PCB repairs
Juad
I have spent my first 3 years of working in repairing control PCB's ,motor drives ,Process controllers....etc
Most of this were coming without schematic diagrams and i usually using the traditional measuring methods dor electronic component such as diodes ,transistors,Scr and using digital voltameter.
Regarding IC's i was have three devices for testing
1-IC testing system(I don't remember it's name now)but the new
version of it is "SYSTEM 8" by ABI for testing IC's in board.
Sometimes the result was not accurate because to test IC on boared
you must generate a high impedence around it to be isolted from the
rest of the circuit hence the testing result will br for the IC not
the Thevinen equivelent.
2-Digital IC tester BY ABI ,testing difital IC's out board.
3-Analog IC tester BY ABI ,testing Analog IC's out boared.
These 2 methods were taking alot of time in desoldring and
soldring the IC,s from PCB beside you have to draw the layout of
the PCB to know exactly the location and direction of each IC when
you resolder the IC's.you must be profissional in slodring and desoldring in order to remove the IC's without any damage to the PCB tracks or the IC it self.
4-I-V curve comparator by Huntron and you must have a good PCb to compare with in this case.
Any how this field is vanishing know in Egypt due to the newest technology in PCB's and IC's like multilayer PCB's and Surface mount technology in IC's.
Regarding repairing PLC cards usually as i mentioned above i got the cards without any schematics,when i got a failed power supply module it's easy to repair and i do it many times ,when you get I/o Modules it's easy to repair when the fault in the ISolation stage usually Opto coupler or in the output stage(Output module)to replacea malfunction relay or transistor or whatever.
I alawys refuse to recieve CPU modules for repair and i apologize for the client that we can't repair this type of cards(Multi layer PCb,ASIC IC's not commercial one,and others)
I hope that this information could help you.
Good luck