I need help to diagnose power supply issue on Siglent SDS1104X-E scope  - Page 1
Forum section: electronics / testgear

author: TK
author_rank: Super Contributor
timestamp: February 02, 2020, 03:39:58 pm
content: I have a Siglent SDS1104X-E scope that is not powering on. Green light on power switch is missing. Fuse is OK. I opened the unit and I get nothing out of the power supply. It is supposed to supply: +15V, -9.5V and +6.5V, but I don't get anything in the output pins It also has a pin named POW-SIGNAL, I am not sure if this is the low voltage supply that goes to the soft button circuitry or is an input from the soft button switch. POW-SIGNAL is also dead at 0V. I see no blown components, no smell, everything looks OK on the inside. I can hear a hissing noise very briefly when I plug in the unit to 120V, but the noise goes away and nothing happens.I contacted Siglent Americas to request warranty repair and I hope to get an answer next week.I appreciate any help / tips you can provide.EDIT: Power supply does not output anything.

author: nctnico
author_rank: Super Contributor
timestamp: February 02, 2020, 05:12:23 pm
content: I'd trace where the soft power button and LED are connected to and go from there IF the warranty has expired. If you have warranty then just send it back.

author: tautech
author_rank: Super Contributor
timestamp: February 02, 2020, 05:46:52 pm
content: 3 year warranty so no worry but what's blown ?Open thermistor ?As Dave says, for those playing along at home .....his teardown at the start of the PSU section:https://youtu.be/Kay4Jk2DHuE?t=375

author: TK
author_rank: Super Contributor
timestamp: February 02, 2020, 05:49:13 pm
content: The power supply is supposed to supply something to the standby soft button circuitry, correct? At the input there is a 4N35 optocoupler and the LED pins are on the primary side. From pin 1 and 2, I can measure 0.79V AC / 0.29V DC.

author: TK
author_rank: Super Contributor
timestamp: February 02, 2020, 05:53:32 pm
content: Quote from: tautech on February 02, 2020, 05:46:52 pmI sent an email to Siglent Americas support... waiting for an answer. I can measure 164V DC on the bulk capacitor, I think thermistor is OK. What I don't know is if the soft button circuit should be receiving supply from the power supply or not, as there is a green LED, I assume it needs some supply. Just curious while waiting for the reply from Siglent

author: tautech
author_rank: Super Contributor
timestamp: February 02, 2020, 06:04:25 pm
content: Quote from: TK on February 02, 2020, 05:49:13 pmLine triggering circuitry I imagine. The opto's output should go straight to the header then onto the mainboard.

author: TK
author_rank: Super Contributor
timestamp: February 02, 2020, 06:24:00 pm
content: Quote from: tautech on February 02, 2020, 06:04:25 pmIndeed, pin 5 from opto coupler (collector) goes directly to the header (POW-SIGNAL) and to the mainboard.

author: tautech
author_rank: Super Contributor
timestamp: February 02, 2020, 06:33:48 pm
content: The smaller 4 pin opto next to the transformer does the SMPS feedback.Check the fault finding section on P78http://siglentna.com/wp-content/uploads/dlm_uploads/2018/05/SDS1000X-E_ServiceManual_SM0101E-E01A.pdfCheck the keypad ribbon cables are seated correctly and/or jump the 2 pads mentioned that mimic the ON/OFF button.

author: CDaniel
author_rank: Frequent Contributor
timestamp: February 02, 2020, 07:25:27 pm
content: In this design the main power supply is allways ON , the soft stand-by button is just for microprocessor and the different small regulators wake-upSo the problem should be on the power supply module , usually something shorted or interrupted ... try power-up without the connector to the main board and check if there are voltages on the secondary electrolytics .

author: TK
author_rank: Super Contributor
timestamp: February 02, 2020, 07:33:42 pm
content: Quote from: tautech on February 02, 2020, 06:33:48 pmI don't get any voltage out of the power supply

author: TK
author_rank: Super Contributor
timestamp: February 02, 2020, 07:34:17 pm
content: Quote from: CDaniel on February 02, 2020, 07:25:27 pmI will measure the voltages on the secondary electrolytics and report back. Thanks

author: tautech
author_rank: Super Contributor
timestamp: February 02, 2020, 10:30:43 pm
content: Can you near field probe it to check for any SMPS switching activity ?Try when you power it up too as the PSU might be shutting down due to a short somewhere.There's a SMD LED on the mainboard that should be lit whenever mains is connected.Does this flash briefly when power is connected ?

author: rf-loop
author_rank: Super Contributor
timestamp: February 03, 2020, 03:50:44 am
content: Quote from: TK on February 02, 2020, 05:49:13 pmBtw, when you look PSU remember that there is also Trigger signal source for 50/60Hz mains trig.Your scope have warranty if you have purchased it from sources what are valid for NA Siglent warranty. (Even beginning of availability units have not reached 3 year age) So best way is wait free repair.

author: ArcticPhoenix0
author_rank: Contributor
timestamp: February 10, 2020, 04:45:31 am
content: Hopefully opening it up didn't send you down the river for your warranty.

author: TK
author_rank: Super Contributor
timestamp: February 10, 2020, 11:43:41 am
content: Quote from: ArcticPhoenix0 on February 10, 2020, 04:45:31 amSiglent issued the RMA for warranty repair after I let them know that the unit was opened for inspection for loose wires, etc. They said that they need to do a root cause analysis and repair it within warranty if they don't find any user caused failure (I guess they need to verify for broken display or case due to drop... blown input stage with clear sign of overvoltage, something visually obvious that caused the failure). I sent the unit, waiting for their reply.

author: ArcticPhoenix0
author_rank: Contributor
timestamp: February 10, 2020, 04:33:51 pm
content: Good to know they're working with you. Mine's got that tamper proof tape on the case seam so I presume yours does too. I've been told tough luck with other companies before if that seal was broken.

author: TK
author_rank: Super Contributor
timestamp: February 10, 2020, 07:26:53 pm
content: The warranty stickers are illegal since the 70’s in the US. Google “warranty label ftc warning companies” or something similar

author: ArcticPhoenix0
author_rank: Contributor
timestamp: February 10, 2020, 07:40:09 pm
content: Magnuson-Moss Warranty ActVery good info to have in this hobby/line of work. Thanks!

author: tautech
author_rank: Super Contributor
timestamp: February 10, 2020, 07:46:36 pm
content: Quote from: TK on February 10, 2020, 11:43:41 amGood, yes proper analysis needs be done in case there is a weakness in the design or substandard parts in the supply chain.With sales of many hundred Siglent units now I have never seen a PSU failure.

author: TK
author_rank: Super Contributor
timestamp: February 24, 2020, 08:19:27 pm
content: I received the scope back from Siglent North America. It is working now andfor excellent Siglent warranty service (They had the scope for about 1 week)!!!