I have a bench supply that looks like this one:
http://electronickits.com/kit/complete/powe/HY3005D.jpg
I've seen numerous "brand names" on the same type.

The supply works normally unless the load draws more than a few
milliamps (say 100 or so), in which case it will drop into current-
limiting mode and remain there until I power cycle it, even if the
load is removed.

I suspect this is a pretty simple fix, but since there are so many
rebranded versions of this supply someone might have a schematic that
would speed things up a little. Any ideas? I think it just has 3-4 op
amps inside and a few power transistors.

In article , stickyfox wrote:
I have a bench supply that looks like this one:
http://electronickits.com/kit/complete/powe/HY3005D.jpg
I've seen numerous "brand names" on the same type.

The supply works normally unless the load draws more than a few
milliamps (say 100 or so), in which case it will drop into current-
limiting mode and remain there until I power cycle it, even if the
load is removed.

I suspect this is a pretty simple fix, but since there are so many
rebranded versions of this supply someone might have a schematic that
would speed things up a little. Any ideas? I think it just has 3-4 op
amps inside and a few power transistors.

Well, here's a schematic at least...

http://www.technica.ru/objects/images/scheme/50.gif

-- Adam

wrote:
I have a bench supply that looks like this one:
http://electronickits.com/kit/complete/powe/HY3005D.jpg
I've seen numerous "brand names" on the same type.

The supply works normally unless the load draws more than a few
milliamps (say 100 or so), in which case it will drop into current-
limiting mode and remain there until I power cycle it, even if the
load is removed.

I suspect this is a pretty simple fix, but since there are so many
rebranded versions of this supply someone might have a schematic that
would speed things up a little. Any ideas? I think it just has 3-4 op
amps inside and a few power transistors.

I'm not sure I understand exactly how your supply works but my 25 year old
analog B&K power supply would shut down and indicate an over current
condition when there was none. It seems I was always pressing the reset
button. After some careful troubleshooting, I found that the front panel
current limiting control pot was intermittent. I cleaned it and now it as
good as new.

HTH.
--
David Farber
David Farber's Service Center
L.A., CA

On Sep 16, 6:59*pm, " wrote:
I have a bench supply that looks like this one:http://electronickits.com/kit/complete/powe/HY3005D.jpg
I've seen numerous "brand names" on the same type.

The supply works normally unless the load draws more than a few
milliamps (say 100 or so), in which case it will drop into current-
limiting mode and remain there until I power cycle it, even if the
load is removed.

That's called foldback current limiting; it's a positive feature, but
not in this kind of power supply; I suspect something is broken.
Open the box up; if there's a schematic printed inside, you're in
luck.
Otherwise, maybe there's a switch labeled 'foldback current limiting'?

On Sep 17, 4:36*am, (Adam Goldman) wrote:
In article , stickyfox wrote:
I have a bench supply that looks like this one:
http://electronickits.com/kit/complete/powe/HY3005D.jpg
I've seen numerous "brand names" on the same type.

The supply works normally unless the load draws more than a few
milliamps (say 100 or so), in which case it will drop into current-
limiting mode and remain there until I power cycle it, even if the
load is removed.

I suspect this is a pretty simple fix, but since there are so many
rebranded versions of this supply someone might have a schematic that
would speed things up a little. Any ideas? I think it just has 3-4 op
amps inside and a few power transistors.

Well, here's a schematic at least...

http://www.technica.ru/objects/images/scheme/50.gif

-- Adam

Well I see one annoying thing.. whoever made mine swapped the digits
around in the model number to make it "unique." This one looks close
enough anyways. Now if I can just figure out what's going on in there.

I have the exact problem with my HY300D-3.. Have You found a solution ?!

On 4/16/2014 2:11 PM, wrote:
I have the exact problem with my HY300D-3.. Have You found a solution ?!

Mine puts out full current, but has the unusable current limit latchup.
Almost impossible to charge a battery with it.

Reverse engineering it exceeded my attention span, given that the schematic
doesn't match the unit.

Whoever designed the thing must have been standing on his head
and drunk.
I stuck mine under the bench. Decided to redesign it and throw
out 3/4 of the parts if I ever get really, really bored.

Holler if you find the solution.

The original post is 4½ years old.

On 4/16/2014 6:43 PM, wrote:
The original post is 4½ years old.

Yep, you can read dates.
Doesn't change the fact that at least two of us still seek
a solution.

"Doesn't change the fact that at least two of us still seek
a solution. "

True, but realize that some newsreaders have this thread waaaaaaay down at the bottom of a very long list. I see you use gmail, so do I. When you post a reply gmail brings it up to the top. This is not always so with people who use other methods of access. To get to the maximum number of people it is better to start a new thread, after seeing if any of the links are good in the old one of course.

It is a bit surprising that there is still a print available via that link. If you see an old post like this and a link is to a tinypic or an imageshack, it is not likely to still be there. Russian (.ru) links seem to stay put, possibly because they are not a throwaway society and keep things running, instead of dumping everything in a landfill every two years.

Anyway, according to the print, current sensing is done by R15. Anythng wrong with N2 or its associated circuitry could be at fault.

Question, what does the current meter read ? Is it zero or does it read a bunch of current ? It could be as simple as something shorted across the output terminals.

I assume the constant current LED is lit, if you turn the voltage all the way down does it switch to the constant voltage LED ?

On 4/17/2014 10:02 AM, wrote:
"Doesn't change the fact that at least two of us still seek
a solution. "

True, but realize that some newsreaders have this thread waaaaaaay down at the bottom of a very long list. I see you use gmail, so do I. When you post a reply gmail brings it up to the top. This is not always so with people who use other methods of access. To get to the maximum number of people it is better to start a new thread, after seeing if any of the links are good in the old one of course.

