Cebora pocket 25 Plasma cutter issues

[Richie08]

Hello Folks, I bought a Cebora pocket 25 Plasma cutter at an autojumble last year, the seller telling me it was in good working order, however when I got it home to try it out, it turns out that it didn't work.

I've opened the case and on the plus side, nothing is burnt or appears damaged. When you switch it on, the fan kicks in and the power switch lights up, which is always a good sign!

When the button is pressed (and the nozzle pressed into the workpiece as this doesn't have an HF start) nothing happens. No arc, no flow of compressed air, not even a click of a relay.

I've done a bit of fault finding on the torch and have proven that the thumb switch and the nozzle switch both open and close as they should, checking continuity and insulation right back to the PCB.

I managed to get a basic electrical diagram from SCREWDRIVER'S POST, he has the same cutter and had a similar issue. However, what I'm not sure of is what each component on the diagram is, I can work out some of the obvious ones but not all of them.

The contactors are all open, if i close the one towards the rear, the transformer starts humming ; not sure what to make from that.

So, I noted that if the air pressure switch had failed, this might prevent the cutter from doing anything else even when buttons pressed. Would this be right?

If so, can I short it as below (also can anyone confirm that i've correctly identified the air pressure switch and the solenoid valve)

Finally, does anybody have a cct diagram for the PCB?

 

[rikrobson]

I seem to remember that the air pressure sensor (11) was at fault in a previous thread.
12 is the air solenoid.

make sure there is air and position the cutter on a test piece. iirc there is a trigger too.
if this does not work bypass the air pressure sensor and try again. it may just need cleaning.

Not realt that much to these.



in the diagram the air line looks like an electrical wire, just to confuse things.

in your piccy i think you have the two devices labeled the wrong way round.

24 is possibly a (thermal) cutout. Therefore the air sensor will have 2 wires 1 to the contactor via the cutout/switch and the other to terminal E on the pcb. the air solenoid will go to teminals f and c.

13 is the air reg and 14 the gauge, see what i mean with the air line being just a line

19 is the christmas tree afair.

I expect the contactor (4) is mounted on the other side of the centre plane as well as the rectifier (5)

23 is the caps. if you are gonna touch these make sure they're discharged. looks like they will hurt.

as for the pcb


b and d look to operate the contactors (4) via the return e via the air switch

G&H are the 240 feed to the pcb


c and f are as mentioned the air solenoid.

Hope that helps

m&n detect the DC feed to the cutter head and i&J are the trigger

 

[Richie08]

Hi Rik, thanks for your reply. Just to confirm, before I trip out the whole house, is this the air pressure switch:

And therefore, should I just short the two wires supplying it to bypass it?

Thanks,
Richie.

 

[Robotstar5]

Certainly looks like a pressure switch, personally, I'd stick something (non conductive) to push the switch closed for testing.

 

[rikrobson]

yup looks like its just a microswitch activated by the air pressure sensor pushing down.

I'd buzz the switch 1stly using a screwdriver to activate it before shorting it out altogether.

the air solenoid must activate first though as the pressure sensor is behind it. so in normal operation you should hear that. and i'd check with a meter to see if you are getting a voltage across it.

I would have thought if the air gizmos were working correctly you would see the switch activate. The solenoid should have its rating on it and then operate it by applying the correct voltage and with air attached and the reg correctly adjusted. you should see the switch operate and it should pass continuity when tested.

it thats all good meter the solenoid feed and the trigger feed.
you can short the trigger feed and you should get the correct voltage at the solenoid.

you should also get the contactor trigger voltage across d&e and b&e. these feeds from e are controlled by the switch 11 and whatever the 24 is poss cut out.
it thats all working, follow the wires to the 24 device as this could be faulty. you should get continuity from the air switch to terminal e if not the 24 device will be faulty. id just bypass that to check.

if all that's ok then it should work.

 

[rikrobson]

i'd also buzz out the transformer windings and the rectifiers too just to be sure.

 

[Richie08]

Certainly looks like a pressure switch, personally, I'd stick something (non conductive) to push the switch closed for testing.

yup looks like its just a microswitch activated by the air pressure sensor pushing down.

I'd buzz the switch 1stly using a screwdriver to activate it before shorting it out altogether.

Ok guys, tried closing the switch till it clicks using an insulated screwdriver, nothing happens.

the air solenoid must activate first though as the pressure sensor is behind it. so in normal operation you should hear that. and i'd check with a meter to see if you are getting a voltage across it.

The air solenoid doesn't appear to be opening at all. I checked the voltage across the two terminals and was surprised to detect an AC voltage, rather than DC? Was a permanent voltage of 21volts AC, does this not seem unusual?

I would have thought if the air gizmos were working correctly you would see the switch activate. The solenoid should have its rating on it and then operate it by applying the correct voltage and with air attached and the reg correctly adjusted. you should see the switch operate and it should pass continuity when tested.

it thats all good meter the solenoid feed and the trigger feed.
you can short the trigger feed and you should get the correct voltage at the solenoid.

I suspect that's where things are going wrong, there appears to be 21V AC at the solenoid permanently, regardless of whether the trigger's pulled or not. Rectfier fault perhaps?

you should also get the contactor trigger voltage across d&e and b&e. these feeds from e are controlled by the switch 11 and whatever the 24 is poss cut out.

I'll check this tomorrow, presumably this should be a DC voltage?

it thats all working, follow the wires to the 24 device as this could be faulty. you should get continuity from the air switch to terminal e if not the 24 device will be faulty. id just bypass that to check.

if all that's ok then it should work.

i'd also buzz out the transformer windings and the rectifiers too just to be sure.

Will try both of these tomorrow too.

Thanks for all the advice so far guys, much appreciated

 

[rikrobson]

ac is not unusual for solenoids. the square block is the coil and should have its rating in it

 

[Robotstar5]

ac is not unusual for solenoids. the square block is the coil and should have its rating in it

Although 21V is odd, depends how accurate your meter is? I would expect something like 24 or 42Volt AC in welding plant.

 

[rikrobson]

From the photo it looks like a 240V solenoid. if there is an earth lead then it's 240V

you would need to trace the pcb to find out what the score is.

At a guess one of those relays will operate 240v to the solenoid to open it.

confirm what it solenoid coil is rated at and apply that voltage directly. you should here it click and pass air.

you are gonna have to debug with the meter i'm afraid.

if the solenoid is gubbed you should be able to replace it.

on of the euro torch conversion gass solenoids should do.

 

[Richie08]

Thanks gents, I'll maybe get time to tinker with it tomorrow, cant get near my garage as just painted one of the project cars in there.

It seems that the PCB's not supplying the air valve with the voltage it needs to open, when the triggers pulled. will need to check values at the various pins of the PCB and make sure the correct inputs are getting to it, and whether it's giving the correct outputs.

Richie.