Bottlehead Forum
Bottlehead Kits => Kaiju Stereo 300B amp => Topic started by: Sawgolf4me on January 09, 2018, 02:17:31 PM
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Hello Folks!
First time builder. First time poster. I finished putting together my Kaiju over the weekend. Fired it up Sunday night and everything was working great. Over the next two days, I probably listened 10 hours and turned it on maybe 5 times.
Well I get home from work today and I turn it on and I blow a fuse after listening for 30 minutes. So, I go to the store and get new ones. Now it blows fuses right when i turn it on.
So, I flip it over to inspect what is going on and don't see anything different. I am guessing the problem lies somewhere in one of my solder joints? My best guess is that warming up and cooling down a couple times caused one (or more) of the solder joints to break down? Any pointers on maybe where to start to look?
Thanks for the help!
Steve
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Go back through the resistance test again. That should identify the short blowing the fuse.
Are you sure you got the same value and fast or slow blow fuse that you had in the amp?
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I just looked and I bought 2 amp fast acting fuses. I’ll make a trip to an electronics store. To be honest, until about an hour ago when I searched fuses on here I thought all fuses acted as fast as possible.
I did the ground buss check on page 40. They were all at most 0.5 ohm. Is there another resistance check than that one?
Thanks for the help.
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Try a 3A fast blo fuse if that's all you can get. Buy 5-10 of them, as there are a bunch of checks that can be done to figure out where in the circuit the issue is.
The first test is to pull all the tubes, then see if the amp fires up. Let us know how that test goes.
You can also consider taking some build photos and posting them here, as we may be able to see something.
Also do be sure that the center lug of each hum pot isn't touching the chassis.
-PB
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I'm back in business! I found 1.6 amp time delay fuses. However, I'm still not sure what caused the fuse to go in the first place?
I ordered a BeePree, but it hasn't shipped yet. So I am listening from my MacBook Air straight to the Kaiju. I had some Jay-Z going at a pretty good volume. I'd bet the Kaiju around 80% volume. Can the fuse blow if you are listening too loud or pushing it too much?
Here are the checks I did today before I turned it back on.
1) I went through the Ground Buss check and everything measured 0.5 ohms or less.
2) Checked the rectifiers to make sure they were functioning and oriented correctly.
3) I visually checked that the center lug of each hum pot wasn't touching the chassis. I then did a continuity check and I got a buzz for a split second and then it went open line. Then I did a resistance measurement and they both measured almost exactly 1.00 kilo-ohm. Is that correct?
4) Then I turned it on without the tubes and it worked.
5) Then I put the tubes in and turned it on. Everything worked.
6) Then I did a music test and everything worked.
Pictures attached.
Thanks for the help!
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So literally as I hit send on that posting, the fuse blew again! I mean within 2 seconds of hitting post.
I was listening for maybe 10 minutes on low volume.
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I put a new fuse back in about a minute later and that one immediately blew when i turned it on.
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Ok. I think the only other datapoint I have to point out is that both of my tubes on the right side are dimmer than the left side.
I was doing some reading and clothes dryers seem to sometimes pop fuses after a period of time. And it is usually from the heater getting shorted to ground.
Thanks!
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I believe that time delay fuses are not the same as slow blow.
The fuse that shipped with your kit is a 2A slow blow. Some early kits shipped with 1.5A, but we were finding they would blow on first startup. As PB suggested, if all you can find is 3A, that's probably OK. His testing steps are going to be the way to find the problem; checking voltages could be helpful as well.
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I'd go with the 3A fuse and let us know if it holds.
Playing music really loudly won't make any difference. The real stress on the fuse is when the amp is first turned on, as the power supply has to be charged up, and those 300B filaments draw significant current when they are cold.
-PB
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I put in a 3 amp slo blo fuse and turned it on with tubes in. Fuse blew immediately.
Then I tried with without tubes. 30 seconds later I had smoke coming out of the bottom of the transformer. So I turned it off. I had the plate face up at the time so I couldn't see what was smoking, but it was coming out of the bottom of the transformer. Not one of the open slots.
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Don't run it again until this is sorted out. That will only damage it more. You will need to test the rectifiers with a diode test to see if any are blown. Also look to see if you installed any filter capacitors backwards.
