EA 40V/3A lab power supply K-3206

[Sam Highley]

I purchased the above mentioned kit from Dick Smith, and i'm having a
tough time getting it working properly. The first time I powered it up
I realised I hadn't correctly hooked up the collectors on Q1 and Q4 as
they were connected to the heatsink, rather than their respective
transistor cases (collector).

Needless to say things were not running properly at this point. I
powered it down, made a thorough inspection of things and worked out
the Q1/Q4 collector problem. I fixed this up and powered up the supply
again, but things are still not working properly. This is what the
supply is doing:

* "limit" light is on pretty much continuously, other than when both
voltage and current dials are wound almost right down

* with voltage and current set to maximum, total voltage output is
only around 4.5 to 5 volts

Anyway, i've pulled out all the capacitors and checked them, as well
as the transistors, but I have no idea how to go about checking the
IC's, which I suspect might be the problem.

How do I go about checking the IC's, which are 3x TL072's and a TL071

Sam

 

[Ken Taylor]

"Sam Highley" <sh@sam.sh> wrote in message
news:d18d670f.0307130254.6f636891@posting.google.com...

I purchased the above mentioned kit from Dick Smith, and i'm having a
tough time getting it working properly. The first time I powered it up
I realised I hadn't correctly hooked up the collectors on Q1 and Q4 as
they were connected to the heatsink, rather than their respective
transistor cases (collector).

Needless to say things were not running properly at this point. I
powered it down, made a thorough inspection of things and worked out
the Q1/Q4 collector problem. I fixed this up and powered up the supply
again, but things are still not working properly. This is what the
supply is doing:

* "limit" light is on pretty much continuously, other than when both
voltage and current dials are wound almost right down

* with voltage and current set to maximum, total voltage output is
only around 4.5 to 5 volts

Anyway, i've pulled out all the capacitors and checked them, as well
as the transistors, but I have no idea how to go about checking the
IC's, which I suspect might be the problem.

How do I go about checking the IC's, which are 3x TL072's and a TL071

Sam

Can you post a link to the circuit?

Ken

 

[Sammy]

How do I go about checking the IC's, which are 3x TL072's and a TL071

Sam

Can you post a link to the circuit?

I'll scan it and upload shortly.

Sammy

 

[Rob Judd]

Hi Sam,

I just rooted around and found the circuit for this, which I had
sensibly filed away with other test equipment circuits in a manila
folder.

As I understand it, the collectors of Q3 and Q4 were both shorted to the
heatsink, right? If you have a look at what this does, it effectively
short-circuits from +20v to -20v. So, the most likely problem is a
failure in the raw power supply, at bottom left of the circuit.

Check with a voltmeter that you have raw +20v and -20v first, and if not
you should test/replace the bridge and/or regulators. Let us know how it
goes.

Rob


Sam Highley wrote:

I purchased the above mentioned kit from Dick Smith, and i'm having a
tough time getting it working properly. The first time I powered it up
I realised I hadn't correctly hooked up the collectors on Q1 and Q4 as
they were connected to the heatsink, rather than their respective
transistor cases (collector).

Needless to say things were not running properly at this point. I
powered it down, made a thorough inspection of things and worked out
the Q1/Q4 collector problem. I fixed this up and powered up the supply
again, but things are still not working properly. This is what the
supply is doing:

* "limit" light is on pretty much continuously, other than when both
voltage and current dials are wound almost right down

* with voltage and current set to maximum, total voltage output is
only around 4.5 to 5 volts

Anyway, i've pulled out all the capacitors and checked them, as well
as the transistors, but I have no idea how to go about checking the
IC's, which I suspect might be the problem.

How do I go about checking the IC's, which are 3x TL072's and a TL071

Sam

 

[The real Andy]

May I add that this circuit is a very unstable one, very prone to
oscillation. If you can get access to CRO I highly recomend doing so. I did
build one of these many years ago and I remember adding a couple of caps
accros the pot(s) to help alleviate the oscillations. Might pay to check the
SC site for errata that might not be included in the kit.

