partyanimallighting

OK. I'll order one online. I hope there will be a positive update in a few weeks when it arrives and it's installed.

Well, no need to test via DMX I suppose. I tested for voltage at the WHITE wire from LOGIC GROUND with the battery test. 4.9V both ways. No voltage drop at all. Does this once again point to the OPTO?

I took some more readings so here goes. NO OPTO CHIP. POWERED ON OPTO PINS 6 +tive and 8 +tive 5V (PIN 5 -tive probe) 75176 BATTERY TEST PIN 1 +tive 4.5V (PIN 8 +tive 5.1V) BATTERY TEST REVERSED PIN 1 +tive 0.155V (PIN 8 +tive 5.11V) This seems to be correct to what you said to expect via the battery test. WITH OPTO INSTALLED. POWERED UP. 75176 BATTERY TEST PIN 1 +tive 4.6V (PIN 8 +tive 5V) BATTERY TEST REVERSED PIN 1 +tive 0.4V (PIN 8 +tive 5V) OPTO WITH BATTERY TEST PIN 1 +tive 0.1V PIN 8 +tive 5V OPTO WITH BATTERY TEST REVERSED PIN 1 +tive 5V PIN 8 +tive 0.19V The voltage from logic ground to WHITE wire is 4.9V. I hope this helps. Question. Is there the possibility that the display for this unit is maybe not holding the DMX address? Could this be an possible cause to the "no DMX" issue?

Of course you should ask. It's been a lot of posts but the orientation would have been correct. And after replacing the opto I was sure to clean up the solder points. I'll go through the process again and report back here.

I metered the OPTO for continuity first and every pin is OL from PIN 3. I then checked resistance from PIN 3 -tive as you requested and, as you said, OL across all pins except for PIN 2 (0.9 M ohms). I then ran a diode test across PINS 2 and 3 and got 1.29 and OL. Are these readings consistent with the OPTO being fried?

I tested as you asked with the new 75176 installed (no OPTO) and without powering up I checked voltages at the DMX solder points PINS 2 and 3 and got 1.6V as expected from the battery and 0.37V and 0.35V with the battery wires normal and reversed respectively. On powering up, at PIN 5 -tive and PIN 1 +tive it reads 4.65V and with battery polarity reversed it reads 0.135V so this seems correct based on what you stated to expect. I then installed the OPTO and checked voltages from the battery at the DMX solder points PINS 2 and 3 and got 1.6V and without powering up I got 0.14V and 0.27V at PINS 1 and 5 on the 75176 respectively with battery leads normal and reversed . On powering up, at PIN 5 -tive and PIN 1 +tive it reads 0.196V and with polarity reversed on the battery it reads 0.39V so it seems that the OPTO is "dragging down" the voltage. Just to be sure I then tested via DMX control and still nothing. I then removed the OPTO to double check the voltages at the 75176 and got the correct readings as before, 4.65V and 0.135V respectively. I then tested the voltage from logic ground to PIN 3 on the Molex and that's 4.9V. Soooooo.....is the OPTO the guilty component and do I order a new OPTO?

OK, the 5 PIN Molex was changed out completely and I reconnected the mainboard and the 5 PIN harness to check for for continuity to logic ground and the other connection points for GREEN, WHITE, BLACK and YELLOW at the opto and 75176 pin seats and all is fine, full continuity all all relevant points even with the harness wire jiggled wildly. I then powered up and checked for voltages at PIN 5 and 8 on the opto seat and PIN 2 (3,4, and 5) and 8 on the 75176 and both give good readings of 5V. Do I replace the chips and test? Could that faulty harness have caused me two weeks of stress?

OK. I'm happy that I did not make the error of reversing the Molex connector but I firmly believe that the original problem was that hard to find short on the 5 PIN harness. I was doing some measuring as you requested and the problem popped up again and on checking, the insides of a couple pins had a little corrosion so I'll change out the Molex terminal on the mainboard completely to resolve the problem once and for all. New terminal. New harness wires. I've traced the 5 wires as requested to their continuity points on the pin terminals for the 75176 and the OPTO and took the pix as requested. My next step is to remove the old cruddy Molex connector on the mainboard and replace it with a new connector to get rid of the short once and for all. Then, if you guys think I should, I'll replace the opto and the 75176 and test. I suppose if there's still an issue with the DMX function, the chips are fried. I'll be able to source a 75176 easily but the opto will be a problem to source locally. Let me know what you think will be the best way to proceed. And thanks for all the help so far. I've once again learned a lot!

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.

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.

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.

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?

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.

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.

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.

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.

Quick question. Shouldn't I first of all be sorting out the short in the harness that causes the fluctuating voltage at the yellow and black wires? I'll replace the existing Molex connector but I don't see how this will help and the original one seems to be fine and I'm figuring that the short when the harness is jiggled is caused by a bad solder point on the mainboard terminal but I touched these up already. Or maybe components feeding the RED and GREEN wires? I also just checked the voltages at the other 3 wires (with the second meter in the yellow/black on the shorting harness) and I'm getting 4.98V from both the RED and the GREEN to chassis ground on the mainboard and I'm also getting 4.6V from the RED and GREEN to pin 5 (-tive GND) on the optocoupler so that's the voltage that feeds the 75176, correct? . . . . . . . . . . I'm lost. I'm just not sure how to proceed. Try to find the cause of the short? Replace the Molex? What if it's a component feeding those 5 wires that's causing that fluctuating voltage?

