Vselect doesn't work as expected

[Snkfear]

OSCR firmware version

13.1

OSCR hardware version

HW5 Rev5

Attach OSCR_LOG.txt file here

No response

System used

all/none/doesn't matter

Describe the issue.

I've populated everything like the wiki says but when I do the last test, Pin 8 doesn't switch to 3.3V it remains 5V.
When I poer on the system, I measure the expected voltages:
Pin 6 and GND -> 5V
Pin 8 and GND -> 3.3V
Pin 7 and GND -> 3.3V
Once I select "Mega Drive/Genesis" :

Pin 6 and GND -> 5V
Pin 8 and GND -> 3.3V (should be 5V)
Pin 7 and GND -> 3.3V

All smd components are soldered as they should and there isn't any bridge between the legs of the IC.

What else should I check?

[sanni]

I don't use Vselect myself so I can't really confirm it but to me it sounds like a typo in the Wiki.

Pin 8 is a voltage input so it should always be 3.3V.
Pin 7 should be 3.3V in the main menu and 5V after "Mega Drive/Genesis"->"Game Cartridge" was chosen.

So as far as I understand it, on the Wiki page:

On the OSCR, select "Mega Drive/Genesis" and use your multimeter again to check the voltages between:
- Pin 6 and GND, should be 5V
- Pin 8 and GND, should be 5V
- Pin 7 and GND, should be 3.3V

should be:

On the OSCR, select "Mega Drive/Genesis"->"Game Cartridge" and use your multimeter again to check the voltages between:
- Pin 6 and GND, should be 5V
- Pin 8 and GND, should be 3.3V
- Pin 7 and GND, should be 5V

Can you check the voltage on pin 7 again after "Mega Drive/Genesis"->"Game Cartridge" was chosen?

[Snkfear]

Yeah, like you said, it was a typo on the Wiki. It's working great and I've dumped GBA/GBC game without issues.

The only thing that annoys me is that the menu isn't displayed correctly.

But as you can see on the last photo, some menus are displayed perfectly.

[sanni]

Is there a pattern like it only happens with 3V systems but 5V systems are ok?

The Vselect by default switches the Cart Reader to 3V and only after a 5V system has been set up it switches to 5V.
In case of Mega Drive, the "Mega Drive Reader" menu would be the first menu where the Cart Reader is running at 5V.
By this logic the menu should be ok e.g. when you select Game Boy (Color) too.

If this is the case then it might be that your Mega Pro can't run at 3V. This seems to happen more frequently in the last years.

[Snkfear]

You nailed it!

This is weird because I ordered the mega with a row of 5 smds according to the Wiki... and I've dumped GBA and N64 games that work without issues.

[Ancyker]

@Snkfear try enabling 3V3FIX in the config. It might help as I wrote it to try to address the 3.3V issue but no one has reported if it helps or not.

/* [ 3.3V Stability Fix (3V3FIX) ---------------------------------- ]
    Enable this if you are having stability issues when using 3.3V,
    works best with VSELECT.

    If not using VSELECT, always turn the cart reader on with the
    voltage switch set to 5V and switch to 5V before selecting a
    cartridge from the menu.
*/

#define ENABLE_3V3FIX

[Snkfear]

@Snkfear try enabling 3V3FIX in the config. It might help as I wrote it to try to address the 3.3V issue but no one has reported if it helps or not.

/* [ 3.3V Stability Fix (3V3FIX) ---------------------------------- ]
    Enable this if you are having stability issues when using 3.3V,
    works best with VSELECT.

    If not using VSELECT, always turn the cart reader on with the
    voltage switch set to 5V and switch to 5V before selecting a
    cartridge from the menu.
*/

#define ENABLE_3V3FIX

The fix solved my problem!

I had to remove the mega and bridge the fuse because the board was restarting every time the ide started uploading the sketch... I guess it's because of the Vselect.

By the way, would be great to add test points for the TPS in future hardware revisions, it was a nightmare to test each leg for shorts.

[Ancyker]

I had to remove the mega and bridge the fuse because the board was restarting every time the ide started uploading the sketch... I guess it's because of the Vselect.

This is odd. My best guess is that it didn't like flashing in 3.3V mode. You could try putting it on the MD menu so that it goes into 5V mode before flashing. You can also remove the SD card and then power it on. It should prompt you to press the button to enable 5V.

By the way, would be great to add test points for the TPS in future hardware revisions, it was a nightmare to test each leg for shorts.

There are lots of places to check this around it without the need for test points, here's a reference:

As you can see, of the 8 pins 2 are ground, and one isn't connected to anything, leaving 5 pins of which all of them are already broken out nearby. The only one slightly hard to test is the one going to the resistor, but you can just touch the leg of the resistor instead of the pin on the IC for that one.

The fix solved my problem!

I'm glad it worked for you :)

Do note the fix will make dumping 3.3V systems a bit slower (super noticeable on the N64). It seems that, as I suspected, the issues come from the instability of the 2560 being run at 16MHz on 3.3V. The fix works by lowering the clock to 8MHz when 3.3V is being used.

The mega isn't designed to run at 16MHz on 3.3V, though most chips can do it, it's similar to overclocking a computer's CPU (or, more accurately, undervolting a CPU). Reducing the clock speed fixes the issue as the mega is rated to operate at 8MHz on 3.3V.

If you are dumping a lot of 3.3V games, N64 games especially, it may be worth playing the silicon lottery again and getting another mega to see if you can get one that is stable when running at 16MHz on 3.3V.