Digimess HV30001 repair - 300V 1A bench DC power supply

[tom66]

Re: Digimess HV30001 repair - 300V 1A bench DC power supply

Success! Powered it up with my bulb tester this time instead of blowing it up again, but no need, after replacing that diode and two MOSFETs the supply works.

Seems like the full 1 amp isn't available at 300V, will have to look into whether it has some kind of power limit, hm. Or something else is amiss. Max I've got is 135W into a 240V light bulb.

Was able to get max output voltage to 310V, will look at modifications to see if 350-400V is possible. All output caps are 400V rated.

Repair cost was about £15 all in...not bad really.

[tom66]

Re: Digimess HY30001 repair - 300V 1A bench DC power supply

By the way, what is that "thing" in the middle of this picture??!?
https://www.badcaps.net/forum/attach...0&d=1464014985
I can see the transistors attached to a heatsink. But the stuff on top and especially that wire soldered to them and then merrily going through the board?

Uh...yeah...about that. At the time I thought it might be a temperature sensor for the output diodes, but at only 1 amp that seems somewhat unnecessary. Didn't look too closely.

Later determined it to be a second set of diodes bodged on top - MUR460 devices. They feed the large inductor, which is also connected to the transformer. The diodes are covered in thermal gloop in a vain attempt to thermally couple them to the heatsink.

It seems to be some kind of very strange full-bridge rectifier... I'll draw out a schematic later.

[momaka]

Re: Digimess HY30001 repair - 300V 1A bench DC power supply

I like the name digiMESS.

Me too.
Must be a sub-division / company of PowMax

By the way, what is that "thing" in the middle of this picture??!?
https://www.badcaps.net/forum/attach...0&d=1464014985
I can see the transistors attached to a heatsink. But the stuff on top and especially that wire soldered to them and then merrily going through the board?

The RRP for this is £500+VAT - I would feel very ripped off if I'd bought this full price!

Lol 500 Quid is insane for that hunk of junk.

[tom66]

Re: Digimess HV30001 repair - 300V 1A bench DC power supply

Got new parts in. Turned it on and the displays worked...but not for long. I increased the voltage beyond a few volts and it went bang again. I tested a few more things and found the output diode is shorted...this thing has no current limiting on the primary side(!) so a shorted output diode kills the switching transistors.

First round: Two MOSFETs and a fuse.

Didn't have my bulb tester at the time so couldn't power it up slowly.

Will now try replacing diode and FETs.

[tom66]

Re: Digimess HY30001 repair - 300V 1A bench DC power supply

I like the name digiMESS.
How are you doing with you job any way? You like it?

Haha, it's a typical Chinese name, and the design is a bit of a mess inside so...

I do like working at my job. It's part time though, I still go to uni. I work from home, so I can work whenever I need the income, and relax on the other days. Perfect.

[budm]

Re: Digimess HY30001 repair - 300V 1A bench DC power supply

I like the name digiMESS.
How are you doing with you job any way? You like it?

[tom66]

Originally purchased this working from Farnell from clearance for low price. Bought this to experiment with some high voltage Tesla coil stuff. Also, I have a problem with collecting test equipment.

Got it home and found it was popping fuses. Took it back to the shop, they tried a new fuse and it popped again. So they refunded me and let me keep the broken unit...so lets now figure out what's gone wrong here.

It's a switchmode supply with an adjustable output voltage. The supply works like a normal PC ATX supply, it appears to use a two-switch half bridge (capacitor coupled) converter with a transformer gate driver. The pre-converter supply generates an output voltage some volts above the desired output with ripple and noise. A pass transistor then regulates the output (removing ripple and improving transient performance) and provides current limiting functionality.

All four bridge diodes test OK. The two main switching transistors are dead short, as expected. NTCs and caps test OK. The capacitors appear to be a mix of Chemicon, Rubycon and some odd Chinese brand with a Rubycon vent, though the Rubycon caps all look a little off, so they could be fakes.

There's a standby/aux supply which powers the logic and displays. The fan operates off a separate tap on the main supply - I guess the idea is as the output voltage goes up the fan speed goes up too. Neat way of doing that, I guess. But this will mean the fan won't operate until the supply reaches something like 100V (assuming it starts spinning around 5V), which is already a pretty decent amount of internal power dissipation. I don't know why they don't just run it off the aux supply...it would be easy enough to add temperature control too.

The anemic input filter is surprising for a piece of test equipment, and the caps across the input are not X-caps, nor do they have the required discharge resistors. There is no way this thing would ever pass CE / LVD!!

Since the supply is designed to withstand a dead short at maximum output voltage, the pass transistor needs to be rated for the maximum output voltage across its drain and source with a 1 amp current limit. This means it has to dissipate a peak power of over 300 watts. I have a great deal of doubt that the transistor can manage that! Especially given that at 1 amp, the output capacitor will take at least 100ms to discharge. So, the transistor will have to dissipate >150W for 100ms. Ha. It won't survive many short circuits doing that.

All main input and output wires are soldered directly onto the PCB - these guys have not heard of using connectors for this stuff. There's a 115/230V switch at the back, but that's at the correct setting. The 600V transistors would likely survive if the supply were set to the wrong voltage, but the main caps would probably pop since they're only 250V a piece.

The RRP for this is £500+VAT - I would feel very ripped off if I'd bought this full price!