12VDC Power Supply outputting 19V?

[Glenn Ashmore]

I have a Nippon America DVP-3212 power supply that I fear has had an
encounter with a power surge. Now instead of 13.8VDC it is putting out
20.4V. Checked it with the 'scope and it is still smooth and ripple free
but the voltage fine adjust pot has no effect. It looks like the voltage is
controlled from a little PC board on one side.

I have the schematic from NA but I don't know where to start looking.

Any suggestions?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Jerry G.]

If this is supposed to be a regulated supply, then the fault is in the
voltage regulator circuit. Any component going defective in the regulator
circuit, including the output stage, can cause a fault condition.

The only way you can fix this is to properly troubleshoot it. You will be
required to have a descent background in electronics theory and have a DVM,
to troubleshoot this.

Most of these simple regulated supplies have a regulator board that feeds an
output transistor or output IC. Some of these low end small current rated
supplies use a single power IC to do the regulation, and output together.

As for ripple in the output of a power supply, the ripple will show more if
the supply is loaded. When there is no load, there may still be no ripple
showing on a scope, even if the filtering is not fully working.

--

Jerry G.
======


I have a Nippon America DVP-3212 power supply that I fear has had an
encounter with a power surge. Now instead of 13.8VDC it is putting out
20.4V. Checked it with the 'scope and it is still smooth and ripple free
but the voltage fine adjust pot has no effect. It looks like the voltage is
controlled from a little PC board on one side.

I have the schematic from NA but I don't know where to start looking.

Any suggestions?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Sam Goldwasser]

Some of these can be tricky but the first thing to check assuming it doesn't
need a load to regulate, would be to see if the pass transistor is shorted.

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[Glenn Ashmore]

First of all put that schematic in place that is accessible to us so we can
see what we're talking about.

Where are you guys putting up temporary graphics? I tried posting to the
a.b.s.e newsgroup but it hasn't shown up yet and most of what I see there is
BS.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Glenn Ashmore]

No ICs on the regulator board. Just 4 transistors with Korean codes that I
am trying to figure the equivelent values for. Three TO-92 transistors
marked 3DG9014 which I believe to be .45W 50V general purpose NPNs and a
TO-220 marked JDD313 of yet to be determined function.

I realize that ripple usually comes under load but the best I could do was
to put a couple of 24V light bulbs in the circuit when I looked at it on the
'scope.

Output is an array of six 2N3055 transistors and the regulator board is
feeding them 20V.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Franc Zabkar]

No ICs on the regulator board. Just 4 transistors with Korean codes that I
am trying to figure the equivelent values for. Three TO-92 transistors
marked 3DG9014 which I believe to be .45W 50V general purpose NPNs and a
TO-220 marked JDD313 of yet to be determined function.

I realize that ripple usually comes under load but the best I could do was
to put a couple of 24V light bulbs in the circuit when I looked at it on the
'scope.

Output is an array of six 2N3055 transistors and the regulator board is
feeding them 20V.

It looks like a linear supply with six pass transistors. Like Sam
says, one more of the 2N3055s are probably shorted C-to-E. Check the
base drive for any additional problems.


- Franc Zabkar

 

[Sam Goldwasser]

It looks like a linear supply with six pass transistors. Like Sam
says, one more of the 2N3055s are probably shorted C-to-E. Check the
base drive for any additional problems.

But he says the driver is feeding the 2N3055s 20 V, so need to check
the feedback. Need to see circuit as someone else requested.

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[Glenn Ashmore]

But he says the driver is feeding the 2N3055s 20 V, so need to check
the feedback. Need to see circuit as someone else requested.

Finally figured out what was happening to my web site. My 5 year URL
registration expired Sunday! Back up now so I put up the rather fuzzy
schematic that Nippon America sent me at:
http://www.rutuonline.com/dvp-3212.gif

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Sam Goldwasser]

Finally figured out what was happening to my web site. My 5 year URL
registration expired Sunday! Back up now so I put up the rather fuzzy
schematic that Nippon America sent me at:
http://www.rutuonline.com/dvp-3212.gif

Measure the voltage at the base of V28. It should be somewhere around
14-15 V when the regulator is working. If it's that or less, check the
check each of the driver transistors for shorts. If it's higher, check
the components in the feedback circuit from the output.

Sometimes it's as simple as a bad or dirty adjustment pot.

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[Glenn Ashmore]

Measure the voltage at the base of V28. It should be somewhere around
14-15 V when the regulator is working. If it's that or less, check the
check each of the driver transistors for shorts. If it's higher, check
the components in the feedback circuit from the output.

Sometimes it's as simple as a bad or dirty adjustment pot.

Well, the base on V28 is barely 20mV with 30V on the collector and the
emmiter is outputing about 5V out to V27. By driver transistors you mean
the ones feeding V28?

