That'd be my guess, Eric.. that the control circuit is capable of monitoring
the resistance of the heater. The circuits are much more sophisticated than
just a diac/triac dimmer in the 24V units.

There is likely to be a method of monitoring the resistance (or current?) of
the heater. I dunno what the coeficient properties of ceramic heaters are,
but it's likely that the resistance of the heater changes as the temp does
(as seen in lamp filaments, for example).

Some sort of differential circuit that causes a balance shift, to be made
when the temperature control is increased, otherwise just matching the
applied power to the setting of the temp control setting at a duty cycle, in
effect, idling until a significant change in heater resistance is detected.

It's been years since I've seen schematics for the Ungar controller
circuits, and I may not have any of them now.

--
Cheers,
WB
..............



wrote in message
...
On Tue, 2 Apr 2013 10:16:37 -0400, "Wild_Bill"
wrote:

You didn't say whether you looked inside the Pace tweezer plug, but if
you're going to relocate the heater wires you'll probably end up doing
that
anyway.

I'm quite confident that you will find only 3 wires going to the
handpiece,
as mentioned before.

If you stick the hot tip of any of the irons I was speaking of earlier
onto
a cold surface, the LED will change from briefly coming on (idling), to
come
on steady.. and yet, there are NO sensor leads going to the handpiece
(only
because there is NO SENSOR).

The same LED action is seen when the adjustable temp control is turned
up/increased from a previously lower operating temp.. when the higher temp
is reached, the LED returns to briefly coming on (idling again).

I obviously don't need to say this, but.. hey, don't take my word for it.
Buy a used Ungar soldering iron handpiece with the same 6-pin connector on
eBag and open the connector.
It doesn't even need to be a working iron.. doesn't even need a heater, so
it should be possible to find one cheap.

I'm sure I have several extra handpieces, but don't know where to look for
them.


Greetings Bill,
If the LED comes on when the tip is cooled, and the LED being on means
that the iron is being powered, then the control must be sensing that
the tip has cooled, of course. If there is no separate sensor in the
tip then this must mean that the base unit somehow senses then cooling
tip. Couldn't this be done by measuring the resistance of the heater?
Eric