Possible to reverse engineer this PCB heater controller?

[Jay112]

I'm sure this is "possible", but my question is "Is it worth my time and effort?" The manufacturer will sell me a new board for $100, but that seems expensive for such a simple board, especially when I already have all the components. Also this would be a good learning experience for me.

The item in question is a 120v 1,500 watt infrared heater that looks similar to this one, except the one I have has a cord hanging down with a temperature sensor at the end:


This is a picture of the front PCB:


And this is the back (obviously it's much more difficult when the back is covered like this):


The piece missing at the top is a burned out TRIAC (CQ3P-25D). I already have a replacement for that piece. I was planning on just popping in the new TRIAC, but unfortunately it looks like some of the traces got burned out on the back of the board as well, so that's why I'm interested in just re-making the entire circuit if possible.

Items on the board:
-1 large (looks like 2 or 3 watt) 10K resistor.
-4 smaller resistors, measured at 2.7K, 2.1K, 87K, and 42K
-1 analog potentiometer
-1 100uF 64V capacitor
-1 1uF 50V capacitor
-1 CQ3P-25D TRIAC (datasheet: http://pdf.datasheetcatalog.com/datasheet2/8/0ux48tck2xw8d4qyo4eychws54cy.pdf)
-1 V14241U “ZNR” Transient/Surge Absorbers (datasheet: https://industrial.panasonic.com/cdbs/www-data/pdf/AWA0000/AWA0000CE2.pdf)
-1 CA3059 "Zero Voltage Switch" (datasheet: http://www.onsemi.com/pub_link/Collateral/CA3059-D.PDF)

The datasheet for the zero voltage switch contains some example circuit diagrams, like the one below:


The 3 wires coming out of the top of the board are Line, Neutral, and Output to the heating element.

The 2 blue wires coming out of the bottom are for the temperature sensor.

The device changes the heat levels by changing the frequency that it's turned fully on and off. If the pot is set to the highest setting then the heater might stay on constantly, but if you put it in the middle, it'll flash on and off a few times a second, depending on the temperature of the sensor at the end of the cable.

Thanks for any advice!

[Paul Price]

From what you have written describing the operation of the damaged unit, you seem to have a very good understanding on how the device works and this means you should have enough information to put together a circuit that closely duplicates the function of the original or surpasses the original in quality.

Whether you should do this or not depends on your decision on how best to use your time and money and appease your curiosity and will to solve this electronic puzzle. You have to ask yourself if you like solving electronic problems and if it is more worthwhile for you to spend, time on a puzzle or just spend your money to save time?

But, if you decide to hack it and even then you run into problems, you might find a lot of help on this forum and also learn something as well.

[stmdude]

Hard to tell, but it seems like only two traces are burnt.

Everything is through-hole, so maybe you could just beep out the schematic?  Or, everything but the burned traces. With the rest of the schematic, figuring out where the burnt traces went should be easy.

[newbrain]

A good starting point for reverse engineering mght be the application note for the 3059, there are high chances that the circuit is or resembles one of those presented here:
http://www.soloelectronica.net/triac/AN6182.PDF

[Jay112]

Thanks, everyone! You gave me the confidence boost I needed! I guess next I'll try to study the datasheet for the 3059 switch until I can understand how to make a circuit from that, and then go from there.

[Jay112]

This one from the datasheet looks pretty close, huh? 

[Jay112]

Does anyone know what that black coating is on the back of the PCB? If/when I recreate the circuit myself, will I have to cover it with a black coating like that?

[hamdi.tn]

Hi,
this is a schematic for a board of a heater that i did the pcb layout last year, it's basically operate the same way as your product.
it's built around an UAA2016 and for a 230VAC main J1 is where the thermal sensor is connected J2 is for main input and load output.
Hope this help

[Zero999]

Does anyone know what that black coating is on the back of the PCB? If/when I recreate the circuit myself, will I have to cover it with a black coating like that?

