Repairing a ENERTRES Biomass BI-650 heater

[edugimeno]

Hi all!
A friend asked me to repair his biomass (pellet) heater. This heater has a pellet feeder powered by a relay that's not switching anymore

I measured the voltage at the relay coil socket while entering the individual tests procedures and it has 6-7v while the relay is NOT on the socket, and drops to 0v when the relay is plugged in the socket, like the source is providing nearly 0 mA. I measured the relay coil and it is correct and not shorted so the issue is in the board, fed no amps to this output

I checked the board at home and this output is driven by an dual OpAmp LM358 (see pictures). This IC uses pin 1 to output to the relay socket and pins 2&3 for inputs. I checked voltage supply to this IC and Pin 4 (V-) has -12.6v and Pin 8 (V+) has +14.8V. Not balanced but I guess this is normal (?).

As the owner has only partial interest in the board to be repaired (pellets price has gone x3 in the last years in Spain) I don't think a quick repair can be done here.

• Option 1: Replace IC LM358, a little out of my scope as I don't have much practice with SMD IC's and my poor sight won't help...
• Option 2: Weird solution, as this output still has some "power", providing 6-7v while no load, would you apply something here (maybe a darlington Q) to increase the power to feed the relay and have a "patch solution" for a while?

Or can you suggest another way to solve it with my limited skills?

Thanks in advance!

[truclacicr]

Measure the voltage on each side of the 470 ohm resistor.

[lotas]

Something strange connection, for the operational amplifier LM358 to directly control the relay coil, there must be at least a "key" transistor or something like ULN2003 (DARLINGTON ARRAYS)

[edugimeno]

Something strange connection, for the operational amplifier LM358 to directly control the relay coil, there must be at least a "key" transistor or something like ULN2003 (DARLINGTON ARRAYS)

Thanks, the fact is that when I got there, there had been another guy, an electrical guy, who left some relays around there, of varied voltages like 6V and 9V, and left the place saying the issue must be at the board as none of the relays work... This makes me think, maybe he modified something in the circuit and what was in the relay socket was not a normal mechanical relay?

What could it be? An electronic relay? There was a rail mounted relay socket, that's all I found there

[edugimeno]

Measure the voltage on each side of the 470 ohm resistor.

You mean the resistor between the OpAmp output and the header right? I can't get a valid measurement now as I got this board at my house (15 km from the original machine) and I can't force the output to HI, but if we find out the relay should not be a normal mechanical relay, I will be back there soon

[edugimeno]

I talked to the owner, he said the electrician left saying the relay wasn't working and he was going to find another relay, he took the original. Then he came back with a bunch of other relays and none worked. I bet there was a solid state relay and he tried to replace it with a mechanical relay? Does it make sense? Do you thing there are SS relays that match pinouts with classic mechanical relays to use their sme socket? Maybe he swapped the socket too. He's calling this electrician to ask for a photo of what he took

[lotas]

What could it be? An electronic relay? There was a rail mounted relay socket, that's all I found there

So how am I supposed to know what's there and how it's connected? The board is in front of you...

How can you trust a simple electrician with complex equipment?

[edugimeno]

So how am I supposed to know what's there and how it's connected? The board is in front of you...

How can you trust a simple electrician with complex equipment?

No, I have the board, but the board is part of a large machine installed at the basement of this building. I only took the board. The relay socket (din rail mounted) along with other boards and modules were left in the machine, from which I took no photos... The owner is asking the electrician for the original relay PN or a photo

[lotas]

Yes, without a photo, and even with a photo, it is difficult to imagine how everything is connected and how everything is interconnected. Maybe where the relays are located, there are additional components that control the relay itself...

[edugimeno]

No worries, maybe you misunderstood me. I was just asking what would be the "usual" device to have out of the board to be controlled directly by the output of an OpAmp in order to drive a 220v AC motor. Assuming the electrician didn't change the socket, I guess there would be a SS relay, but anyway my friend is going to find out soon when the technician sends a picture of the "relay" he took., I am 100% positive the board itself has not been altered my any means, but any component out of the board might...

Thanks!

[lotas]

Here, maybe, on these contacts, as you say, not only the output through the resistor lm358 is suitable. What is the marking of this chip?

[edugimeno]

Here, maybe, on these contacts, as you say, not only the output through the resistor lm358 is suitable. What is the marking of this chip?

That IC is an LF444 (Quad OpAmp), I already checked it before, it has some inputs connected to some other headers (I guess sensors) at the board, it seems like one track is connected to the same header (see scratched varnish) but I removed the header and this track goes across to another header on top if it. I checked and there's no electrical connection at all between this LF444 and the pellet feeder output header

Thanks

[lotas]

It is clear from it that it has already been soldered or replaced (not factory soldered).
Maybe there is some kind of opto relay there (a 470 Ohm resistor limits the LED current), and not a regular one with a coil.

[edugimeno]

I think what you are seeing is the remain of flux from when I desoldered the header that drives the relay for the pellet feeder, right on top of the LF444, but I didn't touch that IC at all, and I am the only one who has touched this board. No, I don't think this IC has anything to do with this function, which seems to solely relay on the LM358, the LF444 is used for INPUTS, as it is wired to other headers for detectors.
Im still awaiting for the owner to get a picture of the original relay that the electricina removed

[edugimeno]

Ok, we got a reply from the electrician, this is the relay he removed, it looks like he swapped the socket as well...
Eltako ER12-001-UC
So GPT states that this is NOT a SOlid State relay but it is electronically triggered (darlington inside?) so it takes really low power and also it says it works by pulses (toggle??) so it won't take current while ON...does it make sense?

[truclacicr]

https://www.eltako.com/fileadmin/dow...nternet_gb.pdf


State-of-the-art hybrid technology combines advantages of nonwearing electronic control with high capacity of special relays.

Universal control voltage 12 to 230 V UC.

Low switching noise. Contact position indicator with LED.

Integrated free-wheeling anti-surge diode (A1 = +, A2 = -).

By using a bistable relay coil power loss and heating is avoided even in the on mode.

[edugimeno]

Thanks. The owner is going to find another relay, same part number this time, and see what happens
Will keep you all posted. Thanks