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Just did a test of the rectifiers and they all measure .635 volts.
I did a comparison of the capacitors to the final build picture at the end of the manual and they are all oriented the same.
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Top level shots
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Close in shots
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In close up picture number 2, is the wire bridging the 220 caps touching the terminal strip ground tab (the one screwed to the chassis)?
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You'll have to very carefully run the tests on page 47. You might want to use a pair of clip leads and power up the amp very briefly to get a look at those voltages. Alonzo could be correct that you have half of a capacitor bank shorted to ground. If things are getting hot enough to start smoking in the amp, this will alter the voltages a bit.
It would also help to see a photo of where the UF4007s connect to the PT and terminal strip.
-PB
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Ok. I started it up one more time to try to measure the voltages and it immediately shorted (with a 3 amp fuse).
I added a couple pictures of the rectifiers and the caps.
Here is a recap of everything i've seen:
When I first built the unit, the power transformer was humming pretty good. I read on the forums that usually this is from the screws not being tight enough. So I tightened them down and then the humming went down quite a bit. This may or may not have been the day before the first fuse blew. I can't remember, but I tightened them before the fuse blew.
Then I blew the 1.6 amp fuse after listening for 30 minutes.
Then I put in a 3 amp fuse and the power transformer started smoking after 30 seconds.
Now I immediately burned a 3 amp fuse.
When I measure the resistances of the power transformer, I get these:
14-90 ohm
13-90 ohm
12-90 ohm
11-90 ohm
10-90 ohm
9-90 ohm
8-1 M ohm
7-1 M ohm
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Also, when I measure the power transformer mounting screws to ground, they measure 0.3 ohms. I thought maybe with the fabric washers, the power transformer was likely supposed to be isolated from ground?
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0.3 ohms is pretty small - could this be the normal resistance of your leads?
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14-90 ohm
13-90 ohm
12-90 ohm
11-90 ohm
10-90 ohm
9-90 ohm
8-1 M ohm
7-1 M ohm
If you're measuring from each terminal to ground, that wont tell you anything. One must measure the DC resistance of each winding, which is a pair of terminals.
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Also, when I measure the power transformer mounting screws to ground, they measure 0.3 ohms. I thought maybe with the fabric washers, the power transformer was likely supposed to be isolated from ground?
They are isolated from the chassis but then hard grounded to the safety ground.
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The next step for you is to disconnect each UF4007 where it connects to the power transformer. After these are disconnected (the disconnected ends can just be left sticking up), then test the amp with no tubes installed to see if it blows a fuse.
-PB
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Ok. I desoldered those two from terminal 8 and I turned it on with no tubes.
3 amp fuse blew after 1 second.
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Red and black wires connect to power transformer lugs 1-6. Remove them from the power transformer and pull them so they are sticking up but not touching each other, then retest.
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I removed the black wire from 1 and the red from 6. When I turned it on, nothing happened. No power coming from transformer.
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Could a theory be that there was something with the power transformer internals?
Things worked ok for the first 10 hours or so and then a couple heat and cool cycles shorted something inside? Then it self healed a bit when it cooled after the fuse blew. And thats why it worked for a couple minutes when i put a new fuse in, until it shorted again. Then when the 3 amp fuse went in, the higher amperage really shorted something inside and thats why it started smoking.
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Could a theory be that there was something with the power transformer internals?
Things worked ok for the first 10 hours or so and then a couple heat and cool cycles shorted something inside? Then it self healed a bit when it cooled after the fuse blew. And thats why it worked for a couple minutes when i put a new fuse in, until it shorted again. Then when the 3 amp fuse went in, the higher amperage really shorted something inside and thats why it started smoking.
That is one of many, possible scenarios. PB is leading you through a sequence of tests to determine what the actual problem is; each step of the sequence is chosen using the results of the previous one. It seems very meticulous, but it's much, much faster than any other approach we've found. Patience!
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I removed the black wire from 1 and the red from 6. When I turned it on, nothing happened. No power coming from transformer.
Did the fuse hold?
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Did the fuse hold?
Fuse held. And I am using a 1.6amp time delay because I ran out of 3 amp.
