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Bottlehead Kits => Crack => Topic started by: Steve468 on November 14, 2020, 05:41:36 AM

Title: Crack w/ Speedball blowing fuses after working [resolved]
Post by: Steve468 on November 14, 2020, 05:41:36 AM
Unfortunately, I'm at my wits end with this problem and I have to ask someone to please kindly help me out.

Here's the overly long story: I built the Crack stock first, and used it with no problems for two weeks (was really surprised and impressed with how it sounded!). I then installed the Speedball, which worked fine for a few days aside from a hum in the right channel only when RCAs were plugged in. Decided to take a look into the hum issue, see that the sleeve of the black wire from 3U to the headphone jack was frayed a little, so I replaced it with a new length of wire. Powered up fine, but the hum was still there, only a bit quieter. Went back again and resoldered some connections that looked iffy. Found the UF4007 going from 18L to 21L was loose, so I resoldered that. Powered on, and nothing. No voltage readings whatsoever. See the fuse is blown (the little wire inside was broken, I've never worked with these fuses before). Change the fuse, notice the leads of the rectifier I resoldered were touching the other UF4007 going from 18L to 20L, so I bent them back apart. Power on, fuse blown instantly.

After checking some resistances, I've noticed that I'm getting very high resistance at B3 and B6, as opposed to 2.9k ohm, and terminal 3 now has very low resistance. I don't know if that's from the Speedball or something I did. Most every other terminal, including the Speedball boards, read as they should.

I should add I'm very new to this. The Crack is the first thing I've done...ever. I've never soldered, never worked with electrical bits, never even sanded and stained wood before. I had no idea how to use a multimeter, and frankly still don't. So it's been a learning experience to say the least. And unfortunately, this problem is beyond my extremely limited capabilities. I've attached a picture, as well as some closeups of 3U. Can anyone please offer some advice? Thank you!
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Paul Birkeland on November 14, 2020, 08:42:17 AM
I see a lot of long leads still and a bunch of leads that need to be trimmed.  What kind of fuse did you replace the blown one with?

The resistance at 3 should be 0.

The resistances at 7 and 9 will not be 3K because you took out the 3K resistors and put the Speedball in.

A fuse that blows immediately when you turn the amp on is either not rated for sufficient current, you have things touching that shouldn't be, or a component is in backwards. 
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Steve468 on November 14, 2020, 11:43:51 AM
Thanks for the advice!

I'm using Bussman "fast-acting" GMA 1a fuse, rated up to 250v. I thought those were the right ones, but maybe I misread something.

I take your point about the untrimmed leads. That's something I wasn't even aware had to be done, and it did cause some issues during the initial build. I have been slowly going around clipping things back. After your post I had another look and trimmed back a bunch more. Moved some things around that looked a little too close for comfort, found another loose solder on the power switch that I SWEAR was fine before, checked again that resistances are good (3 is 0), and had another go. Boom, fuse gone. I don't think it's components in backwards, because I didn't change anything around from when it was working. I really just don't understand what I've done to make this go so far south so quickly. Thanks again for the help.
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Deke609 on November 14, 2020, 12:03:13 PM
Try a "slo-blo" 1A fuse. They give you a bit of slack on start up before fixing the max current draw. If the slo-blo fuse blows, then there's definitely a installation error somewhere.

cheers, Derek
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Paul Birkeland on November 14, 2020, 03:51:03 PM
If you slip the red wire out of terminal 13, then pull it up straight up in the air, will a fuse hold?  (Be aware that you'll need to wait ~2 minutes for the power supply to bleed down if the fuse holds)
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: diynewbie on November 15, 2020, 12:18:59 AM
Are the heat sinks mounted correctly?
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Deluk on November 15, 2020, 03:59:03 AM
Is B+ on the large board soldered? You could use the meter's buzzer to see if you can find any shorts to earth maybe?
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Steve468 on November 15, 2020, 10:17:25 AM
Thanks everyone for the suggestions, I really do appreciate it. So, stupid confession time: this morning I went through the manual step by step, and much to my dismay found that the black wire on terminal 16 of the transformer (that goes to terminal 13 of the transformer) was NOT soldered. So I soldered that, went through the rest of the manual just to be sure, plugged in my last fuse, and...nothing. Blown again.

