Identifying if these are SCR’s or transistors  - Page 1
Forum section: electronics / beginners

author: zupta82
author_rank: Regular Contributor
timestamp: January 14, 2021, 12:57:56 am
content: 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

author: zupta82
author_rank: Regular Contributor
timestamp: January 14, 2021, 12:59:19 am
content: Sorry I meant scrape away the silkscreen lettering

author: zupta82
author_rank: Regular Contributor
timestamp: January 14, 2021, 01:03:50 am
content: I can faintly see the Motorola logo on one of them

author: bob91343
author_rank: Super Contributor
timestamp: January 14, 2021, 01:11:00 am
content: Looks like they are Q numbers, more likely transistors. Have you tried measuring? The cute little Chinese tester might help.

author: zupta82
author_rank: Regular Contributor
timestamp: January 14, 2021, 03:05:13 am
content: 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

author: zupta82
author_rank: Regular Contributor
timestamp: January 14, 2021, 03:06:32 am
content: Here is backside with the copper rivets I drilled out that were soldered to the large pads

author: bob91343
author_rank: Super Contributor
timestamp: January 14, 2021, 06:14:22 am
content: What is this thing? That method of assembly really sucks. If they saved a penny on 100 units it wasn't worth it.

author: zupta82
author_rank: Regular Contributor
timestamp: January 14, 2021, 12:15:58 pm
content: 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.

author: CaptDon
author_rank: Super Contributor
timestamp: January 14, 2021, 02:11:09 pm
content: 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.

author: zupta82
author_rank: Regular Contributor
timestamp: January 14, 2021, 06:04:40 pm
content: 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

author: zupta82
author_rank: Regular Contributor
timestamp: January 14, 2021, 11:58:31 pm
content: 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

author: zupta82
author_rank: Regular Contributor
timestamp: January 15, 2021, 01:17:07 am
content: Okay I think I got a partial image of what one of the devices are. I think at least one of these is a MotorolaJE170 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

author: zupta82
author_rank: Regular Contributor
timestamp: January 15, 2021, 01:21:47 am
content: 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

author: zupta82
author_rank: Regular Contributor
timestamp: January 15, 2021, 02:09:09 am
content: Ok I think I figured out the other device it is a Motorola JE180. Here is a pic

author: bob91343
author_rank: Super Contributor
timestamp: January 15, 2021, 05:38:08 am
content: That is a 450V NPN transistor.

author: zupta82
author_rank: Regular Contributor
timestamp: January 15, 2021, 12:33:08 pm
content: 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.