Lennox G24mce3 - 60A -5T control unit burnt

[3man]

Hello,
I have a lennox gas furnace like in the title. For some reason (probalby bad contacts) one of the relays has burnt so badly that it has destroyed part of the printed circuit board. I have bought new relays but now i have a small problem with the circuits. Because of the burnt board about 2cm square have been destroyed and i want to fix it somehow. My tehnician wants me to buy a new board - that's about 500$. The two relays have cost me 2$. Equation is easy- i wanna fix the board . With this control unit burnt as it is the furnace works except for the main fan. The furnace starts normally, fumes ventilator, burner and after some time the main fan should start but it doesn't so the whole furnace shuts down after a while because of too high temperature.

I looked through the internet and i can't find anywhere either the electrical diagram of the board or the picture of it. My question is - does anyone has got a picture of the same board i have, or the diagram so i could fix it. I enclose the pictures of my control unit
and a picture of the burnt place
and a close up

can anyone help me with this? how to connect it? if someone has the same board I would really appreciate if I could have a picture of it

hmmm can't add urls to outside sites.

[paul52446m]

Hello,
I have a lennox gas furnace like in the title. For some reason (probalby bad contacts) one of the relays has burnt so badly that it has destroyed part of the printed circuit board. I have bought new relays but now i have a small problem with the circuits. Because of the burnt board about 2cm square have been destroyed and i want to fix it somehow. My tehnician wants me to buy a new board - that's about 500$. The two relays have cost me 2$. Equation is easy- i wanna fix the board . With this control unit burnt as it is the furnace works except for the main fan. The furnace starts normally, fumes ventilator, burner and after some time the main fan should start but it doesn't so the whole furnace shuts down after a while because of too high temperature.

I looked through the internet and i can't find anywhere either the electrical diagram of the board or the picture of it. My question is - does anyone has got a picture of the same board i have, or the diagram so i could fix it. I enclose the pictures of my control unit
and a picture of the burnt place
and a close up

can anyone help me with this? how to connect it? if someone has the same board I would really appreciate if I could have a picture of it

hmmm can't add urls to outside sites.

Do you have AC on this furnace, or are you useing just one speed of the blower. paul

[HayZee518]

gently clean off the charred side of the printed circuit. with a magnifying glass see if you can see any impressions of the orirginal foil patterns. once you've established this, install the relays into the holes. bent the pins slightly to hold the relay in place and use #18 solid wire to go from the pins to the foil connections. once you've tested the board apply clear rtv on the component side to hold the relay to the board.

[3man]

No AC. Just heating so the blower is either off or on.

[3man]

gently clean off the charred side of the printed circuit. with a magnifying glass see if you can see any impressions of the orirginal foil patterns. once you've established this, install the relays into the holes. bent the pins slightly to hold the relay in place and use #18 solid wire to go from the pins to the foil connections. once you've tested the board apply clear rtv on the component side to hold the relay to the board.

The problem is that the board is burned so badly that I just can not see any impressions left. I have enclosed a close up picture in the first post. It really looks better on the picture than in reality. The red numbers correspond to white 30A relay and blue to the black 10A relay pins

[HayZee518]

let me find the relay's pin outs. maybe by super imposing the pins I can determine what goes where.

[3man]

Hello again,

In the enclosed picture i have marked what i have found out so far. I have changed two relays A and B. Relay A 30Amp has red numbers on pinouts and relay B 10Amp has blue marked pinouts. From traces left on the burned out place i think that circuits went like yellow dotted line. I have taken apart old relays and since i don't know much about electronics i will try to explain how they work. Relay A and B pinouts 2 and 4 - are the coil pinouts. Relay A when current is applied to coil shortens pinouts 1 and 5. Relay B - when no current is applied to coil shortens 1 ad 3 pinouts and when current is applied shortens 3 and 5 pinouts. I got this far. However i have no clue where pinout 3 on relay B should be connected to. Any help?

[paul52446m]

If every thing works except the blower, and you don't have air on it, and you are using just one speed. It would much simpler to just add a $20 some dollar relay with a 24 volt coil to turn the blower on. If you don't want the blower to come on too fast, then put a 30 second
timer on it. Paul