. The cap is a 4.7uF 35-volt electrolytic. This is THE culprit of the backlight-but-no-picture video issue. Replace it and your video works again.

tefixfinal.jpg

Just a final look at the board after I was done with it. I had to run wires to remote-mount a few of the replacement caps due to not enough room on the board, etc. FYI, there is plenty of open space down behind where the batteries sit where you can remote-mount caps if you need to.

There you have it. It's a simple fix, really, and luckily it's probably the most easily accessible cap on the entire board.

Sinistron · 04/06/2008, 03:23 PM

OldRover · 04/06/2008, 03:30 PM

That's a hell of a lot easier than fixing the audio capacitor!

nectarsis · 04/06/2008, 03:31 PM

Nat saves the day again

Ceti Alpha · 04/06/2008, 06:37 PM

That's awesome nat!!! Sin's a happy camper and you saved a TE from going to the garbage dump.

esteban · 04/06/2008, 07:51 PM

When my TE's fail, I will not be as depressed as I would have been, say, yesterday.

nat, you rock!

SignOfZeta · 04/06/2008, 10:09 PM

This is very good news. If we can get a source for those little gears for the OG CDROM units, then what else is there left to fix?

Turbo D · 04/06/2008, 10:16 PM

Nat is the man!

This thread should be a sticky!

OldRover · 04/06/2008, 10:41 PM

Quote from: SignOfZeta on 04/06/2008, 10:09 PMThis is very good news. If we can get a source for those little gears for the OG CDROM units, then what else is there left to fix?

I'm working on that issue right now.

NecroPhile · 04/07/2008, 12:31 AM

Awesome work, nat. Someday my poor little Express will undergo this little operation; he thanks you from the bottom of his pcb.

Mobius · 04/07/2008, 12:37 AM

Quote from: SignOfZeta on 04/06/2008, 10:09 PMThis is very good news. If we can get a source for those little gears for the OG CDROM units, then what else is there left to fix?

It makes me feel all warm and fuzzy to think that my Turbo hardware could last forever with the fixes this board has documented.

chop5 · 04/07/2008, 01:55 AM

excellent!

Jitawa · 04/07/2008, 04:24 AM

Well darn, I have another thing I have to send Nat now.

Keranu · 04/07/2008, 04:50 AM

Outstanding!

Paisa49 · 04/07/2008, 09:57 AM

A somewhat related video question, other than actually replacing the entire lcd screen on an Express, has anyone figured out how to fix dead pixels? If not, how expensive is it to replace the lcd screen on an Express?

nat · 04/07/2008, 07:32 PM

Quote from: Paisa49 on 04/07/2008, 09:57 AMA somewhat related video question, other than actually replacing the entire lcd screen on an Express, has anyone figured out how to fix dead pixels? If not, how expensive is it to replace the lcd screen on an Express?

I don't know of any sources for the LCDs that the TurboExpress units use. I would imagine they'd be very expensive, if you could even find them anymore.

For dead/stuck pixels, you could always try the "eraser trick" which involves quite literally "rubbing out" the bad pixel. Perhaps someone else who's actually done it can provide a more detailed description of the procedure.

OldRover · 04/07/2008, 09:22 PM

It's not really possible to fix dead or stuck pixels because of how they become dead or stuck. Replacing the screen is likely to be a pint-sized nightmare...finding that exact screen is going to be virtually impossible due to its age, and I don't know if anyone's found a suitable replacement yet. But I do remember reading something about someone using one of those portable PSone screens with a TE...

NecroPhile · 04/08/2008, 01:03 AM

Quote from: The Old Rover on 04/07/2008, 09:22 PMIt's not really possible to fix dead or stuck pixels because of how they become dead or stuck.

That's not entirely true. Dead pixels (where all three sub-pixels are non-operative due to a manufacturing defect) indeed cannot be resuscitated. On the other hand, stuck pixels (where a sub-pixel is permanently on due to a transistor malfunction or to uneven distribution of liquid) can sometimes be fixed with gentle massage (as nat mentioned) or with special software that rapidly cycles different colors on screen. These methods can be quite effective on modern LCDs (PSP, DS, etc.), but I'd be really surprised if it worked on an ancient Express.