Another design fault is the earthing. If they still sell these kits with the
metal front and back panels, do your self a favour and earth them..

"Rob Judd" <judd@ob-wan.com> wrote in message
news:3F122DB9.B577F2A7@ob-wan.com...

Hi Sam,

I just rooted around and found the circuit for this, which I had
sensibly filed away with other test equipment circuits in a manila
folder.

As I understand it, the collectors of Q3 and Q4 were both shorted to the
heatsink, right? If you have a look at what this does, it effectively
short-circuits from +20v to -20v. So, the most likely problem is a
failure in the raw power supply, at bottom left of the circuit.

Check with a voltmeter that you have raw +20v and -20v first, and if not
you should test/replace the bridge and/or regulators. Let us know how it
goes.

Rob


Sam Highley wrote:

I purchased the above mentioned kit from Dick Smith, and i'm having a
tough time getting it working properly. The first time I powered it up
I realised I hadn't correctly hooked up the collectors on Q1 and Q4 as
they were connected to the heatsink, rather than their respective
transistor cases (collector).

Needless to say things were not running properly at this point. I
powered it down, made a thorough inspection of things and worked out
the Q1/Q4 collector problem. I fixed this up and powered up the supply
again, but things are still not working properly. This is what the
supply is doing:

* "limit" light is on pretty much continuously, other than when both
voltage and current dials are wound almost right down

* with voltage and current set to maximum, total voltage output is
only around 4.5 to 5 volts

Anyway, i've pulled out all the capacitors and checked them, as well
as the transistors, but I have no idea how to go about checking the
IC's, which I suspect might be the problem.

How do I go about checking the IC's, which are 3x TL072's and a TL071

Sam

 

[Sammy]

Another design fault is the earthing. If they still sell these kits with the
metal front and back panels, do your self a favour and earth them..

The rear panel is earthed, not sure about the front panel though, i'll
check on that.

Sam

 

[Sammy]

As I understand it, the collectors of Q3 and Q4 were both shorted to the
heatsink, right? If you have a look at what this does, it effectively
short-circuits from +20v to -20v. So, the most likely problem is a
failure in the raw power supply, at bottom left of the circuit.

I suspect you are thinking of Q1 and Q4, and the way I read the
instructions, the collectors have to be isolated from the heatsinks, and
hooked up to their appropriate points on the PCB.

Check with a voltmeter that you have raw +20v and -20v first, and if not
you should test/replace the bridge and/or regulators. Let us know how it
goes.

Where would be the best point to check this?

Sam

 

[Sammy]

I inherited one of these and it is impossible to get the 300mA range current
limiting to work properly. ie if i put a short on the output, you would
expect it to limit the output current irrespective of whatever volts have
been dialed up. Instead it just goes into full output and bends the needle.
The 3 amp range is fine. (Interesting though about the oscillation. I'll
have a look with the CRO )

With this in mind, what do people think about the value of the following
kit, which is currently on sale:

http://www.dse.com.au/cgi-bin/dse.storefront/3f13763808bc09e02740c0a87f9c
06c9/Product/View/K3202

Sam

 

[The real Andy]

"Sammy" <usenet@sam.sh> wrote in message
news:usenet-281EF5.13360915072003@news-server.bigpond.net.au...

I inherited one of these and it is impossible to get the 300mA range
current
limiting to work properly. ie if i put a short on the output, you would
expect it to limit the output current irrespective of whatever volts
have
been dialed up. Instead it just goes into full output and bends the
needle.
The 3 amp range is fine. (Interesting though about the oscillation. I'll
have a look with the CRO )

With this in mind, what do people think about the value of the following
kit, which is currently on sale:

http://www.dse.com.au/cgi-bin/dse.storefront/3f13763808bc09e02740c0a87f9c
06c9/Product/View/K3202

Never seen it or tried it, but it is probably based on the same concept as
the one the OP is talking about, and is no doubt dogged with the same
problems.

As for the dual powersupply, once you find all the problems (and there is a
few) it is quite a good unit - especially when consider the price compared
professional units.