Cave Dweller 2015 - 78l05 output above 7 Volts

[geklimper]

Hi, build the Cave Dweller 2015 on stripboard and have a strange problem with the 78L05. The output is a bit above 7 Volts. Changed it of course, but same result. Without the PT2399, the output of the 78L05 is exact 5 Volts (I changed the PT2399 also, no difference). I don't understand how this can be, googling didn't help either, so if somebody could help me out here would be great.

[ElectricDruid]

Sounds like you need this thread! -

https://www.diystompboxes.com/smfforum/index.php?topic=122232

Same problem...

[geklimper]

Thanks for the link. Wrong direction was the first thing that came to mind, but after double (triple) checking everything was right. Out of curiosity, I changed the direction, and got 7.7 Volts. Changed again, and 7.68 Volts. Input and common are in the right place (measuring resistance: around 33 kohm).
I find it curious, that without the PT2399 there are 5 V, but I can't find anything wrong near the chip.

[geklimper]

Changed the 78L05 with a 7805. Result: 7.38 Volts on the output (in: 8,41 V, ground: 0,05 V, source: battery with 9 V)

[GibsonGM]

Changed the 78L05 with a 7805. Result: 7.38 Volts on the output (in: 8,41 V, ground: 0,05 V, source: battery with 9 V)

Have you tried just putting a resistor across the output?  What does the PT2399 draw (read data sheet)?   Figure a resistor that will draw that much current, see if the regulator cooperates...this is odd, almost like something is 'adding voltage', no?   I wonder if there is something going on at the 2399 end...a bias voltage or something shorted to the power pin, something like that.  No real clue tho, sorry.

[anotherjim]

Remember the 7805 pins are opposite to the 78L05.
I wonder if your 0v is hooked up. Are you using a wiring scheme that needs a plug in the input jack to connect the Ov of the power to the circuit?

[geklimper]

I placed the 7805 and the 78L05 according to the datasheet, the ground of the 78xx is connected to 0V. Tomorrow I will look at the connections with the 2399 with fresh eyes, there must be something I didn't see.

[geklimper]

Looked again over the board, especially for shorts, but didn't found anything. Also looked after the positioning of parts, everything seems right, so I'm at a total loss here. I don't know enough to understand what's happening here.
By the way, I build this from here: https://tagboardeffects.blogspot.com/2016/09/madbean-cave-dweller-2015.html, some unknown guy got it working without any problems, so there is still hope.

[ElectricDruid]

You said that there's 5V at the PT2399 socket when the chip *isn't* in place? But then it goes up if you measure when the chip is installed? Is that right?

That's weird, but it suggests that the problem isn't the regulator.

[anotherjim]

It suggests that 9v is getting to one of the PT2399 pins and then going through that chip to its pin1.
With the PT2399 out, can you read 9v on any of its socket pins? My money is on pin2 or pin16 due to a bridged track cut.

[geklimper]

PT2399 out, I have 5 V on 7905 and on socket pin 1, and I have 9V on the socket pins 15 and 16. I will look into it now.

[geklimper]

Found the error, kind of embarassing. As I want to put this in an eurorack, I placed an 79l09 on the board to reduce the 12V. But forgot to cut the line to the circuit, so the 9V got straight to socket pin 16. Now everything is working.
Thanks to all for your tipps, that's really great support!

[ElectricDruid]

Good find. They're *always* embarrassing, but we manage to live with it, somehow...

[geklimper]

That's it. Making errors is not so much the problem, I'm learning with everyone (I hope) ...

[GibsonGM]

Good deal!  This is the most common kind of error, and we still make them even after years of building, ha ha.