Hey guys.
Currently I am banging my head on a 25KVA Spot welder.
Cannot find any schema but just a block diagram
Itis an old one with opamps and logic gates PCB. Funny thing is the PCB is firing on the bench without the SCR connected.
Back to back SCR is driven via 1:1 transformer.
Once I connect the SCR and main stepdown TX, it will do only one weld and just stops. I had checked everything. Replaced the timing and amps pots too. Faulty logic chips and the 555 timer.

I like to know if any one did a uC based one on the same SCR configuration. If so, can you drop me some advice on it.

 

Block Diagram and Pulse Driver transformer
Connection is C1,K1,C2 & K2

 

What happens if you swap the transformer for a bulb or resistor, does it still shut down?

 

What happens if you swap the transformer for a bulb or resistor, does it still shut down?

Main TXMFR ?

 

The transformer being pulsed by the thyristors.

 

now why did I not think of tht?