Dead Xantrex HPD 30-10 repair (FIXED) - Page 1
Forum section: electronics / repair

author: Seekonk
author_rank: Super Contributor
timestamp: April 29, 2017, 02:25:30 pm
content: I picked up another power supply on ebay that I needed like a hole in the head. I justcan't resist buying a Xantrex supply for under $50 shipped. Physical condition wasgorgeous. Thought I would document the steps in the diagnosis and repair for thosestarting out in repair.I always test equipment with a lamp in series. I used a 100W for this testing as Icouldn't find one with a little less wattage. Lamps have a positive temperaturecoefficient and have minimal resistance at low currents. Should a fault be present,currents are limited by an increase in resistance of about 10 times. This allows youto test with power and at least gives you a chance to turn it off before major damagehappens.Unit as received will not power up, no display. Checked the large replaceable internalfuses, these were ok.There is an on board soldered in tan rectangular block 3A fuse F3that I can not check located just below. The underside of the board is blocked by heatsink. From appearance of board and printing, the BUZ80 FET that powers control electronicsappears to have been warmer than I like. This FET will at least get an additional heatsink. FET gate to drain resistance is 138 ohm, D-S is not shorted. There is a smallfuse F4, located just below the screw, connected to the FET and it is OK. Will checkthis section further later.Powered up unit and then disconnected AC. Plus and minus of bridge rectifier measured300ish volts before decay. Capacitors are powered, but that power does not get to theinverter FETs or control power FET. Control power FET does connect to the converterFETs. It appears F3 is open. The converter FET gates are not shorted or D to S. I loveXantrex supplies, but getting to parts of them is a mechanical nightmare. This unit hasthe additional M5A remote board which would complicate disassembly.It became obvious that F3 was bad. I always try to exhaust every possibility beforecommiting to a tough disassembly. It was tight, but I believed I could reach the boardwith the soldering iron to add some wires for a remote fuse. I went in with a needlenose and bent the fuse till it broke off the board. Checking it, found it was open.Soldered in a length of wire to be used for a more convenient fuse.I powered up the unit with a 100W lamp in series with the AC. The surge limiting resistor(shorted by a relay after delay) began to heat up and smoke. No damage done. Q4 thecontrol power FET was a little warm. Checked the diodes of the control supply outputand no shorts were found.Checked the Q4 gate resistance again. This time it was 77 ohms instead of the 138 ithad been. One of the resistors looked a little overheated near it. The four to the rightare of interest Pulled U6 the UC3842 switcher out to see if the gate resistance changed,it didn't. Things are pointing to Q4 BUZ80 that I had suspected earlier. Pulled up thedata sheet for the 3842 to see what went where.When I checked the resistors I found something interesting. R55, the current senseresistor, red black black silver (2 ohm) was measuring in the thousands of ohms. Liftingit up I found a small chunk had blown off the bottom. This was replaced with two 4.7 ohmresistors and another 15 ohm all in parallel. That combination measured 2.033 ohms. TheBUZ80 Q4 located top center of the board, which I stock, was just replaced without furthertesting and I added a small heat sink to it. R56 which had been heated measured 28 ohms,seemed about right for a gate drive resistor and it wasn't changed. Pretty amazed thatthe 3842 switcher chip didn't blow. It is nice that they socket this and other chips.Powered it up with the lamp still in series with the power and it functioned perfectly.All repairs were made to the top side of the board and no disassembly was necessary.All non functional dust was removed. So that was it, a fuse, 2ohm and a FET. As this isa little smaller footprint it will take the place of the Lambda on the bench.

author: eKretz
author_rank: Frequent Contributor
timestamp: April 30, 2017, 01:33:01 am
content: Nice job, love these PSes as well.