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You can put back the wires that connect to terminals 1-6 on the power transformer, then disconnect all of the remaining wires on the other side of the power transformer and recheck.
-PB
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You can put back the wires that connect to terminals 1-6 on the power transformer, then disconnect all of the remaining wires on the other side of the power transformer and recheck.
-PB
All the wires on terminals 7 to 14?
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Yes.
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Yes.
Fuse immediately blew.
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OK, sounds like the transformer is shot. The most important thing is to determine why before replacing it. Otherwise you could just end up blowing another one. In rereading the thread one thing that stands out to me is your mention that the transformer was humming a lot from the get-go. That could indicate a short or lifted ground that was loading down the transformer.
If it was my amp the first thing I would do is look for a missed solder joint. Then I would go over the entire assembly again, step by step, to try to find a miswire. Then I would reflow ll the solder joints. Try to get the joints to look like the ones pictured in the end of the manual.
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Reflow every solder joint in the whole unit? It seems we are back to the issue could be anywhere. I'll recheck the build schematics.
Before throwing a total resolder at the whole unit and potentially causing other issues, are there critical resistance measurements I could make? I'd rather exhaust that before I either fix the issue and not know where I did, or cause other compounding problems.
If there is a grounding issue, I should be able to measure this as a high resistance somewhere? Or if I am shorted, I should be able to test parts of the circuit and get a lower resistance than would be expected? Since the unit still popped the fuse without the tubes in place, that should eliminate part of the circuit?
As we were going through the troubleshooting, it seemed we were disconnecting parts of the circuit to see if the unit still failed. If we got to a point where it held, that would mean the issue was downstream? Since it kept tripping the fuse even down to where we only had the power transformer connected, that would mean the issue was around there?
I realize in these kits that problems are 99.9% build issues. However, is there a way to determine if there was something going on with the power transformer?
Would a short downstream of the power transformer have led to a blown capacitor, rectifier, or a burned resistor in part of the unit?
I'm not trying to point blame at anything, I'm just trying to see what all can be tested to try to hone in on the potential issue. I don't think the humming was any better or worse from the first voltage checks on pages 33/34 through the rest of the build and listening.
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The sequence of events does not indicate that the transformer was bad and other parts might have failed because of it. It indicates that something downstream of the transformer was bad and that eventually took the working transformer out.
Our repair tech has a very heavy load at school this quarter, so I have temporarily taken over repair duties. I have thus been reminded that with most repairs we get in the builder could usually have found the problem with his amp if he had gone through the assembly instructions step by step one more time. That is the reason I am suggesting rechecking every step and reflowing the joints.
We have found over the years that our original method of having a builder run a lot of resistance checks on a finished build tended to create more confusion than resolutions. So we don't have those terminal by terminal resistance tests anymore, but rather the voltage tests that are done as one completes a section of the assembly.
You are right that we were having you disconnect parts of the circuit to see if that allowed the fuse to hold, which would indicate that the disconnected part of the circuit had a fault. Unfortunately in this case it seems the damage to the power transformer was already done and thus that process of elimination was not productive in terms of isolating the problem. And the kinds of shorts we are talking about don't always show up as blown components downstream of the power transformer, particularly if there is a miswire.
You can try comparing the resistance measurements of the same test points in the right and left channels for some of the circuit, to see if there is a major difference. For example socket B1 vs. socket C1, T27 vs. T51, etc. If the issue is confined to one channel that will help to narrow down where the problem lies.
For the common to both channels circuit parts like the power supply caps you can check resistance across each of the filter caps and see if the resistance climbs (red probe on + terminal of cap, black probe on - terminal) indicating that the cap is properly charging. If they show a low resistance that does not change it is likely there is a problem in that part of the circuit.
If none of this points to an obvious problem the best bet might be to send it in for repair.
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Thanks for the all the help!
I've been staring at this thing for a week now. I am going to take a couple days off, get some fresh eyes and then go back through the schematic over again from the beginning. If I'm still stuck, I'll send it back to you guys for repair.
I'll send out an update once I hop back into it in a few days.
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That is an excellent plan. Taking a break and coming back fresh is a very important part of troubleshooting.
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I did a complete look over and I didn’t see anything wired incorrectly. I’ll send it in for a service.