Maisheng MS-605D Power Supply

[tristate]

Hi,
bought this from taobao China for 339RMB + shipping
performs well with no overshoot (load /no load)
I traced the schematic for repairs
Here is a similar one on youtube from user  Elecifun:

All four of the front potentiometers failed, reading far too high.
There are 2x10K and 2x1K single turn pots. The failure is due to poor manufacturing I think, because the resistive track still measures correctly with a meter, but after the joint between the solder post and the track the value is very high.

tristate

[Cliff Matthews]

Everything OK? You say "performs well with no overshoot (load /no load)"  So then, you're happy with it?
Then you say, "I traced the schematic for repairs" So then you are studying it expecting a future failure?
Then you say, pot values are too high, without giving info or pics for the front panel board connected to 8-pin CN5/6.. (between TL431's and LM324)

What is it that you expect here? Your subsequent post (which you should delete) just says "test"     

[tristate]

I posted the test message, after my original message posting failed but with no error message from the forum (turns out due attachments being too big).

After posting worked, I tried to delete the post 'test', it wouldn't let me, it seems to be gone now.

Expecting nothing, after I replaced pots, everything fine (excellent value).

Just uploaded schematic because it doesn't exist online and others may find it useful.

Here are pics of the control board and a failed pot.

tristate

[DTJ]

Very nice work on documenting, I'm sure others will find this info very useful for repairs.
It also helps others like me who are in the market for a low end bench supply.

Cheers!

[Harvey17]

Just a quick note to anyone who has one of these, the rear left foot is held in with a screw which if overtightend will come in contact with the PCB right at the point where the mains input connects.  "Interesting" results would occur.

They also are fairly awful at any form of constant current limiting, being switchmode they jitter between CV and CC, especially at low current settings.

[Robert99d]

Hi sorry for opening up an old topic.
New here nice to meet you all
I've just got this power supply from eBay the 10A version, model ms3010D seems to be the same PCB
All seemed to be fine but when trying to current limit both CC and CV LEDs come on and it emits a high frequency buzzing ( from the transformer I think)
Is this normal for them to not current limit very well, as stated above?

On opening it up to have a look noticed R47 is snapped
Think seller is going to offer a partial refund but wanted to know if anyone can tell me what R47 does and is it likely to have caused any damage or can I just replace the resistor
Thanks for any advise
 Robert

[belvoir]

hello sir,
I have a problem with a Maisheng MS3010D when switched on the output voltage is at 39.00 volts and slowly goes down to zero, nothing adjusts, I have replaces fets but still the same I have also solderd front pots like you say... I wonderd if you new how to obtain some service information as I am a fully qualified tv engineer thank you so much for your help all the best kev…. cornwall england

[josephgut]

Hi, I have basically the same power supply, but the 10A version. Mine does not power up properly. When I turn it on a hear a high-alternating high-pitched noise. No display is active. I've heard that on a power supply this noise is typically from not enough voltage to the transformer? I've looked at the soldering and re-soldered things, tested the capacitors and don't see anything obvious. Any suggestions would be greatly appreciated.

Thanks,
Joseph

[xavier60]

I can't make much sense of the driver circuit. I wonder if Q4, Q5, Q6, Q7 are really all NPN?

[flindersit]

Hello reading on from the post I've been searching high and low for a replacement transformer marked on the board T3. The closest thing I found was a transformer called ERL 35 found on Ali Barbara link below (https://www.alibaba.com/showroom/erl-35-transformer.html)
I believe this is for the 30 V version and I'm needing the 60 V. The pinout is slightly different as seen pictures in AliBabaa.com
is anyone able to assist me to locate a new transformer after mine has gone short-circuit the primary site and it also took out IRF 840? Surely appreciate your assistance, I am an amateur electronics enthusiast learning as I go.

Kind regards Adrian.

[ste222]

Hi great article  I have 2 of these and  found that they  both put out  noise   and make   readings  using a scope   useless if they are near  the equipment being tested causing mis triggering  my  digital scope is  terrible  when near them and  my old tektronic one also misbehaves  any waveform has noise superimposed on the waveform only if i run the ps on a 15ft  mains lead extension do i get a more stable reading ive tried fitting   ferrites inside on all  leads  even some on the  mosfets and added another mains filter unit the  only way to get the noise down is by using an extension lead i would add i am looking at low voltage  signals  about 1 volt   at say  6KHZ range but  the noise from the ps makes them virtually  useless for   this type of work once again thanks for putting the info on here

[felipex1969]

 I share my experience. I purchased a MS3010D bench supply from Mercadolibre one year ago. The equipment was in the box for almost a year. I beginned to use this month and suddenly the CC LED turned on, the output is zero and the volts reading is actually 0. When the supply was functioning  I heard a small and high noise, think is the oscillator transformer.
After checking all, no wires open and no resistors are burned. Checking voltages at the cursor of 1K and 10K Pots for coarse and fine current  leads to 0 volts, with pots for voltage the reading is between -2 and 2 volts.

I changed the 4 pots and the power supply came back to live.
Thanks to the previous colleages for posting the schematics and the pictures.

My PS have a two layer PCB and SM resistors, all of it which made more difficult to trace the paths.

For the original poteniometers, they are not very good in quality, only one was open, the 10K Pot for current, but i decided to change all.


I disconnected the resistor R47, but the value is Ok but L2 is a problem to resolder it, so I soldered in the opposite side of the PCB.

Thanks for the help and comments.

