Cebora 883 (Pocket Mig) Wire speed not working.

[bloobloo]

Hello all! Once again I have bought another welder in need of a bit of love.....
I bought this Cebora 883 for a whopping £15 of FB Marketplace, it had no torch or earth and needs a top roller / tensioner.
I have put a torch on that I had spare and powered it up. pressing the trigger makes the wire feed motor spin. However turning the wire speed knob does nothing at all.
I have tested the output on the wire speed PCB that goes to the motor and get from 12v on its lowest 1-min through to 25v on 2-max power setting.

I have looked at the board and can't see anything obvious that could be blown, however I only had a quick glance.

Anyone had any similar issues with one of these sets or similar?

Thanks in advance

 

[Hutcho]

Dry joint maybe

 

[bloobloo]

Dry joint maybe

I didn't notice anything unusual when I looked earlier, no furring or discolouration on the rear of the board where the joints are. However as I say, I didn't really inspect it properly.
In fact, I'll nip and take a pic and post it

 

[bloobloo]

Having just took the pcb off for a better look, maybe something is wrong. Looks like it’s got a bit warm at some point. I’m also not quite sure that the motor and trigger wires were connected correctly?

 

[bloobloo]

Just found this vid ( fixing uneven wire feed) on YouTube. This clearly shows my wiring is wrong.
My trigger and motor negative are wrong way around. Just a bit worried now that it could have burnt the resistor out?

 

[500e]

Never worked out why manufacturers fit WW resistors against board heats the board and removes 1/4 of the heat dissipation of the thing.
The left hand end of the WW could do with a touch of solder just to make sure, it got hot enough to cause solder to sag

 

[bloobloo]

Never worked out why manufacturers fit WW resistors against board heats the board and removes 1/4 of the heat dissipation of the thing.
The left hand end of the WW could do with a touch of solder just to make sure, it got hot enough to cause solder to sag

I've just put it back together to try it again. The wires were the wrong way around. The contactor now clicks when the trigger is pressed. However upon testing that 3ohm WW, nothing at all on the multimeter. I don't have any 3ohm resistors but I do have 3 x 1ohm resistors, would this work ok?

 

[Neilj]

I don't have any 3ohm resistors but I do have 3 x 1ohm resistors, would this work ok?

Yes, if you wire them all in series. What wattage are your 1ohm resistors, that wirewound 3 ohm one is rated at 7 watts.

 

[500e]

What wattage are the 1 Ohm's you need 7 watt ones @puffernutter may have the correct one from my box of resistors
You checked across the 3 Ohm with one end disconnected
Not that expensive new

 

[bloobloo]

Yes, if you wire them all in series. What wattage are your 1ohm resistors, that wirewound 3 ohm one is rated at 7 watts.

Absolutely no idea! I only want to use them to test until a proper one can be bought.

 

[Neilj]

They're wired in series in your pic above, so end to end (the two legs that are not twisted) they will be 3 ohms. You need to make sure the intermediate joins (twisted bits) are insulated somehow as you don't want them contacting anything else. However, they only look like (at a guess) 2 watt resistors so they're going to get very hot and quickly. Probably ok to use for a quick test to see if the unit works but I wouldn't rely on them for long.

 

[bloobloo]

Great news! It’s alive lol. I’ve put the resistors in as a temporary solution to test and it seems to be working.

 

[500e]

It is the correct motor ?? the voltage is varying to motor so you should see some speed variation
Sen your trial keep the body of the resistor away from board when you put in the correct one, good to see it works check how hot the new one gets a10W will run colder

 

[bloobloo]

Well that was short lived! I snipped the the legs of the resistors, put the case back on and now back to just the contactor clicking when the trigger is pressed. I've resoldered the joints on the board just in case I had knocked it loose with the snips when cutting the legs off. I've checked the resistance again an it still shows 3ohms. I will order the correct resistor and hopefully that will fix it again?

 

[bloobloo]

Just ordered the resistor (well a pack of 10) -- from Amazon £3.44. will be here tomorrow, Very cheap!

I'm quite tempted to order a mix pack of resistors etc and change the bloody lot!

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[bloobloo]

Well, one of those days today!
fitted the new correct resistor. and..... nothing!
So did a bit of probing and found that the SCR in the middle of the board is shorted. No power is getting to the wire feed motor, and the track on the board goes directly to the gate on the SCR.
Now I need to find a TIC116D.
I don't think that I'll be able to get one from Amazon though :-(

Hey well keep plodding!

 

[Neilj]

Sounds like it's gone open circuit not short circuit if there's no voltage to the motor? The motor would run continuously if it was shorted. Plenty on eBay at about a quid each, but I'm thinking there may be a bigger fault going on here. The 3 ohm resistor is in series with the supply to the SCR, your original resistor fried itself and now you've replaced that the SCR has failed. I wonder if you have a motor issue and it's drawing far too much current, making the board components fail?

 

[bloobloo]

Sounds like it's gone open circuit not short circuit if there's no voltage to the motor? The motor would run continuously if it was shorted. Plenty on eBay at about a quid each, but I'm thinking there may be a bigger fault going on here. The 3 ohm resistor is in series with the supply to the SCR, your original resistor fried itself and now you've replaced that the SCR has failed. I wonder if you have a motor issue and it's drawing far too much current, making the board components fail?

As far as I understand these should be open circuit cathode - annode & vice versa and then show continuity on the gate?
The one I have shows continuity on all 3 legs.

When I tested it yesterday with the temporary resistors in series, the motor ran perfectly, up until I turned it off and trimmed the excess off the resistors and put the case back on. I then tried it again and nothing happened apart from the contactor clicking.
today I replaced the resistors with the correct one and tried again, but got the same result. I then put the meter on the earth and to the middle terminal (motor positive) and there is no voltage at all when trigger is pressed but the contactor happily clicks away when the trigger is pressed.
Upon testing the SCR it seems to be shorted across all 3 legs.

It would be much easier to lob another board in but I don't think they are made anymore so this leaves me the only option of repairing the original.

 

[Neilj]

The gate is the trigger on an SCR, anode & cathode are effectively your 'contacts' if you think in terms of a relay. So with the SCR untriggered, anode to cathode will be open circuit. Once triggered by a gate signal, the anode to cathode will be a low resistance.
Do you get any voltage on the trigger wire when you press the torch trigger?

 

[Neilj]

Looking at your first pic in Post #4, there is something mounted on the pcb to the left of the relay and under the red speed control pot but I can't see it due to the angle of the pic. Any chance of another pic of this area?