Loading...
 

Random Tips

Metcal MX-500P Soldering Station Review & Repair

Published by coflynn on Wed 09 of May, 2012
For some time I've been using a METCAL soldering station. I picked mine up used on E-Bay, as they are expensive new.

They have phenomenal heat transfer ability - they use RF energy to transfer heat right to the tip. It means you can go from soldering a 0402 capacitor to desoldering an entire SMA connector with the same tip, and it all works perfectly.

There is a few "must" tools for anybody deeply involved in electronics. The Metcal soldering station is very high on that list. Simply put you are wasting your time with a normal soldering station. I previously used a fairly good soldering station - ceramic heater element, good temp control, etc. The Metcal is still just that much better.

Here are a few videos of it in action, showing SMA soldering only because that is something normally very difficult.

Flash player not available.

Flash player not available.


I also collected some technical documentation. I can't seem to find the original source though, so the following is NOT FROM ME, but I don't know who credit goes to. If you know the original source let me know & I'll credit it. All the links I've found are too recent - I originally found it several years ago.

Getting the security torx bolts out is difficult. Once you remove them I highly suggest replacing them with normal 8-32 1/4" stainless steel pan-head machine screws. Because they are so recessed a normal universal screwdriver doesn't fit down - I had to grind down mine to fit in the recess. I eventually ended up drilling out one bolt because it was stripped. In retrospect I would have just drilled all the four corner bolts out & would have been easier.

I blew a fuse soldered onto the PCB a few times. Once for unknown reasons, once because I tried to use the Metcal with an inverter, which the transformer-input didn't like at all.


METCAL MX-500P-11 TECHNICAL DOCUMENTATION

This documentation was carefully reverse engineered from several actual MX-500P units, and although it has been meticulously triple checked, it may contain errors and omissions so use it at your own risk. It is provided solely for the purpose of helping you satisfy your personal curiosity about how a Metcal MX-500P works, and you must
never use it for any other purpose, especially not for any commercial or business purpose, and certainly not as an aide to experimenting with or performing work on MX-500P units, as it is inadequate for such unintended use. Reproduction is strictly forbidden. (Note from editor: I'm not original author so cannot comment on reproduction)

MECHANICAL DESCRIPTION:

The small plastic cover at the two RF output connectors is held in place by it's two plastic hooked clips which descend into the aluminum housing at the top and bottom. Beneath this plastic cover are two hex nuts that bolt the RF connectors to the aluminum housing. The RF connectors are soldered directly into the circuit board. On the rear of the MX-500P are four deeply recessed T15 tamper proof Torx screws which hold the two halves of the aluminum casting together. Loosening the single screw in the upper-middle back of the MX-500P by a few turns releases the internal heat sink which is attached to the circuit board. The internal heat sink couples heat into the MX-500P aluminum case from where it can dissipate into the ambient air. Good thermal coupling between the internal heat sink and the case is aided by a thin coating of white thermal compound. The circuit board inside the MX-500P is fastened down by six internal screws, four of which are rather large because they also hold down the line transformer. The tiny grub screw on the upper right hand side of the MX500 controls the Auto Sleep feature and should not be tightened past the point where it gently activates the switch. Note that it can be dangerous to power up an MX-500P unit that has been taken apart or that has been reassembled by anyone other than an trained Metcal service technician.

DESCRIPTION OF FUNCTION:

The MX-500P Power Unit provides RF energy at 13.560MHz to the
Soldering Tip Cartridge, which contains an induction heater consisting of an 18 turn AWG33 wire coil wound around a 0.11" diameter by 0.5" long slug. The slug is composed of a copper core, clad in a thin magnetic alloy having a curie point equal to the desired soldering tip temperature. The magnetic alloy absorbs RF energy from the coil, causing the slug to heat up until the curie temperature is reached. At this point absorption stops and heating ceases, because the RF energy is now reflected back to the power unit by the copper core.

