Hantek DSO5102P oscilloscope PSU repair - Page 1
Forum section: electronics / repair

author: punkieys17
author_rank: Newbie
timestamp: September 14, 2022, 01:34:12 pm
content: The psu has a problem with all the power rails fluctuating, when disconnected from rest of machine. The oscilloscope obviously didn't like the fluctuations so various buttons etc were flashing. A few questions to help me get started please as I am not confident in pwm power supplies. Firstly one of the 3 pin large semis with heat sink is marked NSD618 B2045G - can't find it anywhere. It sits directly after the bridge rectifier and smoothing cap. Thinks it's a high power transistor but can anyone help. As all the power rails were fluctuating I am suspecting that chip. Unfortunately I then managed to incinerate components when my hand slipped. As a result the 3 resistors on the back of the board mounted in parralel are toast. They are marker R2x x3 ( can't read the second digit) and from memory were 1.8 ohms...if anyone can tell me would be grateful. The PSU board is marked for the DSO5000 series. Don't suppose anyone has a schematic....

author: mushroom
author_rank: Regular Contributor
timestamp: September 15, 2022, 01:27:59 pm
content: Google, first answer for hantek dso5000p schematics :https://www.mikrocontroller.net/attachment/175587/Hantek_Tekway_Voltcraft_DSO_hw1007.pdfCould the 5000P share the same PSU ? my 5102P has a different PSU. Yours is v1.1, Mine has no version # ; could be 1.0 ...

author: tunk
author_rank: Super Contributor
timestamp: September 15, 2022, 02:02:14 pm
content: Quote from: mushroom on September 15, 2022, 01:27:59 pmProbably not, the components and their numbering are different.Could you post a photo of the back, showing the burned resistors?If it's a marking on an SMD resistor, then R2x could mean that it isa 0.2x ohm resistor.

author: mushroom
author_rank: Regular Contributor
timestamp: September 15, 2022, 02:55:33 pm
content: Found this thread, could help a bit (just a bit !) :https://www.eevblog.com/forum/repair/hantek-dso5072p-power-issue/msg3080305/#msg3080305definitely not my PSU (all THT components), nor the OP's PSU : PCB is labeled 1.0, but there's a high res picture of the copper side : Rnxm means Rn is made of m resistors in series or parallel.

author: snoop33
author_rank: Contributor
timestamp: September 15, 2022, 03:16:57 pm
content: They are 153 (15k).Mine is also a "1.0" board, but it has a different bridge diode and I spot an additional transistor N4.I guess a low level PWM is provided to the big transformer by N2 then isolated feedback by N3 and N1 adjusts it.N5 on the rear is a 5V buck.

author: tunk
author_rank: Super Contributor
timestamp: September 15, 2022, 03:33:34 pm
content: Quote from: punkieys17 on September 14, 2022, 01:34:12 pmNo expert on this, but I think some SMPS power suppliesneed a load in order to regulate. How do you measurethe fluctuations, and are they still there when the PSUis connected?

author: snoop33
author_rank: Contributor
timestamp: September 15, 2022, 03:40:54 pm
content: I followed the first stage through and those 6 resistors with the optical transistor (N1, PC817X) are applying a load across the first (smaller) transformer.Being AC I would have thought the transistor would breakdown in reverse, they're usually 6v rated in reverse iirc.Also being 6 x 15k = 90k, that's a small load to be applying across the transformer output. I don't see it being enough to make it sag (220/90k = 2.4mA).Edit - my wild guess is with the yellow cap it's adjusting the AC phase. It handles the 110/220v switching.

author: tunk
author_rank: Super Contributor
timestamp: September 15, 2022, 03:59:41 pm
content: Quote from: snoop33 on September 15, 2022, 03:16:57 pmMost likely a TL431 voltage regulator:https://en.wikipedia.org/wiki/TL431Quote from: snoop33 on September 15, 2022, 03:40:54 pmIf you're thinking about the one between the twoyellow capacitors, it's a common mode choke:https://en.wikipedia.org/wiki/Choke_(electronics)#Common-mode_choke

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 15, 2022, 04:01:01 pm
content: If I'm correct N1 is used to make a 50 or 60Hz (depending on the mains frequency) signal, the scope uses for something. This is also found in the newer DSO2000 series.Look at the orientation of the optocoupler on the board. Pin 1 is on the 220V side, and that is the LED side of the optocoupler.So the 2.4mA you calculated is the forward current to drive the optocoupler.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 15, 2022, 04:03:47 pm
content: Quote from: tunk on September 15, 2022, 03:59:41 pmI think so too. It is just an input filter to get rid of some noise on the mains.

author: snoop33
author_rank: Contributor
timestamp: September 16, 2022, 11:47:02 am
content: Makes perfect sense, I had N1 operating the other way round in a moment of assumption.If the OP has burnt out those resistors (how, that's a hell of a voltage?) then N1 is toast as well.Going back to the original question, it looks like the 5V (buck) and 3.3V (unsure) lines are drawn from the +14v supply, so if the board still works without smoking I'd look at what the 14V line is like. It may require a second DSO though!

