Rigol RSA3015N Power Supply Board help - Page 1
Forum section: electronics / repair

author: soyouzka
author_rank: Newbie
timestamp: February 18, 2025, 07:59:58 am
content: Hello I am having trouble finding the problem in this Rigol3015N power supply boardThe problem initially was the RSA would not turn on. The fuse in the AC input port was blown - there was another fuse on the main board itself that was blown too. Replacing both did not help (250V 3.15A)-Probing the board, It looks like the 5V and 12V is OK, but the 20V is not OK:Nothing on the board looks broken and there is nothing obvious I can tell, but one of the transformers (the one responsible for the 20V) is measuring 5Megs across the primary & secondary terminals:Does this mean the transformers broken?If I use an external voltage supply, she turns on no problem, so I am almost certain its a problem with the power supply:bonus pic!

author: benj38
author_rank: Frequent Contributor
timestamp: February 18, 2025, 08:06:07 pm
content: You can either start testing components on the 20V portion of the supply blindly, or trace the circuit and draw a schematic of that portion, and then proceed more systematically.

author: reodor
author_rank: Contributor
timestamp: February 19, 2025, 08:04:22 am
content: No, that does not mean the transformer is broken. In fact, it is critically important that there is isolation between the transformer windings, especially between the primary and secondary. If there was no isolation, the secondary side would be live at mains voltage, which would make the device unsafe to touch.You can see on the PCB there is a wide area between the primary and secondary side, where there are no tracks at all. This is the isolation distance, where primary and secondary are kept well apart. Only the transformers and optoisolators straddle this gap.Did the new fuses also blow? Blown fuses can indicate a shorted semiconductor. A bad semiconductor could be caused by a failing capacitor.Have you checked the output diodes?

author: daisizhou
author_rank: Super Contributor
timestamp: February 19, 2025, 08:14:30 am
content: Quote from: soyouzka on February 18, 2025, 07:59:58 amIs it normal to measure the two MOS tubes offline? Usually it is NMOS

author: reodor
author_rank: Contributor
timestamp: February 19, 2025, 08:55:11 am
content: The two components you have circled are most likely the output, or secondary, diodes. They could have three pins, in which case they are probably dual diodes. Are there any markings on them?The output capacitors might interfere with an in-circuit test, but the diodes should still show as conducting in one direction.

author: daisizhou
author_rank: Super Contributor
timestamp: February 19, 2025, 09:15:40 am
content: Quote from: reodor on February 19, 2025, 08:55:11 amYes, it's possible, so it's best to measure offline

author: Harry_22
author_rank: Frequent Contributor
timestamp: February 19, 2025, 02:06:04 pm
content: Hi!What is about high tension at PFC capacitor C52?

author: soyouzka
author_rank: Newbie
timestamp: February 20, 2025, 08:25:17 am
content: Quote from: reodor on February 19, 2025, 08:04:22 amHey thanks for the info - The new fuses are not blown. When the old fuses blew we had a power outage - maybe the problem is related to a power surge but I do not know for sure.Quote from: reodor on February 19, 2025, 08:55:11 amI tested the diodes with a diode tester on a multimeter.2 of them after the transformer are both working (https://www.onsemi.com/download/data-sheet/pdf/mbr20h100ct-d.pdf)1 before the transformer of interest is working too (https://www.wontop.com/uploadfiles/56/sort_excel/pdf/er1000f.pdf)various thru-hole diodes seem to be working alsoQuote from: Harry_22 on February 19, 2025, 02:06:04 pmI am measuring this one at 120uF (its markings say 100uF)Maybe it is best to draw up a schematic; stay tuned :p

author: daisizhou
author_rank: Super Contributor
timestamp: February 20, 2025, 08:36:01 am
content: Are these MOS tubes? Are they normal? I mean open circuit, not straight through

author: daisizhou
author_rank: Super Contributor
timestamp: February 20, 2025, 08:39:20 am
content: As for these optocouplers, it is best to measure them offline to confirm whether they are faulty.