I then (after getting more fuses) tried pulling out the red wire from terminal 13, holding it straight up, and it still blew it's fuse. I also checked that the heat sinks were correct, and checked that B+ was soldered. Both look good to my eyes. I'm not entirely sure how to use the multimeter to check for shorts. I've been reading about this, and will keep trying.

But is there a chance I did damage to the power transformer because terminal 16 was not soldered properly?
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Deke609 on November 15, 2020, 11:01:57 AM
But is there a chance I did damage to the power transformer because terminal 16 was not soldered properly?

I think that's very unlikely. The fact that the fuses blow instantly means that current/voltage is cut almost immediately after turn on. People have accidentally shorted half of the rectifier diodes before without reporting any damage to the transformer. Plus, I can't see a loose connection on a PT terminal causing the fuse to blow - if anything, I think it would prevent current/voltage - unless it was also touching something it wasn't supposed to be and creating a short.

Since you're now out of fuses, I would suggest buying a few of the slow blowing (slow acting) 1A kind and trying again. If even that blows, then there is a likely a dead short somewhere - something wired or touching ground that shouldn't be. Or even a stray clipped lead that go lodged somewhere unfortunate (it happens). The usual fix the for the latter is to hold the amp firmly in the air with the wiring facing down and give it a good shake at different angles. 

cheers, Derek
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Paul Birkeland on November 15, 2020, 02:16:07 PM
What's your AC powerline voltage?

The next test I would do is to remove the red wire from power transformer terminal 11, then see if a fuse will hold.

Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Steve468 on November 16, 2020, 12:21:53 PM
It held! I even found that the red wire going from power terminal 11 was a bit loose, but was wedged in so tight with the other things at terminal 19 I never would have found it had I not detached it. I got so excited about finding that issue I re-attached the red wire and had a go, and another fuse bit the dust. But that means that whatever the issue is, it's on that terminal board (17-22), right?
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Paul Birkeland on November 16, 2020, 03:03:25 PM
I would go ahead and replace all your UF4007 diodes.  It's possible that one has been damaged by the incidental contact earlier that was causing problems.  The fuse holding means your power transformer is OK.  That information combined with the fuse not holding when the wire leaving 13 is removed means there's a short in the high voltage supply somewhere.  You may find that terminal 13 shows 0, 270, or 540 ohms to ground?
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Steve468 on November 16, 2020, 03:43:12 PM
Thanks again for that info. I will replace the uf4007s. I checked terminal 13, and it shows very high, moving resistance, consistent with what I understand the '*' is meant to signify in the manual's resistance checks. 
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Paul Birkeland on November 16, 2020, 03:46:32 PM
You can move along the chain of 270 ohm resistors to see if any end of any of those resistors measures low.  You can also use the continuity beep function on your meter and place it across each of the UF4007 diodes to see if one makes the meter beep.
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Steve468 on November 20, 2020, 01:01:27 PM
So, I've replaced all the UF4007 diodes, and unfortunately, that wasn't it. I measured all the 270 ohm resistors, and all of them measure just about 270 ohm.  I'm really not sure what to check next. Can I ask yet again for some more assistance?
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Paul Birkeland on November 20, 2020, 03:03:13 PM
Can you fold the 220uF caps down and post some photos of the power supply build around the power transformer?

Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Steve468 on November 20, 2020, 03:46:25 PM
Here's some pictures. Thanks again for taking a look.
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Paul Birkeland on November 20, 2020, 04:21:19 PM
I would put a 3A fuse in there and see if you can get something to smoke and sizzle a little bit. 
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Steve468 on November 20, 2020, 04:25:05 PM
Really? Um...okay... what would I be looking to sizzle, and what would that tell me?
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Paul Birkeland on November 20, 2020, 04:26:15 PM
Yeah, it seems a little odd, but it may be a matter of something on the amp that we can't see that's conducting, or a marginal part that needs a little more motivation to make itself known.

Title: Re: Crack w/ Speedball blowing fuses after working
Post by: kgoss on November 21, 2020, 04:48:45 AM
Well something in your amp is causing a short which is blowing the fuse. PB will help you resolve the problem so don’t get frustrated. Your issue is definitely unusual.
One thing I would do is go over the amp with a bright light and a magnifying glass. Look for a clipped lead that is touching something and the plate. Or maybe bridging two terminals. That lead could have been in the amp since you built it. Then moved when you worked on the amp to cause the problem. Look closely at the edges of the power transformer too. It won’t be easy to find or you would have seen it already.

