Need help troubleshooting cob build

Randomblame

Randomblame

Well-Known Member
Sureshot2 said:
Alright so I swapped the drivers over and both drivers lit the working string of lights so the drivers are fine. I went ahead and disconnected the fourth light from the working string and starting subbing lights from the other string one at a time and found that only 1 of 4 lit. Thinking this was odd, I removed all the cobs from the holder and took the 3 that didn't light and put them in a holder from one that worked... aaaand .... they all lit. So as I suspected there's some bad connections between the tabs in the holder and the cobs for some reason(tried moving the wires around to make sure it wasn't a loose wire going into the holder).

I did notice that the small metal tabs seemed to be slightly pushed to the side, but I don't think this was caused by me as I attached them all the same, and have had no problems in the past building other cob fixtures. Not sure if maybe they got bounced around in the mail and bent and I didn't notice or what, but that seems to be the issue. I haven't tried using the ideal holders over the bjb ones but now I'm wondering if maybe those ones have a better build quality/QC ?

On a side note, while testing all the cobs I noticed that one of them had 3 or 4 rows on one side not working. To be honest I have never really checked all my other cobs for this since they are so damn bright, but is it relatively common to have dead rows?
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The defective COB should be the reason! Did the defective string work with the other driver? You can sort out the defective COB and try to fire up the other three. If it's working you did find the culprit.
COB's are sensitive!
You only have to slide over the carpet and touch a COB, the rest will do the electrostatic charge. Better be earthed with an antistatic bracelet, like the PC builder have.
Ceramic COB's are the most sensitive and also break easily like egg shells!
A narrow, not visible hairline is already enough to break the circuit inside the COB.
 
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Sureshot2

Sureshot2

Well-Known Member
Randomblame said:
The defective COB should be the reason! Did the defective string work with the other driver? You can sort out the defective COB and try to fire up the other three. If it's working you did find the culprit.
COB's are sensitive!
You only have to slide over the carpet and touch a COB, the rest will do the electrostatic charge. Better be earthed with an antistatic bracelet, like the PC builder have.
Ceramic COB's are the most sensitive and also break easily like egg shells!
A narrow, not visible hairline is already enough to break the circuit inside the COB.
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I think you may have misinterpreted my post? I have already found the culprit to be faulty cob holders, not the cobs themselves. The "defective" cob you are speaking of still lights in the non faulty holders, it just has several rows that aren't lighting, making it dimmer than the rest of them.
 
Randomblame

Randomblame

Well-Known Member
Sureshot2 said:
I think you may have misinterpreted my post? I have already found the culprit to be faulty cob holders, not the cobs themselves. The "defective" cob you are speaking of still lights in the non faulty holders, it just has several rows that aren't lighting, making it dimmer than the rest of them.
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Okay, my bad!
Happy you figured it out..
I would try to get a new one for the faulty one.
 
Sureshot2

Sureshot2

Well-Known Member
So I went ahead today and wired the four cobs with new holders and wire, and what do you know, it still isn't working. I took a meter and checked the voltage along the path and found it was getting power across each holder, and also confirmed there was no accidental grounding somewhere. Each of the four cob chips was tested and worked on the other string, as well as the four new holders working. The driver on the non working strip also lit the other string just fine so again that is ruled out.

Here's what I found though: If I jump the last cob in the non working string the remaining 3 light and work perfectly fine - remove the jumper and they all turn off. I tried swapping a different (working) cob chip into that fourth holder and still it wont light unless I bypass it. The only thing I can think of is if the metal tabs that contact the cob pads are making a poor connection or are not contacting at all internally.

EDIT: removed the fourth holder from the string and contacted the wires directly to the cob and all four chips lit. Not sure what is going on with these holders but either this was from a bad batch or there's some serious QC issues over at bjb. I've confirmed 5 out of 12 holders are causing connection problems. I have never had this problem before with the bjb holders on any of my previous builds.
 
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nfhiggs

nfhiggs

Well-Known Member
Randomblame said:
OMG, how could one understand what you mean !?
I'm not your dude and do not try to make me look stupid. That goes wrong!

"Cud"," sant", "lolo", " pong" and so on" sounds like baby's language, so you are a teletabby?!
Or could also come from "Bibo" from the "Sesame Street"!
Name things by their name, damned!
Nobody wants to puzzling 15min. about your meaning!
It is a "two channel potentiometer" or "stereo poti", not a "6 prong dimmer"! Such a thing don't exsists!

And now I'll give up to tell you anything ..
It seems you are not willing to change something in your expression!
So, sorry...!
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This knucklehead's posts were giving me such headaches I finally put him on ignore. Yes, I was able to figure out who you were replying to even though I can't see his posts.
 
Sureshot2

Sureshot2

Well-Known Member
So what I ended up doing was cutting a small square out of each holder directly over the contacts to reveal them. After doing this I was able to carefully inspect the connection between the contact tabs and the pads on the cobs and noticed that one of the tabs was sticking out too far, and was stabbing into the white part of the chip just after pad. Instead of fucking around with trying to bend the tabs to make good contact I just went ahead and soldered the tabs to the pads on the cobs so that I could still use the holder to mount the cob without using thermal adhesive.

You can see what I did in the pics below. Before soldering on the left.

2017-08-07 23.57 - Copy.jpg 2017-08-08 00.07.13 - Copy.jpg
 
Growcob5

Growcob5

Active Member
Randomblame said:
OMG, how could one understand what you mean !?
I'm not your dude and do not try to make me look stupid. That goes wrong!

"Cud"," sant", "lolo", " pong" and so on" sounds like baby's language, so you are a teletabby?!
Or could also come from "Bibo" from the "Sesame Street"!
Name things by their name, damned!
Nobody wants to puzzling 15min. about your meaning!
It is a "two channel potentiometer" or "stereo poti", not a "6 prong dimmer"! Such a thing don't exsists!

And now I'll give up to tell you anything ..
It seems you are not willing to change something in your expression!
So, sorry...!
Click to expand...
I'm mean no disss there is a six pod. Tanchy. So u can see that if u look up on ebay u fing one or mabey i sand a link

PS what's the difference between audio and stereo
Screenshot_2017-08-06-23-17-52.png
 
GBAUTO

GBAUTO

Well-Known Member
nfhiggs said:
This knucklehead's posts were giving me such headaches I finally put him on ignore. Yes, I was able to figure out who you were replying to even though I can't see his posts.
Click to expand...
Don't you realize that trying to decipher his posts promote mental health.....
 
CobKits

CobKits

Well-Known Member
Growcob5 said:
. If you got a couple destructive ones to you live gotten so many defective chips its not funny
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well as weve seen from your post youre always looking for the absolute cheapest chips you can lay your hands on so thats not entirely unexpected.

good quality cobs have defect rates around 1 in 1000, and most of those even pass datasheet flux spec where most mfrs give +/- 10% on flux. (as the 90% of good rows each absorb the <10% bump in current). if anybody ever has a row out i swap em out no questions asked. ive seen less than 5 bad chips, mfr swapped them for me as well.
 
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