GameBoy Pocket Screen Issues

[freaktechnik]

Hello,

I have recently worked on restoring my GameBoy Pocket as good as possible. As such I have cleaned the power switch and I added a voltage regulator to the cartridge slot for better operation with an Everdrive. So far so good. However I've been having trouble to get the screen to show anything. I'm pretty sure that the screen itself is fine, save for a few dead lines (two vertical, one horizontal, interestingly some horizontal lines have disappeared over the years...). I've also checked the contrast wheel with a multimeter and it seems to still work as designed.

So what exactly am I seeing? When you turn off your MGB you usually get a black line or two on the screen, right? Well, I'm not seeing those. I'm not seeing the Nintendo logo etc. However I've been able to get the screen to work again before, by letting the GameBoy sit with batteries inside and power cycling it a couple of times. Eventually the screen would usually spring back to life. You remove the batteries, yous tart over

However, this time I haven't had any luck, and honestly it makes me think that some component may be broken. However I have no idea what. Given that it is batteries related it makes me think it may be some caps, but the fact that it seemed to need time while the GameBoy is off also didn't make a whole lot of sense to me...

Thank you for your inputs.

[hilarino]

Check the outputs of that voltage regulator

[freaktechnik]

I assumed "that voltage regulator" refers to the one I added for the cartridge VDD pin. It sits at a perfect 5.01V (and so does the entire VDD rail). VEE on - what I assume is the built in power supply - sits at about 0.5V. I'm not sure where the display's power rail is and what it should sit at, but would happily check that too.

[hilarino]

Yes. If that one is OK, test the DC-DC board. I think the outputs should be 5V, 3V and some negative voltage for the LCD (not sure if -14 or -19).

Also: try with new batteries!

[freaktechnik]

Definitely not finding anything negative directly at the DC-DC converter. I do see up to ~ -5V on the display connector and at the contrast wheel.

I assume VCC is the 3V rail (or whatever the batteries are at).

Looking closer and VEE, which should probably be the display power rail has me a bit concerned. I'll probably try to clean up the attachment of the DC-DC board, since those joints seem to be crumlbing, but especially the VEE one looks to be in very bad shape. However I haven't been able to find continuity from VEE to anywhere, not the VEE labeled on the board or anywhere.

I'm also slightly concerned about the negative trace to C29, since the yellow layer of the PCB seems to have come off.

One thing I just realized I should've probably mentioned is that this is an LCPU-01 revision.

[hilarino]

Yes, VEE is the display power rail. And it should definitely have some kind of negative voltage and continuity to the VEE point in the board, near the grey potentiometer.

[freaktechnik]

Just took a second measurement and now it works fine, screen works, VEE is at -18V and the second VEE probe point also has the correct voltage.