tracking problem in a dual bench power supply  (FIXED !) - Page 1
Forum section: electronics / repair

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: October 12, 2014, 02:24:42 pm
content: Dear all,I get hold on a 30 V 3A dual bench power supply Selectronic SL-1731SB, which seems to be the sameas the Velleman PS23023, and maybe some other ones.Both canals are OK, but when I coupled them in series, the coupling is totally wrongexampleTracking not activated : A : 5.4 V B: 10.3 V (photo 2)Tracking activated : A :25 V B : 10.3 V (photo 3)While one would expect to see both channels at 10.3VI could find a schematic of the PS23023 on the webhttps://www.velleman.eu/downloads/2/ps23023gbnlfresd.pdfBut I cannot locate the place I should look for some faulty component.In the power supply, apart from the display section,there are two same boards for each channel, an additional board forthe 5V channel, and a small board with lots of diodes thatI do not identify the role. (photo 1)Can anybody help me, by telling me where to search forthe faulty tracking behavior ?Thanksjxlbbb

author: Andy Watson
author_rank: Super Contributor
timestamp: October 12, 2014, 11:35:33 pm
content: Are you sure that the Vellerman manual corresponds to your power supply? The manual indicates two power transformers; I can only see one in the photo!The small board with diodes is possibly providing floating power supplies for the four panel meters.In independent mode, do the two channels function properly through their entire range? If they do, I would strongly suspect poor contacts on the two push buttons. Try exercising the push buttons and/or some contact cleaner.

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: October 13, 2014, 05:18:38 am
content: Thanks Andy,Are you sure that the Vellerman manual corresponds to your power supply? The manual indicates two power transformers; I can only see one in the photo!The photo is a partial view. There is a second transformer. I have also added a photo of the main board where the components can be easily identified. There is no doubt the power supply is the same as in the schematics of Velleman PS23023.The small board with diodes is possibly providing floating power supplies for the four panel meters.Thanks, I checked a few components there and everything seems OK.In independent mode, do the two channels function properly through their entire range? If they do, I would strongly suspect poor contacts on the two push buttons. Try exercising the push buttons and/or some contact cleaner.Yes, the two channels were OK over the whole range. I tested them with a 22 ohm load and a multimeter.I will test the push button. Thanks for the hint !Jacques

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: October 13, 2014, 07:26:11 am
content: Bingo !Andy, you were right !I measured the resistors at the pins of the push button. It was well conducting when closed,but seems to be problems for the open state. I dried everything with the hair dryer,fiddle a little bit with it, and then it went right in the proper state. The slave now follows themaster properly within 0.1 V. Maybe it remains to do a little bit of tuning.Does anybody know the proper sequence for tuning the RP1, RP2, and RP9 pots on the board ofthis power supply, following the schematics of the PS23023.https://www.velleman.eu/downloads/2/ps23023gbnlfresd.pdfThanksJacquesPS : The answer to the latest question has been given in the following threadhttps://www.eevblog.com/forum/repair/tuning-a-ps23023-power-supply/