author: wasedadoc
author_rank: Super Contributor
timestamp: September 17, 2022, 05:57:07 pm
content: Quote from: pcprogrammer on September 15, 2022, 04:01:01 pmOn many scopes the mains AC is one of the source selections for timebase trigger.

author: wasedadoc
author_rank: Super Contributor
timestamp: September 17, 2022, 06:12:25 pm
content: Quote from: snoop33 on September 15, 2022, 03:40:54 pm@snoop33. Your VD1 on the underside is across the input side of the opto and conducts when the opto's diode is getting reverse voltage.The OP's board appears to have the diode in series with the opto. Compared to yours that halves the power dissipated in the resistors.See below.That first small "transfrormer" isn't. It is a common mode choke to reduce switching noise going out on the AC input cable.You wild guess is wrong too. Those yellow capacitors are also part of interference suppression. Nothing to do with "adjusting the AC phase" or 110/240 Volt switching.

author: pcprogrammer
author_rank: Super Contributor
timestamp: September 17, 2022, 07:00:21 pm
content: Quote from: wasedadoc on September 17, 2022, 06:12:25 pmWhen you take a real good look at the original posters PCB photo, you can see that it is not in series, but also in parallel to the optocoupler. It is hard to tell where the series resistors are following the traces, but probably in the same spot. The left trace coming from the input goes to the right pin of the diode, and then goes up to pin two of the optocoupler. The right trace runs below the right pin of the diode to the left pin of it and then to pin 1 of the optocoupler.A bit strange though is that the boards are both 2016/04 Ver 1.1.

author: wasedadoc
author_rank: Super Contributor
timestamp: September 17, 2022, 07:11:24 pm
content: Quote from: pcprogrammer on September 17, 2022, 07:00:21 pmYes, a real good look confirms that.

author: snoop33
author_rank: Contributor
timestamp: September 17, 2022, 08:20:44 pm
content: [Agree to the common choke and noise suppression]Yes I can confirm that diode is in parallel as wasedadoc states and agree with the reasoning.I hope OP doesn't try 1.8ohm resistors before reading that they are 15k, that isn't going to end well at 110+ volts.

author: TDogg
author_rank: Newbie
timestamp: September 13, 2024, 12:50:35 pm
content: If anyone is still interested in this topic, to fix the power supply to stop the problems reported here replace the 100uF 400V capacitor (C6) on the DC side of the mains rectifier BD1. It is dry and if you (very carefully) measure the voltage on the DC side before replacing the capacitor you will only get around 200VDC with 100VAC ripple!!

author: Mangy_Dog
author_rank: Newbie
timestamp: December 07, 2024, 11:45:30 am
content: Hi sorry to necropost but my scopes psu just exploded....First saw the fuse had blown then turned the pcb over and saw the three resistors R14 blew...This is one of the few posts I've seen talking about repairing this PSU... Sooo wanted to drop this question in...What would cause this failure?The caps still look solid and not expanded or leaked.I can fix these resistors fuse but, I might only be repairing the symptoms not the cause.Can anyone confirm the values of the resistors. From the photos at the OPs post show I think 125 1200000R? But its a little pixelated so not sure.Any ideas what made it go pop?

author: pcprogrammer
author_rank: Super Contributor
timestamp: December 07, 2024, 12:59:13 pm
content: For the resistors 1R5 is more likely. Burning up a resistor like these requires energy and with the resulting resistance still being 400k with 3 1.2M in parallel you need a high voltage to get that energy. But it is possible though on the primary rectified side.For this to happen the switching MOSFET driving the transformer can be shorted out. Can happen due to overheating.Best to check the scope circuit first to see if there is a short on it somewhere due to a failed capacitor or some other component. With a proper lab power supply you might be able to power up the scope to see if it still works and check the current draw. If it is al good, then work your way back to the power supply of the scope itself.

author: Mangy_Dog
author_rank: Newbie
timestamp: December 07, 2024, 01:55:49 pm
content: Sadly I only had this scope. I have a fairly budget labI do have a bench supply but its currently wired up with a work project so its kinda awkward to swap things around. I might have to put this onto a possible repair sometime later pile.I did wonder if it was 1R5 but it was hard to tell.I have the V1.1 PSU. out of interest is there a schematic for this?It does look like from a couple of other posts, these same resistors releasing the smoke... So I suspect its a design fault.I will look deeper into the unit and check the rest of the PCB to see if anything else has gone...Sadly it happened over night while I left it running in trigger mode hoping to capture an irregular fault were having with a work project. So maybe something did heat up over the long period and just went pop... Again design fault :p

author: tunk
author_rank: Super Contributor
timestamp: December 07, 2024, 03:43:48 pm
content: Wouldn't know, but a few days ago My Mate Vincerepaired a 12V battery charger where (IIRC) thebridge rectifier, two low value resistors and fusehad gone. Maybe you could check the rectifier?https://youtu.be/g1Z9M7g9H-A