Repairs to fog machine

[partyanimallighting]

Hi everyone, I'm back again with a problem that I'm having with a large fog machine that is used for concerts and large stage . jobs. The unit consists basically of a heater block, a pump that forces the fog fluid through the heater block from a fluid reservoir bottle, and a circuit board which controls the unit manually or via DMX. When the unit is plugged in, the display on the remote will state "WARMING UP" and, once the heater block reaches the appropriate temperature, the display will then display "READY TO FOG". When the MANUAL button is pressed on the remote, this switches on the fluid pump and the fog fluid is forced through the heater, creating a dense cloud of fog. The unit however, seems to have a problem with the pump output. When the MANUAL button is depressed, the pump does not output at full output and barely pulls fluid from the reservoir bottle. I tried bypassing the circuit board completely and I hooked up the pump directly to a 110V supply and it works fine so I believe that the pump output on the circuit board may be faulty. I checked the voltage at the pump terminals with the pump removed from the output and I am getting 110V whether or not the MANUAL button on the remote is depressed. I then hooked up a small 30W 110V lamp to these terminals and the lamp lights when the MANUAL button is depressed. I also removed the pump completely, disassembled. serviced and reassembled it and it works fine with a direct 110V input. Any ideas?

 

[KrisBlueNZ]

Can you show us a close-up of the board covering everything between the AC mains input and the output to the pump?

 

[shrtrnd]

Yes. It sounds like you know the pump pretty well. Your problem is most likely on the electronics printed circuit board. Looking at the board would be helpful.
You don't happen to have a schematic of that board, do you?

 

[partyanimallighting]

 

[partyanimallighting]

I hope this image helps.

 

[partyanimallighting]

Can you show us a close-up of the board covering everything between the AC mains input and the output to the pump?

 

[partyanimallighting]

 

[partyanimallighting]

Hi guys, I hope you receive the images of the pcb with the back mirrored and the schematic I received from the company.

 

[Gryd3]

Is it at all possible to see your board.
Are there any visible signs of damage?

 

[KJ6EAD]

Based on the testing you've done and the corrosion present on the base plate, I'd suspect a fault in the pump cable/connectors.

 

[KrisBlueNZ]

I guess you should check the cable from the board to the pump, but with those symptoms I think it's more likely to be the triac (Q5, BTA16) or the optocoupler that drives it (PHOTO2, K3023), or perhaps R25 (1k 1/2W).

Most likely Q5 isn't triggering until quite a long way through the cycle, so the mean voltage to the pump is quite low.

You can measure R25 in circuit (with the power off, of course). You should probably also measure R19 (also 1k) in circuit with power off, and check that there's 5V at the end that doesn't connect to PHOTO2, relative to the circuit's GND rail, when you push the Manual button.

If all of that is OK, you could try swapping Q5 between boards, or just replace Q5 and PHOTO2. If you can't get a K3023 (it's a Vishay part), you can use an MOC3023 from Fairchild or ON Semiconductor.

 

[partyanimallighting]

Hi Kris, I checked R19 (0.975K) and R25 (0.987K) and these readings seem to be fine. What's the next step? Do I check for the 5V at R19 with the machine heated up and with MANUAL button depressed? I did a little research on how a triac functions and, I see from the YouTube video, that it's basically a switch to send 110V to the pump when it receives a signal, which comes from the remote. If the triac, BTA16 is faulty, is there a way I can check it with a meter? I did a lot of repairs to some 4 channel dimmers recently and the problem with all of the non-functional channels was either no output or leaking 110V directly and the BTA16 600B triac was the cause of the problem with all of these dimmers. Quick question. From the video, I saw that the triac sends output in two directions. So, on the dimmers I repaired recently, if there was no 110V at the output, one switch side of the triac was faulty and, it there was a constant 110V at output, the other switch side of the triac was faulty. Am I correct here? Also, what does the optocoupler do exactly?

 

[(*steve*)]

I would try shorting the output of the opto coupler (effectively connecting the 1k resistor directly to the gate of the triac.

Briefly power up the circuit. If the pump runs at full speed, then the triac is triggering.

The next step is to disconnect this short, and apply 5v through the resistor at the input of the optocoupler. Thu pump should again run at full speed when briefly powered up.

You need to be very careful carrying out these tests as you are operating either on or very close to mains power. Do all changes with the device switched off and unplugged.

 

[KrisBlueNZ]

Good advice Steve. The optocoupler output you need to short out is pins 4 and 6. If you want to feed 5V into the left hand end of R19 you should first disconnect it from whatever it's connected to. It may be simpler to press the Manual button and measure the voltage.

