GW Instek GPS-3030dd Lab DC Power Supply Voltage is constantly 49V.

[somekoreanguy]

Hello everyone! 

I've just purchased a GW Instek GPS-3030dd Lab DC power supply and here are the specs:

Product Features:

Power: 0 - 90W
Voltage: 0 - 30V
Current: 0 - 3A
Light and Compact Design
Dual LED Display for separate readouts
0.01% High Regulation
Constant Voltage and Constant Current Operation
Series or Parallel Operation Function
Remote Control for External Programming
Internal Select for Continuous or Dynamic Load
Low Ripple and Noise
Overload and Reverse Polarity protection
Available in alternate configurations:
GPS1830D - 0-18V, 0-54W, 0-3A
GPS1850D - 0-18V, 0-90W, 0-5A
GPS3030D - 0-30V, 0-90W, 0-3A

The problem is.. The package didn't arrive very nicely.. the box was dropped I guess and I see that the output knob panel was pushed into the device (not a big deal)

But! when I powered it on, the adjusting AMPS and Voltage didn't work... The amps won't adjust (when it's turned, it'll click and make show the amp and voltage though!) and the voltage stays at 49V. No matter which knob I turn it just stays there.. =( Also, the AMP knobs do the same.

My question is.. Do you think this is a complicated problem? I would like to fix this so that I can save money because the seller has claimed this shipment damaged with their insurance and has refunded me my money back  So, If I can fix this, it'll be a GREAT experience and be worth it too!!   

If you had this issue before, please guide me to where I should be looking first! Thanks in advance YOU! 

P.S. I couldn't find the schematics for the boards....

-Jason

[TheSteve]

Have you opened it up yet - if so take some pictures and post them. If it was dropped the problem may be easy to spot.

[somekoreanguy]

Have you opened it up yet - if so take some pictures and post them. If it was dropped the problem may be easy to spot.

Yes, I did. but since I'm at home now, I'll take some pictures when I get back to the shop! But, as far as I can see, nothing was actually broken... only the plastic legs that the screws are screwed in place on the backside of the front panel to hold the output panel in place. I'll just screw it in with a longer screw =)

Also, I checked the voltage output and it is giving 49 volts as it's displaying if this helps.. I've probed around ends of the output and they all measure the same voltage.. 

[Kleinstein]

Normally a broken supply that give something like this would clearly indicate damages output transistors FETs due to overload / heat.  But it is unusuall to see this due to a mechnical damage.

The first thing to loock /  check is for damaged (insulation) or loose cables - this might be the sense wire does not have contact any more. Though this might have stoped the internal reading too.

[somekoreanguy]

Normally a broken supply that give something like this would clearly indicate damages output transistors FETs due to overload / heat.  But it is unusuall to see this due to a mechnical damage.

The first thing to loock /  check is for damaged (insulation) or loose cables - this might be the sense wire does not have contact any more. Though this might have stoped the internal reading too.

Thank you! I'll check them when I get to the shop and write an update! 

[tooki]

Also, check the output filter cap. Some supplied cannot regulate without it.

[wraper]

If it was dropped on the front panel, most likely some potentiometer(s) was broken.

[somekoreanguy]

Have you opened it up yet - if so take some pictures and post them. If it was dropped the problem may be easy to spot.

Ok, so here are the pictures!

So, today I turned it on and 3 things are different...

1. The voltage and the amp are both at 0.00 (before it was 49v and some numbers in amps)
2. when I turn the knobs nothing happens (before when I turned the current knob C.C. led came on and off)
3. when I measure the voltage from the output holes, it's 0v. (before it used to read 49v)

Normally a broken supply that give something like this would clearly indicate damages output transistors FETs due to overload / heat.  But it is unusuall to see this due to a mechnical damage.

The first thing to loock /  check is for damaged (insulation) or loose cables - this might be the sense wire does not have contact any more. Though this might have stoped the internal reading too.

None of the cables seems to be loose =(
If you can tell me which is the sense wire is from the pictures I would really appreciate it! 

Also, check the output filter cap. Some supplied cannot regulate without it.

May I know what that looks like from the pictures I've attached? or is that not possible..? 

If it was dropped on the front panel, most likely some potentiometer(s) was broken.

I've checked the resistance of them and it seems to be reading to what I adjust to.. 

[somekoreanguy]

I found 2 fuses on IMG_0223.jpg blown.. I will replace it and let you guys know!

[somekoreanguy]

the ones that are blown are 250v and .315A and I only have 250v .5A.. I will order them and give you guys an update!

