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need schematic or pinout for Ungar 9900 soldering station. Wannause it on a Pace Iron.



Jan 1, 1970
I have a Pace tweezer soldering iron. 21V
I have an Ungar 9900AS power unit. 24V
I'd like to mate them.
The 6-pin round connector plugs in...I'm afraid to turn it on.
I found some pinout info on Pace systems,
but nothing on the Ungar.

A schematic or pinout info would save me reverse engineering the

Thanks, mike


Jan 1, 1970
I haven't had a 9900 series controller, but I do have a few 4000 series
desoldering stations, and there should be 3 conductors from the plug.

By taking the cover off the unit, you should be able to determine which
connector pin is for earth ground (the heater barrel & tip), and the 2
pins for the heater.
I'm fairly certain that there are not any other pins used (no temp
feedback device).. I've only seen 3 conductors used for Ungar
Typical Ungar variable temp iron has six-pin connector with
typically 5 used.
Turns out that the temp sensor resistance is incompatible.
Without a schematic, it's just too much work to redesign it.


Jan 1, 1970
I've owned at least 4 models of different series of Ungar varaible
temperature units (from the 1970s to 2000) but also repaired other
models, and all of 'em only used 3 conductors for the handpiece heater.

The units I've had that were combination soldering/desoldering units had
an extra (1 or 2) conductors for the vacuum circuit.

If your station doesn't have a vacuum circuit (not mentioned
previously), the heater was likely only 2 wires plus an earth ground.
So.. no, not really typical for Ungar units to use 5 conductors for a
soldering iron.

If the 9900 unit did use 5 wires for just a soldering iron, it may have
been the only Ungar station that did.
I don't know why there would be more than 3 conductors for the soldering
iron that went with that unit, unless it has a digital temperature display.

You could connect two small 12V lamps in series to find the heater pins.

I haven't seen a temp sensor used in Ungar soldering irons, and I don't
remember seeing any in my Pace tweezers either.

I guess you could always use a variac and a 24V transformer, or find a
lamp dimmer for 24V.
Can't speak for yours, but my Ungar 9900AS uses two wires for the heater,
two for the temperature sensor and a safety ground.
As does the Pace SensaTemp II tweezer.
Problem is that the Pace us 100 ohm sensor.
The Ungar changes duty factor over the range from about
10K to 5K, so completely different sensor technology.

If I could find a schematic for the Ungar, I'd hack it to work
with the Pace. Just not sufficiently motivated to reverse engineer
the whole thing.


Jan 1, 1970
If you take the plug apart on the Ungar soldering iron cable (not fun),
you'll see there is a mini variable resistor inside the plug.. no sensor
used for the iron, in case I forgot to mention that.

The variable resistor is used to set/match the iron temp to the chart
supplied with the soldering station (so all the models have some
consistency when set to lowest to highest temp settings).

If you remove the leads to the soldering iron and put the Pace heater(s)
and ground leads in the same place, the Ungar station will provide
adjustable temperature for the Pace tweezers.

This isn't complex.. essentially the same as a light bulb circuit.

Very interesting.

9900 AS Anti-Static Electronic Soldering System
This premium, ESD-safe, modular system meets the full range of
electronic soldering applications by
means of four 24V-AC quick-connect micro and macro soldering irons.
Electronically controlled, variable temperature.
System meets military specifications: DOD-STD-2000- 1B, WS-6536E and
Temperature range 450
F to 850
Dimensions 3.33"H x 3.80" W x 7.00"D weight 3 lbs.
120V-AC, 6 Hz., 3-wire grounded. UL Listed.
Two year limited warranty on power base.

Temperature variation less than ++ +10 oF

I don't have the ungar iron, just the power unit,
but I remain skeptical.

So, they adjust the power, not the temperature...but the dial is
calibrated in temperature and spec'd within 10 F.

What I did was put a variable resistor on the sense pins.
The duty factor of the power source was a strong function
of the external resistor and only minimally affected by the
setting of the temperature slider.
I can imagine that there's a calibration pot that normalizes
the variation in sensor resistance between units.

It's hard to imagine that they have all that circuitry to implement
a light dimmer.

The pace units actually measure temperature, so it stays constant
under varying loads.
Weller EC3001 works the same way. Draws about 27W cold and ~3W at
temperature, pretty much independent of temperature setting.


Jan 1, 1970
I located some notes on Ungar units, and the 6-pin connector.

I didn't write down what the actual connector pin numbers were, but can
describe them, compared to a clock face.

With the key notch at 12:00, there are 5 pins surrounding one center pin.

The 2 pins closest to the key (10:00 and 2:00) are for the variable
resistor located in the plug body of the handpiece.. I didn't write down
a value, but sketchy memory leads me to believe the value is under 25k
ohm (could be much lower).

The next pins at (4:00 and 8:00) are the heater pins.. either lead to
either pin, wire colors are likely to be black & white.

The next pin (6:00) is the handpiece earth ground pin (wire color is
likely to be green).

The center pin isn't used for soldering irons.. it's for the pump switch
in desoldering handpieces (or to actuate vacuum flow in units that don't
have internal pumps).. although some designs utilize a foot switch to
activate the vacuum source.

