Working Kaiju suddenly blowing fuses

[ashbrook.m]

I completed my Kaiju a few weeks ago and it has been working great. I have been running it for a few hours (the first time it has run for this long) when suddenly it blew a fuse. I replaced the fuse and it instantly blew another fuse. Any thoughts on what could cause this behavior?

[joepiecuch]

I had a similar issue a while back with a Kaiju that'd been in service for a couple years. PB suggested that a loose something...a solder blob, a wire or lead trimming...has migrated to a place where it could cause a short. I stood it on end, shook it as vigorously as I could and blew it out thoroughly with compressed air. I don't recall that I actually found the problematic fragment, but the issue has not recurred since.

[ashbrook.m]

Tried to clean it out and it still blew. I removed the tubes and desoldered the rectifiers to test just the transformer. The DC supply remains connected. Still blew a fuse. I’m starting to think its an issue with the transformer. How else could I check this?

[Paul Birkeland]

Disconnect the wires going into the DC filament supply.

When a power transformer fails, usually it will smell up your house horribly.

[ashbrook.m]

I sequentially disconnected all the outputs and still blew fuses. I then did the same on the input side of the transformer. Disconnecting the winding across terminal 3 resulted in the fuse not blowing. I reconnected to 3 and blew the fuse. I think it is that winding that failed.

[Paul Birkeland]

Can you post some build photos?  I think you would be the first person in the history of the company to have a power transformer that failed at random.

[ashbrook.m]

I have these two on my phone pre-removal of the transformer connections. One before the DC upgrade and one after. I can post close up photos of any specific area this evening when I get home if needed

[Paul Birkeland]

With the winding to PT terminal 3 disconnected and the power switch off, you could check the DC resistance of the winding from 1-3 and also from 4-6 to compare.

[ashbrook.m]

1-3: 3.2 ohms, 4-6: 3.4 ohms.
I checked the outputs too. All the low voltage windings : 14-11, 12-13, 9-10 all measure at 0.2 ohms. The high voltage winding from 7-8 is infinite.

[Paul Birkeland]

You may need to bump up the scale to read the 7-8 winding.

On second though, can you check DC resistance from terminal 7 to 1-6, then also from 8 to 1-6?

[ashbrook.m]

Set my meter to 60 M ohms, OL across 7-8 still

Terminal 7:
1-OL 2-OL 3-OL 4-7.1 ohm 5-4.0 ohm 6-4.3 ohm

Terminal 8:
OL across all terminals

[Paul Birkeland]

You definitely do have a blown power transformer. 

When you get the replacement (shoot an e-mail to Eileen and be sure to provide a link to this thread), I would recommend doing the following:

1.  Connect all the primary connections on the incoming AC side and check the AC output voltages as directed in the manual.
2.  Hook up just the low voltage winding feeding the STP wiring going to the 5670 tubes and verify that they are glowing properly.
3.  Hook up the two green twisted pairs and verify appropriate DC voltage coming out of the DC filament board (it will show 6.3V across the output terminals).
4.  Hook up the high voltage winding last and do a complete voltage check. 

PJ would have a more complete image in his head of how the high voltage winding might open up and short itself to one of the primary windings.  I seem to remember that the low voltage 6.3V winding would be between these two, so another check you might want to do is to checK DC resistances between power transformer terminal 9 and the rest, as well as power transformer terminal 10 and the rest.  9 and 10 should show as almost a dead short and should be open to the rest, though in circuit you may see a few hundred ohms to 1K of resistance and that wouldn't be a problem. 

In a situation like this it pays to be super careful when installing the new power transformer in case there was a problem in the amp that toasted the first one, as you could end up also toasting number two!

[ashbrook.m]

Thanks for your help! I did notice that when it failed, the transformer was quite warm. Not hot to the touch, but much warmer than the identical transformer on the BeePre2 has ever gotten.

[Paul Birkeland]

The Kaiju does draw a substantial bit more current through the HV winding compared to the BeePre, so that isn't completely out of the question.

[ashbrook.m]

I received the transformer this afternoon. It passed all voltage checks and the Kaiju is making music yet again. I will be sending the original transformer back to you guys to check it out. Thank you for your help!