Please help fix my display issue!

Morning everyone!

A bit of a convoluted story, please bear with me!

About 3 years ago, a friend gave me a broken 17” Unibody MacBook Pro Early 2011 to retrieve the data from the hard drive for him, which I did. The issue with it was the display just stayed black when you turned it on, but also there was no image to an external monitor when connected. I presumed it was a logic board issue, which meant it was economically unviable to repair so it went on a shelf, with grand plans to strip it down and sell the parts on eBay.

Fast forward to a month ago and I found the laptop again. With a couple of hours to spare, I decided to put it on my bench to start seeing if the was anything obviously wrong. I reconnected the battery which I had disconnected 3 years ago and surprisingly the fans started spinning. I flipped it over, opened the lid and to my surprise and delight the screen came to life!!

I tested it, popped a new SATA SSD in there, rebuilt it with High Sierra and had plans of giving it to my wife to use because it’s literally in pristine condition.

2 days ago, I turned it on and …. Black screen again. I was SO disappointed - I thought I was onto a winner. I’ve tried all that I know how: Re-seat the screen cable (and check for wear and bent pins), disconnect and reconnect the battery, reseat the RAM, PRAM reset, SMC reset.

Last night I found an article about booting it without the battery, which I tried and it actually came back to life again!. Until I reconnected the battery and closed down to test again. Now back to the black screen.

There SEEMS to be life in it, but not consistently. Which is where the IFIXIT community comes in to flood me with your wisdom please!!!

With it being a 9 year old machine I don’t think it’s worth the money spending on it to replace big-budget items like the screen or logic board, but if anyone has a permanent low-cost/free fix I’d be eternally grateful.

Thanks for reading my ramblings.