Siglent SDG1025, output stage CH1 not right - Page 1
Forum section: electronics / repair

author: Lightages
author_rank: Unknown
timestamp: May 24, 2015, 09:00:55 pm
content: I am an idiot.I managed to connect 30V+ to the output of my SDG1025, by accident of course.It is now outputting 1.4X the specified voltage. For example when I ask for 1Vrms I get 1.35 to 1.45 Vrms out of it. I suspect the output driver IC is fried, the surrounding feedback resistors, or both.Does anyone have a schematic of the output stage for channel 1? Any suggestions?The IC for the output stage is IC U19 in this picture. Probably it is the blown component and not the resistors but it would help to have the schematic.

author: kwass
author_rank: Frequent Contributor
timestamp: May 25, 2015, 05:38:29 am
content: I had the same thing happen to me too. I don't think I feed in quite as high a voltage as you but I freaked out a bit when I found the output had shifted up. Luckily all I had to do was cycle the power and everything was back to normal. Since you took this pic, you must have already tried this. Could you have a stuck relay?

author: Lightages
author_rank: Unknown
timestamp: May 25, 2015, 05:45:57 am
content: I haven't poked around too much yet. I can't see how the relay would have stuck from a high voltage but I have no idea yet until I see a schematic what I should be tracking down.Yes I powered off and powered up. It was outputting 1.35Vrms when I set 1Vrms. After self cal it outputs 1.45VRMS.

author: Armxnian
author_rank: Regular Contributor
timestamp: May 25, 2015, 06:39:10 am
content: Probably a blown IC. Have you tried setting it to the other output mode, e.g high impedance or 50 ohms. What is the reported and actual output voltage?The design isn't that complex, I bet it would be faster to poke around for dead passive components first, then check the internal voltages, than to find a schematic from Siglent, if one even exists.

author: tautech
author_rank: Super Contributor
timestamp: May 25, 2015, 11:02:21 am
content: @ LightagesAfter a hunt through thehttps://www.eevblog.com/forum/testgear/the-sdg1000-and-sdg800-thread/thread, I've found a few bits of info that should help.http://sigrok.org/wiki/Siglent_SDG1010Output amps:https://www.eevblog.com/forum/testgear/the-sdg1000-and-sdg800-thread/msg646787/#msg646787PS. I've pointed Jade (Siglent) to this thread.

author: Lightages
author_rank: Unknown
timestamp: May 25, 2015, 12:42:20 pm
content: Thanks for the help. I had already determined the part number for the output amp. Yes I would say it is most likely the problem. I am surprised it still outputs a clean sine wave though.

author: Siglent
author_rank: Regular Contributor
timestamp: May 27, 2015, 01:10:41 am
content: It seems that some IC has been burnt, please check the service manual first.http://www.siglentamerica.com/USA_website_2014/Documents/service_manual/SDG1000_ServiceManual_SM02010-E01B.pdfplease feel convient to contact ussupport@siglent.comorsales@siglent.com

author: Lightages
author_rank: Unknown
timestamp: May 27, 2015, 01:34:13 am
content: Thank you for the reply. Yes I have the service manual but it has no schematic. I am sure that it is IC U19,which is the output driver for CH!, that is damaged. Without a schematic it is just easier to me replace U19 when I can get a replacement part. Hopefully that is all that is blown.

author: Lightages
author_rank: Unknown
timestamp: May 27, 2015, 05:46:18 am
content: OK, just went over all the test points and the behavior again. It appears both channels only change levels with the relays and nothing happens in between while adjusting the outputs. The outputs look basically clean a sine wave like and vary in frequency correctly.

author: Lightages
author_rank: Unknown
timestamp: May 28, 2015, 06:21:43 am
content: Siglent:It was nice of you to respond, and I have followed the test procedure your pointed to. I have also sent you two emails and I have had no response. Any information yet?

author: nctnico
author_rank: Super Contributor
timestamp: May 29, 2015, 07:40:56 pm
content: How about just tracing the schematic from looking at the PCB? While you are at it, measure the levels going into and from the output stage. You can fix these kind of things without a schematic.

author: Lightages
author_rank: Unknown
timestamp: May 30, 2015, 01:18:55 am
content: Well it seems I have two choices. I understand that Siglent won't release schematics to me, even though I don't agree. So I can try to trouble shoot the board and spend many hours poking around and trying to trace down the fault. It will probably require lifting parts, hoping I don't damage them in the process, to see where the signal path goes wrong. And then buy the parts, if they aren't hard to obtain, or don't contain proprietary code, and try to solder them back into place and see if it works. This is not an easy or short term task here in Chile. It could take months for parts to arrive, and more months when I discover I ddn't change the correct parts.The other option is to accept the offer from Siglent. Yes, Jade responded saying that from the test point measurements I sent her it looks like the PGA got fried and I have to buy a new board. It is probably the most economic option in time and money in the end. At least I might have some parts from the fried board to play with too.Lesson? Don't be an ass and try to do things in a hurry. Always check that your connections will be OK before you make them.

author: Lightages
author_rank: Unknown
timestamp: June 20, 2015, 12:40:03 am
content: The end of the story:After consultation with Siglent, they advised me that there was there was something blown on the board that they could not help me troubleshoot and suggested I buy another main board. The diagnostics indicated it was more than just an output amp, more likely many more parts. I decided to buy the replacement board. At least it was much cheaper than a complete new unit.I arrived today and I swapped it for the old board. Yes it worked fine. I then pulled the TCXO from the old one and and put it in the new one and everything is back to normal for me.So now I have an old board with probably lots of good parts that could be used in other projects. The problem is that they are all surface mount of various pitch. What is the easiest way to harvest these? Heat the whole board in an oven and shale/scrape the parts off?

author: tautech
author_rank: Super Contributor
timestamp: June 20, 2015, 01:00:29 am
content: Stick it in an anti-static bag and only harvest what you need when you need it with hot air.Or better still, see if there's any interest in it on eBay, somebody just might need other than output stage bits.

author: Lightages
author_rank: Unknown
timestamp: June 20, 2015, 03:52:11 am
content: Yeah, I will probably squirrel it away for parts. Selling on EBAY for me is pointless. Shipping costs minimum $60 to ship anything outside of the country.

author: nctnico
author_rank: Super Contributor
timestamp: June 20, 2015, 11:07:21 am
content: Quote from: Lightages on June 20, 2015, 12:40:03 amIt is good to read Siglent sells replacement boards for a reasonable price.

author: Lightages
author_rank: Unknown
timestamp: June 20, 2015, 06:24:26 pm
content: Quote from: nctnico on June 20, 2015, 11:07:21 amYes! And it was reasonable too. The board cost $137 and shipping to Chile $35 by DHL. Much cheaper than buying a new unit. This was my first Siglent and my first dealings with their customer service. They have gained my confidence.

author: ivan747
author_rank: Super Contributor
timestamp: June 20, 2015, 06:49:56 pm
content: Quote from: tautech on May 25, 2015, 11:02:21 amNiiice, the thread is actually useful for something

author: Lightages
author_rank: Unknown
timestamp: June 20, 2015, 10:35:23 pm
content: Well harvesting parts from this board seems to be easy enough. A few seconds with my hot air gun and the parts come off no problem. This in contrast to another board I tried to get some parts off that wouldn't budge. I think the other board had the parts of interest glued down somehow in addition to being soldered. I was afraid my soldering skills had gone bad!