Cebora 1665DC TIG... Problems!

[tinwelp]

Hello people,
I'm looking for help with my Cebora TIG please. It's given sterling service for four years now with not so much as a stutter, but suddenly I cannot adjust the current setting.

It doesn't matter which mode I operate in, or if I run one of the pre-sets then try to make an adjustment... the current resolutely stays unadjustable no matter what I do with the dial!!

Has anyone any experience of this and if so, suggestions to make a repair?

My first thought is the potentiometer has made itself unhappy in some way, but I've yet to open the case.

Any thoughts?

Cheers... Paul

 

[NotANormalCoder]

Unfortunately, this machine is controlled by a microprocessor on the main pcb. If you are unable to adjust any parameters using the program buttons and control knob, it is likely that this has failed and it is a very expensive repair as you will need a whole main board. One thing that can fail, is the control behind the knob. This is not a potentiometer but a rotary encoder that sends a series of pulses to the pcb, so it cannot be checked in the same way as a variable resistor (or potentiometer). Your best bet is to get it to a service centre or somebody experienced with this type of electronics.
Sorry to be the bearer of bad tidings but I've done a few of these in the past and altough they are great when working, they are a pig when they fail.

 

[tinwelp]

Thanks for the input. Bad news indeed, but I'm not ready to give in just yet. Most importantly for me, the machine seems to function perfectly with the exception of being able to adjust anything with the rotary knob. It'll switch to any mode and weld, even pulse or MMA, and all the pre-set programs work OK... it's just the input from the rotary knob that doesn't work.

This tells me a lot, but as I don't have circuit schematics for the machine, I'm at a stop.

I'm going to have a very close look for broken tracks and damaged components and dry soldered joints... if that turns up nought, I'll be looking for help. Do you have any suggestions on this front?? I'm regularly in the UK, so at least that won't cause me issue.

Thanks for your help so far.

Cheers and regards... Paul

 

[NotANormalCoder]

From what you have said, it does sound like a failure of the rotary encoder, or it could simply be a failure of the front pcb that contains this control. As I said before, it's not easy to test the function of this, so replacement would be your only option.
It is possible that I may have a spare front panel that you could try, so that would isolate this as a source of the problem.
Only other thing that I would check is the seating of all the ribbon connectors between the various pcbs, especially the front panel. Where possible, diconnect then reconnect them all, which should clean any dodgy pins.
I am off to France this afternoon (far to much to the northwest to pop in I'm afraid) but when I get back (around the 27th) I'll check and get back to you if you still have problems.
Bon journee. Dave

 

[tinwelp]

Hi Dave,
thanks for your offer of help. Last night I stripped the front board out and opened the encoder. Dirty, but with no obvious faults. I've resoldered all the joints on the front board and checked the ribbon cables carefully. Again, no obvious faults, but no joy either when I reassembled everything.

I'll move onto the main board tonight, trying to trace the circuits from the ribbon cable...

Enjoy your holiday. Hopefully I'll have a solution by the time you return. If not, I may trouble you again. Either way I'll let you know what I find.

Many thanks for your help.

Cheers and regards... Paul

 

[tinwelp]

Dave,
the daughter-board (soldered at right angles to the main board, carrying the main processor) checked out OK with no obvious faults. I followed the circuit through from the encoder to the processor and all seems well. BUT still no joy on reassembly.

So much for a broken circuit, so I started to see if the encoder pulses were reaching the processor... erm, nothing, no matter what I do with the encoder knob or how I search with my oscilloscope!

Back at the encoder terminals is the same story: the centre pin has a 5V supply but nothing sensible comes out of the other two pins when twiddling. Not what I expected...

Do you know if the centre pin of the encoder should be at 5V relative to what seems to be the main board ground?

I could really do with a circuit schematic for this...

Any help please?

Cheers... Paul

 

[NotANormalCoder]

Sorry for the delay in replying, been away then had quite a bit to do.
Sadly, I don't have a schematic for this machine - Cebora are really tight with any service info, we are supposed to be a service agent but are not allowed access to their web site that has the detailed tech info. I do have a spare front PCB for this machine, it is known to be good and you are welcome to try it - if it works, we can come to an arrangement, if not you can return it. To be honest though, most faults stem from the microprocessor, if my past experience is anything to go by.
PM me if you want to try the pcb.
Dave