Mastech DC Power Supply HY3005DX - Cheap and very impressing! - Page 1
Forum section: electronics / testgear

author: Zucca
author_rank: Unknown
timestamp: August 09, 2014, 06:52:52 pm
content: I was looking for a decent and cheap power supply. I found this:http://www.mastechpowersupply.com/dc-power-supply/linear-power-supply/volteq-regulated-variable-dc-power-supply-hy3005dx-30v-5a/prod_67.htmlQuotefor about $110, and I took it home.It was working just fine for a while, then my bad I dropped that thing on the bench and it started to have a sporadic failures. I decided yesterday to open it up and repair it.Impressing! I was so blown away I decided to report it.Internal overviewPower boardDigital Control board for V and I displayRear front PCB output panel: on the left the left positive output, in the middle the earth and on the right the negative output. Attention to detail: black sensing wires are connected to positive output positive (purple big wire) and red sensing wire are connected to negative output (black big wire)Front PCB output panel, to improve the space efficiency and reduce the cost elco filtering cap is mounted touching the board on the side with no glue compound to hold this rocking chair in placeIn this way the elco cap solder joints can easily crack. That increased resistance located in the cracked joints will protect that output cap during unwanted output overvoltage situationsUnder the power board, carefully trimmed bad solder joint to precisely increase joint resistance under the calibration pots.Generous amount of flux residual everywhere to protect the delicate precision power circuit from dust and other external dirtA beginner could think the development ran out of space in the main power PCB. No, that lovely balcony mounted PCB mounted on the power transistors heat sink will use the hot air to stabilize the little transistor pnp junction to ensure a jitter free (and stable in a wide range of ambient temperature) safety relais actuation to cut the main lines.Also the 5V 7805 heat sink is carefully placed close to the elco caps for thermal stabilization.At the end of the day after my last score in ebay...eBay auction: #371113062026I feel like I throw my money out of the window with Mastech.-----------For High Resolution pictures:http://postimg.org/gallery/1mzeoqfa/

author: radhaz
author_rank: Regular Contributor
timestamp: August 09, 2014, 07:07:48 pm
content: Looks like you could replace the large cap with 3 smaller caps.

author: Electro Fan
author_rank: Super Contributor
timestamp: August 09, 2014, 08:41:10 pm
content: The HY3005DX looks nice on the inside but maybe for a few dollars more they could add an output on/off switch.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: August 09, 2014, 09:05:48 pm
content: Don't you love how, in the headline pic, the "VOLTEQ" logo looks painted on? Like... Windows Paint-ed on?Same POS is rebranded by any number of sellers; beats me if there's one or many companies ultimately manufacturing the things.Last time I had one of those available, half the time the fan wouldn't start, and in any case, the "heatsink" (no fins whatsoever, just an aluminum plate with three TO-3 transistors on it -- yeah, like more transistors will handle more dissipation or something!) got much too hot even at half rated load. Eventually, the fan itself died (its BLDC circuit kicked, but the fan didn't turn over, hence the circuit just sat there cooking itself into a single winding), and the rest of it followed later.The higher power (switching) models are pure shit. They lack sufficient EMI filtering, creepage distance, anything reminiscent of proper design (e.g., switching transistors grossly mismatched to a piss-weak drive circuit), and the output doesn't even begin to meet the already generous specs claimed in the datasheet (such as SOA and ripple). The failure mode I observed: high current, low voltage: because the gate drivers swing in microseconds, a low duty cycle output utterly destroys the transistors.Conclusion:If you need a bench supply, don't be a cheapshit. Find some good old iron, like HP, Kepco, etc. If you want new / computerized, find something with at least a little quality, like an up-scale Rigol. Expect to pay over $1/watt capacity. New name-brand equipment, >= $3/W.Or make your own, so you have only yourself to blame for its failure (and there's nothing that you can't fix).Tim

author: Bored@Work
author_rank: Super Contributor
timestamp: August 09, 2014, 10:54:18 pm
content: Quote from: T3sl4co1l on August 09, 2014, 09:05:48 pmThat particular one is apparently manufactured by Longwei. The LW on the front panel PCB gives it away.

author: Zucca
author_rank: Unknown
timestamp: August 10, 2014, 01:40:55 am
content: Quote from: T3sl4co1l on August 09, 2014, 09:05:48 pmAMEN BROTHER! O0