Transistor Identification - older Weller soldering station

[alecjahn]

A while back I tried repairing one of the soldering pencils for my old Weller soldering station that I use quite frequently (sure, there are fancier models out there nowadays, but it has given me years of great service!).

I tested the repaired pencil only momentarily until recently when I decided to try it out for a project instead of using the old standby pencil that has always worked.

Well, something fried in the base/station and now it won't heat up either pencil. I'm blaming the "repaired" one on this.

It -appears- that a transistor, located on the little daughterboard that the pencil actually plugs into, has bit the dust. Whoops.

My problem now, is identifying the part - a google search for any or all of the numbers on the transistor can ("TO-18" packaging, as I have learned) brings up nothing to help.





Am I out of luck unless I can find a schematic (no luck there - yet!)? Or is there some magical way to divine the part's rating/numbers with a little more education?

Thanks, y'all.

[sofTest]

Re: Transistor Identification - older Weller soldering station

Any chance you could give us the model of the station, and a picture of the underside of that connector board?

[eccerr0r]

Re: Transistor Identification - older Weller soldering station

I don't have a Weller so I can't comment on the specific unit you have, but my Ungar also uses low voltage heaters (it has a transformer) and IIRC uses a TRIAC to do heat control of the heating elements.

If my eyes aren't fooling me I thought that was a TO-5 case...

hmm...

http://www.hutsonind.com/TO5SCR.shtml

[redwire]

Re: Transistor Identification - older Weller soldering station

The part is a Hutson SCR HS04 4 amp, 50V sensitive gate. It controls power to the heating element from the thermostat switch.

I would put in a TO-220 part like S4006L, BT150, C106M (w/heatsink), since TO-5 can parts are obsolete.
Low voltage through-hole SCR's are a bit hard to find, so a 400V part might be easier.

Teccor SCR's pdf

Weller MP soldering station schematic

It's a good station worth repairing.

[alecjahn]

Re: Transistor Identification - older Weller soldering station

The station is a MP101.

And ah, so it's not a transistor, then! I see now. (my ignorance is showing, whoops!)

thanks for everyone's help! Hopefully I can find a suitable replacement part. Is a modern plastic part going to have the same pinout?

Here's a picture of the back anyway:

[eccerr0r]

Re: Transistor Identification - older Weller soldering station

Likely you'll have to replace with a TO-202 or TO-220 and they may not have the same pinout... but if you get the right ones in the right holes it should work. The three terminals for SCRs are the cathode, anode, and gate.

But likely since the TO5 did not have a heatsink, you won't need one on the TO-220 either. The TO-202 is a maybe... but likely not either.

BTW, wouldn't these SCR-controlled solder irons have horrible power factors? I suspect the TRIAC controlled ones aren't much better...

[redwire]

Re: Transistor Identification - older Weller soldering station

I'm not sure why they didn't use a triac. Otherwise, the heater gets 1/2 wave DC, so it is not optimal. It makes the transformer run hotter and things get magnetised. Newer Weller stations (i.e. WTCP), the thermostat can handle the heater's full power. Perhaps the contacts arc and get stuck.

The date code on the SCR is 1977...?

I have Hakko, Ungar and the Weller WTCP is still a great soldering iron.

[alecjahn]

Re: Transistor Identification - older Weller soldering station

Ordered a S4006L and a BT150 from digikey. Hopefully one will do the trick (if not I'm only out a $1 part). Thanks again everyone, I'll update again when I get one installed.

[alecjahn]

Re: Transistor Identification - older Weller soldering station

Well, no luck. I'm suspecting the transformer.

[ben7]

Re: Transistor Identification - older Weller soldering station

Well, no luck. I'm suspecting the transformer.

Have you even tested the resistors?

Did you put the new part in the right way around?

[budm]

Re: Transistor Identification - older Weller soldering station

Yes, should verify the pin out of that SCR.

If you jump Anode to Cathode, the iron will have full power if the transformer is working.

[alecjahn]

Re: Transistor Identification - older Weller soldering station

Yeah, I checked the pinout many times before turning it on the first time.

Resistors seem fine to be fine.

Tried this jump trick and no results.

I'm getting no voltage out of the red lines (from the transformer).

[redwire]

Re: Transistor Identification - older Weller soldering station

There are usual checks - heating element resistance, thermostat (with tip in and out), transformer secondary voltage - which you have zero... Neon lamp comes on?
Check ohmeter continuity for the transformer primary. I usually go right across the AC line cord prongs (unplugged end!) open-circuit tells me to check the on/off switch etc.

If your transformer shows open-circuit on its primary, then the thermal fuse is probably blown. Rarely, you can replace one using micro-surgery.

[alecjahn]

Re: Transistor Identification - older Weller soldering station

As it happens, my father had this lying around:


The iron operates with the original transformer disconnected and this in place.

I assume the thermal fuse is blown in the transformer. Is this a horrible task to replace? where might it be located - around the windings under the paper?

[redwire]

Re: Transistor Identification - older Weller soldering station

If you get no ohmmeter continuity on the primary, it's shot and you don't have anything to loose if surgery goes bad.
The thermal fuse is on the lead-in to the primary winding. Look for a bump or something resistor-sized, just after where the wires start to go into the bobbin. I use an exacto-knife and carefully cut back some of the paper until I can see it. The magnet-wire is pretty fragile. You just want to desolder the fuse and replace it.

You can get a new transformer for $20 on eBay, which might be less hassle: ebay.com Weller-soldering-station-TRANSFORMER-MP-201-NEW-OLD-STOCK-/181024341913

[ben7]

Re: Transistor Identification - older Weller soldering station

Sometimes the fuse will be in under a layer of the windings, but yes, it usually is on the outside. Be VERY careful when taking at apart, the windings are probably VERY fine wire... which is easy to break!

[ben7]

Re: Transistor Identification - older Weller soldering station

You know, If you can find out what the secondary voltage of the original transformer is, (using documents, design circuits, etc...) you could just buy a new transformer with the same secondary voltage (and current capability!).