Author Topic: Fixing my Mastech HY3005D-3  (Read 16960 times)

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Offline TeraHz

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Fixing my Mastech HY3005D-3
« on: May 26, 2013, 04:50:50 pm »
Hi guys, I've had this PSU for few years and recently as I was charging my lipo batteries (via charger, not directly) on both psu outputs at 17.8V @2A, my PSU went berserk and flipped one of the outputs to 50V and the other to 0. Needless to say, the charger on the 50V output died.

So I changed the input diodes, the power transistors, a bunch of caps (while I was at it) with good brand ones and managed to bring one of the channels (I think the secondary) back to life. It lost some of its upper range (only goes to about 26.4V), but I'm guessing because it needs recalibration from the new parts. However the other channel lost quite a bit of its upper range, doing 0V-0.02V :)

I've checked the voltage multiturn pots and they are still doing their 0-6.8kOhm range. Changed almost all of the transistors and regulators. Checked the big power caps, the diodes etc. I can't find what's busted.

I'm attaching the schematic of the PSU with some test voltages that I've done. I tried to trace the control signal from AC to the transistors which control the load. The green numbers are from the working channel, the red from the non working, as you'd expect.

I'm sure a better educated than me person can probably spot the issue right away, so I figured I'd ask.

Thanks
 

Offline Paul Price

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Re: Fixing my Mastech HY3005D-3
« Reply #1 on: May 26, 2013, 05:20:46 pm »
Looks easy enough for me. Need the V readings on the of the schematic:  N2, V22, V21, V13, V14  to give you a verdict
« Last Edit: May 26, 2013, 05:35:09 pm by Paul Price »
 

Offline TeraHz

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Re: Fixing my Mastech HY3005D-3
« Reply #2 on: May 26, 2013, 08:33:01 pm »
Here are more measurements.
 

Offline Paul Price

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Re: Fixing my Mastech HY3005D-3
« Reply #3 on: May 27, 2013, 12:40:38 pm »
I think I've localized the problem to a few parts.  V13 is the most suspicious, with V14 coming in as a close second.
Check the base-emitter, base-collector junctions carefully.

If they somehow seem to check out ok, I want you to momentarily connect a 1K resistor to the + output of the bridge supply to the base of V13 and look at the output voltage of the supply.  Whadja get?
 

Offline TeraHz

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Re: Fixing my Mastech HY3005D-3
« Reply #4 on: May 27, 2013, 03:10:38 pm »
Ok, just waking up :). The two transistors check out. Desoldered them and tested them (I had already replaced them).

By bridge supply are you referring to the 7812?
« Last Edit: May 27, 2013, 03:48:14 pm by TeraHz »
 

Offline Paul Price

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Re: Fixing my Mastech HY3005D-3
« Reply #5 on: May 27, 2013, 03:15:46 pm »
The 18V measured high power V7-V10 bridge + point.
 

Offline TeraHz

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Re: Fixing my Mastech HY3005D-3
« Reply #6 on: May 27, 2013, 04:01:26 pm »
With 1K resistor to the base of v13, the relays all click and the output voltage goes to 40+.
 

Offline Paul Price

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Re: Fixing my Mastech HY3005D-3
« Reply #7 on: May 27, 2013, 04:41:32 pm »
Ok, set  output voltage control to 1/2 range of travel. Connect 1K resistor from v5 cathode to pin3 of N2
 

Offline TeraHz

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Re: Fixing my Mastech HY3005D-3
« Reply #8 on: May 27, 2013, 04:49:26 pm »
Nothing happens. Tried from 12V as well. Dead opamp?
 

Offline Paul Price

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Re: Fixing my Mastech HY3005D-3
« Reply #9 on: May 27, 2013, 04:52:22 pm »
If you disconnect V16 and the circuit behaves the same, the op-amp is kaput.
 

Offline TeraHz

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Re: Fixing my Mastech HY3005D-3
« Reply #10 on: May 27, 2013, 04:54:40 pm »
V16? That's the CC mode led connected to the output of N1?
« Last Edit: May 27, 2013, 04:57:13 pm by TeraHz »
 

Offline TeraHz

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Re: Fixing my Mastech HY3005D-3
« Reply #11 on: May 27, 2013, 05:16:10 pm »
Removing V16 makes no difference, other than when I turn the CC pot all the way down it doesn't enter CC mode.

Removing V15 (the CV led) sends the supply to 42V+
 

Offline TeraHz

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Re: Fixing my Mastech HY3005D-3
« Reply #12 on: May 27, 2013, 06:21:35 pm »
Well, it is not N1 or N2. Just swapped them between the channels and nothing changed.
 

