Hello, I was wondering if these two black devices are SCR’s or transistors, I can’t read the silkscreen and I’m afraid to scrape away the conformal coating with a xacto knife which could scrape away the conformal coating, they are labeled Q3 and Q4
Sorry I meant scrape away the silkscreen lettering
I can faintly see the Motorola logo on one of them
Looks like they are Q numbers, more likely transistors. Have you tried measuring? The cute little Chinese tester might help.
Well I think I might be in deeper trouble, how can I get these things out. I tried desoldering the heat sink pads and drilling out the rivets. I now can’t get them to pry loose so I can look at them under magnifying glass and test them out of circuit. I snipped the leads and cracked one of packages. Here is a pic
Here is backside with the copper rivets I drilled out that were soldered to the large pads
What is this thing? That method of assembly really sucks. If they saved a penny on 100 units it wasn't worth it.
Well if I don’t get them out in one piece, can anyone recommend a replacement. It’s a 25 amp output pulsed dc plasma cutter.
What, no schematic? They appear as transistors, but even so, now that you have destroyed them what were they, we may never know. You didn't know what they were, you didn't have a clue how to try to test them in circuit to possibly identify them as NPN/PNP/SCR/Dual Diodes now you are totally screwed. I am sensing a pattern here all the way back to the Tek power supply. I recommend a bigger hammer and oxy-acetylene torch for the newest additions in your repair efforts.
Ok, I’ll admit it was my fault. Sorry for being annoying I have been under a lot of stress lately at work. I have a lot to learn, I thought tinkering with electronics after work might relieve some stress. I know stress and electronics don’t mix. I’m a big auto mechanic tinkerer for most my life. I don’t know why I went to school for electronics. I thought if I could at least salvage one and get the numbers on them. I just realized today that these devices are heatsinked with a copper plate and the rivet releases them I think I’m just gonna have to put this thing away or throw it out. I have a lot of thinking to do
Here is a pic over the capacitive discharge area of the schematic. I figured they would be thyristors or SCR’s because they are close to the output current adjustment potentiometer and the schematic has a symbol for a thyristor
Okay I think I got a partial image of what one of the devices are. I think at least one of these is a Motorola
JE170 in a to126 package. I’m afraid to pick the other one any good trick for taking off conformal coating. I was thinking a heat gun but it might burn the silkscreen. This has got to be weirdest conformal coating it just flakes of. It’s definitely not Humiseal
I definitely learned from my mistake. I got to learn to concentrate, I’ve always had attention issues growing up and struggle with them in daily life
Ok I think I figured out the other device it is a Motorola JE180. Here is a pic
That is a 450V NPN transistor.
I guess these devices can work like a switch to turn on the flow of high current similar to SCR’s and Thyristors but in this case the bulk of the current is handled by the Mosfets . The funny thing is I remember before I started this project no matter what setting on the adjustment knob, I always had weak output power.