Crack + Noob = Help!

[Zerostar]

Ok so I spent alot of time trying to really make sure that I soldered everything very well.  When I first did the resistance checks all seemed well so I continued to the voltage checks, tubes lit up and continued to test volate. Everything was matching up fine until I tested pin #13.  At this point I blew the fuse, and tripped the breaker to my room circuit. 

At this point I re-checked all my joints visually and everything seems to look ok.  I replaced the fuse and tried to power it on again, now it just blows the fuse on power.

So I started again with the resistance checking, here is my results:

1    *
2    *
3    0 ohms Result: 0.5ohm
4    *
5    *
6    2.4K ohms Result: 2.5K
7    2.9K ohms Result: 2.943k
8    0 ohms Result: 0.5
9    2.9K ohms Result: 2.95k
10    2.4K ohms Result: 2.5k
12    0 ohms Result: 0.5
13    * will climb slowly toward 270K ohms Result: 1.7Meg
14    0 ohms Result: 0.5
20    0 ohms Result: 0.5
22      0 ohms  Result: 0.6
B3      2.9K ohms Result: 2.94K
B6      2.9K ohms  Result: 2.95K
RCA jacks:
Ground lug    0 ohms Result: 0.5
Center pin    90K ohms

 

[Grainger49]

The checkout says any resistance or voltage reading +/- 15% from spec is good.  So you are ready to go.

If you touch your meter leads together measuring resistance you will see that the leads have a resistance, usually under an Ohm.

So the wire measured will also have a resistance.  For those points called out zero anything under an Ohm will be fine.

 

[Zerostar]

Ok so next I would follow the voltage test, tubes in, volt meter connected to ground, fuse in.  Turn on the power and the fuse burns out instantly.  Sounds like a short, but I don't know what to do to trouble shoot this.  I've reviewed all the connections and they look good, now what?

Thanks for the help!

 

[Grainger49]

Yes, this is what a short will do.

Look at your 4 diodes.  Then have someone else look at them as you read which end the stripe should be on.  Diodes are the most often thing to cause a fuse to blow.  Shorted wires are next.  Mis-oriented caps can do it but usually they blow themselves up, the flat end is no longer flat. 

Check the diodes, then look for shorts (post a picture of back and front of the power supply, we can help) then the capacitors. 

Post back.

 

[Zerostar]

Ok double checked the diodes, caps and wiring again, I can't really find anything visually wrong.  Attaching a bunch of close up pics.  What can I try next?

You can find the pictures I just took here: https://adsupply.box.com/s/py8wop4w07jr3qldi7o6

Thanks for the help!

 

[Grainger49]

Ok, good pictures.  I'm checking the pictures against the manual.

The diodes are according to the manual.  The high voltage wires on the transformer check out. 

For the fuse to blow immediately (you looked at it, right, measured resistance?) there is a huge inrush of current. 

Look at the wires on your power transformer.  The low numbers, back of the amp, should be substantial wires, the front ones should be tiny wires.  I just want to be certain your transformer didn't get the sticker on backward.

And finally, this is dumb and basic so bear with me... pull out the power cord, turn the power switch to "ON", replace the fuse and measure across the two non-grounded lugs on the IEC power connector.  I get 11.8 Ohms.  This just verifies the power input to the primary winding of the power transformer.

Now I have to go see what is wrong with my Speedball installation I did for another Bottlehead. 

 

[Zerostar]

Ok looking at the transformer the nodes numbered 4 and 5 are the most substantial wire size while  nodes 6 and 7 seem to be the thinnest wire size.

I replaced the fuse, set power switch to on and I get 12.1Ohms.

I also checked the resistance on the blown fuses, 0.  I can see the fuses blow with a blue flash when I flip the power on.

If we did a continuity comparison would that help?

 

[kgoss]

If you bought fast blow fuses try slow blow with the same rating.  It might not solve the problem but it can't hurt.

 

[Grainger49]

If the resistance of a fuse is zero, it is good.  If it is infinity, or OL, it is blown.

Your reading of 12 Ohms says that all the wiring from IEC power module through the transformer is normal.

 

[Zerostar]

I'm going to go pickup some slow burning 500ma and 1amp fuses and give them a try next.

Crosses fingers.

 

[Chris65]

Some info on fuses here: http://www.bottlehead.com/smf/index.php/topic,4877.msg46989.html#msg46989

Good luck!

 

[Zerostar]

Ok using .5ma SlowBlow fuses and the tubes are lighting now, cool!

Going to continue on with the voltage tests.

Thanks!

Forrest

 

[Zerostar]

Ok voltage checks came in good, and now I'm listening to music!

Thanks so much for the help guys.  It looks like I was blowing through .5ma fastblow fuses, and now I'm working fine on a .5ma slowblow.

Yay!

 

[Grainger49]

I'll bet if you put a slow blow fuse in now it will hold forever.  The caps have charged fully once and will never let go of all the charge.