DM3005XE (generic adj 30V-5A PS) incorrect output after getting reverse voltage - Page 1
Forum section: electronics / repair

author: JPortici
author_rank: Super Contributor
timestamp: July 14, 2025, 11:54:16 am
content: Wrong story short, it was being used to slow charge a 12V battery and the guy connected it backwards.The output protection diode broke as a short. After changing the diode we got an output, however after 10-15 seconds it started to rise to about 2-3 times the set voltage. Then i opened it up again to make sure i didn't miss anything. Nothing obvious. I poked around some supply lines and they seem correct, none of the ICs are getting hot. however there is obviously something still wrong in the feedback loop.. i think.I tried to find a schematic, but couldn't find an exact match, but something that looked like a dual output version of this.There are some trimmers, i suppose for calibration, but moving them didn't have any effect on the output.The power supply is labeled DM3005XEbut it can be easily found online with a number of other names. It actually surprised me i couldn't find a schematic.. but even then, i'm a bit at loss. My next step would be to get and replace all ICs in the control board but i hope i can get some advice from you guys

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: July 14, 2025, 08:58:50 pm
content: These type of cheapo power supplies rely on the ADC of an microcontroller for the voltage display.If I had to take a guess, that ADC is shot. Since you cannot replace it without having the firmware, that's pretty much a total loss.

author: JPortici
author_rank: Super Contributor
timestamp: July 15, 2025, 04:53:06 am
content: Wrong.The display is on a separate board and has nothing to do with regulation.Because i'm not stupid i took out a multimeter to check if there actually was whatever was read on the display.

author: coromonadalix
author_rank: Super Contributor
timestamp: July 16, 2025, 10:01:38 am
content: checks would be if it has protection diodes on the output, or other devices on the output ...having no schematics try to reverse engineer it, is it an linear model, not an smps / switching model ?they are known too as Digimaster DM xxxx

author: JPortici
author_rank: Super Contributor
timestamp: July 16, 2025, 10:35:20 am
content: Only protection at the output was the reverse polarity diode, which failed short and was replacedthe attached schematic is for a different unit (this one is one channel, and has a potentiometer to set the target voltage instead of a cpu board + dac) but the analog part looks rather simillar, ICs and most components values checks out. I don't really understand how it reads back the voltage for regulation

author: coromonadalix
author_rank: Super Contributor
timestamp: July 16, 2025, 03:22:06 pm
content: ok thks if they are somewhat similar, the pass power transistors may have been damaged q1 q2 q3 q4even this schematics is kinda shit, not easy to follow

author: JPortici
author_rank: Super Contributor
timestamp: July 17, 2025, 05:21:26 am
content: Quote from: coromonadalix on July 16, 2025, 03:22:06 pmYeah, i know.

author: Kleinstein
author_rank: Super Contributor
timestamp: July 17, 2025, 08:42:15 am
content: The circuit looks like the kind of normal floating regulator type. With all the connectors the signals are hard to follow.Damaged output transistor are defintely a condidate and easy to check.