EA 40V/3A power supply kit problem

Bought this kit a while ago when it was on special @ $100.

Finally completed assembly and it works except for one annoying problem
that I discovered during stress testing.

When the output is short circuit, the current limiter works as it
should but only to about 2A. Above that and the blinkety-blink of the
ceiling fluro plays havoc with the positive rail regulator section. I
wouldn't have discovered this problem had the fluro tube not started
dying (blinkety-blinkety-blinkety-blink)

When the current limit is set above about 2.2A and the fluro starts
blinking, the positive regulator stops current limiting and fully
saturates, dumping over 5A into the short before I flick the load
switch off. When the fluro is turned off the limiter behaves normal.

The negative regulator behaves normally all the way to 3A and is
unaffected by the blinking.

Anyone have any idea what is going on?!

 

[The Real Andy]

On 29 Mar 2006 18:31:30 -0800, chinsta00@hotmail.com wrote:

Bought this kit a while ago when it was on special @ $100.

Finally completed assembly and it works except for one annoying problem
that I discovered during stress testing.

When the output is short circuit, the current limiter works as it
should but only to about 2A. Above that and the blinkety-blink of the
ceiling fluro plays havoc with the positive rail regulator section. I
wouldn't have discovered this problem had the fluro tube not started
dying (blinkety-blinkety-blinkety-blink)

When the current limit is set above about 2.2A and the fluro starts
blinking, the positive regulator stops current limiting and fully
saturates, dumping over 5A into the short before I flick the load
switch off. When the fluro is turned off the limiter behaves normal.

The negative regulator behaves normally all the way to 3A and is
unaffected by the blinking.

Anyone have any idea what is going on?!

I built one of these when i was an apprentice. They have some nasty
problems with oscillation, and if IIRC, the fix requires a cap across
one of the pots and and across a couple of tracks. You might get lucky
and find that google will turn up the fix.

What is the kit number?

 

I have googled and only found a reference to a 0.47uF cap fitted to the
voltage pot's wiper & gnd. I didn't have one handy so I tried a 0.1uF
and it did not solve the +ve regulator saturation problem during fluro
blinking. If anything I think it made the circuit worse because I can
hear a (much louder) screeching noise from the supply during current
limiting!

I found no reference to the cap across tracks, so would be interested
to know which nodes the cap is placed across.

The DSE catalogue number for this kit is K3206.

The Real Andy wrote:

On 29 Mar 2006 18:31:30 -0800, chinsta00@hotmail.com wrote:

I built one of these when i was an apprentice. They have some nasty
problems with oscillation, and if IIRC, the fix requires a cap across
one of the pots and and across a couple of tracks. You might get lucky
and find that google will turn up the fix.

What is the kit number?