CHAUVET Arena Hazer 3 DMX issue

[partyanimallighting]

Hi all. Anyone familiar with the Chauvet Arena Hazer 3? It's your basic fog machine with a fan disguised as a hazer and I've got one that's working fine but only manually via the remote, no DMX function. The mainboard is straightforward, AC in feeding relays which power up the heater, low fluid and thermal sensors and output to the pump. The unit heats up fine but doesn't function via DMX control so I'm wondering if anyone has encountered this problem with these. I took a look at the mainboard and also the DMX input PCB which carries a 75176B transceiver so I'm figuring that maybe the LM7805 or LM7812 on the mainboard is not feeding the DMX input PCB or maybe it's a faulty remote control. I'm just throwing this out there without going into too much details (as yet) in case someone has encountered the problem before, resolved it and can point me in the general direction of a solution. Any feedback would be nice. Thanks in advance.

[timsabre]

If you have an oscilloscope, trace the DMX through from the sockets to the mainboard. It goes into pins 6+7 as a differential signal and should come out on pin 1 as a normal serial data stream. Most likely, in common with all DMX devices, the 75176 has got blown up.

 

[partyanimallighting]

Sorry timsabre, I don't consider myself technically inclined enough to invest in a scope as yet (maybe some day) but I could simply swap out the 75176B with another and see if that resolves the issue. That's a simple enough attempt to start with. There's another 8 pin IC on the DMX input board but I can't identify it because the PCB is coated in lacquer. I was suspicious about the 7805 and 7812 but, seeing that the hazer functions fine in manual mode, I can't see how these can be faulty so that's why I was thinking that the remote/display could be the issue but one of these regulators should be sending voltage to the 5 pin input/output on the DMX input PCB so maybe I should check for voltages at these pins. That DMX PCB has a 5 wire terminal so I'm figuring two wires for + and - and three wires for DMX +, - and data ground. By the way, can you enlighten me? You say that the DMX goes into pins 6 and 7 as a differential signal and comes out on pin 1 as a normal serial data stream. How would this differential signal and serial data stream appear on the scope?

[DrV]

As Tim says, almost certain to be the 75176. At a pinch you could connect a 1.5V battery across the DMX lines (pins 2 and 3) and check pin 1 with a meter. With the battery one way round you'll get 0 volts on pin 1, the other way round you'll get about 5V. But checking it with steady voltages won't verify that it works at 250kbaud. However if it doesn't behave correctly with this test then it's definitely blown up. Probably easier just to change the chip. If you need further help you'll need to post pictures of both sides of the whole DMX board.

[timsabre]

DMX through a scope looks like this at pin 1 of the 75176 (the yellow trace). The long "low" at the beginning is the breaktime which is used to detect the start of the packet

The differential signal into pins 6+7 looks the same except one of them is upside down. Also the signal may be a lot smaller and have noise / wiggles on it.

(picture from https://community.element14.com/technologies/open-source-hardware/b/blog/posts/DMX-explained-dmx512-and-rs-485-protocol-detail-for-lighting-applications

which is a good read for DMX background info)

Edited November 30, 2022 by timsabre

[Muller_Light]

What 'scope have you got, Tim?

[timsabre]

I've got a Siglent SDS1104X-E but that picture isn't mine, however it looks pretty similar on the screen. £379 in the UK, it is a good bit of kit for the money.

[partyanimallighting]

Hey guys, based on what you've advised, I've basically ignored the mainboard and I've focused on the small DMX input PCB with the 75176B transciever. I swapped out the 75176 with another from an old LED PAR mainboard and tried DrV's method using a AA battery and testing at pin 1 and used ground at pin 5. In both instances the two readings were around 0.1V with a very slight increase to around 0.3V when the battery wires were reversed. Now this immediately put doubts in my head that the 75176 from the old mainboard was bad so I took out a brand new LED PAR mainboard, tested it via DMX first, and swapped out the new 75176 onto the DMX PCB but same result. I then cleaned off as much of the lacquer as I could and checked the few resistors and diodes and they all seem to be fine. I'm then started pointing an accusing finger at the 8 pin IC which, with a good magnifier, turned out to be 6N136, a high speed optocoupler. I'm thinking that this controls the voltage coming into this PCB via the 5 pin connector at the DMX output and thus powers the 75176 and maybe this is the problem component. I checked the datasheet and tested across pins 2 and 3 and 7 and 8 and I'm getting continuity both way across 2 and 3 and OL across 7 and 8 which, according to the datasheet, doesn't seem to be correct to me. Am I on the right track here?

 

Edited December 2, 2022 by partyanimallighting

[DrV]

Before going any further,

1) that test I suggested needs to be done while the 75176 has some power on it.

2) when measuring the voltage in the test the -ve lead of your meter needs to be on pin 5 of the 75176

3) there should be 5 volts on pin 8 of the 75176.

If all that was satisfied then my test should work as the enable pin (2 or 3) looks to be grounded.

If you aren't getting 5v on the 75176 then nothing on the DMX board will work.

[DrV]

It looks to me as though the isolated 5V supply for the 75176 is being derived from the incoming DMX signal via R7 & D3. Never seen that before and I can't see how it could comply with DMX512 but surely a company like Chauvet wouldn't do anything like that. Tim, have you ever seen such a circuit? If I'm right then you have to have a DMX stream going into the board for any of the voltages to be correct (and my test is a nonsense)

[alistermorton]

Some of Chauvet's early, DJ level stuff was what you might call low quality. I have a Chauvet DJ fogger which uses standard IEC mains connectors for the remote control. The potential for misplugging is immense. Surely a company like Chauvet wouldn't do anything like that, I also thought, but then my unit is in all probability just a bought in and rebadged cheapo from a generic factory.

[partyanimallighting]

The solder traces from R7 and D3 lead to or feed from the 3 pin Molex connector but this 3 pin Molex only feeds the 5 pin DMX input/output on another board located below this DMX PCB on the chassis, no circuitry involved, only 5 pin XLR in/out terminals. I believe the 5 pin Molex terminal feeds the DMX signal via 3 of the 5 wires back to the mainboard for control and the other 2 wires feed power from the mainboard to this DMX PCB to power the 76176. But I could be wrong. Maybe the mainboard is not sending voltage to this DMX PCB and I have to check that? There's an LM7805 located right next to this terminal on the mainboard. Maybe this LM7805 powers the DMX PCB but maybe it's faulty and is not sending power to the DMX PCB??

[themadhippy]

Quote

Maybe the mainboard is not sending voltage to this DMX PCB and I have to check that

first rule of fault finding check thy voltages,pointless trying to chase a missing signal around a circuit if part of the circuit isn't powered

[DrV]

I think I got it wrong, and I apologize to Chauvet! You need to buzz out the 3 way connector - is it connected to pins 5 and 8  of the 75176?. I guess that it carries an isolated supply to the chip. And, as themadhippy says, check whether that is present.

[partyanimallighting]

Hey guys. I powered up the unit and tested for voltage coming into the DMX input PCB from the 5 pin harness and I'm getting 4.2VDC across the yellow and black wires so I'm guessing that this is from the LM7805 to feed the DMX mainboard and I am assuming that this means that the 7805 is OK. This is the only significant reading I'm getting at the 5 pin terminal fed from the mainboard so does this point me back to the DMX PCB and that optocoupler? I'm guessing that the other 3 wires, RED, WHITE and GREEN are sending the DMX signal from the 751756 on this DMX PCB back to the mainboard for control. Any ideas?