Problem Programming PIC18F2550

[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.

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

Are you kidding or are you serious?

[Firelord]

Are you kidding or are you serious?

I'm dead serious -- that's what you yourself suggested in the 'Buying components' section (if you follow the link to Farnell): CAPACITOR, 470NF, 50V. What's wrong with it?

[dmitri]

Are you kidding or are you serious?

I'm dead serious -- that's what you yourself suggested in the 'Buying components' section (if you follow the link to Farnell): CAPACITOR, 470NF, 50V. What's wrong with it?

I only suggested that it should be 470nF. In the Farnell link it also says "Dielectric Characteristic:Z5U" but it doesn't mean I suggested that it should be.

[Firelord]

I only suggested that it should be 470nF. In the Farnell link it also says "Dielectric Characteristic:Z5U" but it doesn't mean I suggested that it should be.

Fair enough. But you did not answer my question.

[dmitri]

I only suggested that it should be 470nF. In the Farnell link it also says "Dielectric Characteristic:Z5U" but it doesn't mean I suggested that it should be.

Fair enough. But you did not answer my question.

I think I did. But I can re-phrase - in this case voltage rating doesn't matter just like dielectric characteristic, temperature range and etc.

[Firelord]

I think I did. But I can re-phrase - in this case voltage rating doesn't matter just like dielectric characteristic, temperature range and etc.

All right, but then why did you say this:

Are you kidding or are you serious?

It made me think that I made a fatal mistake with that cap. Anyway, I think there's no sense in discussing this anymore until I investigate further into the circuit.

[dmitri]

All right, but then why did you say this:

Are you kidding or are you serious?

Because the highest voltage anywhere on the board is 5V.

[Firelord]

You think that was weird -- check this out. I've unsoldered the capacitor and there was still a positive voltage floating around on the pin without the PIC! Then I found out that even poking the meter's terminals around the pins on a surface with NO COPPER AT ALL did show up on the meter as some positive potential (0.5...0.9V). When the power is disconnected the resistance between any point alive during power-on is not exactly infinite on the 2-20MOhm scale, for different points it ranges from 0.5 to 1 MOhm.

For soldering components on the PCB I used soldering grease DIN 8511 F-SW 21. Could the remains of it possibly obtain conductivity when the power supply is connected? Seems like total crap, but hey -- I've heard stories about glycerine having those abilities (some people use it for tinning the board). And I greatly doubt that there's copper remaining after the etching process...

[jman 31]

I have had weird results when I haven't cleaned a board after soldering. I would clean it really well with some isopropyl alcohol (min. 91%) and get all the traces of flux off of the board.

[dmitri]

As long as the resistance between any of PIC's pins is above MOhm I don't think it should effect its operation, especially so for pin 14.