Sorry for digging this up but I had the exact same heat problem and I solved this issue with a small variable power regulator module that takes almost any input from 4.5-28V and can regulate it to  anything from 0.8 to 20V (as long as it's less than the input; it's no step-up converter / inverter). What you do is to connect the input of the power regulator module to the unregulated + and the GND as shown in irony7's post with one wire each. Since the DMG's switch switches this power source, your backlight will actually turn off together with the DMG. After having soldered the module to the power source and before connecting the backlight you switch on the DMG, measure the output voltage with a multimeter and regulate it to 5V with the module's potentionmeter using a small flathead screwdriver. After that you simply connect the backlight's wires to the output and put everything back into the case. After this you basically have two parallel power regulators, the original DMG's and the new one. It works like a charm even with the EMS flash cartridge. You can easily find these regulators by searching for "DC Buck Converter Step-Down Module" at your favourite online store. I got six of these for 9 €. Make sure you buy small form factors.

This requires running wires between the main board and the LCD screen board, please note.

I use an extra power regulator board (5v step up/step down from Pololu)in connection with the unregulated power to keep the voltage to the backlight steady. The rgb screens I've tested use about 200mA when all channels are activated, so a 400mA board should be enough, even if choosing to add button lights and running them through the extra power board.

unexpectedbowtie wrote:

Can anybody point out the power LED solder points to use to avoid the heating up problem? I'm not 100% sure on what ones are correct, and it'd be good to sort out a few of my DMGs that get pretty hot before I fry anything. (!)

Hey, I'm sorry to bump this. But did you get an answer on which points to use?
I'm enjoying some time off to look over my trusty old DMG.

I didn't... but I spoke to BennVenn about this, and he didn't seem to think this would work anyway, so I've given up for now!

Can anybody point out the power LED solder points to use to avoid the heating up problem? I'm not 100% sure on what ones are correct, and it'd be good to sort out a few of my DMGs that get pretty hot before I fry anything. (!)

Hey, I'm sorry to bump this. But did you get an answer on which points to use?
I'm enjoying some time off to look over my trusty old DMG.

I also have some questions for you catskull, would you mind sharing the 'regulated' points of the DMG you switched to ?
Also, do you have any news regarding that replacement regulator board you were talking about? I was just thinking, could I maybe just replace some capacitors on the regulator board with some caps with higher capacitance to lower the heat coming from the regulator board and reduce the stress on the DMG hardware?

Answer coming after workday is finished.

Thanks a lot!

I should rephrase that... Connecting directly to the battery terminals won't turn off the backlight when you switch off the gameboy. So yeah, power LED source is a good place to tap into.

Haha,  good point!!

edit - rereading it all, I would run it over the power led, no need then for running wires between the boards.

That's connected to regulated 5v source. Connecting to the unregulated power source is not bad for the console, it bypasses everything. Putting strain on the regulator with the high current draw from an EMS cart and a backlight is damaging to the console.

Ah damn, thank you for pointing this out! I'm a bit noob on all these different solder points, which ones are considered the best to drive my nonelectronics V5 without having to add resistors etc. ?

What about running an extra regulator (buck/boost 5v dc-dc) parallel to the stock regulatorer to power the backlight?  Could that work to relieve the stock regulator from overheating?

If you mean regulating directly from the battery terminals, yes. It's not even really needed to be honest. Backlights are plenty bright, and people connected them to the power LED source for years without any serious issues.