First build, resistance issue

[tonyalves88]

Good idea Paul, I tested a 9V battery I've had in it's package for a while but haven't used, it measured at 8.12volts so looks like the meter works. EDIT: checked another battery I had and it registered at 9.1 volts, so I definitely don't think it's the meter. I think I'm just getting very low voltages from my kit? I honestly have no idea hah, any help is always appreciated, thanks.

[tonyalves88]

You mentioned how I might have a nasty short in the power supply, I remember when I first turned it on the transformer was buzzing, after re-soldering some sketchy looking joints it didn't buzz again. Maybe that was what happened initially? I remember T13 climbing to 270k as it was supposed to before I turned it on a first time, now after checking T13's resistance it doesn't climb, it stays put at .5, did I mess up the 270ohm resistor?

[Paul Birkeland]

You may have a blown fuse.

You'll know when a resistor is bad, as it will generally no longer be in one piece.

[tonyalves88]

I should have mentioned I already suspected a blown fuse, I checked the fuse but it was still intact, I replaced it with another 1 amp 250v slo-blo fuse just in case, but nope, same results. Sorry, Any other ideas?

[Grainger49]

I'm not sure if Bottlehead has changed the IEC connector.  It has a place for the fuse that will be inline with the power and a place for a spare.  Sometimes builders put it in the wrong part.  It should go in the crook that is the farthest from the back that says "fuse."

Just checking.

[tonyalves88]

Thanks for the suggestion Grainger, I could see how that could be mixed up. Unfortunately that's not the problem, I have the fuse in the right place. Like you said on the bottom piece, I know it's the right spot because it physically clicks into place when you push it down, without the fuse in the right spot it doesn't quite click, and can easily be popped back out without resistance. So the ordeal goes on...

[Paul Birkeland]

Try measuring AC voltage coming into the transformer (the two lugs on the transformer receiving voltage from the power switch and IEC entry module).

-PB

[tonyalves88]

ok for the terminal 1 which is coming from the switch, measuring AC I'm getting 120 volts on the 600v setting. For terminal 2, coming from the power cord, I'm getting very low voltage, .052 on the 2v setting, I'm guessing that's my problem? or at least one of them?

[Paul Birkeland]

ok for the terminal 1 which is coming from the switch, measuring AC I'm getting 120 volts on the 600v setting. For terminal 2, coming from the power cord, I'm getting very low voltage, .052 on the 2v setting, I'm guessing that's my problem? or at least one of them?

You would generally want to measure with one probe on each pair of terminals.

This check tells us that power is coming in.  (Your AC neutral is tied to ground at your service panel)

Now perform the same measurement on the 0-6.3V pair (power transformer terminals 4 and 5 IIRC).

-PB

[tonyalves88]

Hey OK so when measuring the first two power transformer terminals I get just under 120 volts, around 118. But when measuring terminals 4&5 I get barely any voltage, .005 on the 600v setting, is that any indication?

[Paul Birkeland]

I would try another pair.

There are times when we see builders accidentally cut the wires coming out of the transformer, most likely while trimming parts in the area.  You may want to double check the wires that come out of the bobbin tape and wrap around each tab on the transformer.  If you've cut one, usually you can reconnect it with a piece of bare wire and get back in business.

Having the correct voltage on another winding would indicate a cut on the 6.3V winding.

-PB

[tonyalves88]

I'm getting 1.1volts from power transformer terminals 9&10 and .4volts from 6&7, the wires coming out of the transformer seem ok to me, I don't think that's it.

[Paul Joppa]

That indicates that the power line voltage is not getting inside the transformer. Could be a broken wire at the terminal (1 or 2), or just a bad solder joint on those terminals.

A simple check is to measure the resistance between power transformer terminals 1 and 2. It should be around 14 ohms; if it is over the range (very high) then one of the terminals is not connected to the winding. If it is near 14 ohms then the wiring is not electrically connected to the terminal.

Of course it's always conceivable that the winding is broken internally, but we have never seen that happen and we've gone through many hundreds of PT-3 transformers, so that would surprise the heck out of me!