CHAUVET Arena Hazer 3 DMX issue

[indyld]

Yes to solving the intermittent supply to the DMX board first.

Is it a short or actually an internal break in the wiring harness? You can often verify such things with your ohmmeter as a dodgy conductor can display a much higher resistance end to end, compared to the others in the harness which are usually 1 ohm or less.

When measuring, keep the boards connected together at first and choose probe points that mean you are also checking the connector and it's solder joint, such as the nearest component connected to that line. 

Check all conductors in the loom, not just focusing on the chip supply. Also do the same with the DMX port connections if not already done. 

Btw the way to confirm which is the chip supply is by tracing with your continuity tester. Reading voltages and guessing what they do isn't the same as confirming what is connected to what. 

 

Edited December 7, 2022 by indyld

[partyanimallighting]

OK. Update. I changed all the wires in the harness and no matter how much I shook and juggled the harness after, the 5V was constant so that's one problem solved. I don't know what was causing the short because initially I only probed the yellow and black wires but the problem has disappeared although I didn't check the voltages on the RED and GREEN to GND. I also took a clearer picture and some readings. I hope this helps.

 

 

[DrV]

Based on that picture I have been making some wrong assumptions. Is the 5 way connector really that way round? And, unusually, they have used green for +5 and red for logic ground.

If so then the red and green wires are the supply to the opto (you can actually see the tracks right there in the pic).

Secondly, please just buzz out the connections to pins 5 and 8 of the 75176 and find out where they go. No voltages, no power on anything, don't even connect the two boards together. It will be far more informative to verify the circuit before bothering about what voltages are where.

 

Edited December 7, 2022 by DrV

[partyanimallighting]

As requested. There's full continuity on Pin 5 on the 75176 to the BLACK -tive wire terminal and full continuity from Pin 8 to D3 and through the via to R3, C2, R5 and C3 and to the YELLOW +tive wire terminal so the BLACK and YELLOW feed the 75176 if I'm not mistaken and the RED and GREEN feed the opto as the traces do show that.

[DrV]

2 hours ago, partyanimallighting said:

As requested. There's full continuity on Pin 5 on the 75176 to the BLACK -tive wire terminal and full continuity from Pin 8 to D3 and through the via to R3, C2, R5 and C3 and to the YELLOW +tive wire terminal so the BLACK and YELLOW feed the 75176 if I'm not mistaken and the RED and GREEN feed the opto as the traces do show that.

I think you mean C1, not C3.

Next thing is to check where logic ground comes in from the main board because I think you've turned the 5 way connector round at some point. My reasoning for this is that the picture of the Molex connector shows the locking ramp facing the camera. If you look at the picture of the DMX interface PCB the silk screen for the connector shows the locking ramp on the top side of the connector, adjacent to the XLR and not the edge of the PCB. When that picture was taken you had pulled the plastic of the 5 pin connector right off the pins so it could now go on either way round. If you align the locking ramp with the silkscreen that puts the Yellow and Black wires across C3, with the black being the -ve and the yellow being +ve, and it puts the Green and Red wires across the 75176 with the Green being -ve and the Red being +ve. These colour combinations are much more logical.

To verify this, with the power OFF check for continuity between logic ground on the main board and the 5 way connector on the main board. There should only be ONE pin with solid continuity (less than a couple of ohms) to logic ground. The best place to access logic ground would be on the copper fill to the left of the crystal as that fill can't be anything other than logic ground. Whichever pin connects to logic ground is definitely the pin which should connect to pin 5 of the OPTO.

Once you've verified this we can continue with measuring voltages, preferably without putting the chips back in yet. However, both chips may now be toast as they will have had their supplies reversed.

 

1347326365_DMXInputPCB.JPG.342535778b6b351335ff302aab15bb84.jfif

[partyanimallighting]

I very much doubt that I would do something like that as I always carefully label terminals to their respective cables before removing but maybe I made a mistake through pure frustration. The terminals on the mainboard are correct as they are all oriented in the same direction but you're saying your concern is with the 5 pin Molex on the DMX PCB and not the mainboard. Yes, I did remove the Molex plastic terminal completely to retouch the solder points and I did replace all the wires in the harness but I was sure to put the wires back in the correct orientation. The Molex connector even lines up with the rectangular shaped etching on the DMX PCB as the Molex pins are a little offset from center and if it's reversed it would be noticeable but anything could have happened due to the length of time I've spent on this unit trying to get it up and running. I'll connect the harness to the mainboard and check for logic ground as you suggested and report back in a bit.

