Hantek DSO2102P power supply - Page 1
Forum section: electronics / repair

author: Mjolinor
author_rank: Frequent Contributor
timestamp: October 24, 2020, 05:54:50 pm
content: Having a diddly of a noodle baker trying to mend this thing.The symptoms are that the power supply cycles every second. The rails come up and are stable then it cycles and starts again.I am making the following assumptions based on the schematic that I downloaded from here.1) There is no feedback from the main scope board to the PSU2) Only the five volt output from the power supply is monitored and fed back through the opto to the chopper on the mains side.The scope was like this when I got it (ebay purchase). The guy I got it off had tried to sort it. Checked soldering and replaced the main chopper IC/transistor.I have checked all the components and they all seem fine. I have changed the TL431 and the opto isolator. The appearance is as new, no dust or grime anywhere, the scope has clearly not been used over much at all, possibly never.My power supply differs slightly from the one on this forum and this is (as far as I can work out) the difference.R13 and R14 are getting hot, > 50c and this is without the supply plugged into the scope, just sitting powered form mains. I have run it from a variac and it does the same down to 90volts when it stops working, sort of what one would expect.The circuit seems not sensible to me. I have fed varying voltage volts into the five volt rail and the opto does work, at some point it goes short on the mains side.Stuck now, suggestions please.

author: George Edmonds
author_rank: Frequent Contributor
timestamp: October 24, 2020, 06:10:50 pm
content: HiSorry to say, but the main problem that you have is a complete misunderstanding of how switch mode power supplies work and how they should be tested.Where did you find the partial schematic?George G6HIG Dover UK

author: Mjolinor
author_rank: Frequent Contributor
timestamp: October 24, 2020, 06:14:42 pm
content: Quote from: George Edmonds on October 24, 2020, 06:10:50 pmSorry to say but you are mistaken. I understand completely how switch mode power supplies work.I found the full schematic on this forum following links from this thread:https://www.eevblog.com/forum/testgear/hantek-tekway-dso-hack-get-200mhz-bw-for-free/3050/

author: George Edmonds
author_rank: Frequent Contributor
timestamp: October 24, 2020, 06:33:57 pm
content: HiI say again you have no concept of how a switch mode power supply works, and this is from your own words.FIRST THERE CAN ONLY BE ONE FEEDBACK PATH, and it is invariably from the most heavily loaded supply +5VDC in your case.What you are seeing is most likely caused by an overload on the supply by the rest of the scope, switch mode power supplies normally will not operate correctly without a minimum load on one supply, again in your case it is the +5VDC supply.I have repaired thousands of switch mode power supplies and know exactly how to do it.George G6HIG Dover UKt

author: Mjolinor
author_rank: Frequent Contributor
timestamp: October 24, 2020, 06:39:57 pm
content: Quote from: George Edmonds on October 24, 2020, 06:33:57 pmPlease do not reply in this thread again. If you have never seen a switched mode supply with multiple feedback paths then you are not as experienced as you believe yourself to be.I too have repaired hundreds of them I have also designed them as far back as the 1970s from discrete components. I did not ask for help because I needed someone to tell me I do not know what I am doing but I don't mind being told that if there are some constructive comments accompanying that will assist in the problem that I have.I believe that the schematic is incorrect in other ways and would appreciate some help from someone that knows about these specific power supplies, not some inane, non-contributory personal attacks from someone that clearly believes themselves to be better than I am but can only spout about it with no helpful constructive input.

author: Mjolinor
author_rank: Frequent Contributor
timestamp: October 25, 2020, 12:28:46 pm
content: Sorted. R9 and C10 up the spout.Problem now is that the backlight only flashes on power on and power off.

author: Mjolinor
author_rank: Frequent Contributor
timestamp: October 25, 2020, 07:29:05 pm
content: So, in6dh blown on the back of the display. It provides the power to the LED and runs from the five volt that was all over the place. I can buy one for £14 or a full display for just under £20, no brainer that really, display every day of the week.However I can just run the backlight off the 12 volt supply with a suitable resistor. Forward drop on the LEDs is about 8 volts so I reckon it is two in series probably, possibly three but I don't know what to set the current at. It is reasonable at 30ma, dim at 20 and worries me at 40.Anyone have an idea of what it should be for max brightness? Obviously it is a once only test if I go over, pretty terminal.

author: Kartika
author_rank: Regular Contributor
timestamp: March 30, 2021, 07:59:51 pm
content: Hi Do you fix your supplay ?

author: PKTKS
author_rank: Super Contributor
timestamp: March 31, 2021, 02:06:09 pm
content: Quote from: Mjolinor on October 24, 2020, 06:14:42 pmHello.. that thread is more than 100 page long..Would you care to .. or remember if..Where is the exactly reference for this PSU ?Thanks a lot.Paul