I may have lifted JP9 - What do I do?

Anything about this unique oscilloscope DIY kit
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amocjr
Posts: 9
Joined: Sun Aug 06, 2017 1:20 am

I may have lifted JP9 - What do I do?

Post by amocjr »

I may have lifted the pads for JP9. (I don't know why, but the jumper pads are really hard to solder. I had trouble with every one of them.)

My board successfully passed the first power-up test, and I am now ready to mount the LCD and conduct the second power-up test. The instructions say JP9 must be closed.

Two questions:

1. Will I damage anything if I proceed with installing the LCD and conducting the second power-up test if JP9 is not bridged (closed)?

2. If I have lifted the pads, and that results in JP9 not being closed, what's the fix? How can I close JP9 if the pads are gone?

Thanks,
Tony
jye1
Posts: 1221
Joined: Wed Feb 20, 2013 4:58 pm

Re: I may have lifted JP9 - What do I do?

Post by jye1 »

JP9 being open won't damage anything. It is the path that connects digital ground and analog ground. If its pads are gone you can find two pads that are close and belong to digital and analog ground respectively, then use a piece of wire to connect them.
amocjr
Posts: 9
Joined: Sun Aug 06, 2017 1:20 am

Re: I may have lifted JP9 - What do I do?

Post by amocjr »

That's a relief! Thanks for your speedy and helpful reply.

Could you point me to some other potential connection points for the digital and analog grounds?

Thanks,
Tony
jye1
Posts: 1221
Joined: Wed Feb 20, 2013 4:58 pm

Re: I may have lifted JP9 - What do I do?

Post by jye1 »

The ground pins of R20 and C28 can be used for the connection.
amocjr
Posts: 9
Joined: Sun Aug 06, 2017 1:20 am

Re: I may have lifted JP9 - What do I do?

Post by amocjr »

Excellent, thank you for the suggestion.

Just to confirm, the ground pin of R20 is going to be the side that measures (almost) zero resistance to the groundplane, using a VOM, right? The other side of R20 measures 10K to ground, which is the value of the resistor.

And on C28, the ground pin is going to be the negative pin, the side with the grey strip (the polarity marking on the PCB being covered by the cap), right?

There's also a plated through-hole marked GND right next to C28 (and next to 3 other through-holes, marked V5, AV-, and AV+). That seems to show zero resistance to the groundplane as well. Could I use that instead of R20? I've already partially mounted the LCD, so that hole is going to be easier to get to than R20, and it's right next to C28.

Thanks so much for your help.

Cheers,
Tony
jye1
Posts: 1221
Joined: Wed Feb 20, 2013 4:58 pm

Re: I may have lifted JP9 - What do I do?

Post by jye1 »

The positive pole of C28 should be its ground pin. This is digital ground. You can use the pad marked GND for this digital ground. The ground pin of R20 is analog ground. You can connect analog ground to digital ground using the ground pads mentioned above.
amocjr
Posts: 9
Joined: Sun Aug 06, 2017 1:20 am

Re: I may have lifted JP9 - What do I do?

Post by amocjr »

Ah, ok! So, I can connect the grounded side of R20 to the nearby GND pad/hole, then. That should be easier than connecting R20 to the positive pin on C28.

Thanks for the help. I'll give it a try this weekend.

Cheers,
Tony
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