[partyanimallighting]

I just scraped a little patch on the copper fill next to the crystal to test. You didn't confirm if you meant my left, your left or left of the crystal but I took the readings 🙄. There's no continuity on RED, BLACK or YELLOW but there's a beep then a reading of 400 on the GREEN (capacitor in the line?) and 644 on the WHITE (no beep). Just in case, the picture shows the area next to the crystal that was scraped to take the reading. Your comment about me probably reversing the Molex connector really put some doubt in my mind so better safe than sorry.

 

 

[DrV]

That was the correct place to probe logic ground. There has to be a solid connection between there and one pin of the 5 pin connector (on the main board). Until you can establish which pin that is I can't go any further. Check your meter probes are clean and you get a reading of less than say 5 ohms when you short them together then check again for where the logic ground is on the connector.

[timsabre]

There's definitely something weird about the order of the connections in that cable.
From your pic it looks like the left two pins (which you have labelled Red+Green) are the supply to the opto, the middle one is the decoded+optoisolated DMX data signal, and the right hand two are the isolated supply to the 75176.

You've remade that cable, are you sure you have remade it correctly and not mirrored one end?

Edited December 8, 2022 by timsabre

[partyanimallighting]

OK. And big OOPS here. You guys are pretty sure about what you're seeing and I'm the novice so I try to follow instructions to a T. timsabre, I removed each cable individually when I was rebuilding it so I am sure that the orientation is correct. DrV, you put some doubts in my mind about the orientation of the Molex terminal on the DMX PCB and I did admit I wasn't sure in a post above but unfortunately I don't have a picture of the cable in the PCB to confirm. I retested again at the logic ground and the terminals twice and got the same readings so I removed the mainboard completely and soldered a pin to the point and reassembled and took readings again and, as expected, you guys were right and I'm getting solid continuity at the RED wire unlike my previous tests before. I'm not ashamed to admit that I might have connected the Molex in the wrong orientation and once you confirm, I will willingly admit I made a faux pas. So, first things first, reverse the Molex connector on the DMX PCB, right? Then, as DrV stated, the chips are probably toast and I'll have to replace them. Another question, would any of the other components (resistors, diodes, caps) have suffered damage due to my error?

[DrV]

There are clamping diodes on the 75176 inputs. Those might have been damaged, but with the chips off the board and with it disconnected from the main board you should be able to use the diode test setting on your meter to check them. They should read O.L. one way round and about 0.5 - 0.7V the other way round.

[partyanimallighting]

I tested all the diodes and they are fine. I also tested the resistors and all seem fine except for R4 and R8 (154) and I think the reading's a little low at 129k and 137k respectively but I'm not too sure. Just to confirm, I'm just waiting on some feedback confirmation before I reverse the Molex connector as I don't want to do more damage that I've probably already done.

 

[DrV]

Yes, reverse the Molex connector. Confirmation that it's wired correctly will be if you measure a good low resistance between logic ground on the main board and pin 5 on the opto.

And when measuring, be sure to press hard and twist the probe slightly to be sure it's contacting well.

 

[partyanimallighting]

I reversed the Molex on the DMX PCB (note that the 75176 and the opto are still removed from the PCB) and I'm not getting any continuity from the logic ground pin to any solder point where the opto sits. I then removed the harness from the mainboard to test directly from the wires in the Molex and I am getting continuity from PIN 5 on the opto seat to the BLACK wire and from PIN 6 to the WHITE wire and PIN 8 to the YELLOW wire. The only continuity I am getting on the RED wire is to PINS 2, 3, 4 and 5 on the 75176 and I know these are not the readings you were expecting. Now, as I mentioned before, I very much doubt that I originally put back the Molex connector in the wrong orientation on the DMX PCB but I could be wrong. I do know the harness wiring is correct after I rebuilt it so let me know if there's a next step. From what I can tell of the overall problem, the original problem was caused by a faulty current feed to the DMX PCB because of the damaged harness which was a problem I only managed to stumble upon. That problem has been resolved so now the issue seems to lie solely with this DMX PCB and it's correct wiring but I could be wrong.

 

 

Edited December 9, 2022 by partyanimallighting

[partyanimallighting]

If you look at this image of the original 3 PIN DMX PCB and the5 PIN DMX input you can see traces of the glue from the factory are on the outside of the Molex connectors at the bottom so I honestly believe that it was in the correct orientation and should not be reversed but I have to go with your advice.

 

 

Edited December 9, 2022 by partyanimallighting