FC

[DarkWolf1945]

Xavier, you are in the right direction, transistors Q5 and Q6 are PNP 2TY, S8550, the schematic looks wrong!
On my MS3010D y changed all the four transistors, and now works well! The schematic must be the same of MS-305D with some component different, i have not found the MS3010D schematic, if someone have the correct one, please, send it to me. Hope i was useful to someone.

[Luke_029]

Hi. I wish to thank you for the documentation. It helped me solve my Lab power supply. Mine is QW-MS305D.

In fact the schematic is wrong. Both Q5 and Q6 should be PNP. I'm posting the corrected circuit.

I also found that it had poor regulation in low current setting. If, for example, I connected an LED and adjusted the current to about 10 - 15mA the LED will burn because the current rises above 200 mA or so and stay that way. I solved this problem taking of the capacitor C38. Now the circuit is stable in current regulation even in values of some mA.

[ThermallyFrigid]

No, two are NPN and the other two are PNP

(for the benefit of future travelers to this destination)

[ThermallyFrigid]

There are several versions of this power supply available.  The schematic in this thread does not cover them all precisely.  The designs are very similar but can vary slightly.

One example....in the schematic posted in this thread it says D19 and D21 are unpopulated.  However on the version I have, there is a ES2G diode at each of those locations.
The board I have has no C43 nor C44 ceramic capacitors
Also, at D1 this schematic list an MUR1660 diode but the one I have uses an STTH1602CT
Instead of a KA7500, mine uses a TL494CN
The board I have also utilizes a TL084CN Op Amp

The board in mine is dated September 17, 2015....and may be an older version

Some of the other components are different.  I need to do a complete schematic on the one I have.
That said, the schematic provided I believe is for a 60v version, I have a 30v version.

[Doctorandus_P]

I've also got some cheap chinese power supply (NG1620 16V, 2A) and it also has problems with the pots. The rivets with which the pins of the pots are connected to the pcb with the resistive track do make intermittent contact.

[solderjoint]

Hi
I know this is an old post
Please can someone upload details of replacement potentiometers such as shaft size etc
Thanks all

[Chrizzly92]

thanks for sharing your reverse-engineering work. after the PSU was only able to deliver around 400mA at around 5V, i took a look and measured the components. turns out Q1 and Q3 aswell as R5 was dead, even though all components looked okay.
my unit was equipped with FQP13N50C instead of IRF840's, which are hard to track down, at least here in germany. after looking around for some time i found your schematicss. simply replaced them with IRF's and the PSU works just fine again. 

[Circlotron]

All four of the front potentiometers failed, reading far too high.
There are 2x10K and 2x1K single turn pots. The failure is due to poor manufacturing I think, because the resistive track still measures correctly with a meter, but after the joint between the solder post and the track the value is very high.

tristate

I have the MS-305D 30V 5A version. Just recently the voltage setting became all unstable and jumping around several volts when set above about 24v. We shifted factories at work several years ago and there was this big bag of 10K pots that hadn't been used for 17 years and I was chucking stuff out left right and centre but I saved the pots for some unknown reason.

After reading this thread I looked at my big bag of pots and they were 10K and the four in the PSU were also 10K and the exact same size. Unbelievable... So I replaced all four at zero cost and so far the thing seems to be going fine. You win some.

[MrWoo]

The other corrections I found were the opto diode wrong polarity and pins 7 & 6 on pots board interchanged. wipers 4 & 7.
My unit had the quad op amp defunct - replaced with socket and back in business.
Don't like the design, would think the inductor should be on the positive side with a freewheel diode.

[Dannyx]

Seeing how this thread is fairly up to date, I'll join as well:

I recently fixed my QW-MS3010 supply after I blew it up about a month ago . I was charging my E-bike's battery pack, trying to balance the cells individually and I accidentally left the positive clip of the supply connected to the "hot" end of the battery, while moving the GND clip to a "lower" set of cells that I wanted to charge (instead of disconnecting the "hot" clip FIRST). There was a loud bang and some sparks flew out of the vents of the power supply. The display was still going just fine though ....(WTF is the fuse for ). The clip had welded itself to the nickel battery strip

I took the case off and thankfully the damage wasn't that bad (at first glance): Q1 and Q3 were obliterated, as well as R2 and R5. I replaced those with some "beefier" transistors I had laying around. I tried powering it up, but the current immediately shot to 10a and stayed there no matter what I set the knobs to. There was a direct short between the positive and negative output terminals caused by D19 and D21 (ES2G diodes), which in my case exist on the board, despite the schematic listing them as unpopulated - someone else mentioned this. I took them off and replaced them with a suitably-sized thru-hole diode (since I didn't have any SMD ones of this size on hand) - they're for reverse-polarity protection anyway, so they're not that critical.

Now, I was able to adjust the output like normal, but it quickly dropped to 0v when any load was applied....what gives ? Turns out U6 had ALSO died, which in my case is a TL084. Replacing it FINALLY fixed the problem and I had a working supply

I noticed with my thermal camera that R13 gets pretty hot, as well as the two 51R resistors near D1 at the top - they are glowing against the rest of the board ! This got me thinking whether anybody has done any improvements to this supply, like changing the values of any of the components to make it work better in terms of regulation or something else. I don't have an oscilloscope, but I ASSUME the output ripple is pretty bad, esp. as high currents and low voltages......

[justincr83]

I had some issues with this model. Psu blew while up powering an bmw fan radiator… it took out both irf transistors, ka7500, q5 and q6, and one diode near them…
I replaced all the faulty parts according to above schematic and first time blew again and second time only blew one diode and q4…
It turned out that indeed q5 and q6 are PnP tranzistors (s8550)
Now it’s working again, with a little hissing on the big transformer, only when it’s over 5v.