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FOG MACHINE PCB FAULTY

KrisBlueNZ

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That's odd. It looks like there are NO tracks going to the relay terminals on the top side. Is that right?

If that's right, then both of those relays control the heater, and I can't see any reason why there are two of them.

Have you measured the voltages on the four north end pins of the relays?
 

partyanimallighting

Oct 22, 2012
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Hi Kris, the rail with the diodes reads 12V to ground at heatsink tabs. I checked the voltage from the striped end of the diodes to the transistors and I am getting 12V on the right hand leg of the top diode and 12V at the left hand leg of the bottom diode. From the diodes to ground I'm getting 0V on the top transistor and 0.782V on the bottom transistor. Hope this is helpful.
 

KrisBlueNZ

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I'm not sure I understand.

First, can you confirm there are no tracks running to the relays on the top side of the PCB.

Second, are there any part number markings on the relays?

Thirdly:

Connect your voltmeter black lead to the 7805 heatsink tab.

Connect the red lead to the stripe end of the diodes (they're connected together). You get +12V, right?

Connect the red lead to the non-stripe end of the outermost diode. What's the voltage?

Connect the red lead to the non-stripe end of the innermost diode. What's the voltage?
 

KrisBlueNZ

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Sorry, I was just talking about the six holes at the south end of each relay. There are no tracks to them on the top side, are there?

Can you answer those other questions?
 

partyanimallighting

Oct 22, 2012
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The tracks run as follows:
Inner relay ~
Cathode end of diode to relay pin directly below.
Other end of diode to relay pin directly below.

Outer relay ~
Cathode end of diode to relay pin directly below (inside pin)
Other end of diode - empty (I think it goes to the outer relay pin on the bottom of the pcb)
 

KrisBlueNZ

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Right. And there are no connections on the top side to the six other holes on each relay.
 

partyanimallighting

Oct 22, 2012
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Part number markings on the relay - OZ-SS-112L 12VDC 20A/120VAC 16A/240VAC.

Red lead to the stripe end of the diodes = +12V

Red lead to the non-stripe end of the outermost diode. 12V

Red lead to the non-stripe end of the innermost diode. 0.13V
 

KrisBlueNZ

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OK. It seems that both of those relays are in the path from the mains input to the heater, and both of them are in the opposite state from what they need to be to operate the heater.

The outer (west-most) relay needs to be energised to activate the heater. In that state, there would be 0V on the non-stripe end (the anode) of the outer diode.

The inner relay needs to be de-energised to activate the heater. In that state, there would be 12V on the non-stripe end (the anode) of the inner diode.

Both of the relays need to be in the appropriate state to energise the heater.

So the relays are probably fine; they are just being driven into the wrong states. The relays are controlled by those two transistors north-east of the relays. The transistors are controlled by their base terminals, which are on the east side of each transistor.

The outer relay is controlled by the north-most transistor. The base of this transistor is driven through a resistor that's immediately east of the transistors, which is fed from a track that heads north towards the IC labelled with a sticker that ends with "702". Can you measure the voltage on the north end of that resistor. I expect you will find that it's 0V or close to it.

The inner relay is controlled by the south-most transistor (the one nearest the relays). The base of this transistor connects to a track on the top side that heads up towards the "... 702" IC as well, and connects to a resistor near the small 4-pin IC (probably an optocoupler). Can you measure the voltage on the other (eastern) end of this resistor. I think you'll find it's +5V.
 

KrisBlueNZ

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Thanks for that nice explicit picture. As I thought, the relays are both being driven to the wrong states. The control signals are wrong. These signals come from one or both of the microcontrollers.

The east end of R29 currently has 5V; this should be 0V.
The nnorth end of the resistor closest to the transistors currently has 0V; this should be 5V.

Can you trace these tracks and see where they come from. My guess is they both come from the IC labelled 6608V1-702. (I suspect the other micro may just do the DMX processing.)

So the microcontroller has decided not to turn on the heater. There could be many possible reasons for this, since the micro probably monitors a number of conditions. Obviously it monitors the temperature signal, but there might be others.

Without seeing a schematic and being able to look at the code in the microcontroller, or some detailed technical information on the board, it's not really possible to diagnose the fault any further.

You could try measuring all the semiconductors on the board; semiconductors fail more often than most other types of components. Also you should inspect the board carefully for damaged components, damaged tracks and component leads touching each other (both sides).
 

partyanimallighting

Oct 22, 2012
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Thanks Kris, I'll check carefully and get back to you. Can I swap out the microcontroller from a working pcb to test without damaging it?
 

KrisBlueNZ

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Yes, but the fault may not be the microcontroller itself - it's more likely to be a fault affecting one of the signals that the microcontroller is monitoring.

If the microcontrollers aren't socketed, you should install sockets so they will be from now on.
 

KrisBlueNZ

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Not really. It would be possible to go further if we at least had a schematic, but tracing a schematic from a board isn't easy and requires some experience. With a schematic you can compare voltages on a good board and a bad board and we should be able to figure out which difference is causing the microcontroller to refuse to enable the heater (assuming that's what's happening).

It might be helpful to know the markings under the sticky labels on those ICs, and measure the pin voltages on a good and bad board. But without a schematic it would be hard to diagnose the faulty component.

Have you measured all the semiconductors? Do you know how to check diodes and transistors?

I guess you've swapped both programmed devices over between the two boards and the fault stays with the faulty board?

What external components and devices connect to the board, apart from the heater and the pump? There is a temperature monitor of some kind, right? Anything else?

I can trace out the circuit, but I'm a long way away. You would have to send me two boards, and the external temperature sensor and anything else that's needed (apart from the heater and the pump), and pay me for return postage or courier. Do you know anyone nearby who can do it?
 

partyanimallighting

Oct 22, 2012
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Hi Kris, I'll write the main company and their distributor in the US and see if I can get my hands on a schematic. I'll keep you updated.
 

KrisBlueNZ

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That schematic is a redacted version. It shows some of the important stuff that I'd already figured out, but the details of the microcontroller connections are missing. They are shown as grey boxes, without even part numbers or pin numbers. This schematic has been produced because someone - probably a distributor - demanded "a schematic"; it is not designed to actually be helpful.

I very much doubt that you will get a full schematic. Full schematics are actually considered trade secrets by many companies, hence this sham spam scam schem that you have been given.

You could try answering the questions I asked in post #36. But I think you will need to find someone who can trace out the schematic properly, and make voltage measurements. Without this information it's not really feasible to diagnose the fault.
 
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