I was helping a friend troubleshoot an Airco Tig Welder. And I am pretty sure we found a GE SC26502 that is bad. I am reasonably sure it is an SCR. But can not find a datasheet for a SC26502 anywhere on the internet.
Does anyone have a catalog or something that has any info on this part?
Sorry about that. My email address is firstname.lastname@example.org The one that is on my posts is a very old address that I have not updated. I do not know if that reduces the amount of spam I receive, but it might.
Thanks a lot. Knowing what kind of semiconductor it is will make a big difference. Typical of welding manufacturers the schematic in the manual just shows the connections to a circuit board and no info on the actual circuit. But the board has all discrete components, so should not be hard to get it working correctly. The symptom is that the current is at the max. It uses a saturable reactor and the control voltage stays at the max regardless of what the current pot is set at.
Good grief Tim - they use them stacked on top of each other to make a totem pole output power buffer in amplifiers and power supplies.
Common today are not the bipolar ones but FET ones. Generally easier to design with in DC circuits as they work on voltages while bi-polar are current driven. Different designs by a little here and there.
I don't know if the spell checker got it or my flu was still killing me a bit.
Yes NPN and PNP parts are transistors and the field effect ones that are used extensively now and many in motor speed controls in remote control cars/airplanes and such are FET's N-channel and P-channel.
Mart> Last time I checked they called those things transistors, not resistors. >
It was a chunk - Wedge of germanium with a plug inserted. The wedge conducted current and when current was injected onto the plug, the current either increased or decreased - depending on the vector or magnitude and direction (polarity). AT&T patent.
My friend read the manual. It lists a 40 amp 400 volt triac as part of the PC board assembly. The schematic does not show said triac, but it does show up on the parts list. The parts list shows the PC board, the triac, and the PC board assembly. We did check that the triac did not block the voltage with the circuit open to the control pin. Still could be a bad snubber circuit on the PC board so I recommended some checks he could do on the triac to verify it is really bad.
They are 4 layers and a little tough to test. The bad news is it might work with low voltages/currents but arc over or punch through if high voltage or current.
Usually they are high impedance ans won't conduct from the anode to cathode if plus flow. MT1 to MT2 might be terminal names now.
A 40 amp triac is thumb size and has a large heat sink. It isn't on the pcb unless there is a large heat sink on it. Likely it is on the chassis or the sink is mounted top, center, bottom..... somewhere.
I have a curve tracer, but can't run those currents. Nominal functional is possible.
Mart> >> I was helping a friend troubleshoot an Airco Tig Welder. And I am
The triac is wired to the PC board, but mounted to an aluminum plate next to the PC board. That is probably why they had the triac and PC board listed as part of the PC board assembly. The original triac is a stud mount. Smaller than my thumb but definitely a power semiconductor.