Bench PS Problem (Volteq HY3010D)

[orientalsniper]

Bought this bench power supply a few years ago, recently when I start it up, the output voltage is about 25V and I cannot knob it down to zero.

How can I tell if it's a problem with the knobs? Or is it something else?

[stj]

Re: Bench PS Problem (Volteq HY3010D)

probably has a shorted output transistor.

[PeteS in CA]

Re: Bench PS Problem (Volteq HY3010D)

If the output transistor is a 2N3055 (very common) it's $2 or $3. It could also be a bad potentiometer.

Open it up, clean out the dust, and post some pix!

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

They seem to be 2N3055

Here's the photos: http://imgur.com/a/r0P2z

Forgive me, how do I test the transistors? Solder them out and test for resistance?

[stj]

Re: Bench PS Problem (Volteq HY3010D)

yes, but you probably dont need to desolder them unless they meter bad to begin with.
i'm impressed that it has 4, they can manage 7A or more each!

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

I suppose the problem is not actually current limit but dissipation limit. I think 4 is actually about right for a single stage series dissipative design with the specs of this psu...

I know my homemade 1.2-15V 2A does exceed the power dissipation of the single series pass transistor... at least the heatsinking is not great. I've fried it a few times already :o However due to the circuit topology I'm not sure if any learnings from its failure can be applied to the OP's supply.

[PeteS in CA]

Re: Bench PS Problem (Volteq HY3010D)

The 2N3055 is one of those ancient parts that is too good for the price for it to be obsoleted. I'd guess it was designed in the late 1960s.

That 14-pin IC may be a uA723, another ancient part. the linear regulator IC. Basically, it has a precision reference, an error amplifier (with the output pin accessible for compensation purposes), and an output transistor that could be used to drive higher current transistors.

If the output transistor leads are accessible, testing for shorts should be easy, though discerning which one would require removal. There may also be a high current rectifier across the transistors' CE, with the anode at the collector, and the cathode at the emitter. This would provide some protection to the transistors against a higher voltage being externally applied at the output. This could short instead of one of the output transistors shorting CE.

Finding a schematic - dead-tree or online - could be valuable. I'm just working from memory of typical linear power supplies.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Perhaps while varying the adjustment pot, testing the voltage across it and voltage at the base of the transistor(s) would be some first order tests even without schematics.

[R_J]

Re: Bench PS Problem (Volteq HY3010D)

This is a different model (Hy3020)but might help, I found this one also (HY3010D)

[stj]

Re: Bench PS Problem (Volteq HY3010D)

http://www.volteq.com/volteq-regulat...new-model.html

looks like a rebadge of:
http://www.mastechpowersupplies.com/...h-hy3010d.html

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Thank you all for the assist, I'm gonna try all your suggestions and will let you know.

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

I tested the 4 2N3055 in circuit and they don't appear to be shorted. I'm gonna have to desolder them and do this test ( https://www.youtube.com/watch?v=xyKzUCrwTpA ) to make sure.

I attached better and more focused pictures (log in to see) so you get an idea of what's inside.

[stj]

Re: Bench PS Problem (Volteq HY3010D)

shit, that's some scary foto's!

the cap almost? touching the heatsdink, the rectifier just bolted to the case without sleeving on the outputs, the soldering!

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

I just replaced the 4 power transistors (2N3055) and still got the same problem.

[budm]

Re: Bench PS Problem (Volteq HY3010D)

So you verify that the Output transistor driver V13, V14 are good?

[redwire]

Re: Bench PS Problem (Volteq HY3010D)

It's the usual circuit, where the pass-transistor (array) is normally on (R4, V11) and the control op-amps turn it off through an OR-gate (V15,V16).

Like budm mentions, check the driver transistors. I would check the +12V, -6.2V rails.

Circuit-common for the control op-amps and stuff is the power supply's +OUTPUT, once you get a handle on that, these chinese bench PSU's are easier to repair.
But like this one, a potpourri or kludge of parts.

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

OP rezzing thread, just replaced V14 and V13, still voltage high, 45V now.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Ah... problem still exists we thought you fixed or gave up!

Well M1 and M2 (LM741s) are the error amplifiers - M1 being the voltage error amplifier (M2 is the current limit feedback). What is the voltage at each of the pins of M1 when you have the voltage turned down all of the way?

In case it's not clear, M1 is the LM741 that has the unpopulated C8 near it and J7 on the other side. M2 is the one that's between C10 and RP9.

Oh gosh 45V??? I think that will kill the LM741, you may need to replace them regardless now. But still report the voltages an the pins. A proper working PSU probably should look like:

(Note: voltages reference to GND, or output negative pin)

Pin 8 - NC - ignore
Pin 7 - V+ 12V over what your output voltage is
Pin 6 - OUT your output voltage minus somewhere from ~3 to ~11 volts.
pin 5 - Offset - ignore
pin 4 - V- 12V under what your output voltage is
pin 3 - IN+ this should be fairly low, no more than 1V or so
pin 2 - IN- this should be whatever your output voltage is
pin 1 - Offset - ignore

[orientalsniper]

Re: Bench PS Problem (Volteq HY3010D)

Oh yeah, I just didn't need the PSU urgently and had things going on in life. I had the parts ordered months ago and just replaced them.

You mean UA741CN? You want the voltage to ground? I can't seem find ground in this PCB.

Edit: Just read your edit, I'm just going to order the UA741CN and LM324, will report back when I replace them.

[eccerr0r]

Re: Bench PS Problem (Volteq HY3010D)

Actually don't be hasty and replace them, we don't know what's wrong yet. If you report the voltages on those pins then we could help pinpoint the problem.

I tried to make a guesstimate based on the schematic. I referenced "Ground" as the negative output of the main power supply, just to pick an arbitrary point.

And yes, UA741CN, same op amp circuit as LM741.