OldRover · 04/08/2008, 07:54 AM

Quote from: guest
Quote from: The Old Rover on 04/07/2008, 09:22 PMIt's not really possible to fix dead or stuck pixels because of how they become dead or stuck.
That's not entirely true. Dead pixels (where all three sub-pixels are non-operative due to a manufacturing defect) indeed cannot be resuscitated. On the other hand, stuck pixels (where a sub-pixel is permanently on due to a transistor malfunction or to uneven distribution of liquid) can sometimes be fixed with gentle massage (as nat mentioned) or with special software that rapidly cycles different colors on screen. These methods can be quite effective on modern LCDs (PSP, DS, etc.), but I'd be really surprised if it worked on an ancient Express.

If the rapid color cycle method could possibly work for the TE, I'll write a piece of software to do it and put it onto a neohucard. It would be great if it could fix the problem.

nat · 04/08/2008, 10:40 AM

That would probably be a very easy piece of software to write, and if it fixed the stuck pixel issue in even just SOME cases it would be fantastic.

Paisa49 · 04/08/2008, 11:49 AM

Man, you guys rock. The dead pixels issue seems to be pretty common with the TE's. Luckily, I'm not having any issues with my TE yet, but it's good to know more people like Nat are stepping up to the plate.

OldRover · 04/08/2008, 12:51 PM

My beloved TE recently developed a stuck pixel...I hope it can be corrected.

Yeah nat, it will be braindead easy to write.

Now it'd just be a matter of getting it onto a card...gotta find a chip supplier, and an efficient method of producing the circuit boards.

nat · 04/08/2008, 12:58 PM

If you want to just write the program and give it to me as a PCE ROM I can test it because I can put it on my flash cart and do it that way. I have a few units with stuck pixels (stuck red, green, etc) that would be perfect to test. That way you don't have to eat the cost of producing an actual cart if the program doesn't correct the issue.

OldRover · 04/08/2008, 07:37 PM

Okay then, give this app a try:

nodtveidt .net/tefix.rar

and let me know if this is along the lines of what you need.

Joe Redifer · 04/08/2008, 07:47 PM

Wow, I didn't know NAT was into modding and the such. Didn't seem like the type.

SignOfZeta · 04/08/2008, 07:54 PM

My friend uses one of those epilepsy inducing flashing programs on a LCD he bought for his computer. It had several dead pixels as shipped, and this program fixed all but one of them, I think. Certainly worth a shot.

NecroPhile · 04/10/2008, 11:07 AM

Quote from: The Old Rover on 04/08/2008, 07:37 PMOkay then, give this app a try:

http://www.nodtveidt.net/tefix.rar

and let me know if this is along the lines of what you need.

Nice Express pic.

If this piece of wizardry doesn't work, then I suggest trying one of the myriad offerings for TVs and monitors. Running one of those via a TurboVision might work a little better, since it wouldn't be limited to the Turbo's color palette.

nat · 04/10/2008, 12:27 PM

Sorry Nod, I've been busy like you wouldn't believe and haven't had a chance to test your program yet. I'll get around to it by this weekend.

OldRover · 04/10/2008, 01:36 PM

That sucks...I was kinda hoping you'd run it on my TE before sending it back.

nat · 04/10/2008, 01:41 PM

~~Really? You should have asked.~~

I didn't even notice any dead pixels on your screen, but then I wasn't really looking.

You might be in luck. Check your PM.

OldRover · 04/10/2008, 03:33 PM

Dead pixels are unfixable, but stuck pixels seem to be fixable in some cases. As for the screen, I've now managed to tear a TE completely apart, so I can study how the screen works and see if a replacement screen can be used. There's always the possibility of molding new plastic shells and using newer, larger screens, while in the process, reducing battery usage. I'd even like to find a way to attach the backup RAM, but that's more than likely a pipe dream.

nat · 04/11/2008, 12:41 AM

I'm currently running the program on a PC Engine GT that I own. It has two stuck pixels. So far, no luck. I'm wondering how long I ought to let it run. I'm running it on "FAST CYCLE" right now.

...still no luck, just switched to SLOW CYCLE...

Oh well, no luck. Tried it on two units (one of them was yours). It was worth a try, I guess.

WoodyXP · 04/11/2008, 03:15 AM

Thanks for posting this, Nat. I'll keep this thread in my back pocket in case mine goes bad. *crosses fingers*

Sinistron · 04/11/2008, 08:49 AM

Well I got my express back from Nat yesterday (QUICK turnaround) and I must say

everything is in fine form, screen is working stellar, sound issue is fixed, and Nat even fixed a stuck pixel- a surprise that I wasn't expecting. Played some Hero Tonma on it yesterday and I am a very happy camper.

