REPAIR GUIDE - TurboExpress/PC Engine GT: Video Fix

[Moudamir]

Hey guys,

I end up changing everything all the caps, now it's worst screen stays greenish, with some shadows if you angle the TE forward.

Kind of lost !!! Any ideas ? Screen is May be dead....

[Keith Courage]

Look around for bad traces. If it was better before changing the rest then a trace or pad must have been pulled up.

[speedlolita]

Hi! Thought I'd post my issues with a PC Engine GT unit I was asked to re-cap.

After replacing all of the caps most of the issues with the unit were fixed.

However, the brightness dial isn't working as it should. That is, after the unit has been on for maybe 15 seconds. If the unit has been discharged for a while then the dial seems to work as desired. Once it settles down though the dial has little to no effect and the image just gets progressively darker.

The main video cap had leaked when I got there so I scraped away the excess junk and reflowed the transistors in that area but that didn't appear to do anything.

Aside from attempting to re-cap the video capcitors again I'm at a loss. Has anyone else experienced similar symptoms?

[thesteve]

its a power hog
battery fade will cause this

[KingDrool]

My son just used these instructions as part of a job-shadow project. It worked brilliantly! Thanks for the handy guide. You made it so simple even an 8 year-old could do it!

[bovined]

I had a perfectly workinh TE but I picked it up the other day to play some Blazing Lazers and it would only power up the screen going from white then quickly to black with no audio. I tried moving the hucard a bit and it will sometimes power up to a green or orange screen and then quickly to black again. The brightness dial still works but thats it. I tried replacing the cap in question from this thread but it seems to be be behaving the exact same way afterwards. Any ideas on what is causing this issue or what the next best caps to try replacing would be?

[thesteve]

going black after white tho i havent seen it on a TE/GT, i have seen on other versions
it means the system crashed shortly after resetting the pallet registers
the cause has been bad 6280/ bad work ram/ bad trace
any one can cause this, and it could be all, but most common is bad traces

[bovined]

Just want to say big thanks to thesteve for fixing my TE! Awesome fast service and communication. A true pro!

[RetroWeirdo]

Hey y'all, I just did a recap on a TurboExpress which had stopped working (This was my 2nd time repairing one of these, 1st one came out great). This time around went a little different. When I was trying to carefully remove the portions of white glob that were covering the solder pads of the caps in the corner, there was a large piece that broke off and took a piece of the black plastic top off the copper coil pack hidden under that white goop. So I assumed this goop was acting as a insulator for the coil/glue for the 100uf 16v caps that it runs into. I attempted to use hot glue to repair this and continued the recap job.

Once I reassembled and tested the unit, I found the screen to flicker and get distorted with pixels in improper places. After double checking all of the solder points and some other trouble shooting without the back half of the shell, I was able to get the distortion to stop but the light flicker continues to occur as if possibly a slight issue with the backlight. But I wonder if this is possibly related to that coil from under the white goop. Could this occur if it is damaged or not adequately insulated?

Thanks

[Keith Courage]

Insulation of that part shouldn't effect anything. I've never seen flickering like you described. Maybe you should post some pics of the graphics issues? Could be bad ram/or damaged trace related.

Also, in the past I've accidentally uncovered the part you speak of before and have even broken off a leg/contact point before. I've always just re-soldered the wire back to where it originally went without any ill effects. Then cover up with hot glue or epoxy. So hopefully neither of the two contact points for the coil have snapped off anywhere.

[XLR-VIII]

Hey guys can someone help me with this....
I replaced all 18 capacitors on my TE. End result is no video....backlight works and I have sound! Anyone got any ideas?

I attached a link to a video of my TE

[Keith Courage]

Looks like something isn't getting the correct voltage. Make sure there are not any broken traces to any of the caps you installed.

[RetroWeirdo]

Insulation of that part shouldn't effect anything. I've never seen flickering like you described. Maybe you should post some pics of the graphics issues? Could be bad ram/or damaged trace related.

Also, in the past I've accidentally uncovered the part you speak of before and have even broken off a leg/contact point before. I've always just re-soldered the wire back to where it originally went without any ill effects. Then cover up with hot glue or epoxy. So hopefully neither of the two contact points for the coil have snapped off anywhere.

Thanks for the advice KC. I tried some additional trouble shooting (different caps, reflow on solder pads) with no change. I posted a couple private videos to YouTube showing the pulsing flicker issue, here are the links:
Video 1: https://www.youtube.com/watch?v=MevovLPARy0&feature=em-upload_owner#action=share
Video 2: https://www.youtube.com/watch?v=g9rXBf_rj4E&feature=em-upload_owner#action=share

If you look carefully in the first video you can also notice that there is a temporary burn-in on the screen that carries over from whatever is displayed previously, so in the video you can see the Keith Courage title screen still faintly showing on the screen once the game starts.

I rechecked the traces as well and couldn't find any issues, though it seems like that could possibly be causing the issue, or maybe the ribbon cable from the hu-card reader to the main board? What do think from the videos?

Thanks

[Keith Courage]

I've seen something similar happen when the 1 10uf cap pads get ruined but not exactly the same. Also, are you by chance using a generic ac adapter? Does the same thing happen on batteries? I wonder if this is the sign of an actual bad screen.

The burn in on the screen is completely normal.

[XLR-VIII]

Looks like something isn't getting the correct voltage. Make sure there are not any broken traces to any of the caps you installed.

I'm getting 7.8v from an AC adapter.
When unit powers on it drops to 3.8v
Checked some the caps, most read about 3.5-3.7v
Measured on pin 3 of the display ribbon cable only get -2.5v

Anything else I should check and where does the 24v start ?

Thanks