Esab c251 gas not stopping

[NB fabrication]

Hi my Esab c251 is constantly running gas , it will stop when machine turned off so I’m presuming electrical fault , have tried changing lance to eliminate and makes no difference , if I disconnect solenoid it stops gas . Looking for a fix on the board or a source for a new board

 

[eddie49]

Hello and welcome to the Forum.

There is an earlier thread about a wirefeed fault on the ESAB C251:

B

Thread 'ESAB C251 wire speed fault'

Jan 19, 2021

ESAB c251 problem with the wire speed motor not working when turned down slow. If u turn speed control up to 3/4 or max the motor works but too fast! Have put a new potentiometer on but has made no difference! Help please!

• Ben Bonnett
• Replies: 16
• forum: ESAB

There is a link to a copy of the service manual on a Russian website:

https://valvolodin.narod.ru/schems/Origo_MigC141-151_MagC171-201-251.pdf

The circuit diagrams and descriptions for the C251 MIG start from page 26 of the online manual linked to above. With the very detailed information there, it should be possible to troubleshoot and fix the board.

According to Page 30, both the gas valve and the contactor ( large On/Off relay for the main welding transformer ) have 42 volt AC operating coils, and they are both controlled by TRIAC TC2 ( an electronic switch for AC power circuits ). It is very common for these two components ( contactor and gas valve ) to be controlled in parallel.
If there is a fault in that circuit, the contactor should also always be on, as soon as the welder is plugged in and powered up. Is that happening?