Thanks again Nat.

chop5 · 04/23/2008, 12:57 AM

did it today works perfect! thanks nat

saved a tg expres from the dumpster. I used a 4.7 50v cap i had laying around the house (was too lazy to go to radio shack)

turbokon · 04/26/2008, 05:11 PM

Thanks nat. I'm going to add this to my list of services. I hope you don' t mind.

nat · 04/26/2008, 05:34 PM

Ha, of course not. Share the wealth.

Jitawa · 04/26/2008, 06:37 PM

I've gotta say, I'm really looking forward to having a working express again.

imnes · 05/12/2008, 09:40 PM

Was attempting this repair and I think I overheated the component, the solder pad for the positive side of the capacitor pulled away from the board. Where else can I attach the positive lead of the capacitor to repair this?

chaoticjelly · 05/23/2008, 12:53 PM

I actually posted the same information in October of last year, but didn't create a breaking news thread

PC Engine GT Screen Fix ?

NecroPhile · 05/23/2008, 01:22 PM

Quote from: chaoticjelly on 05/23/2008, 12:53 PMI actually posted the same information in October of last year, but didn't create a breaking news thread

Not quite the same information, as nat narrowed it down to a single culprit and provided pretty pictures.

Turbo D · 05/23/2008, 06:23 PM

I would like to thank Nat for narrowing it down to one capacitor. If it wasn't for Nat, I would have had to replace every freaking cap on that damn pcb! It was an easy fix to do, thanx Nat!

nat · 05/23/2008, 06:28 PM

Sure guys, no prob...

And I was gonna say! I actually looked at that thread when I was trying to figure it out, and I was just now about to hit my head against the wall if the answer had been there the whole time and I simply overlooked it.

Duo_R · 09/03/2008, 03:16 PM

I see how you remote mount. Is there just enough space to mount SM caps on this thing? Anyone know a trick how to solder SM caps on VS having to use wires?

Also, can you post the list of caps values and quantities that I will need to order (I will probably just want to replace all of them since there aren't that many)?

Duo_R · 09/14/2008, 05:07 PM

Here is how I installed my cap, I am using a technique that doesn't require the use of wires (I realized that you didn't use wires on the video cap, but you can do the same thing for the sound fix)..

/0912082250alm6.jpg

Platinumfungi · 09/24/2008, 10:09 PM

Quote from: Duo_R on 09/03/2008, 03:16 PMI see how you remote mount. Is there just enough space to mount SM caps on this thing? Anyone know a trick how to solder SM caps on VS having to use wires?

Also, can you post the list of caps values and quantities that I will need to order (I will probably just want to replace all of them since there aren't that many)?

Sub Mini caps will work instead of remote mounting

That's what I've been using on all the ones I've repaired.

Awhile back I made a cap replacement chart here in the Repair/Mod forum. It's called "Turbo Express total cap replacement chart ". That will give you all the values and quantities you need. I also made one for the Duo too in there somewhere...

nat · 09/24/2008, 10:14 PM

Insufficient space for the cap is not why I remote mount, it's more a factor of laziness and wanting to avoid dealing with the extremely confining space on the TE PCB. But yeah, you can surface mount to your heart's content. To each his own.

Platinumfungi · 09/24/2008, 10:20 PM

Definitely! Sorry if that came out sounding rude Nat. I just wanted to make sure Duo_R knew that he/she could indeed just use smaller caps if they didn't want to run the wires.

nat · 09/24/2008, 11:12 PM

Quote from: Red Ghost on 09/24/2008, 10:20 PMDefinitely! Sorry if that came out sounding rude Nat. I just wanted to make sure Duo_R knew that he/she could indeed just use smaller caps if they didn't want to run the wires.

Oops, my reply was directed towards Duo_R, not you.

Duo_R · 09/24/2008, 11:35 PM

uhh - I am a he, not a he/she.

Yeah Nat, I actually figured out how to avoid the wires, but then realized that in the original post you didn't use wires for the vid cap (just the audio caps). I am not questioning your work, definitely one of the veteran modders on here.

Now the real question Nat is can u make a good RGB amp??? That is something I have yet to try.

Quote from: Red Ghost on 09/24/2008, 10:20 PMDefinitely! Sorry if that came out sounding rude Nat. I just wanted to make sure Duo_R knew that he/she could indeed just use smaller caps if they didn't want to run the wires.

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REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix