Problem Programming PIC18F2550

[Firelord]

No reading, it is not connected to anything in this case and so consequently you should read infinite resistance between this pin and any other point/pin when PIC is out.

That's right. Pin 14 is connected to the ground through a 470n cap. When I power on the board via USB without the PIC in its socket, I get a falling voltage reading between pin 14 (of the socket in this case) and ground -- as far as I know that's the capacitor discharge and is normal, right?

[dmitri]

No reading, it is not connected to anything in this case and so consequently you should read infinite resistance between this pin and any other point/pin when PIC is out.

That's right. Pin 14 is connected to the ground through a 470n cap. When I power on the board via USB without the PIC in its socket, I get a falling voltage reading between pin 14 (of the socket in this case) and ground -- as far as I know that's the capacitor discharge and is normal, right?

If there is no PIC in the socket then there is nothing to charge the capacitor so there should not be any voltage at all unless you set your meter to a resistance measuring mode which you mustn't do with a powered board.

[Firelord]

unless you set your meter to a resistance measuring mode which you mustn't do with a powered board.

Look, I may be quite new to manufacturing PCB's and flashing MCU's, but I'm not completely new to electronics in general and am able to handle the meter. The reading between ground and socket pin 14 usually starts at about 1.1V and is falling at about a 0.02V/s rate.

[dmitri]

unless you set your meter to a resistance measuring mode which you mustn't do with a powered board.

Look, I may be quite new to manufacturing PCB's and flashing MCU's, but I'm not completely new to electronics in general and am able to handle the meter. The reading between ground and socket pin 14 usually starts at about 1.1V and is falling at about a 0.02V/s rate.

To be honest, I don't know what to say.

[Ken Forgettable]

unless you set your meter to a resistance measuring mode which you mustn't do with a powered board.

Look, I may be quite new to manufacturing PCB's and flashing MCU's, but I'm not completely new to electronics in general and am able to handle the meter. The reading between ground and socket pin 14 usually starts at about 1.1V and is falling at about a 0.02V/s rate.

Then check the onboard regulator and associated cap's too - got the power jumper off?

[dmitri]

Then check the onboard regulator and associated cap's too - got the power jumper off?

He is not using Synthex's PCB.

[Ken Forgettable]

Then check the onboard regulator and associated cap's too - got the power jumper off?

He is not using Synthex's PCB.

Then I think he needs a fresh battery in his meter

[Firelord]

To be honest, I don't know what to say.

Never mind, I appreciate your helping efforts. But I usually get these non-trivial problems, most of them rather challenging (at least they seem to be at first). If I find the reason for this strange board behaviour, I'm going to publish it here.

Then I think he needs a fresh battery in his meter

Much to my regret that's not the case. The second meter that I have here gives a slightly different reading but still -- the voltage between gnd and 14 pin without PIC in the socket is not 0V somehow.

[dmitri]

Forget about measuring voltage on a capacitor which has only one pin connected, it's pretty pointless exercise - it can be a charge from a static electricity, cosmic x-ray and etc. What matters is that pin 14 has infinite resistance to any other pin/track/point and that the capacitor's value is between 200nF and 500nF.

[Firelord]

Forget about measuring voltage on a capacitor which has only one pin connected, it's pretty pointless exercise - it can be a charge from a static electricity, cosmic x-ray and etc. What matters is that pin 14 has infinite resistance to any other pin/track/point and that the capacitor's value is between 200nF and 500nF.

What about the cap's voltage rating? I use a 470nF 50V cap in there.