Hi indyld, just a note, I did not test with a known working DMX PCB but everything basically is correct otherwise. This seems to be dragging on forever and consuming a lot of my time when available and more unreasonably, your time. I did pull the 75176 from the DMX PCB and voltages were 0.9V at pin 1 and 1.1V at pin 8. This was before I discovered what may be the reason for the low and fluctuating voltage coming into the DMX PCB. I got the problem without the DMX PCB plugged in with voltages ranging from 1V to 4.5V so I decided to change the LM7805. I then tested the voltages at the harness and got a steady 5V so I figured, problem solved. So I plugged in the DMX PCB and as I touched the harness the voltage dropped and started to fluctuate. I jiggled the harness wire and I got it into a position where the voltage remained at a steady 5V so the harness appeared to have a short of some kind and these types of shorts I think are the worst type to find. One minute you're fine. Next minute, nothing. So I tested the harness for continuity and flexed it every way but no shorts. I then pulled the mainboard and resoldered the solder points at the Molex terminal and all other components close by (3 capacitors and a transistor below the LM7805) and just to be sure, I replaced the yellow and black wires in the harness. I then reassembled and tested and got a steady 5V........until I touched the harness and the fluctuation started again. I finally got the harness into a position where the short disappeared and clamped it securely in place. I then put another meter into the harness to confirm a constant 5V into the DMX PCB and then connected the hazer via DMX to a console. With the second meter reading a steady 5V with the harness clamped, I tried control via DMX and nothing, no output. I then tested voltages at the 75176 and got 5V at pin 8 and 3V at pin 1 (pin 5 test probe -tive). Should I now think maybe it's the mainboard with that frustrating short? 5V in at pin 8 should be the correct reading but maybe 3V at pin 1 is a little low? Also, could a faulty component on the mainboard cause the fluctuating voltage at the harness? I can't see how but I'm really guessing here now. The 5 pins were resoldered and wires replaced and the short is still there but I could always remove the Molex connector completely and solder the harness directly to the mainboard. I did change only 2 of the 5 wires. Could a short in the other wires carrying DMX signal cause a faulty component to short and cause this? I'm really guessing here now and it seems that all I'm doing is passing on my frustration onto you guys with these way too lengthy posts.

Sorry about that. I wasn't clear above. I'm not getting anything near 5V from pin 5 (gnd) to pin 1 or pin 8. From pin 5 to pin 1, 0.9V, from pin 5 to pin 8, 1.1V with the -tive probe at pin 5 (gnd). This is a 75176 that was taken off a tested working PCB so it should be fine but.... If required, I could replace this 75176 with another tested working one but I'll still retest this original component when it's removed. Obviously, with the 75176 not outputting 5V, nothing will work and something on the PCB is causing the short as the terminal outputs a steady 5V when the PCB is not connected and all you guys suspect that 75176.

I just reconnected the PCB to the unit to retest and the readings with the 5 pin harness attached to the PCB are fluctuating around 1V and at pin 1 0.9V and at pin 8 1.1V on the 75176. When I powered down the unit and removed the PCB completely and retested at the black and yellow harness wires, I got a stable 5.07V. Once the PCB was reconnected that voltage dropped back down to >1V so there's something sketchy on the PCB itself. I hope this helps.

Hi DrV, I did as requested and the voltage to the optocoupler was the same as those on the yellow and black harness wires as expected. I know that the 3 pin Molex is just a signal feed from the 3 pin DMX PCB to the 5 Pin DMX PCB and there were no voltage readings on this harness and there are no components on the 5 pin DMX PCB but I've still attached pictures. I suggest you verify that by checking continuity between pin 8 on the 75176 and the + pin on the 3 pin connector, (PROBE - at RED terminal wire OL. I'm assuming this is because the solder trace passes through diode D3. Probe + at RED terminal 612 ohms and continuity is fine across all solder traces from the 3 wire harness back to DATA+ input and output) then check continuity between pin 5 on the 75176 and either the - pin or the gnd pin. (PROBE - at BLACK terminal 701 ohms. PROBE + at BLACK terminal OL). I also removed the 75176 and the optocoupler to take pictures of the solder traces if this will help you guys. So from what I can ascertain, the 3 pin harness has nothing to with powering the PCB and only carries the DMX signal to the 5 pin DMX INPUT/OUTPUT PCB but with my limited knowledge of components and how they work I could be wrong. If the 75176 feeds the DMX signal directly to the harness wires then I should a reading from pin 5 on the 75176 to GROUND and I'm getting 200 ohms as the solder trace for DMX PIN 1 passes through R1 (200). I also checked all the small components and I'm getting continuity in one direction only on R3 and R8 and no continuity in either direction on R6 (202) but I'm getting a reading on R6 of 1.98 Kohms and not 0.202 and this I find to be strange. Why would I get a resistance reading but no continuity or am I not taking a correct reading? Please go easy on me. Every time I post it's a learning experience for me.

So based on your advice, even though the voltage is a little low, 4+ volts compared to 5+ volts, I should concentrate on the DMX PCB and ignore the mainboard. I'll power up and check voltages on the optocoupler first. According to the datasheet, pins 5 and 8 are ground and voltage in so I should get 5v (or rather 4+ volts) at these pins. If I don't get voltage at pins 5 and 8 of the 75178 that will point to a faulty optocoupler. Hope this sounds correct...... Is checking the voltage on the 3 pin Molex really necessary? It seems to be only a harness to feed the DMX signal from the 3 pin XLR input/output to the 5 pin input/output below.

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?

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??