Rohde & Schwarz NGSM 32/10 Power Supply FAULT - Page 1
Forum section: electronics / repair

author: jemp
author_rank: Contributor
timestamp: September 20, 2022, 08:52:02 am
content: Hello Everyone,bought at HamFair a defect Power Supply R&S NGSM 32/10by inspection, found a defect 7805 Regulator ( PCB heated very black ) N307 on Regulator Boardthis is the NetSense Regulator and gives 5V out ( 5VMC ) for the CPU and some drivers, and frontpanel PCBwhen replaced, PSU works perfectly in all the functions, but ... the regulator gets very very hot even since the first 10 minutes... so abnormal !! ( hence the Blackspot op PCB )The input is +/- 12-13V and current is 520mAmps, so dissipation +/- 6-7 Watts..Can someone check if this is normal ? or should the current be much less..I checked every load and Display = 250mA - Regulator Board itself = 220mA en IEEE board +/- 50-100mAIf anyone has an idea.. much obliged.Schematics in annex !JP

author: m k
author_rank: Super Contributor
timestamp: September 28, 2022, 03:56:22 pm
content: What kind of a heatsink, picture?

author: jemp
author_rank: Contributor
timestamp: September 28, 2022, 04:22:43 pm
content: See pictures

author: m k
author_rank: Super Contributor
timestamp: September 28, 2022, 06:53:29 pm
content: A regulator designed by a support logic designer?Power by it self is not anything unusual but dissipation of excess heat is a bit limited.Maybe regulator's input voltage is much more than originally expected.

author: jemp
author_rank: Contributor
timestamp: September 28, 2022, 07:20:57 pm
content: it is 12V and circuit draws about 500mA, so 3.5 Watts is dissipated

author: jemp
author_rank: Contributor
timestamp: September 28, 2022, 07:29:48 pm
content: question was.. if the 500mA is OK, or too much..Will place a 10Ohm resistor in front of it.. so 5V wil drop down

author: m k
author_rank: Super Contributor
timestamp: September 28, 2022, 07:48:06 pm
content: 500mA is not too much for the regulator.For exact rise of the temp you need exact datasheet.20C/W is sometimes used and if that is the case then rise is 70C above ambient temp, a bit more than insignificant and obviously must be dissipated by a proper heatsink.

author: junioroqc
author_rank: Newbie
timestamp: March 13, 2024, 02:22:40 am
content: my device same problem

author: jemp
author_rank: Contributor
timestamp: March 13, 2024, 08:03:26 am
content: So normal then ?No so great design, from R&S, which suprises me

author: Hamelec
author_rank: Regular Contributor
timestamp: March 13, 2024, 01:04:35 pm
content: You should check whether one of those famous yellow tantalum capacitors is getting hot and drawing too much current..

author: junioroqc
author_rank: Newbie
timestamp: February 16, 2025, 05:58:13 pm
content: this is problem,after dissasembly cleaning remove old grease add silicone grease,asembly great working.

author: D2236
author_rank: Regular Contributor
timestamp: February 16, 2025, 06:35:16 pm
content: We have a few in the lab. In all we fitted an aluminum encased current bypass resistor (22 ohm/5W), across pin 1&2 of the regulator. The resistor was mounted to the short frame section between the pcb's. That was about eight years ago and all still running with no problems.We also installed a thermal switch to bring in the annoying fan only when the unit is working hard.

author: junioroqc
author_rank: Newbie
timestamp: February 17, 2025, 08:03:41 pm
content: chcel by som tlacitka a dokumentaciuvse co vam ostalo naviac