In the majority of temperature "controlled" soldering/desoldering irons
I've seen which are the duty-cycle type of controllers (not sensor
feedback from the handpiece), the common method of wiring the handpiece
is with a mini variable compensation resistor located in the connector
plug at the end of the handpiece or adjustable internal compensation
pots in the base unit.

The compensation adjustments were provided to allow matching of the tip
temperature range (measured with external equipment) to be adjusted to
match the temperature divisions (or temp chart) of the temp adjustment
setting controls to match approximately.
All of the duty-cycle units I've seen have only 3 cable leads for the
heater.. 2 voltage and 1 earth ground.. this goes back to when heaters
were commonly 120VAC and (simple diac/triac duty cycle) continued up to
the more recent 24V designs (isolated and ESD safe versions).
Ungar/Weller, Pace, Edsyn and others have all used this design for
various models.
The connectors and pinouts change, but generally the irons are
interchangeable as long as the voltage is within a reasonable range.

In many production assembly line scenarios, the soldering temperatures
needed to routinely be checked/adjusted (calibrated) to make sure that
the circuit board assembly temps were within a specified range
(certifications for contract work, not China assembly methods).
Some units have mechanical limiters or locks to prevent the assembly
line operator from increasing the tip temps.

Thanks for the info. The pinout is consistent with my experiments.
Sure wish I had the handpiece to look at.

My experience has been opposite yours.
My Weller EC3001 has active temperature feedback.
If you stick the tip on a cold surface, the heater power goes up.
Same for all my PACE handpieces with the 6-pin connectors.

I have some very early 120VAC PACE desoldering handpieces that are
power instead of controlled temperature and run
off a "light dimmer" in the base unit without temperature feedback.

The Weller 3-pin connector units like the TC201/TC202 have constant
heater power that's interrupted by the "magnastat" attached to the
tip reaching its curie temperature. It's a bang-bang control system
with relatively long on/off times.


Jan 1, 1970
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 was gonna modify the socket. I have other places to plug the iron.
I'm quite confident that you will find only 3 wires going to the
handpiece, as mentioned before.
Well...hate to shatter your confidence.
The info is here:
it includes a schematic showing the sensor.

Here's the troubleshooting chart for the PACE TT-65 handpiece:
Was a PDF chart that got copied as text, but you can see the
4 headers:
No heat
Check resistance - Pin 2 to
Pin 5. Resistance should
be 10 ohms.
If not - -Open Heater

______________Here's the relevant part
Check resistance - Pin 3 to
Pin 6. Resistance should
be 110 ohms.
If circuit
reads less than 105 ohms - -Shorted Sensor
____________End of relevant part.
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 believe that you have experience that leads you to a conclusion
that is incorrect for the systems I have.
Your conclusion seems to be contrary to all my experience. I fail
to understand how power input can change with heat load
without sensing something.

I know of three ways in use to have temperature control with two
active wires (plus safety/static ground).
I have used irons using all three methods.

1)put ALL the electronic controls in the handpiece.
2)the weller magnastat that uses a thermally activated switch in the
3)the Metcal system that pumps RF down the cable and uses a property
of material in the head to absorb the RF and heat only when below
the transition temperature of the tip.

This article describes various systems.
I obviously don't need to say this, but.. hey, don't take my word for

I won't, because I haven't heard a rational explanation.
Can you describe the mechanism that allows
the power input to change based on heat flow without sensing
Finding a calibration pot in the plug doesn't demonstrate that a sensor
does not exist.

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.
You don't need an extra one. Just unplug one and take a meter to it.
The sensor in my Weller EC1301 sensor measures 27 ohms cold and about
43 ohms at 700F.
The only adjustable power supply that I own with the UNGAR name
is the aforementioned 9900AS. It has WAY MORE circuitry than
would be required for open-loop power control (light dimmer style).
The number and type of integrated circuits is consistent with
the schematics for the PACE temperature control systems.
Not having a handpiece or schematic, I can't prove it. I can only
that the power out is dependent on the value of a resistor plugged
into the socket...assumed to be the sensor. It appears that the
type of sensor varies much more with temperature (in the 5K to 10K
region) than the sensor
used by the PACE or Weller EC series.

Are we having fun yet?

Leif Neland

Jan 1, 1970
Wild_Bill formulerede Wednesday:
Well it appears that you're correct about the Pace tweezers having a sensor.

That could be significant if you were wanting to use an Ungar handpiece on a
Pace controller.. but you're not.
The sensor doesn't prevent the operation of the heaters in the Pace
My apologies if I forgot to mention that heaters only require 3 wires.. and
one is for earth ground.

Finding only 3 conductors in the Ungar handpiece and no sensor leads, as I've
done, demonstrates to me that there is NO SENSOR in the Ungar handpieces
(proof enuff for me).
I'm not arguing if the particular soldering iron has a sensor or not.

But, as resistance (often) is inversely related to temperature,
wouldn't it be possible to measure the current and voltage, and use
this to keep the temperature (somewhat) constant?


Leif Neland

Jan 1, 1970
Følgende er skrevet af Leif Neland:
Wild_Bill formulerede Wednesday:
I'm not arguing if the particular soldering iron has a sensor or not.

But, as resistance (often) is inversely related to temperature, wouldn't it
be possible to measure the current and voltage, and use this to keep the
temperature (somewhat) constant?


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