Fuse blown at first Powerline Voltage Test [resolved]

[CrazyMarc]

Hi there. I bought a bottlehead crack kit on Ebay, came from the US and I'm UK but I know the transformer is worldwide and it is the PT-10 so seems okay. I got the board set up and got to page 23 of the crack PDF when testing voltage to determine how to configure the transformer, however upon finding no reading from the multimeter I found the 1A fuse appears to have blown for seemingly no reason. I only had the US plug supplied so I used a UK plug of my own that had a 5A fuse in it already. Not sure if this may have been the problem. I don't think it's the wiring as there's not really much that could have gone wrong at this point.

Not really sure where to go from here, also I'm not sure what size fuse I'd need for replacements as the fuses I'm used to are a bit bigger physically than the included 1A fuse. Is it possible this fuse was just a bad egg? Little bit gutted right now and a feeling of dread is starting to set in x)

Many thanks.
Marc.

[Paul Birkeland]

Did you rewire the transformer for UK voltage?

If you plug a 120V wired Crack into a 240V outlet, hopefully the fuse saved the power transformer.

The manual is written assuming that you've bought the kit, not the completed unit.  You will need to determine your AC line voltage without destroying the amp in the process.

[CrazyMarc]

I don't believe I've gotten that far yet. I've done the bare buss wire to the E tab of the IEC inlet, then through the safety ground lug to 16L. Then I've done the black solid core wire from the safety ground lug to terminal 8 of the PT-10 power transformer. Then the black solid core wire from the L tab of the IEC inlet to the lug of the power switch closer to the edge of the chasis.

Everything is exactly as is shown in the diagrams. I've essentially done Assembly Part Three. The voltage test immediately following is where the fuse blew, which if I understand correctly is PRIOR to wiring for UK voltage; unless there was something I missed that I was supposed to do before even getting the soldering iron out? I think the step I've fallen on is essentially supposed to be checking the voltage to determine the correct wiring needed. Hopefully that makes sense?

Obviously I can't really even go any further until I have a new fuse so hopefully someone can point me in the right direction as to the correct size fuse I'll need.

Also, just to clarify, it is the kit, it didn't come preassembled. Essentially someone bought the kit for a friend, ended up not needing it and so sold it on ebay just as it was shipped to them. I saw it as skipping the 8 week or however long wait when buying direct from Bottlehead. So I'm building it from step 1.

[Paul Birkeland]

Ah, excellent.  I thought perhaps that you bought a pre-assembled kit.

Can you let us know how you know that the fuse blew?  Posting photos of what you have so far may be helpful as well.

[CrazyMarc]

Yeah, I realised you thought I'd bought preassembled after I posted my reply and had to edit in that last part about buying it as kit. I wanted the full experience lol! Just didn't want to wait 8 weeks I tried to send pics and it warned me I'm not allowed to send links; however I just figured out how to attach directly. Third times the charm hopefully.

I know the fuse is blown because where before it was a nice clean tube, now it's covered in splinters of what I can only assume is the filament. (Pic attached) (EDIT: also no reading was coming from the multimeter, was just 0. If the fuse was good I would assume there'd be voltage unless I did something *really* wrong lol).

If you have trouble with any of these pictures then let me know and I'll retake them. Will be going to bed at some point reasonably soonish but will be online tomorrow. Also, I just realised the buss wire is in fact soldered to the wrong hole on the terminal strip... however it shouldn't really make a difference at this stage should it? Obviously I'll have to resolder, but... At this point it's all the same voltage through the same parts etc so it shouldn't really make a difference? Not a whizz with electronics so I could be wrong.

Just so you're aware, a friend who used to make a living in building circuitry etc is helping me with this build, I'm not super confident to do things without him here so advice is brilliant in the meantime but actual changes may have to wait until he's around. Hope thats okay.

[Paul Birkeland]

If the fuse reads 0 ohms, it's still working.

The little plastic thingy that slides into the IEC socket has a clip for the fuse and a square hollow tube for storing a spare.  If you put your fuse where the spare goes, then that might explain the issues you're having.

