I think I have a broken transformer - measurements inside

[senn4lyfe]

I finished my build last night and started voltage checks today.  Plugged in, turned on, and stone dead.

Rechecked wiring, cap orientations, diode orientations and all were fine.  Checked solder joints with point to point continuity checks and all were fine.

Finally worked back to the power supply.  I plugged the cord into the IEC receptacle and checked continuity through to the lugs.  All were fine.

Did some point to point resistance measurements reported here (TX is Transformer lug 'X'):

N to T2: 0.1 ohm
L to Switch: 0.1 ohm
Switch to Switch: 0.1 ohm
Switch to T1: 0.1 ohm
T4 to T5: 0.1 ohm
T6 to T7: 42.3 ohm
T9 to T10: 42.3 ohm
Live IEC prong to L (across installed fuse):0.2 ohm
T1 to T2: INFINITY

So it looks like my transformer has an fault in the primary winding. $^%$@%@$  I checked it multiple times scraping and poking into multiple areas of the tab and solder joint so I'm confident that it is not just due to poor contact from the probes.

Am I missing something, or did I just waste 12 hours building this thing?

Thanks.

[Paul Birkeland]

 I checked it multiple times scraping and poking into multiple areas of the tab and solder joint so I'm confident that it is not just due to poor contact from the probes.

You have to be somewhat careful around those tabs.  If you look closely, you'll see a small wire coming out from under the black transformer tape, then wrapping around the bottom of each of these solder tabs.  If you bend one of the tabs too much, you can snap that wire off.

If you have snapped one of these little wires, you can often use a piece of trimmed component lead to bridge the gap and get yourself up and running again.

As far as out-of-the-box failures, I think we've seen 2 bad power transformers across all kits from our current winder.   So it does happen, but it's extremely rare. 

[senn4lyfe]

OK, I had a broken lead into the transformer at T1.  I probably broke it during soldering as I didn't manipulate the tabs at all.

I managed to expose about 1/8" of the lead above the plastic casing.  I soldered this into T1 and got a resistance of 12.1 ohm to T2.

Does this sound OK to start voltage checks?

And thanks for the almost instant reply!

[Paul Birkeland]

Yup, you're good to go!  Nice job on a rather advanced repair.

-PB

(If you get nice, stable voltages, consider dribbling just a little bit of super glue over your work to keep it tight)

[senn4lyfe]

Thanks, this was my first time soldering.

Super glue on the repair or all connections?  Is this for mechanical integrity?

Thank for the advice.

[Paul Birkeland]

Just on the repair.

[senn4lyfe]

OK, accidentally blew a fuse during voltage checks.  Finally found replacement fuses and 1/2 Amp fast blow keep blowing during power up.  Do I need slow blows?

Put in a 4 Amp just to complete voltage checks and accidentally bridged the A8 and A7 or A9 tabs on the tube socket.  LED on A8 blew.  Sigh.

Other than that, all voltages look OK.

Is there a part number for the LED that I can order a replacement from Mouser or some other shop?

[Paul Birkeland]

Is there a part number for the LED that I can order a replacement from Mouser or some other shop?

The HLMP-6000 is the correct replacement LED.

[Doc B.]

replacementparts at bottlehead dot com

[senn4lyfe]

Thanks CB, two on the way (one to break!).

[squirreldude]

I wanted to stop in and say thanks to you guys. My amp was having the same symptoms as OP's, and sure enough one of my power transformer leads was broken off. I suspect it was not attached when I received the box, because it was significantly bent out of place and I was pretty gentle when building. One problem fixed; now on to the next one