7E LCD blank > chang CPU = good > now blank again

So I've had the 7E for a couple years, but haven't used it a lot lately. I went to use it today after it had sat a while and the LCD would light up, but be blank. Sometimes the LCD would show garbage if I power cycled it a few times. It would show nothing in "programming mode" and show random spots in USB mode. I tried reloading deviation while formatting the memory and copying new data over via USB and that did nothing.

I had previously upgraded the CPU to the STM32F103RCT6 256 kb so I decided that if the LCD was dead that I had nothing to lose. I removed the STM32F103RCT6 and reinstalled the original 128 kb CPU. Flashed back to a 128kb deviation build, formatted the memory and USB copied the files over. Once I did that the LCD worked perfectly... for a bit. Everything came up normal and I flew a quad for about five minutes without looking at the LCD. When the battery was spent on the quad, I looked down to see that the display was split with half on the top and half on the bottom. I power cycled and got no display. I power cycled a couple more times and it looked fine, but after about five minutes of use the display would be wrong again. sometimes upside-down, sometimes garbled, sometimes split. If I power cycle sometimes it comes back online perfect again.

It's been a long time since I worked on this and I kind of forget what exactly I have in the 7E; upgraded power supply, now removed STM32F103RCT6, two three-way switches, two two-way switches, four-in-one module...

I just ordered a STM32F103RET6 to try a CPU again, but I'm hoping someone has some advice because it seems more likely that something is killing the CPU's, but I don't know what. Can anyone think of what to check? I do processional PCB work and all my soldering is good. Is my LCD bad or is this a CPU issue?!?

I've attached a photo of what's in there now. Any advice would be appreciated.



Also, quads fly fine so the 7E is fully functional except the LCD. Has an LCD ever been found that is a drop in replacement or that can be installed with little modification?

Thanks,
craigr

Does anyone have schematics for the 7E?

craigr

Did you check if it is a thermal issue somewhere along the way? Try reproducing the behavior with the case open and just leaving the transmitter on for a while. I also noticed the isolation of the red wire coming from the step down power supply has melted and is just above a pcb routing from the cpu to the display. I wonder if hf coupling from the switching supply to the display signals could also be an issue..

Moeder wrote: Did you check if it is a thermal issue somewhere along the way? Try reproducing the behavior with the case open and just leaving the transmitter on for a while. I also noticed the isolation of the red wire coming from the step down power supply has melted and is just above a pcb routing from the cpu to the display. I wonder if hf coupling from the switching supply to the display signals could also be an issue..

Thanks for the reply.

I'm planning on replacing the power supply wires since I melted them so I'll try getting them further from the LCD traces at the same time... I have my doubts that 3.3 volts at low current will cause the issue though.

I don't think the problem is thermal. I tried freeze spray and the LCD changes slightly when I freeze the CPU, but I literally iced the entire board last nice (totally condensated with ice), and the board remained frozen while running for several minutes. Nothing was hot enough to melt the condensated ice.

Oh well, I'll try the new CPU when it gets here Tuesday and see what happens. I may pull the LCD board off at some point and have a look.

If all else fails I'll buy another 7E when eBay issues a 20% off coupon and get it for $45. Doing all the mods over isn't going to be wonderful though.

If anyone has any more suggestions I would love to hear them. I was hoping I was not the first person with this problem. Today my display is back to just being lit up but blank so I can't change models or anything at all. I've seen other post where people have had just a blank display and the consensus has been a bad display.

Best,
craigr

FWIW, I'd rather buy a fully modded Ultimate 7E (a.k.a T8SG V2+ ) for less than 100 $ and be done with it (may be a can of black spray color, if you prefer )

I met with the exact same problem. I didn't use the 7e for a long time, but it was perfect, Now I tried, and the LCD is mostly blank, rarely garbage on it.
If I push EXT while switching on, the DFU screen is perfect (so the LCD and t it's connection to the cpu is OK). The usb modes (dfu and mass storage mode) are working.
Re-flashing the firmware and file system doesn't help.
Really strange, considering it happens after a long rest too. Maybe it's somehow connected to the battery runout during the long inactive time?

I have the original cpu, a 4in1 module, and the 3 position switch mod.

Any idea?

No idea if it could have any effect on the display (if any lines are shared), but the diodes in the switch matrix, I would replace them by 1N4148 the small glass diodes.

The PSU I use it with great success.