Troubleshooting / repairing basic panel heater

Hello,

I have a panel heater that stopped working. It's a large item, and a relatively basic electrical device. So rather than through it away, I'm going to try and fix it.

It has a relatively simply 2x1 inch component board in it.

What I have determined so far:

1. There is power reaching the input of the board.

2. There is no power at the output of the board.

3. Aside from incoming power, and outgoing power (to the heating element), the only other thing the board is connected to is what I assume is a thermostatic breaker of some kind, in case of over heating. There is continuity on that line, so whatever is on the other end of it creates a closed circuit. I have detached that line from the board, which in effect makes it an open circuit, and it does not resolve the heater malfunction. So I think it's safe to assume that line is meant to be a closed circuit for normal operation.

The Components
Here are photos of the board:

^ The whole board - Front Side ^



^ Whole Board - Back Side ^



^ The components that should trigger the relay ^

The black unit is a power relay. It is a normally open relay, as shown in the following pic.


The live power input terminal runs to this.

So I think it's safe to say either the relay is broken, or one or more of the other parts designed to trigger the relay are broken.

Those other parts consist of two capacitors, a resistor, and two diodes.
1) The smaller black round capacitor (C2 on the board) is a JAKEC 50V 47 uF Radial Electrolytic Capacitor.

2) The larger yellow capacitor (C1) is a MEX GPF 40/085/21/C 0.22uF X2. An equivalent unit is in this picture:


3) The resistor (R1) is 4 band: yellow, blue (looks more like purple), yellow, gold. Assuming the 2nd band is blue, then I gather it's a 460k Ohms 5%.

4) The two diodes (D1 & D2) look the same, although I can't read the writing on each of them. Would need to remove them.

Question:

Based on what I've determined so far, what would be the most efficient way to deduct the cause of the issue? What tests can I go on the various components to check they are working?

Is it possible to test the relay (I don't have an independent and controllable power source I can trigger it with). I've done a resistance test on the two terminals of the relay seen on the left of the relay on the backside of the circuit board (terminal at top left and bottom left corner, as shown in that pic). Came to 3k.

Should I desolder and test all the other components, and then if they are all fine, I can assume the relay is broken?

- - -
I am not an electrical engineer, or anything of the like. Just a person that gets in a fixes stuff when I can. I may have misunderstood how this simple circuitry works, in which case please let me know.

With thanks,

Jonathan

Wow!

The solder joint to the relay, power in, 3rd joint doesn't look good.
there should be a DC voltage across C2 around 24 V when CN1 is shorted.
If it's there, I would check the resistance of the relay coil. It's across C2, so it could be measureable.
(power off, measure voltage first before trying to measure Resistance) You could do this measurement first.
The relay has a 24 VDC coil. The power supply uses the reactance of a capacitor to limit the current.
I didn't look for a datasheet.

Whatever is feeding CN1 is providing the power for the relay. What is the input voltages at CN1? Check the voltage across the Capacitor, it should be in the 24V DC range +/- a fairly wide range (it is only a 50V capacitor, and relay is rated for 24V DC).
Once there is 24V across the capacitor, the large black relay should be pulling in. If it does, and there is no power on the OUT pin (no continuity between IN and OUT), then odds are high the relay contacts are burnt out. If no click of the relay or no 24V on the capacitor, then check the diodes. They will probably be typical 1n400x series, so any 1N4004 to 1N4007 will do (higher voltage ratings).
Otherwise, your input power on CN1 is not working properly.
CN1 would be connected to some thermostat type of device, to control the on/off cycles of the heater.

sagor1 said:

Whatever is feeding CN1 is providing the power for the relay. What is the input voltages at CN1?

Click to expand...

sagor1 said:

Otherwise, your input power on CN1 is not working properly.

Click to expand...

sagor1 I think these statements are confusing.

The TS should look here: https://hackaday.com/2017/04/04/the-shocking-truth-about-transformerless-power-supplies/

No matter what, CN1 has to energize the relay, by closure or "supply". The capacitor is a 50V, and the relay is a 24V, so somewhere along the line, CN1 is probably some 24V control connector. One side of the relay is Neutral, the other side is via CN1, which I now suspect is a contact closure to complete the circuit from D1
You are probably right in that C1 is a reactance to provide the diodes with some "voltage", which is then acted upon by CN1 (not power supplied to CN1 by external as I originally assumed)

Agree that this may be working at dangerous voltages (line voltages), but TS has to determine if the fault is the relay or whatever closes relay contacts via CN1

The circuit is minimalstic and it lacks protections as in the hackaday article.

For contact closures, you can measure the voltage "ACROSS" the contacts, but you have to know that the external circuit is complete.
Picture a battery(B1), lamp(L1) and switch(S1).
1. Measure across S1; S1 closed; ~0V
2. Measure across Sq; S1 open; Battery voltage.