The On/Off switch atop the power unit controls the 18V power supply U8, which runs all the supervisory circuits. When the 18V supply is off, Q6 turns off thereby causing Q7 to turn on and disable the RF generator.

Q5 and Q8 control a small DC bias voltage out to the soldering hand piece, so that U2a can sense an intermittent or disconnected hand piece cable, in which case the yellow LED DS2 will light and U2b will latch Q7 on, thereby disabling the RF generator until the On/Off switch is cycled.

U5a senses small changes in RF generator output power to the
soldering hand piece. If no changes are detected for half an hour then sleep mode timer U6 times out causing U7 to latch Q11 on, thereby disabling the RF generator until the On/Off switch is cycled. This functionality can be disabled by backing out the tiny grub screw in the upper right side of the unit.

If thermal switch TS1 detects an over temperature condition inside the power unit then Q9 will turn on and disable the RF generator until the temperature drops back down to normal.

If Forward Power at T3 and C33 exceeds reasonable limits due to a fault in the power unit circuitry, then Q19 will turn on and disable the RF generator until Forward Power returns to acceptable levels.

U5b monitors the supervisory circuits and lights green LED DS1 if everything is OK, in which case Q12 will be on, enabling U4 to power up the RF generator.

U1 provides a 13.560MHz square wave out to class C driver stage Q3, which in turn drives the class C final output stage Q4, providing RF power to the soldering hand piece. Note that Q3 is unusual in that it has an input capacitance of only 55pF and a gate threshold voltage of only 1.6V.

Diodes D8 and D9 sense the RF voltage level coming out of the RF generator, providing negative feedback to switching power supply U4 Q1 Q2, which powers the final RF output stage Q4 of the RF generator.

J1 provides a DC voltage which is proportional to the power being delivered to the hand piece. It can be connected to an analog meter movement or other measuring instrument.

TRIMPOT DESCRIPTIONS:

RV2 adjusts the RF-Output-Power delivered to the hand piece; if this adjustment is incorrect then the voltage at C8 will likely not correspond to the values given elsewhere in this document.

RV1 sets the Forward-Power-Fault safety shutdown circuit trip point; if this adjustment is incorrect then the voltage at C16 will likely not correspond to the values given elsewhere in this document.

RV3 calibrates the signal out to any Meter connected at J4; the signal at J4 is not normally used so it is hard to imagine how this adjustment could have any impact upon the operation of the unit.

Calibration is well beyond the scope of this document and must not be attempted by anyone other than a qualified Metcal service technician.

MEASUREMENTS FROM SOME GOOD WORKING UNITS:

Whenever unit is plugged into the AC line:
  • Voltage at C2 will measure approximately 26 VDC
  • Voltage at C6 will measure approximately 53 VDC
Whenever the power switch is on and unit is plugged in:
  • U8 pin 3 will measure 18 VDC
  • U7 pin 14 will measure 12 VDC
Whenever a hand piece is connected and the green LED is lit:
  • U4 pin 4 will measure 1.3 VDC
  • U4 pin 5 will measure 0.0 VDC
If the green LED is extinguished but the unit is plugged in:
  • U4 pin 5 will measure 26 VDC
Whenever the hand piece is idling hot in the stand:
  • Voltage at C8 will measure between 17 and 18 VDC
  • Voltage at C3 will measure between 14 and 15 VDC
  • Voltage at C16 will measure approximately minus 1.2 VDC
  • U1 pin 14 will measure approximately 4.8 VDC
  • U1 pin 4 will have a 13.56 Mhz waveform approximately 2.8 Vpp
When the soldering hand piece is heating up from a cold start:
  • Voltage at C8 may temporarily rise as high as 21 VDC
  • Voltage at C16 may temporarily rise as high as minus 0.22 VDC
When the hot hand piece is touched to something cold:
  • U5 Pin 1 will pulse high momentarily
Characteristics of a cold MX Soldering Tip Cartridge:
  • Inductance at 1kHz is somewhere around 2.8 uH
  • DC resistance is fairly close to 0.21 ohms

Newest Blog Posts