FIXED - Turbo Express screen dim, but working. How to fix?

[vetteguy112233]

I bought a TE that somebody attempted to fix and actually did a decent job with the capacitor replacement, but the screen isn't working properly. The game loads and music works perfectly and if I turn the lights off in my room and hold it at an extreme angle, I can see everything on the screen just fine. Moving the brightness dial doesn't change anything whatsoever!

I thought maybe it was a backlight issue, but where I can see everything on the screen at the odd angle, I don't think that's it. I verified all batteries were above 1.6v so I know it's not a battery issue.

Where the brightness dial doesn't work, how do I go about testing from here? I checked the pot and my meter read 0 ohms all the way up to 5 as I turned it, if I remember correctly, so it appears the potentiometer is working.

Please help!

[tbone3969]

Go out and buy some brand new AA Duracels.  Test it with those and report back.  It sounds like it could be the batteries.

[vetteguy112233]

That is the second set of batteries I tried. The multimeter confirmed they were brand new batteries.

[mickcris]

Sounds like maybe they didn't do such a good job on the cap replacement.   Maybe post some pics on here.  Dark screen is usually bad caps

[vetteguy112233]

The file on my phone is 5mb and the max the forum will allow is 128kb, that 1/40 of my pic quality. If I cut it down that much, are you really going to be able to see anything worthwhile without the quality of the pic?

[vetteguy112233]

Let's try this:

https://postimg.org/image/rnb3cfyth/
https://postimg.org/image/t5pri0bor/
https://postimg.org/image/5vd411ydt/
https://postimg.org/image/yhqtjz8ux/
https://postimg.org/image/or74v3159/

[vetteguy112233]

I actually have another working Turbo Express that we'll call #1, so I took it apart and put LCD #2 and system board #1 together and everything works. It does take 10 seconds to warm up and come on, but at least the LCD works! I guess I had better double check the cap job. I found a post that showed the little cap at the top is the video cap, but isn't there more than 1 cap for the video?

I also happen to have a cap kit on hand, so I guess I can change the little one out in the meantime.

[vetteguy112233]

Nope, changing the small capacitor at the top didn't do anything. I'm mainly posting my progress in case someone else has a similar problem in the future.

[blueraven]

The screen warmup when you swapped the LCD to your working unit is indicative of a separate problem. I would suspect if unit #1's screen snaps on, then it is POSSIBLE that just worn down from 24 years of play. Or... (more likely), unit #1 also needs some cap work. 

You're going to need to check the capacitor job on unit #2 for errors, or possibly a broken trace around the video circuit. Are all of the legs in order and flush with the board? Are there some bent or damaged caps that resulted from putting the system back together? Are there any clearance issued from your replacement that could be causing a bad ground? Or are the caps just super shitty quality and are they not functioning?

Sounds like maybe they didn't do such a good job on the cap replacement.   Maybe post some pics on here.  Dark screen is usually bad caps

That's what I think too.

Also, do you have a multimeter? I would check the video circuit to determine what is reading correctly. It may be that you one or two caps that are malfunctioning.

If you post pics, it will be easier for us to help.

[vetteguy112233]

Yes I have a nice Fluke multimeter.

Please help me identify the video circuit. Is there a diagram, what parts make up this circuit and how do I test them? Were the links to pix I posted not what you were looking for?

[blueraven]

Let's try this:

https://postimg.org/image/rnb3cfyth/
https://postimg.org/image/t5pri0bor/
https://postimg.org/image/5vd411ydt/
https://postimg.org/image/yhqtjz8ux/
https://postimg.org/image/or74v3159/

I think you may need to re-do the caps. A few of them look like they are installed incorrectly. CC102 looks like it's overlapping, and you're going to have to remove that blob of polyurethane glue and swap out those two silver 100uf caps right next to CC501, to start. Be careful with those two; the traces like to lift up so go slow when you're removing the glue.

[blueraven]

...And before you put it back together search the forums for the diagram of the video circuit, and check those capacitors. I don't remember where it is at the moment but by the looks of your unit it needs to be "tidied" up and have the rest of the caps replaced.

[vetteguy112233]

I know it's hard to tell from the pictures but all of the Caps are installed correctly and I've double-checked to make sure nothing was bridged or loose. This is for all of the Caps that are visible outside of the shields. I know everything should be replaced but from my understanding the caps under the shields have nothing to do with the video.

The two large silver caps in the white glue do appear to be original so I will try to replace those and see if that helps. It appears that whoever recapped this machine only did the caps outside of the shields, they did not do anything under the shields. With the exception of the two large silver caps I don't think they were replaced at all.

[vetteguy112233]

FIXED:

I found that the capacitor at CC702 looked a little charred. I replaced it and the screen instantly appears and the brightness works perfect.

Thanks for the help.

[Keith Courage]

Check how many volts you are getting from the 22uf 50V capacitor. If it's below 20V then either there is a bad trace somewhere to one or more of the caps or there is a part that is fried on the motherboard in the back light power circuit.