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Glenn Ashmore]

Here are some pictures of the board that might help:

Back side of PCB: http://www.rutuonline.com/dvpbottom.JPG

Component side of PCB: http://www.rutuonline.com/dvptop.JPG

Orange wire at lower left goes to V26 on the heat sink and reads 22V to
ground Not sure where the purple one goes yet but it reads 30.4V. Blue
yellow and brown go to the 4.7K voltage adjust pot. Red and black go to the
output terminals and the fiber insulated wires go to the transformer.

I am getting some strange readings off the pot. As I turn the knob the
yellow center tap varies from .72V to .79V, brown goes from .73V to .26V
and blue goes from 8.6V to .8V. Checking the pot's resistance it goes from
3.8Kohms to .3 ohms. I would have thought that when the pot was all the
way over the voltages would be the same.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Fred McKenzie]

<< Output is an array of six 2N3055 transistors and the regulator board is
feeding them 20V. >>

Glenn-

In another post you mentioned very low voltage on the base of V28 with 5 volts
on the emitter connected to V27's base. It would appear that V28 is cut-off,
and the base-emitter junction is reverse biased, possibly limiting voltage to
its zener value.

That leaves V27, V26 and one of the 2N3055s as a potential culprit.

I suggest you measure the voltages on these transistors. Pay attention to the
base-emitter voltages. I'm not sure you said it, but it appears that the
output voltage is close to the same as the 2N3055 base voltage. If that is
under load, one of the 2N3055s could be shorted. The base-emitter voltage
should be around 0.7 volts.

Fred

 

[Glenn Ashmore]

Need to know the voltages on the bases of V27 and V26.

..
V27 is 5V on the base, 30V on the collector and 22.3V on the emmiter. V26
is getting 22V at the base from V27 and feeding 22.75V to the bases of the
other 2N3055 transistors.

One more lead. The emmiter sides of the 2N3055s are tied together in groups
of 3. I separated the two groups and checked resistance between the
emmiters and base on each. One group is 6.5M ohms and the other is 790
ohms. So I guess everybody that said check the output transistors first
was correct.. Unfortunately the group with low resistance is burried deep
in a double layered heat sink that will require complete disassembly to get
to. :-(

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Sam Goldwasser]

.
V27 is 5V on the base, 30V on the collector and 22.3V on the emmiter. V26
is getting 22V at the base from V27 and feeding 22.75V to the bases of the
other 2N3055 transistors.

One more lead. The emmiter sides of the 2N3055s are tied together in groups
of 3. I separated the two groups and checked resistance between the
emmiters and base on each. One group is 6.5M ohms and the other is 790
ohms. So I guess everybody that said check the output transistors first
was correct.. Unfortunately the group with low resistance is burried deep
in a double layered heat sink that will require complete disassembly to get
to. :-(

Can you just run with the group that works as a test? The current rating
will be cut in half but that's the main difference.

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[Glenn Ashmore]

Gentlemen, and especially Sam, I thank you! Found the bad transistor,
removed it and I am back down to a nice healthy 13.8V. I will put a couple
of 2N3055s on my list for the next Digikey order.

OTOH, I also have a Samlex RPS1215 that uses 2N3055s and is totally dead.
Unless one of you has the patience to guide me through fixing that one too,
I will scavange a transistor from it.

--
Glenn Ashmore

I'm building a 45' cutter in strip/composite. Watch my progress (or lack
there of) at: http://www.rutuonline.com
Shameless Commercial Division: http://www.spade-anchor-us.com

 

[Sam Goldwasser]

Gentlemen, and especially Sam, I thank you! Found the bad transistor,
removed it and I am back down to a nice healthy 13.8V. I will put a couple
of 2N3055s on my list for the next Digikey order.

OTOH, I also have a Samlex RPS1215 that uses 2N3055s and is totally dead.
Unless one of you has the patience to guide me through fixing that one too,
I will scavange a transistor from it.

Totally dead might be easier.

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[James Sweet]

Gentlemen, and especially Sam, I thank you! Found the bad transistor,
removed it and I am back down to a nice healthy 13.8V. I will put a couple
of 2N3055s on my list for the next Digikey order.

If you need them quick, even Radio Shack carries the 3055's.

 

[Fred McKenzie]

One more lead. The emmiter sides of the 2N3055s are tied together in groups
of 3. I separated the two groups and checked resistance between the
emmiters and base on each. One group is 6.5M ohms and the other is 790
ohms.

Glenn-

You reversed the leads on your meter between the two groups. Do both forward
and reverse polarity resistance measurements on both groups, and I think you
will find them to be comparable.

Is it easy to remove V26? If you did, and connected a 1000 Ohm resistor from
the 2N3055 bases to ground, the output voltage should go low with a load. If
it does, then the 2N3055s are probably OK and V26 may be shorted
collector-to-emitter. If output stays high then there is likely one or more
shorted 2N3055s.

Fred