A lot of the UK ones were made by Interlas in Italy. Numbers don't match the Miller manuals. I think I found a circuit board with a date under the LHS panel of mine and downloaded a manual from about the right era.
Switch is for gas pre-flow ON/Off and pot sets the time for the preflow.
Manual is available for download from Millerwelds.com Don't enter a serial number, click search and scroll down to Synchrowave 300 in the list. Interlas/Miller = same thing on these older models.
If you still have problems finding the manual, PM me and I'll email you a copy. May even have a copy of the technical manual.
Apologies for the zombie thread revival ! New here and after a bit of help if possible
I have a 300P and can't find an ID tag either. I've had the thing for 20 odd years and it's been great, but has recently thrown it's hand in. No more HF. After checking the HF gap, I noticed the HF adjuster felt odd and upon inspection found it had shorted and burnt out one of the coils on the resistor, which in turn clipped the carbon brush out of its holder. It's should be still usable (if left alone) now re-instated but is there anywhere else obvious before I go digging ? I have an early user manual from the miller site but not sure if it's the correct year. A technical manual would be very handy
On hols till 19th july so just a quick response. Throw away rheostat, join 2 wires together and insulate well. Clean and set spark gaps to 8thou and you should be ok. If not, suspect hf transformer, hf capacitors or smaller pcb. Relay fails after lots of use.
Dave
So, after a little bit of digging it turns out my 300P is an Interlas built machine too. After I got the covers off, removed the rheostat and linked it out. Reset and cleaned the spark gaps and gave it a try. No HF.
What I did discover while the covers where off when trying to strike an arc was a light glow from the top of the HF transformer. Once I had removed the 'Air Coil' to gain access, I found two link wires on the transformer had been rubbing together with vibration over the years and become brittle with the heat. This shorted them and was causing the glow. Once replaced, we have HF
I'm not convinced all is well yet as I haven't had a chance to fully test, I'll know more soon and keep you posted.