hughes & kettner Tubeman Transformer Blow

[g1]

2. The voltage of the input of the trans drops to 5 or 6V. respectively the output drops to roughly 130V. ( At normal situation it's 13.5V and 240V)
3. It keeps +12V, -12V, +18V, and +12.6V at the other rails.

This is not really possible if the schematic is correct. The power jack goes straight to the transformer primary. If it's dropping down to half at the TX primary, the other voltages would fall off as well.
It could be that the diagram is different from what you have there. Or maybe a bad connection between the jack and the TX primary. Measure the AC right at the jack. When the voltage at the TX primary drops to 6V, does it drop at the jack as well?

[Kick]

Hello there.

I've tried to measure the primary pins of the transformer, but seems like when I touch the pins the voltage goes back to normal maybe due to the connection.
It might be just a mistake that I read the voltage of the primary 5 volts...

I will try a different power supply anyway.

Thanks

[nosaj]

Hello there.

I've tried to measure the primary pins of the transformer, but seems like when I touch the pins the voltage goes back to normal maybe due to the connection.
It might be just a mistake that I read the voltage of the primary 5 volts...

I will try a different power supply anyway.

Thanks

Or you have a bad joint that is opening up due to heat. Reflow pins 1 2 3 4 and then report back.

nosaj

[J M Fahey]

Agree and add, I have sometimes seen this, which is annoying/confusing:
* you have a crack in the track leading to one of the transformer solder pads
very easy to get because a transformer is a heavy part and flexes the PCB
* that crack is very narrow
* when you press meter probes against solder pad, you push the PCB and make it flex, in a way that both sides of the crack touch each other, so "everything measures normal" ... until you remove probes that is

I think nosaj hit the nail in the head.
IŽd only add that besides reflowing the solder pad itself, you also scratch solder mask and expose a couple mm of track(s) leading to pads and extend solder there to bridge any possible gaps.

Because pads are covered in a thick layer of very hot solder when soldering, they contract when cooling and apply a pulling force away from the cold track, so that increases possibilites of a crack appearing just there.

[nosaj]

Agree and add, I have sometimes seen this, which is annoying/confusing:
* you have a crack in the track leading to one of the transformer solder pads
very easy to get because a transformer is a heavy part and flexes the PCB
* that crack is very narrow
* when you press meter probes against solder pad, you push the PCB and make it flex, in a way that both sides of the crack touch each other, so "everything measures normal" ... until you remove probes that is

I think nosaj hit the nail in the head.
IŽd only add that besides reflowing the solder pad itself, you also scratch solder mask and expose a couple mm of track(s) leading to pads and extend solder there to bridge any possible gaps.

Because pads are covered in a thick layer of very hot solder when soldering, they contract when cooling and apply a pulling force away from the cold track, so that increases possibilites of a crack appearing just there.

Every now and them I'm bound to get something right
Hopefully it's the answer.
nosaj

[Kick]

Hi nosaj, Juan, and everyone.

I've re-soldered and powered up for several times, and it seems to be working properly! It's got slightly higher voltages too, 13.8Vat primary and 250V at secondry so I think it was the cause. Thank you very much!

Well, though it's working properly, I wonder if the voltages at the P010, it supposed to be 280V, and -11.1V for the heater, supposed to be -12.6V, are OK?
I think if I change the value of the resistors R46,48,49, it might get higher voltages, but since I don't have a scope, I don't want to get unsteady DC.
Any suggestions are welcome.

Thanks for many times.

Kick

[nosaj]

Hi nosaj, Juan, and everyone.

I've re-soldered and powered up for several times, and it seems to be working properly! It's got slightly higher voltages too, 13.8Vat primary and 250V at secondry so I think it was the cause. Thank you very much!

Well, though it's working properly, I wonder if the voltages at the P010, it supposed to be 280V, and -11.1V for the heater, supposed to be -12.6V, are OK?
I think if I change the value of the resistors R46,48,49, it might get higher voltages, but since I don't have a scope, I don't want to get unsteady DC.
Any suggestions are welcome.

Thanks for many times.

Kick

Before you start fiddling with that how does the pedal sound?
i maybe overlooking it but I do not see a voltage regulator. So see what the wall outlet is putting out, then the AC wallwart.
But if it sounds good to you , then the lower voltage will just prolong the tube life.

nosaj

[Kick]

At the time of writing, the wall outlet is 102V, as I live in Japan. The AC wall wart is 16.8V, which is quite surprising, though it says 13.3V on the label.

The sound is not bad, But I wish it could get a bit more natural sound. Since it uses an op-amp even for by-pass state, it sounds a bit modified.
If I pass a sine wave when it's driven, the level of high frequency gradually decreases, when it's on by-pass state it's not really significant.
Though, I basically like the sound since I've been using it for 20 years.

Thanks