Where to find a replacement transistor (q406) while in the UK - Page 1
Forum section: electronics / projects

author: maxwell
author_rank: Newbie
timestamp: December 16, 2010, 09:12:22 pm
content: Hi all,I recently bought some chinese made christmas lights from ebay and was taking some readings from the controller box with a multimeter (I am extending the 5 core cable) and managed to blow one of the transistors up in the process and therefor need to replace what I broke). The circuit seems simple enough and very crude. A few IN4007 diodes, four q406 transistors (one for each output wire) , and IC to do the sequencing/fading/etc and a cap to smooth everything power wise since it runs directly at 240VAC (yes, nasty!).My question is where can I find a suitable replacement? I have googled q406 transistor but that turns up only spec/data sheets. Any help would be great as I cant put up the lights until I fix them.. I'll attach a photo of the circuit for the curious if it helps. Note that I have removed 1 transistor and 1 diode to get the info from them. They all appear the same.Cheers and Merry Christmas

author: Simon
author_rank: Unknown
timestamp: December 16, 2010, 09:24:00 pm
content: well your best thing is to figure out the main specs of the transistor and try to find an equivalent, if you transistor works in on/off mode (or PWM) you will be in luck as a replacement is very easy to find, can you attach the datasheet you did find to a post ?

author: Psi
author_rank: Super Contributor
timestamp: December 16, 2010, 10:56:55 pm
content: Is there anything else written on the transistor other than q406 ?

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 16, 2010, 11:25:17 pm
content: Assuming it is a transistor, it will probably be a generic type - should be able to determine NPN or PNP from the circuit - my guess would be NPN connected as a common-emitter switch, assuming LED common is positive. Depending on the load current, somethiong like a BC548 would probably do. Just check the pinout - could be centre-collector or centre-base - collector probably connects to the LEDs.Looking at the PCB pic I;d guess centre base, so BC548 would be a good start

author: maxwell
author_rank: Newbie
timestamp: December 17, 2010, 01:03:24 am
content: Thanks all,Here are a few more pics to help. I think they might be NPN but my electronics is very rusty. Whats the voltage rating on a BC548?

author: Unknown
author_rank: Unknown
timestamp: December 17, 2010, 03:00:00 am
content: Every Christmas the same questionAre you sure these are bipolar transistors? From past experience with these evil little circuits is that TRIACs are used.

author: Simon
author_rank: Unknown
timestamp: December 17, 2010, 08:00:24 am
content: thats why I ask to see the datasheet, the OP say's he's seen datasheets but still does not know what type of transistor he is trying to replace, if he posts the datasheet we can see what we are on about

author: qno
author_rank: Frequent Contributor
timestamp: December 17, 2010, 08:50:26 am
content: Try a MPSA42.

author: bogdan546
author_rank: Contributor
timestamp: December 17, 2010, 09:56:13 am
content: tryhttp://www.datasheetcatalog.com/datasheets_pdf/P/C/R/4/PCR406.shtmlis an inexpensive triac

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: December 17, 2010, 10:53:03 am
content: Quote from: Alex on December 17, 2010, 03:00:00 amGood point - does the AC adapter output AC or DC? AC would explain the presence of the diodes, and would point to them being SCRs or triacs.

author: Zero999
author_rank: Super Contributor
timestamp: December 17, 2010, 05:24:32 pm
content: The datasheet is for an SCR not a TRIAC.These circuits are normally powered directly from the mains without a step down transformer.To complicate things the SCRs could be switching unfiltered DC so even if the DVM says it's DC it doesn't necessarily mean they're BJTs. I think this is the case here, given the datasshe and the diodes used to rectify the mains.

author: ModemHead
author_rank: Frequent Contributor
timestamp: December 17, 2010, 05:54:38 pm
content: Found something while googling that might be interesting. It came fromw ww.szhwct.com/upfile/2009715171018_spec.pdf. Not sure about the trustworthiness of the website it came from, it's all in Chinese or something. But it could be relevant...

author: Unknown
author_rank: Unknown
timestamp: December 17, 2010, 07:15:03 pm
content: Woohoo! Thats a Triac alright.Coming from a Chinese website adds credibility in this case!You know the key specs now, time to visit a component distributor.

author: Zero999
author_rank: Super Contributor
timestamp: December 17, 2010, 09:08:28 pm
content: It's not an TRIAC but an SCR, although you could replace it with a TRIAC and it will work.If you can't find it, go for the MCR100 which can be found in most component distributors (RS Components, Farnell and Digikey all stock it). Going from what you've said you're in a 240V area so you need the -6 (400V) version or higher.http://www.datasheetcatalog.org/datasheet/unisonic/MCR100-4.pdf

author: maxwell
author_rank: Newbie
timestamp: December 17, 2010, 11:50:21 pm
content: Thanks again everyone. Hopefully I will have a christmas with lightsI have found this on ebay (http://cgi.ebay.co.uk/MCR100-6-0-8A-400V-THYRISTOR-TO-92-QTY-5-/110614944637?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item19c12a1b7d)MCR100-6 THYRISTORMANUFACTURER = ON SEMI0.8A 400VTEMP RANGE = -40c TO + 110cTYPE TO-92 CASEDoes that look suitable do you think?Cheers all!

author: Unknown
author_rank: Unknown
timestamp: December 18, 2010, 09:29:03 pm
content: Quote from: Hero999 on December 17, 2010, 09:08:28 pmIt would not make sense for these to be SCRs if they were powering the lights directly from the mains. I had a much closer look at the routing of the traces in the pictures. It appears that the light strings are powered from the output of the rectifier. Therefore, chances are they are indeed SCRs.However, the datasheet clearly states thats it is a bidirectional thyristor (top right), aka a TRIAC. But the terminal markings are that of an SCR.To further complicate things, the company on the datasheet is:http://www.forward-tech.com/(use google translator)I could not find that part number in the SCR or Transistor ranges (they have them separate). Crazy...Are the lights LEDs?

author: maxwell
author_rank: Newbie
timestamp: December 18, 2010, 10:21:05 pm
content: They are indeed LED's, 300 to be exact. Each LED appears to be hand soldered along with a resistor with four groups of LED's making up the 300. Each group assumably with 75 LEDs and resistors in each.I didnt have much luck with google. What I found did not look right so I am as confused as youIt looks like a diode rectifier from 240vac, a cap for smoothing and the transistors as gates controlled of a misterious IC which is powered off the 240v through a resistor.Hopefully someone will unravel the mistery. Crazy chineseThanks for the help!

author: Unknown
author_rank: Unknown
timestamp: December 18, 2010, 10:51:27 pm
content: Quote from: maxwell on December 18, 2010, 10:21:05 pmYeah, the whole rectification bit makes sense now. I opened an LED controller that I have here (dont we all these days) and found it is using the PCR606 which is a SCR, from China again.The MCR100-6 that was suggested is a suitable replacement, yes.But watch out! Our friends at Forward Tech make it too!http://www.forward-tech.com/fwsemi/products20f1.html?fncat=431

author: maxwell
author_rank: Newbie
timestamp: December 18, 2010, 11:32:49 pm
content: Thanks again. I have just purchased 5 MCR100-6's for £1.25 from ebay. Hopefully they will arrive before christmas doesWill let you know how it all goes!