Offline TeraHz

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Re: Fixing my Mastech HY3005D-3
« Reply #13 on: May 27, 2013, 06:50:33 pm »
I think I figured it out! The schematic isn't 100% match with the board, but it was very close. There is a big resistor on the board, which I don't see on the schematic, which appears to be between RP4 and the 0-32V line (what I wrongly called GND in the first post). This resistor was about 15kOhm on the non-working board and 470Ohms on the working board... no idea what happened there but it would explain why my output had such a tiny range. The multi turn pot is 10K so adding 15K to that line would mess things up. Changing it to 470 fixed the output. Now to do some more testing in the full range with a DMM see how accurate everything is and to put this piece back together.

Thanks Paul for the time and help!
 

Offline Paul Price

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Re: Fixing my Mastech HY3005D-3
« Reply #14 on: May 27, 2013, 09:49:28 pm »
I cannot understand the your explanation on how the resistor values changing from 4700 to 15k would  limit the output close to 0, and you talk about something way out of these values "470", but congratulations, it works! Perhaps the resistor was  actually closer to open-circuit in operation.

Success needs no explanation.

Better to test the output with a real load (and watch the action on a scope if you have one) before you put the screws back, instead a just a quick voltage test using a multimeter.

And before the screws go in, what about the other channel?

You're welcome, glad to be of help!
« Last Edit: May 27, 2013, 10:08:18 pm by Paul Price »
 

Offline TeraHz

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Re: Fixing my Mastech HY3005D-3
« Reply #15 on: May 27, 2013, 11:05:00 pm »
I changed it from 15K to 470. Not from 15K to 4.7K. I think the issue was that the circuit works over 500-10Kohm range on the  multiturn pot. A 15K resistor in series with that would make it ~15k-22K range instead, so turning the pot makes no difference it is always at its lowest voltage. Does that make sense?

Both channels work now. I'll be testing with load and will watch the scope. Unfortunately have to come up with something to do a proper load. I don't have an electrical, or even a CC dummy load.
« Last Edit: May 27, 2013, 11:08:28 pm by TeraHz »
 

Offline Paul Price

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Re: Fixing my Mastech HY3005D-3
« Reply #16 on: May 28, 2013, 12:43:33 am »
Test Load Ideas for your power supply.

(1) One or more 3 to 10 watt 1 to 10-ohm resistors placed  in a can filled with ice and water...good for several minutes of entertainment. I always enjoy watching the tiny bubbles.
(2) A resistor from collector to base of any power transistor, even a small one on a large heatsink (a bench vise will work clamping any flat surface of the power transistor to a large piece of flat metal) will make a variable load you can use until your workbench catches fire or your little brother keels over from the smell and the smoke.
(3) Even T0-220 NPN or even PNP power transistors or power n-chan MOSFETS mounted to a 2-in sq. heatsink will survive many minutes when biased to handle 3-amps or so(100 to 1K from collector to base), if submerged in a robot's cocktail, made with plenty of ice and served in an old deep dinner plate. add enough water and chopped ice and simmer until done. Use a small PC cooling fan if you run out of ice.
(3)You can usually find one or two 3-15amp  High Voltage NPN power transistors aleady mounted  on a large heatsink in discarded apparatus, such as a discarded PC power supply which you can ravage and just rip the parts you want out quick with handy tools, for example, a chainsaw. If your pets are bothered by the noise, use use a small hammer, a large screwdriver and, if you like to get the job done fast, a hand held saber saw. The fan on it will cool the load if you power it with 12V from the power supply channel you are not testing.
(4) Car 12V lights, the higher wattage ones used in headlights or tail lights are both durable and blindingly good loads.
   
« Last Edit: May 28, 2013, 12:53:41 am by Paul Price »
 

Offline Teneyes

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Re: Fixing my Mastech HY3005D-3
« Reply #17 on: May 28, 2013, 11:48:22 am »
Hello, I picked up a HY3003-D3 on Ebay, and it was Blown apart, I ended up just paying shipping.
 I found debugging was better when voltage measurements were made using the Positive output (X2) as the reference point, Note that all the control logic is riding on top of the Pos, output.  In my PS the big Caps 4700uf were gone (cut out), but you may wish to also check C20 ,470uF , if you see(meas.) AC Ripple.  I my case I added a 3rd 2N3055 and convert to my HY3003D-3 into 5 amps like yours. See pics . I used a  bank of 100 watt ac lights (old style not LED!) for load
Is this a Better Schematic
« Last Edit: May 28, 2013, 12:05:57 pm by Teneyes »
IiIiIiIiIi  --  curiosity killed the cat but, satisfaction brought it back
 

Offline Paul Price

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Re: Fixing my Mastech HY3005D-3
« Reply #18 on: May 28, 2013, 12:40:59 pm »
It appears that the emitter of V26A wiring if definitely in error in your schematic.
 

Offline Teneyes

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Re: Fixing my Mastech HY3005D-3
« Reply #19 on: May 28, 2013, 01:15:47 pm »
It appears that the emitter of V26A wiring if definitely in error in your schematic.
  Yes Missing the connection, emitter of V26A to the output.  It was just one on the many I found.,  It was a fun mod for me, and learning experience :)
IiIiIiIiIi  --  curiosity killed the cat but, satisfaction brought it back
 


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