Original Metcal STSS-001 / RFG-30 Soldering Station Durability?

[Jamieson]

I've repaired/restored a few of the original series Metcal soldering station power units (STSS-001 / RFG-30). A common problem is that the output FET (IRF130) fails, usually a gate to drain short. A pretty simple fix, but NOS IRF130 parts in TO3 packages are getting harder to find and they are getting pricy.

Is this failure mode usually caused by powering up the unit without a tip installed? Does FET burn out immediately in this condition?

Looks like later revisions of this power supply (STSS-002/PS2E, MX500P, etc.) have extra circuitry to detect a missing tip and/or handpiece, and trigger a latching shutdown to protect the power RF stage.

[Jamieson]

Some more digging on these early Metcal designs:

STSS-001 / RFG-30 (serial numbers 200XXXX). This design runs the output FET from the low power 19V rail, except when more power is needed, then a linear regulator kicks in and adds power from the higher 42V rail. This design is described in the Metcal patent 4,626,767 from 1986. The issue here is that if the output is open due to a bad cable or bad tip, there is no mechanism to shut down the RF generator, and it will eventually blow the output FET. The power indicator is a small bulb that backlights the logo (looks cool, bulb is usually burned out). The transformer is a nice toroid properly mounted and is very quiet.

STSS-001 / RFG-30 (serial numbers 400XXXX). To address the output FET failures this design has been kludged up with a small bodge board which detects an open output and disables power to the output FET. The LDO regulator on the previous design has been replaced with a switcher. I don't think it latches off, but keeps trying to power back up. Cosmetically it is the same as the early STSS-001 model and gives no indication that a open/fault condition exists. There are a lot of kludges on this model, kind of amazing it went into production like this. Check out this thread for details on these first two units: https://www.eevblog.com/forum/repair/metcal-stss-001-rfg-30-disassembly-and-measurements/

STSS-002 / RFG-30. New design, still boxy but slightly larger. Single red LED. I believe this design is functionally very similar to the latter STSS-001 design, maybe they just cleaned up the various kludges and bodge boards into a new PCB layout. The toroid transformer has been replaced with a more generic laminated transformer, can be a bit louder. Like the later model STSS-001 it can detect an open/fault condition and power down to prevent tip damage, but it does not latch off and gives no indication of the fault condition.

PS2E-01. Same form factor as STSS-002 RFG-30. Power LED is green and this model adds a red (or later, yellow) LED for fault indication. Requires an MX-RM3E handset which has some additional components installed in the handle. The older RM2 "non enhanced" cables will not work. If the power supply detects a missing/older handset, or a missing/bad tip, or intermittent cable it will kill the output power and latch off, requiring a power cycle to restart. There is no timeout feature.

MX-500P-11. New design, big beefy heavy aluminum cast case with curved front. Keeps the minimalist industrial design thing going with just a single green and yellow LED present. Operation similar STSS-PS2E but adds a 30 minute timeout feature which can be disabled by a very tiny grub screw hidden on the right side. The power switch is on the transformer secondary, so when plugged in the transformer is humming away and the main DC power rail is on. This design is VERY well documented by Stepan Novotny and that PDF has been circulating for the last 17 years. This PDF also shows up on eBay and is purchased by people who don't know how to search for things.