Good luck!
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Steve468 on November 21, 2020, 11:32:26 AM
I was definitely thinking it was a stray clipped lead somewhere at first, but doesn't the fuse not blowing when transformer terminal 11 is disconnected mean it's more likely something miswired in the transformer area? At least, that's my understanding. It is hard not to get frustrated (and I'm certainly driving my wife nuts!) but everyone here, particularly Paul Birkeland has been a great help so far. I've POURED over this amp, and I just can't seem to find this short! Anyway, I'll try Mr. Birkeland's next piece of advice soon and see where that takes me.
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Paul Birkeland on November 21, 2020, 11:43:26 AM
I was definitely thinking it was a stray clipped lead somewhere at first, but doesn't the fuse not blowing when transformer terminal 11 is disconnected mean it's more likely something miswired in the transformer area?
That is the output of the transformer to the high voltage supply.  Something in the high voltage supply is drawing excessive current, which is blowing the fuse.
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Steve468 on November 22, 2020, 05:17:39 AM
Well, I put in a 3A fuse in and it...just worked. Everything lit up fine, nothing sizzled. I let it warm up for about 30mins, and though it seemed like everything got a bit warmer than I remember it getting after installing the Speedball, I wouldn't say anything got excessively hot. I would say the top plate got as warm as it did before I installed the Speedball, and the heatsinks were radiating a tiny bit of heat. This is all based on my foggy memory, as I don't have actual temperature readings and it's been a few weeks since I let it warm up in any way.

I was afraid to poke around too much, because I'm not certain about the safety implications of running it with the 3A fuse. Is it safe to do voltage readings? What else can/should I look for while it's on?
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Paul Birkeland on November 22, 2020, 05:27:09 AM
Yes, check the voltages.
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Steve468 on November 22, 2020, 06:49:54 AM
Here's the readings I got:

1: 69.1
2: 216.7
3: 0
4: 217.3
5: 69.9
6: 0
7: 117.2
8: 0
9: 116
10: 0

Speedball large board:

OA: 115.5
OB: 117.2
G: 0
B+: 217.8

Terminals 2, 4 and B+ are all a bit higher than they were when I initially measured them. Other than that, everything else is basically the same.
Title: Re: Crack w/ Speedball blowing fuses after working
Post by: Paul Birkeland on November 22, 2020, 07:02:33 AM
That looks like a working amp to me. 
Title: Re: Crack w/ Speedball blowing fuses after working [resolved]
Post by: Steve468 on November 22, 2020, 08:06:16 AM
Right, so, I can just use it with the 3A fuse? Is that safe? Thanks again for all your quick replies, even on a Sunday!
Title: Re: Crack w/ Speedball blowing fuses after working [resolved]
Post by: Doc B. on November 22, 2020, 09:17:26 AM
It would give you a better margin for error to use a 1A fuse. There is no harm in going back and trying a 1A fuse now that you have gotten the amp to run. If it holds, stick with the 1A.
Title: Re: Crack w/ Speedball blowing fuses after working [resolved]
Post by: Steve468 on November 22, 2020, 09:43:00 AM
I tried already, it still blew. I do have some 1A slow blow fuses on the way (they don't seem to stock them anywhere in my backwards 3rd world country - Canada), so maybe I'll have better luck with one of those?
Title: Re: Crack w/ Speedball blowing fuses after working [resolved]
Post by: Doc B. on November 22, 2020, 10:13:06 AM
Yup, if the slo blo 1A work stick with them.
Title: Re: Crack w/ Speedball blowing fuses after working [resolved]
Post by: Steve468 on November 22, 2020, 11:01:44 AM
I remembered I had bought a fancy expensive 1A slo blow fuse by accident a ways back (I thought I was getting a pack of 5). I was just too afraid of using it until I made sure it wasn't going to blow. So I threw that in, and it held no problem! Major props to Deke609 for suggesting a slo blow fuse way back on page 1 of this odyssey. And many thanks to Paul Birkeland for his help as well.

I gave it a quick listen, and everything is back to normal. There's even a dead quiet background now, no hint of hum. Thanks again to everyone, I'm going to listen to some music.