Atmega 644 and/or 18F14K50 problem

[funkystx]

The board looks good. However,

1. Remove the green wire on your last photo! Shorting 1 & 3 is only meant for testing the LCD.
2. I don't like how your PIC is sitting in its socket. Carefully remove it, maybe clean the pins with alcohol and place it back.

I know the green wire is just a temp fix, but at least I know for sure that the LCD will display any signal. That mod won't affect any other circuitry, does it?

I removed the PIC with caution, cleaned the pins with alcohol and reinstalled it. I did the same with the Atmega.

I hooked it up to the USB again, but the problem(s) remain. Bummer!

[funkystx]

Hi,

I don't think your boards soldering looks great (sorry Firelord
To bad you have posted 3 pics of the component side and only one of the solder side, the most important one in this case.

You have a lot of "cold joints", that is, yes there is solder on the pin of the component and it touches the circuit-board, but it didn't got enough time to flow and make a good connection.

If you look at your first picture, and look at the third resistor from top, at the left from the Atmega, you see that the solder has flowed trough the board to the top, this is how all your solder joints should look.

So here's what to do, carefully remove your chips from the sockets ( they don't like heat).
Re-solder every pin in the following way;

Put the (clean) tip of your soldering iron on the pad at the same moment add a little more (multi-core) solder, leave the tip at least 3 seconds on the pad, clean the tip of the iron again and move to the next pad.

Repeat the above until all the pads are done.

Inspect the board carefully before placing chips and applying power, even better, post pictures after for evaluation.

Good luck

Rob

I see what you mean. On the bottom side every pin/hole area is completely covered by solder, but it was insufficient to flow to the top side and cover that with solder as well.
I didn't wanted to get overheated components, so I mostly just had brief contact during soldering.
Although my multimeter measurements didn't indicate any bad connections, I'll take your advise and resolder every pin the way you pointed out.
Are you saying I only should redo all those socket pins from the chips, or just any 'cold joint' I can find?

[r0bbie]

Just make sure, solder every pin as discribed.

[Firelord]

I don't think your boards soldering looks great (sorry Firelord

It doesn't look great, but I've seen MUCH worse.

[funkystx]

I don't think your boards soldering looks great (sorry Firelord

It doesn't look great, but I've seen MUCH worse.

I'll take that as a compliment! .. although I'm more of a 'mechanical' guy myself, I like a challenge and it seems I just got a whole lot of that with this project!
I'll work on those cold joints today and make it better. Just to exclude any aspect that might cause this malfunction. Stand by for an update later.

[r0bbie]

Any news?
Please keep is updated!

Regards

Rob.

[funkystx]

Thanks for your concern Rob!

I'm still working on the board .. unfortunately I haven't had much spare time to get things done yet.

I first gave the resistors a try and those cold joints are an easy fix, as you directly see the flowing result on top of the PCB from adding more solder on the bottom.

But the chip sockets are blocking my view to see if I added the right amount of solder to fill it up on top.
If I use just a little too much solder, pins can get interconnected easily and once that happens, I don't think I'll be able to fix that.
Chances are I'll screw it up somewhere along the way, so I'm afraid this job calls for a more experienced hand.

Any suggestions?

[jman 31]

Those solder holes don't have to be filled in on the top side. As long as you have a good volcano shaped joint on the bottom they will be fine. The holes are copper all the way through so they will conduct the circuit for the top traces. It is important to get that good, shiny volcano look as that is a good indicate that you have a clean, well flowed contact.

[funkystx]

Sorry, but I'm getting a little confused here.

In reply to jman 31's comments I can confirm that all joints on the bottom of the PCB have shiny volcano shaped soldering that cover the copper facings completely (photo previously posted in this topic). I have measured all individual components as well as their interconnections with a multimeter according to the schematics. I had no indication of bad connections, shorts, wrongly placed components etc.

Now what about those 'cold joints'? Are these likely the reason why my device doesn't work properly or do I need to consider focusing on other possible malfunctions?
Don't get me wrong as I do embrace quality in my work, but my PCB doesn't need to win a beauty contest. As soon as this problem is fixed, I'll put it in a nice enclosure and hope to have fun with it for a very long time. Like I pointed out yesterday, fixing those cold joints on the IC sockets involves a risk I'd rather not take if I don't have to.

What else is there to investigate / eliminate to get to a solution for my problem?

Just to be clear, I really do appreciate all the effort, wisdom and advise from everyone.
I just had pictured this project to be finished sooner, since the assembly process of the Synthex kit went pretty smooth.
With less spare time now and hardly any progress, this challenge gets a little frustrating for me.

[Firelord]

Ok, here's another suggestion. See if any of the components on the board are getting hot once you plug in the USB cable.

Anyway, it seems to me that for some reason ATmega and PIC are not starting up correctly. They may be in a permanent "reset" state, which can be caused by shorts from solder bridges and flux. Since you occasionally get a recognized USB device the problem is of a "floating", "uncertain" nature, in most cases that's due to flux and/or unexpected floating voltages across the board traces.