Express with seven segment LED problem

[Jeffl]

I have a new Lynx Express V5 that I'm having issues where the seven segment LED display does funky stuff.  When no DMX signal is present the center display does not work.  When a DMX signal is present is it switches between the center and outside two digits.

I have swapped the RS485 chips, PIC, NXP LED Driver.  Checked all the resistors.  I'm stumped.  This is the first one in twenty that I have had problems with that I can't fix.

Video of it in action.  The first 1:30 shows the problem.  The rest is just showing the troubleshooting process.

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Thanks for your help.

[chrisatpsu]

is this a solder bridge?
bottom right of board, yellow arrow

[Jeffl]

Wow that's looking close.  No it's glare from light and whatever the residue is when you solder.  I had another picture that had one of those that I didn't post because it was really bad.

Thanks for looking.

[SteveMaris]

Jeff,
I may be way off here, but I remember reading a thread regarding the 2700 cap being damaged easily and causing problems.
 sorry, it's all I have to contribute...LOL

[KeithTarpley]

Greetings,,,

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Keith

[Jeffl]

I had this suspicion but I was at a point I needed some professional help.  I soldered all my Expresses so I don't have any spares.  I do need to place a mouser order however.

Luckily I do have a bag of tricks (assortment of caps) that I'm going to see if I have one.

Thanks everyone.

[Jeffl]

The 2700pf cap was the problem.  I took out the 2700pf and replaced it with 2200pf and it works.

I'll order a few extra 2700pf caps when I place my next mouser order and get it fixed properly.

Thank you everyone for your help.

[SteveMaris]

Yay!

[Jeffl]

Tested the rest of the batch.  One more with the same problem.  I'll wait to fix this one until I get some replacement parts.

I'm curious if I soldered it too hot or what.

[chrisatpsu]

i heat up the leed, and the hole for about 4 seconds, then apply the solder for only like half a sec to a second, then pull away the iron.
i don't like to keep the iron on linger, cause you never know if that particular resistor or capicitor in the batch might be a little more sensitive to heat.

[Jeffl]

I'm always careful with everything except for the fuse logs, and power connectors.  For those I get out the larger tip and set the iron to about 390c.

It's really nice having people that can help.

Thanks

[comporder1]

I've had the same problem in the past. I have intentionally left that cap a little high off the board since then so it doesn't get too hot.


Sent with Tapatalk/iPhone. Xcuse the spelzing!

[SteveMaris]

I've had the same problem in the past. I have intentionally left that cap a little high off the board since then so it doesn't get too hot.


Sent with Tapatalk/iPhone. Xcuse the spelzing!

After reading the first thread, that's what I do. They mentioned sticking a toothpick under it before soldering to keep it off the board.
I just bend the pins outward to keep it in place 1/8 of an inch off the board before soldering.

[Jeffl]

Thanks for the tip.  I'll try this next time.  I'm also going to order some spares of these parts are are known to have issues because they are usually cheap to pick up when your ordering other parts.  LED's,  caps, PIC, few triacs in case of future problems, fuses etc.

Five dollars of parts that can save the day.

[n1ist]

On some of those caps, the outer insulation (yellow epoxy) goes down the lead enough so that if you put the cap flush against the board, the insulation ends up inside the hole.  Then when you solder it, it doesn't make a good connection.

I have updated the assembly manual with a note to watch out for this; it is OK if the cap isn't flush with the board.
/mike