 

[partyanimallighting]

Latest development. I've got three of these pcb's at hand and I've done some swapping out to see what exactly could be the problem. Let's start with PCB 1. This is a brand new PCB I found this morning, still wrapped up in bubble wrap direct from the company. I installed this and the unit did the norm, "WARMING UP" then "READY TO FOG" and, when I pressed the MANUAL switch, the unit did output, not powerfully, definitely not the loud noisy burst it would normally output. PCB 2 is the original PCB and with this PCB installed, the unit did the norm and heated up fine. Again, the output was not up to par. I have another one of these fog machines that's working fine, so what I'll do before any further testing and shorting, is swap out the pump and PCB from this working unit and see how it goes. When I'm done I'll post my findings and you guys can advise me accordingly. One other thing, the pumps work fine with a direct 110V current, outputting very powerfully, but the output from the machine normally starts off slow and builds up (this is not happening, the output is way below par) and the output is normally adjustable, from a small misty output to a large dense burst like a cloud, depending on the intensity adjustment. Lastly, with PCB 3 installed, I'm getting a "WARMING UP" reading in the display but it does not go to 'READY TO FOG" at all. Sometimes the thermal overload trips, cutting off the voltage to the heater and sometimes, when I unplug and plug back in the unit, the display states "READY TO FOG". So this particular PCB has some issues but we'll leave that for another time. Talk to you soon..................

 

[KrisBlueNZ]

It's possible that the control board doesn't simply produce an ON/OFF signal to the optocoupler. It may be using "phase angle control", as used in dimmers for incandescent lights. It might do this if it needs to vary the pump speed for some reason. Measure the voltage on the left end of R19 relative to the circuit's 0V rail. If it varies smoothly over a range of voltages, rather than being either 0V (for pump OFF) or about 5V (for pump ON), then the board is probably using phase angle control. In that case, any of the input signals coming from sensors (e.g. temperature sensors) could have a problem, and could be causing the firmware to fail to drive the pump properly.

 

[partyanimallighting]

It's possible that the control board doesn't simply produce an ON/OFF signal to the optocoupler. It may be using "phase angle control", as used in dimmers for incandescent lights. It might do this if it needs to vary the pump speed for some reason. Measure the voltage on the left end of R19 relative to the circuit's 0V rail. If it varies smoothly over a range of voltages, rather than being either 0V (for pump OFF) or about 5V (for pump ON), then the board is probably using phase angle control. In that case, any of the input signals coming from sensors (e.g. temperature sensors) could have a problem, and could be causing the firmware to fail to drive the pump properly.

Hi Kris, you're right. The unit would use that "phase angle control" thing to vary the pump speed so you can get a from gentle fog output up to a big burst like a dense cloud. So anyway, I started up the one working unit that I have, tested it for functionality, then swapped out this working PCB with the PCB from the unit with the very low output and the result was the same, low output from the pump. So it wasn't a PCB problem but a pump problem. So I scrapped out and serviced a couple spare pumps that I had lying around and got one to work fine in the unit and it's outputting great now. But........here's my question. The original pump was outputting very low when connected to the pump terminal on the PCB but, when 110V was connected directly to the pump, it worked fine. Can you explain why? And, is there something I can do to prevent this problem from reoccurring in the future?

 

[(*steve*)]

Well, I would be ken to eliminate the triac and the optocoupler. If either of them is faulty it's a relatively simple fix.

 

[KrisBlueNZ]

The original pump was outputting very low when connected to the pump terminal on the PCB but, when 110V was connected directly to the pump, it worked fine. Can you explain why? And, is there something I can do to prevent this problem from reoccurring in the future?

You're assuming that when the board wants to run the pump at its standard speed, it feeds the full-cycle 110VAC into it, so if the pump works on 110VAC it should run at the same speed when powered from the board, when you press the Manual button.

I suspect the board's standard drive to the pump is not the full-cycle 110VAC; this would be reserved for some kind of "overdrive" feature.

To prevent this problem in future, you could keep a known good board for testing pumps with, rather than testing them by connecting them directly to 110VAC, or you could keep a known good pump that you can connect to 110VAC and compare with the suspect pump running directly from 110VAC.

 

[KrisBlueNZ]

Sorry, I didn't read your question properly.

I think it's quite possible that a pump could be faulty in a way that causes it to barely run at all when powered from a phase controlled signal at, say, 50% power, while it would still run at full speed if powered from a 100% AC signal. So if a suspect pump performs the same as a known good pump when they're both powered directly from 110V, that doesn't necessarily mean that the suspect pump will perform the same as the known good pump if they're both driven from the board.