Hardware Only backlight but boots and image on TV

[BenjaminWN]

Hello everyone !

So I'm having a bit of a problem with a HAC-CPU-20

It's a RMA with a broken type C connector that I bought in bulk along with other Switchs, changed the connector and the M92T36. Charges beautifully.

The Switch turns on but without any image, only the backlight.

So I changed the LCD FPC (twice) but to no avail. I get image with the dock so I think repairing it is possible for me but I'd like some input.

The model I have doesn't seem to have any filters on the under the fpc. It's one of those with everything tinned.

Thanks in advance !

Benjamin

 

[severhead]

Since it docks it rules out SoC issues, but tbh thats rare, have you look at the cable that connects the digitizer to the motherboard? Just wanna rule that out

Maybe try swapping out the motherboards between the other models that have a working screen if you still got them laying around?

 

[de9ed]

check the diode/capacitor left of the FPC connector, I have seen it damaged before and no display.

 

[BenjaminWN]

@severhead I have a spare known good LCD that I plugged in with a known good battery. But to no avail, it's like there's just no image data.

@de9ed I just checked, diode is good, flow is from coil to cap and the cap doesn't short the diode. Coil looks good as well.

The IC doesn't seem bad but a collegue suggested swapping it with one from a donor board. Any suggestions ?

 

[de9ed]

@severhead I have a spare known good LCD that I plugged in with a known good battery. But to no avail, it's like there's just no image data.

@de9ed I just checked, diode is good, flow is from coil to cap and the cap doesn't short the diode. Coil looks good as well.
View attachment 258061

The IC doesn't seem bad but a collegue suggested swapping it with one from a donor board. Any suggestions ?

Sorry I meant the IC

 

[BenjaminWN]

Nothing notable unfortunately. Thanks for the tip though, I didn't know this could cause a black screen !

 

[Lord117]

Hi,

any news about this issue ? I have the same trouble. I replace the USB-C port (like everyday) and the Switch has backlight, fast charge (5V & 15v), Dock TV working, but no display image. (LCD fpc is 100% clear and no bended).

I see a strange value on the caps around BQ24 (1.1ohm instead of ~0.50 cf picture) and somes shorted caps around MAX77812.

* PS : Before the usb replacement, the Switch had the lcd screen which worked perfectly

 

[BenjaminWN]

Actually I found out that the shorted caps around the max77812 in fact look like they are but have low resistance to ground to begin with.
About the Switch I still don't have any news, I had to leave it for now since I bought them in bulk and can't stay stuck too long on one.

Have you tried with another LCD ? Honestly if it worked before and the fpc is fine, maybe look around if something moved when the board was hot.

 

[Lord117]

I have other lcd, and it's not the lcd imself infortunately... Nothing it's hot , I have thermal camera and
except bq24 during the charging process, nothing appear. I tried to inject voltage around MAX77812 and nothing. I have a shorted cap on the left to MAX77620H too. (it's not the cap).

So, MAX77620 & MAX77812 what exactly are they used for ?

 

[Lord117]

After fpc inspection diode values, i found 0.8 instead of OL in pin n°5 from the right. Anyone have got information about this trace ?

 

[de9ed]

After fpc inspection diode values, i found 0.8 instead of OL in pin n°5 from the right. Anyone have got information about this trace ?

I am getting 0.671 on pin 5 from the right. V1 unpatch switch