BUT, since the fuses blew, doesn't that mean that there were too much amperage that went to the board....? 

and also, this means that:

1. The sense is working (since it's reading the correct voltage and amp in the panel)
2. the output holes are working (since they were reading 49v before and now it reads 0v)

One other thing is that there's a connector that gets plugged in and have few diodes between these fuse. meaning that whatever is getting connected to this connector is passing too much volume??

It seems like it's the cables that are coming out from the big transformer in the middle of the unit.

Here's the picture of it!

[wraper]

1. The sense is working (since it's reading the correct voltage and amp in the panel)

Wrong, voltmeter/ampermeter is a separate circuit which most likely have nothing to do with sense.

[somekoreanguy]

1. The sense is working (since it's reading the correct voltage and amp in the panel)

Wrong, voltmeter/ampermeter is a separate circuit which most likely have nothing to do with sense.

AH~ I thought that sense was a sensor that reads the output voltage and amps which tells how much voltage and amperage.. =( So, what is it supposed to do? Sorry, I'm still a newbie 

[Kleinstein]

Such power supplies often use separate wires to deliver the current and sense the voltage directly at the output. If the voltage sensing signal does not reach the regulator circuit one could get the full output. This is one possible scenario to result in ful output.

Having the changed voltages  might be due to blown fuses - without working regulation a short may have caused the fuses to blow.

With no obvious visible failure (loose wire, bad solder connections, broken pot) one might have to do just error search in the conventional way. So find a schematics is possible. Check voltages at severals points of the circuit.

[EPTech]

Hi there,

Judging from your photo's it looks like the fuses are indeed meant to protect the regulation circuits. Since the supply may have dropped I suspect that maybe the heat sink has shifted and caused a base terminal of the power transistors to touch the chassis. To check this, put your DMM in low ohm continuity test (beep) and measure between the heat sink and the C B E1 and E2 terminals at the top of the board. There should not be a short.

Also check whether any of the long legged components, like the power resistors are not touching each other.

Also the top relay looks kinda tilted. Is this mounted that way or has the cap lifted? If the cap has come of it may be wrongfully engaging the terminals inside. I do not expect it because that may cause one of the main fuses to blow..

Good luck

[somekoreanguy]

Such power supplies often use separate wires to deliver the current and sense the voltage directly at the output. If the voltage sensing signal does not reach the regulator circuit one could get the full output. This is one possible scenario to result in ful output.

Having the changed voltages  might be due to blown fuses - without working regulation a short may have caused the fuses to blow.

With no obvious visible failure (loose wire, bad solder connections, broken pot) one might have to do just error search in the conventional way. So find a schematics is possible. Check voltages at severals points of the circuit.

I've been searching for the schematics for this board but I couldn't find them =(

Hi there,

Judging from your photo's it looks like the fuses are indeed meant to protect the regulation circuits. Since the supply may have dropped I suspect that maybe the heat sink has shifted and caused a base terminal of the power transistors to touch the chassis. To check this, put your DMM in low ohm continuity test (beep) and measure between the heat sink and the C B E1 and E2 terminals at the top of the board. There should not be a short.

Also check whether any of the long legged components, like the power resistors are not touching each other.

Also the top relay looks kinda tilted. Is this mounted that way or has the cap lifted? If the cap has come of it may be wrongfully engaging the terminals inside. I do not expect it because that may cause one of the main fuses to blow..

Good luck

The only heatsink I see are the huge one on the back of the power supply and two little ones on the front board that projects LEDs readings of voltage and current. C seems to be ground and E1 and E2 has continuity.. Long legged components are not touching one another.

One of the top relay was soldered tilted and I've just fixed that.

I guess it'll be best for me to find the schematic for this.. Any tips on finding this schematics by any chance?? Thanks!!

[EPTech]

Hi there,

C seems to be ground and E1 and E2 has continuity.. Long legged components are not touching one another.

E1 and E2 may be in continuity. They are usually connected using a low ohm resistor like 0.1. I am not sure about the Collector though. How did you measure it? Between the collector and the heat sink or chassis? Are there  isolators,silicone or mica plates, between the power transistors and the heat sink? If so, there should not be continuity between the Collector and the heat sink.

[EPTech]

Hi There,

It is possible for the collector to be connected to the negative output terminal of your supply. In that case the supply is low side regulated. The emitters are probably connected to the negative of the large buffer capacitor, through the low ohm resistors seen below the connector. There should not be a short between the C and either of the E. Have you checked this?