Tear down of 'onehunglow' bench power supply unit (model dhf-1501) - Page 1
Forum section: electronics / testgear

author: d3javu
author_rank: Regular Contributor
timestamp: September 26, 2014, 08:05:52 am
content: Hi folks.First tear down so took a very small and simple tool.I've used this power supply for the past 4 years.It is a 15V 1A linear power supply with 'short circuit protection'.It has no ground. the live wire goes to power switch button and then through tiny yellow wire to transformer while the neutral goes to glass fuse and then to transformers through another tiny yellow wire.The transistor attached to the heat sink is a mospechttp://www.onsemi.com/pub_link/Collateral/MJE2955T-D.PDF]mje3055t.The dip chip is aca723ce.Thank you.

author: Nermash
author_rank: Frequent Contributor
timestamp: September 26, 2014, 08:14:40 am
content: Wow, they couldn't even afford another 3 diodes for full wave rectification...

author: Kostas
author_rank: Regular Contributor
timestamp: September 26, 2014, 08:22:45 am
content: Quote from: Nermash on September 26, 2014, 08:14:40 amThat cylindrical thing on the left (last photo) looks like a bridge rectifier.EDIT: Looks like it has RC202 printed on it, could be aRectron bridge rectifier.

author: d3javu
author_rank: Regular Contributor
timestamp: September 26, 2014, 08:30:01 am
content: Q2 - J92 , Q3 - a42.. no idea what they areDL2 isa94, the one below D1 diode.the Q3 next to C5(green capacitor) is A1225.. again no idea what it is.The beefy D1 is IN540x.. couldnt see the code properly..

author: d3javu
author_rank: Regular Contributor
timestamp: September 26, 2014, 08:39:40 am
content: Quote from: Kostas on September 26, 2014, 08:22:45 amHaa, well i think you are correct. it is printed A94 RC202(four legged) with a diode symbol. The output wires from transformer go to this guy.

author: free_electron
author_rank: Super Contributor
timestamp: September 26, 2014, 09:12:15 am
content: Wow. they must have a huge stock of old harris ca723 chips...Especially since Harris went titsup in the mid 90's ...

author: d3javu
author_rank: Regular Contributor
timestamp: September 26, 2014, 09:20:11 am
content: oh, one more thing is that the big fatty capacitor on top right, it is a2200uf 25v nichicon.

author: ElektroQuark
author_rank: Unknown
timestamp: September 26, 2014, 10:12:59 am
content: A "real" Nichicon? Must cost more than the other components together.

author: d3javu
author_rank: Regular Contributor
timestamp: September 26, 2014, 10:55:48 am
content: Quote from: EdoNork on September 26, 2014, 10:12:59 amHaha, i have no idea. the 2 small caps are "nichicon" as well. the green big cap is samxon branded. So they are either a fake one or one that salvaged from landfill

author: GreyWoolfe
author_rank: Unknown
timestamp: September 26, 2014, 11:38:37 am
content: Back in my ITT days, our power supply quarter project was a dual variable power supply that had more parts in it than that.

author: MadTux
author_rank: Frequent Contributor
timestamp: September 26, 2014, 12:40:54 pm
content: It's your problem, I you live in USA and buy cheap china crap while ebay is flooded with old, good quality HP supplies that just need a little love to work another 30 years. And shipping is cheap within USA.

author: JoeO
author_rank: Frequent Contributor
timestamp: September 26, 2014, 03:29:30 pm
content: Quote from: MadTux on September 26, 2014, 12:40:54 pmThe OP's flag is for Malaysia, not the USA.

author: SeanB
author_rank: Super Contributor
timestamp: September 26, 2014, 05:19:31 pm
content: Don'y knock the 723, it still is a pretty good regulator, usable in a large number of ways. You can even make a switch mode supply using it.

author: MadTux
author_rank: Frequent Contributor
timestamp: September 26, 2014, 05:36:30 pm
content: Quote from: JoeO on September 26, 2014, 03:29:30 pmOOps, Sorry for that.

author: rob77
author_rank: Super Contributor
timestamp: September 26, 2014, 07:52:43 pm
content: Quote from: free_electron on September 26, 2014, 09:12:15 amprobably second hand chips (salvaged from old electronics) - nothing unusual in china especially for very cheap products. but might be also new one - a replica 723 manufactured in china.but otherwise that bench PSU is cute - considering the outsidei like it

author: German_EE
author_rank: Super Contributor
timestamp: September 26, 2014, 08:18:40 pm
content: Clean up the power wiring then add some heatshrink on connections along with a ground wire and you should be OK. I still build stuff using the 723 and when used correctly there is less noise than a 78xx chip.

author: d3javu
author_rank: Regular Contributor
timestamp: September 27, 2014, 03:06:01 am
content: Quote from: rob77 on September 26, 2014, 07:52:43 pmThere were 2 models.. one is this, another one has extra knob for current control, which cost slightly more.. sorry i couldn't find any picture of it. they are identical in every way except the extra knob.

author: d3javu
author_rank: Regular Contributor
timestamp: September 27, 2014, 03:08:48 am
content: Quote from: German_EE on September 26, 2014, 08:18:40 pmYes, thank you for the suggestions. I'll clean up the internal and do a follow up with photos.