Identify this diode - Page 1
Forum section: electronics / repair

author: markm6164
author_rank: Contributor
timestamp: February 17, 2017, 05:24:47 pm
content: Hi, i'm an auto electrician and i have just bought a Snap on test light from eBay. Its a LED test light EECT4H and the 4 diodes on the PCB are blown. Can anyone help me identify them. I have included the datasheet for the light and pictures of the diode and a diagram i did of the circuit. I believe the diode is size SOD323 if that is correct and i'm not sure if the diode is a standard diode or a zener as the lamp works at 6-12v?Many thanks

author: Armadillo
author_rank: Super Contributor
timestamp: February 17, 2017, 06:05:13 pm
content: I think is a BAV16W/1N4148W fast switching diode in SOD123 case.

author: Ian.M
author_rank: Super Contributor
timestamp: February 17, 2017, 06:09:49 pm
content: The application is totally non-critical. Any silicon diode rated at >100mA If and >50V, in the same package and pinout could be substituted.

author: Armadillo
author_rank: Super Contributor
timestamp: February 17, 2017, 06:20:49 pm
content: Wow! $39 for a piece of low current 20mA LED test pen... that'sexpensive.!Yeap, you will need the smd parts to fit into the space and justify the cost of this test pen.

author: markm6164
author_rank: Contributor
timestamp: February 17, 2017, 06:38:39 pm
content: Thanks for the replies everyone.

author: Ian.M
author_rank: Super Contributor
timestamp: February 17, 2017, 06:50:58 pm
content: Substitute a two pin bicolour LED, and remove and bypass the diode bridge and you'll have upgraded it to indicate polarity.

author: james_s
author_rank: Super Contributor
timestamp: February 17, 2017, 07:38:59 pm
content: That's a bridge rectifier, as someone else said, not critical at all. Just pick up any standard diodes that will physically fit. Probably want a PIV of at least 50V but most will have at least that.

author: grifftech
author_rank: Frequent Contributor
timestamp: February 17, 2017, 09:11:52 pm
content: buy one from harbor freight

author: darrellg
author_rank: Unknown
timestamp: February 17, 2017, 10:38:56 pm
content: Quote from: Armadillo on February 17, 2017, 06:20:49 pmThat's $2 for the tester and $37 to have the Snap-on name printed on the outside.

author: Bushougoma
author_rank: Regular Contributor
timestamp: February 18, 2017, 12:50:36 am
content: As others have said a standard 1N4148 or the like diode can be substituted.The current through that LED (based on the resistor) is around 20 milliamps tops (slightly less due to the 2 diode voltage drop from the bridge rectifier).They put the bridge rectifier there so the test light wouldn't be polarity sensitive (like it's incandescent counterpart). It also prevents the LED from becoming reverse biased (most LEDs have a max reverse voltage of 5 volts) a fully charged battery can easily exceed this.

author: james_s
author_rank: Super Contributor
timestamp: February 18, 2017, 07:52:16 am
content: I made a test light using almost exactly that same circuit when I was about 10 years old. I used parts I salvaged from a broken portable stereo and housed it in a Bic pen with a sewing needle as a probe. I used it for probably another 10 years until I lost it. Amazing that SnapOn can get so much for something so simple. I made a similarly built one with a neon indicator for 120V, not sure what happened to that one either.

author: Bushougoma
author_rank: Regular Contributor
timestamp: February 18, 2017, 08:36:01 pm
content: The reason most mechanics buy their stuff is the no nonsense exchange policy if you break it the tool truck guy will replace it no questions asked. You pay for that in the purchase price.I don't believe that applies to their electronic equipment though.

author: Armadillo
author_rank: Super Contributor
timestamp: February 18, 2017, 09:17:27 pm
content: Quote from: Bushougoma on February 18, 2017, 08:36:01 pmThen, may I ask, why the need to be here the first place?

author: Bushougoma
author_rank: Regular Contributor
timestamp: February 18, 2017, 09:59:02 pm
content: Quote from: Bushougoma on February 18, 2017, 08:36:01 pm