Teensy 4.1 butchery

[hungrybutterfly]

Despite the Teensy 4.1's tiny size, I want to go smaller. I'm certain this is frowned upon but I'm trying to be a bit naughty by chopping the board at the place shown in the pic. After this is done, and using this schematic I'm trying to wire the psram directly to appropriate points on the board. This looks like 7 wires for the full 16MB plus 2 for power and gnd. Unfortunately I can't get it to work. I wrote a memory test program which worked before surgery and doesn't work afterwards. I've triple checked all connections, there's no shorts and power is getting to the ram chips. Obviously there could be many reasons why this could go wrong so my question is has chopping the board in this way also severed some other internal track i'm not aware of?

[pictographer]

Would a Teensy 4.0 spare you a heap of trouble?

[PaulStoffregen]

I really want to see a photo of how you've actually connected the wires. Don't be shy! Show a photo.

I'm particularly curious to see how you got the 7 QSPI signals (EMC24-EMC29) without the right hand side of the PCB...

I've triple checked all connections, there's no shorts and power is getting to the ram chips.

How did you check the 7 signals?

so my question is has chopping the board in this way also severed some other internal track i'm not aware of?

I can confirm cutting along that red line will only sever signals which route to the I/O pins, QSPI pads, and SD socket. No special signals critical for Teensy 4.1 operation are routed through that portion of the PCB. 2 of the internal layer are for 3.3V and GND, so there is a possibility of roughness on the cut edge could cause any of those I/O signals to short to 3.3V or GND.

[PaulStoffregen]

I made this map to help you find the 7 SQPI signals. Hopefully it helps.



If you scratch away the green solder mask, you should be able to solder small wires to these vias. Be careful about too much heat, since those vias go right up close to the underside of the main chip's pads. Best to set your soldering iron to a relatively low temperature, and use lead-based solder.

You could run a program like the LED blink, 7 times, with pin number set to just 1 of the QSPI signals on each run. Then use a voltmeter or connect a LED+resistor to each wire to check that it's really connected to the correct signal.

Still really hoping to see photos of this wiring. As far as I know, you're the first people I've heard to attempt such a feat.

[hungrybutterfly]

Still really hoping to see photos of this wiring. As far as I know, you're the first people I've heard to attempt such a feat.

OK it's now working. It turned out to be a short between D3 and 3V, I think caused by a rough edge where it had been cut. Just knowing I was on the right path helped me strengthen my resolve to fix it

Thanks so much for your help. As you were curious here's a pic of what I'd done before fixing it. It's pretty much exactly what you'd suggested in the map you sent. Please excuse my dodgy soldering I could really do with better tools but can't justify the cost.

[hungrybutterfly]

Would a Teensy 4.0 spare you a heap of trouble?

Unfortunately not. I've worked on a 4.0 before but I need the psram memory to be addressable like normal memory rather than having to use function calls. Thanks for the suggestion though.

[PaulStoffregen]

I'm pretty impressed you got it working!

Might mention this on social media. Hope that's ok.

[pictographer]

Wow. Congrats on getting it working!

I'm sure I'm not the only one who is curious about what marvelous gadget will you put this in and what will it do?

[hungrybutterfly]

I'm pretty impressed you got it working!

Might mention this on social media. Hope that's ok.

sure thing

[hungrybutterfly]

Wow. Congrats on getting it working!

I'm sure I'm not the only one who is curious about what marvelous gadget will you put this in and what will it do?

Thanks. I'm making more of these https://www.youtube.com/watch?v=CQdilSVFqRk

[houtson]

Thanks. I'm making more of these https://www.youtube.com/watch?v=CQdilSVFqRk

wow, that looks crazy - I want one!