What if the voltage across S1 was 10% of the battery voltage? It's possible that the contacts of S1 are bad.
--
My guess as to what's wrong. The relay coil is open.

InspectorGadget said:

Is it possible to test the relay

Should I desolder and test all the other components, and then if they are all fine, I can assume the relay is broken?

Click to expand...

Its really simple to just test the relay. Solder some wires to it and use your own safe power supply.
Add 15-24V to 86 and 30, Add ground and test light clip to 85. It should click. Then probe 87 with the light.

I'm sure you have some old power supply laying around that is in the range of 15-24v. Most older laptop power supply's are around 19.5v that should be enough to trigger it.

Thanks for this abundance of input and suggestions. I'll be taking this task up again in the weekend.

A few additional thoughts, after reading above posts...
Regarding CN1. That is a thin wire (x2) the feeds into the heater panel. It (the wire) has continuity across its two pins. No current comes from that wire.
My guess was that on the other end of this wire is some kind of basic thermal switch, which will open if the heater over heats, and thus break the circuit across CN1, to shut the heater down. So in effect it is just creating a circuit (or breaking it, when too hot) across the pins of CN1. I don't think it serves any other purpose, but could be wrong.

I'll see if I can dig up a suitable power supply for testing the relay. I've recently moved house, and got rid of a lot of "old power supply" type stuff. Figuring it was a box of crap I'd not used in years, so best to pass it on. Murphy's law, I suppose.

Cheers,

J

sagor1 said:

No matter what, CN1 has to energize the relay, by closure or "supply". The capacitor is a 50V, and the relay is a 24V, so somewhere along the line, CN1 is probably some 24V control connector. One side of the relay is Neutral, the other side is via CN1, which I now suspect is a contact closure to complete the circuit from D1
You are probably right in that C1 is a reactance to provide the diodes with some "voltage", which is then acted upon by CN1 (not power supplied to CN1 by external as I originally assumed)

Click to expand...

Yes, I agree. Re deducing CN1 simply provides closure to the circuit.

Agree that this may be working at dangerous voltages (line voltages), but TS has to determine if the fault is the relay or whatever closes relay contacts via CN1

Click to expand...

There's line voltage through the input of the relay and up to C1. After that, the capacitor drops it to around 34v. The relay passes the line voltage through to the live output once relay is activated. The rest of the circuit board is at 34v. Although I am sure you've figured all that out. But yes, this board has 220v coming directly into it.

I had a chance to do a little on this last night.
I see that on the dead IC the voltage after C1 is only 5.2v
As mentioned above, on a working IC the voltage after C1 is 34v.
Is that a fairly good indication its C1 that has failed?

I suspect what caused the failure was a power spike after the power was turned off at the mains, and back on again, a few times. The hot water cylinder was having something fixed on it that day. I didn't realise this heater was on, nor that it would be so sensitive. But the next day it was dead.

Is it plausible that a small spike killed the capacitor (C1), and that's the fault on the IC?

Can someone tell me what the numbers MEX GPF 40/085/21/C actually mean, on the yellow capacitor?
I'm looking for the replacement, but most of the options that come up are MEX MKP 40/100/21/C 0.22uF X2.
I am not sure if the GPF | MKP part, or the 085 | 100 part of the coding is of any significance.

So I've determined that the MKP showing up on most of the similar capacitors I am finding online refers to the materials... MKP = metallized polypropylene.

Haven't found was GPF refers to, as it doesn't show up in the materials list I discovered (https://kaizerpowerelectronics.dk/theory/capacitor-code-table/). None of the other info on that web page makes any sense to me at all. Seems to have no relevance to the C1 capacitor on my IC.

It needs to needs to be an X2 series capacitor 250-275 Volts AC, 0.22 uF

X2 is a safety capacitor. https://www.hunker.com/13408990/differences-in-x1-x2-y1-and-y2-capacitors

KeepItSimpleStupid said:

It needs to needs to be an X2 series capacitor 250-275 Volts AC, 0.22 uF

X2 is a safety capacitor. https://www.hunker.com/13408990/differences-in-x1-x2-y1-and-y2-capacitors

Click to expand...

Thanks.
So the "MKP 40/100/21/C" portion of the info on the capacitor is not something I need to take into account, so long as it's an X2, 0.22 uF, 250-275 V?

Those are the important ones. If you get some hits, you could select based on other parameters. e.g. temperature.

the AC rating is important.

Thanks very much.
So I think I found a suitable replacement. https://au.element14.com/panasonic/ecqu2a224kla/cap-0-22-f-10-pp/dp/1673311

0.22 uF, 275 Volt, X2, +-10% tolerance (which I gather is what's denoted by the K on my capacitor)

Also, I am starting to suspect the 40/085 refers to min temp of -40 C and max temp of 85 C. But that's just a hunch, after reading through spec sheets for these things.

KISS, would you agree that this (in link above) is functionally equivalent protective capacitor?

Highly probable. I found this: **broken link removed** Lots of info.