A roasted fuse will leave black schmoo all over the glass.  A blown fuse will measure infinite DC resistance.

[CrazyMarc]

Here's something I forgot to mention that I definitely should have; I tested the fuse for continuity with my multimeter. The multimeter is working because when I connect the two test nodes I get a beep. But no beep from the fuse. There's no black schmoo but there's definitely lots of little shards rolling around inside the tube. Will resolder the buss wire into the proper hole tomorrow and see if that works any better but as it stands I think the fuse is the problem, and if the fuse is indeed the problem then it's indicitive of a bigger problem; I just don't know what that is. There was no readout from the multimeter when presumably 240 odd volts should have been passing through. I'm really at a loss for cause.

(Edit: and yep, it was definitely in the clip and not the square holder, this actually gave us some trouble to begin with because we couldn't work out where the fuse went. Only when we flipped over the board did we find the fuse holder lol.)

[Paul Birkeland]

I'd just grab another fuse and try again.  there isn't anything in your build that would complete the circuit to blow the fuse.

*however*

If you have your meter set to continuity beep and you attempt to measure AC voltage, that could blow the fuse.  Additionally, if you have the probes plugged in to measure current (if your meter does this), that can also blow the fuse.


The placement of the buss wire isn't a problem.  The lack of #8 nuts on the transformer screws is a bit of an issue though.  (The T-strip will fatigue and the screws will become loose)

[CrazyMarc]

Haha, now we're circling back to my original comment in which I asked what size the fuses physically need to be (EG Xmm x Ymm or something like this) as this isn't the fuse I'm used to, all the ones I've ever used have been a bit bigger, so I'm not sure exactly what I need to look for. When looking up 1A fuse on ebay it looks like it could possibly be 5x20mm, however I'd rather double check and get it right now than order the wrong thing and have to double check anyway, then wait longer for the right thing.  (edit: not sure if I need slow blow or fast acting either).

You're absolutely right about the fuse in the meter and this was the bane of my existence back in college where I must have blown about 3 multimeter fuses, so I checked and double checked and it's definitely working sweet as a nut. We also tried on my friends multimeter with the same result.

Good shout on the #8 nuts, will get that sorted! Surely since the buss wire is on the wrong hole though that's going to cause problems when it comes to soldering other bits? Think I'll put it on the right hole all the same, I bought a desoldering braid so I might as well use it  .

Guess once I know what fuse I need it'll be a matter of waiting for it to turn up and try it, so in the meantime I'd like to thank you for sticking with me and helping me out. It's good to know there's support out there for when I get stuck! 

[CrazyMarc]

Did a bit more digging and figured I need a 5x20mm fast blow, so it's a waiting game now. TY again for all your help.

[Paul Birkeland]

Yes, a 5x20 is the size.  Anything from 1-3A will get the job done.

[fullheadofnothing]

It appears that the 3/8" screw was used on the mounting hole behind the octal socket. This is incorrect. All of the hardware should be mounted exactly as shown and stated in the manual. Again, this won't cause a fuse to blow, but it is important to slow down and follow every step.

[Paul Birkeland]

It appears that the 3/8" screw was used on the mounting hole behind the octal socket.

Good catch!

If the Speedball is ever to be installed, this error will make that process a bit more difficult than it needs to be.

[CrazyMarc]

I'm finding it hard to tell the screws apart to be honest. I assume what I need to do is take one of the screws from each socket off and ensure each socket has a longer screw in the appropriate hole?

I will slow down and take greater care during assembly. It does seem I've been a bit gung-ho so far and I thank you for pointing out my mistakes.

[fullheadofnothing]

You have installed the octal with both of the 3/8" screws. There should be one 3/8" and one 1/4" on each socket. See pages 15 and 16 of the manual. There are two full pages of the manual devoted solely to the topic of correctly mounting the tube sockets, with a total of nine images showing where each item should be used and the screws are called out explicitly by length, in their imperial lengths with a metric approximation provided.