It is a bit surprising that there is still a print available via that link. If you see an old post like this and a link is to a tinypic or an imageshack, it is not likely to still be there. Russian (.ru) links seem to stay put, possibly because they are not a throwaway society and keep things running, instead of dumping everything in a landfill every two years.

Anyway, according to the print, current sensing is done by R15. Anythng wrong with N2 or its associated circuitry could be at fault.

Question, what does the current meter read ? Is it zero or does it read a bunch of current ? It could be as simple as something shorted across the output terminals.

I assume the constant current LED is lit, if you turn the voltage all the way down does it switch to the constant voltage LED ?

First problem is that there seems to be a bunch of similar designs with
the same model number.
Mine doesn't match this schematic.

Second problem is that it's an upside-down backward design.
Negative supply floating with the most positive end the internal
ground reference.
Theoretically, not a problem. Practically, it makes it harder to
instrument/diagnose...especially without a correct schematic.
The digital readout is mixed up in all that floating stuff
and the schematic for that part doesn't seem to exist anywhere.

This appears to have been "designed" by someone who had never used
a bench power supply, much less ever designed one.
You can do a working power supply with far fewer parts.
It's a crap design with unbounded op-amp
inputs that can go "out of bounds" and latch up...patched with
a bunch of zeners to try to limit that. But there can be and apparently
are transient issues that can latch it up. Another consequence of this
is that you can't set the current limit near zero. I had to adjust the
minimum
to 340ma to keep it from latching up.

While I'm on a rant, I don't like the way the thing works.
The fine voltage control is a percentage of the coarse setting.
So, with the coarse at zero, the range on the fine setting is from zero
to zero.
The whole purpose of digital readout is to know the outputs.
0.1V resolution is insufficient.
The power switch doesn't turn off the output. Output stays up for
a long time after you cut the input power. Who knows where the
transient voltage/current go during that time.

Mine seems to work kinda normally as long as you don't need a current
limit lower than 340ma and you don't have transient load conditions
near the limit setting and you don't try to hook it to something
with voltage, like to charge a battery. The only things that don't
work are the things I most expect from a bench power supply.

My conclusion was that it isn't really broke; it's a crap design
doing the best it can...and wasn't worth redesigning. But if someone
comes up with a quick patch, I'd do it.

My response to the posting was, "me too", "let us know if you find a
solution." Ranking optimization was not a priority.

Actually I didn't want to pontificate but I was going to say that it looks like someone studied instrumentation design but forgot basic circuit design.. Someone should tell him that more components don't make the design better..

I think using the upside down design as you put it results in a bit better stability, that is if you know how to do it. If the thing can't foldback lower than 340mA, they didn't know how to do it. In that state you couldn't test a 12 volt 1 watt Zener.

If the design is anything at all like the one posted, I don't see any quick fixes. I could probably redesign it faster. Maybe you should guve that a go. You have a transformer and a box, and apparently two readouts.

I think some of these kits might just be junk. Not too long ago I was asked to look at an old Heath/Bell & Howell scope. It had an intermittently shorted HV cap and a couple of minor porblems, not the least of which is that it had never been aligned. This ain't the first time...

Anyway, it is DC coupled but the sweep generatior doesn't have a split supply, so when you go from external to triggered to freerun the trace needs to be recentered. At first I couldn't believe it, I thought there was something wrong with it buit nope. That is how it works. I've seen them only use short little ramps at higher seep speeds, which I really don't like, but not this before.

Maybe that's where some crappy designs go when they got too much money into them - kits. Then the buyilder thinks he screwed it up and everything is fine. The only problem is if they give the option to send it in for repair, but then someone else gets a crack at it. Business is business.

Seems like you could keep their power transistors and big resistors, take a coupe of your own OP AMPs and make it into something useful.

In the meantime you might want to repost, or I think they call it "top post" this so everyone sees it. SOmeone might have an idea who uses Thunderbird or something to get here. Alot of the oldtimers do.

On 4/17/2014 1:44 PM, wrote:
Actually I didn't want to pontificate but I was going to say that it looks like someone studied instrumentation

design but forgot basic circuit design. Someone should tell him that
more components don't make the design better.

I think using the upside down design as you put it results in a bit better stability, that is if you know

how to do it.
Not sure that's true.
I'd bet that someone did it because they had NPN transistors and didn't
know any better. Then that design got stolen and "improved" by some
competitor...repeat
a few times...add digital readouts...and this is what you get.
This does not look at all like a design.
Looks like a bad start that kept getting patched instead of fixing the
design.

If the thing can't foldback lower than 340mA, they didn't know how to do
it. In that state you

couldn't test a 12 volt 1 watt Zener.
It's not foldback.
There are pots galore. You can set the low limit below 340 ma, but mine
latches up if you do.

If the design is anything at all like the one posted, I don't see any quick fixes. I could probably redesign

it faster. Maybe you should guve that a go. You have a transformer and a
box, and apparently two readouts.

snip

s like you could keep their power transistors and big resistors, take a
coupe of your own OP AMPs and make it into something useful.

If I wanted another analog supply, I've got a design I did over 40 years
ago that works fine.
As you probably know, the schematic is trivial.
The "art" needed for proper operation is a scarce commodity.
I've fixed many "production-ready" designs by experienced engineers.
What shows up as an element on the schematic is only a part of what's
important.

Then, there are issues with making the meters autorange and the relays
that switch the transformer...and the circuit board and and and and...
It's all a royal pain in the ass.

I don't need another power supply or another project.

In the meantime you might want to repost, or I think they call it "top post" this so everyone sees it.

SOmeone might have an idea who uses Thunderbird or something to get
here. Alot of the oldtimers do.