The black coating is a potting compound which protects the PCB against moisture and chemicals. It's a good idea to coat the board with something to protect it, but you can use a silicone rubber compound, which should be easier to remove, than the hard resin.

[all_repair]

By the way CA3059 is difficult to get.   Just got 2 fake one from Taobao.  I dont even bother to beg them for refund.  One negative feedback and they come chasing to pay me back including shipping.   Just bought another 3, hope they are good.

[alsetalokin4017]

By the way CA3059 is difficult to get.  (snip)

Not according to Ebay.
Listings include RCA, Motorola, On-Semi NOS, Intersil, Harris, etc. US and Canadian sellers, along with reputable Chinese sources like UTSource. Running around 7 to 9 dollars per chip, with some outliers.

[Jay112]

Hi,
this is a schematic for a board of a heater that i did the pcb layout last year, it's basically operate the same way as your product.
it's built around an UAA2016 and for a 230VAC main J1 is where the thermal sensor is connected J2 is for main input and load output.
Hope this help

Thanks! I'll definitely take a look at it!

I don't need the heater until about 6 months from now, so I'm giving myself a lot of leisurely time to study. I apologize if this thread keeps popping up sporadically within the next few months!

[Jay112]

By the way CA3059 is difficult to get.   Just got 2 fake one from Taobao.  I dont even bother to beg them for refund.  One negative feedback and they come chasing to pay me back including shipping.   Just bought another 3, hope they are good.

The one that seemed difficult to get for me was the CQ3P TRIAC. I think I had only seen a couple listings on ebay. But I bet if I was more familiar with TRIACs, I'd probably be able to find a similar substitute.

[Jay112]

Does anyone know what that black coating is on the back of the PCB? If/when I recreate the circuit myself, will I have to cover it with a black coating like that?

The black coating is a potting compound which protects the PCB against moisture and chemicals. It's a good idea to coat the board with something to protect it, but you can use a silicone rubber compound, which should be easier to remove, than the hard resin.

Thanks for the information.

Do you think this one would be suitable ("MG Chemicals 419C Acrylic Lacquer Conformal Coating, 55 ml Bottle, Clear")?
http://www.amazon.com/MG-Chemicals-Acrylic-Lacquer-Conformal/dp/B008OA77NG

[Jay112]

Interesting update: I was modifying a working pcb from the exact same heater model, and I noticed that most of the traces are visible from the front side of the board, like in the picture below. Some of the close traces are hard to discern, because there seems to be some kind of semi-opaque coating over them that makes the traces seem blurry. But it's a nice help for figuring out the circuit.

Just as a sidenote: I'm going very slowly with this project because I have 6 months until I have to fix it. I'm hoping to understand temperature control circuits enough by then so that it should be easy at the time.

[Jay112]

Can anyone please explain to me why there's a 100uF cap on the left side of this circuit, between pin 2 of the zero voltage switch and the other side of the thermistor?

And here's another version:

It seems from the datasheet that pin 2 is a 12v DC output, and pin 13 is used to detect the voltage being passed through the pot and thermistor.

[Jay112]

I'm trying to replicate the circuit in the last image I posted (in the post above), in order to be able to test if the CA3059 switches are working correctly. I've never built a pcb for an AC circuit before. I had no idea what was a good way to test something like this.

Assuming that I have the wiring correct, does anything else seem obviously wrong with the following 2 pictures? Is this not how you're supposed to test AC circuits? I'm only going to use it to test the switches, and then I'll probably never use it again. Obviously I'll be very careful with what's touching the board.

(Sidenote: Instead of the NTC sensor, I'm just using a 90k resistor, since that resistance is about the same as the regular NTC sensor gives at room temperature).




Edit: Also I connected 2 rails to be the ground, and connected them in a few places. And I'm hoping to connect pin 4 with the gate of a triac, but I'm not planning on passing high power through the triac for the test.

Edit2: Updated the pictures, because I had one leg of the pot in the wrong spot.