Bottlehead Forum
Bottlehead Kits => S.E.X. Kit => Topic started by: Loquah on May 02, 2014, 08:06:54 PM
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Hi all,
I'm currently trying to salvage a bit of a mess. A friend of mine tried to build a SEX, but has made a bit of a hash of it (no offense intended to him).
After rebuilding the obvious issues, I've tested the resistance and everything is ok, but the SEX keeps blowing fuses. I've tried testing for shorts in the power circuit, and the first thing I'm wondering is if (testing from the main earth near the power inlet) 0.4 ohms at the transformer terminals 4 and 5 is my issue.
Any other suggestions for tracing a fuse-blowing short when all resistance checks are fine and there are no visual signs of shorts?
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Is it instantly blowing when you try to power up? Do you see the heaters starting to glow?
.4 ohms is so low it doesn't sound like the issue to me, but i might be wrong. What do 1 & 2 read?
As usual post some close up pics if you can, fresh set of eyes might spot something...
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Thanks Jamie.
Terminals 1 & 2 have infinite resistance measured from T23.
The fuses blow instantly with no sign of glow from the tubes.
Should there be something lower than infinite resistance between transformer terminals 6&7 and either transformer terminal 1/2? I'm wondering if the transformer was buggered during initial power up.
Here are some picks. Sorry about the mess - I'm trying (in vain) to clean up as much as I can without a full rebuild.
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Sorry, going back to your original post, i assumed when you said terminals 4 & 5 you were talking about the heater supply not the high voltage supply. The HV supply terminals should give you a very high reading and changing as the caps charge from the meter. From my notes i was seeing over 100k and counting so .4ohms is certainly not right. I dont see anything obvious in the attached pic, can you post a few more from further down the power supply trail..
Also double check the heater diodes, one of them i cant really see but the leads for the two going to terminal C5 look very close together, just make sure none of them are contacting each other.
Are you 100% the rest of your resistance measurements are within spec?
P.S. I'm Mark, Jamie is the other one who posts too much :P
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The filament winding (terminals 4 and 5 of the power transformer) are grounded, so those measurements are fine.
The first thing to check is the DC resistance at the power cord. You should see infinite resistance with the power switch Off, and around 10 ohms with it On. If you pass this test, then you can eliminate the input power wiring and the power transformer primary. If you don't pass this test, then stop here and we'll help you trace the fault in the primary power wiring.
Once you've confirmed the primary wiring as above, and if you have not tested it without tubes, do so now. I assume you have a stock of spare fuses, we may go through a few in this process! If the fuse still blows then there is a problem in the power supplies; if the fuse does not blow then the power supplies are not at fault.
I think it would just make this post confusing to offer next steps, because they depend too much on the results of the above tests. Report back and we'll keep working!
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Sorry, going back to your original post, i assumed when you said terminals 4 & 5 you were talking about the heater supply not the high voltage supply. The HV supply terminals should give you a very high reading and changing as the caps charge from the meter. From my notes i was seeing over 100k and counting so .4ohms is certainly not right. I dont see anything obvious in the attached pic, can you post a few more from further down the power supply trail..
Also double check the heater diodes, one of them i cant really see but the leads for the two going to terminal C5 look very close together, just make sure none of them are contacting each other.
Are you 100% the rest of your resistance measurements are within spec?
P.S. I'm Mark, Jamie is the other one who posts too much :P
LOL. Sorry, Mark! I do know the difference between you and Jamie, but I think in my tired state and having had so many great discussions with you both about caps and attenuators, the two of you temporarily became one in my mind. ???
I checked the diodes after my post because I was wary of them too, but all is clear despite being close. I've moved them a little to create more space as well.
All other resistance checks are 100% within spec.
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The filament winding (terminals 4 and 5 of the power transformer) are grounded, so those measurements are fine.
The first thing to check is the DC resistance at the power cord. You should see infinite resistance with the power switch Off, and around 10 ohms with it On. If you pass this test, then you can eliminate the input power wiring and the power transformer primary. If you don't pass this test, then stop here and we'll help you trace the fault in the primary power wiring.
Once you've confirmed the primary wiring as above, and if you have not tested it without tubes, do so now. I assume you have a stock of spare fuses, we may go through a few in this process! If the fuse still blows then there is a problem in the power supplies; if the fuse does not blow then the power supplies are not at fault.
I think it would just make this post confusing to offer next steps, because they depend too much on the results of the above tests. Report back and we'll keep working!
Thanks Paul. I have plenty of fuses (1A quick blow - is that ok?)
I've tried testing the power socket this morning, but not sure if I'm doing it right so I'll share my process:
1. With switch off I measured resistance between earth (chassis screw) and the three pins in the power socket. Readings are E: <0.5ohms, L: infinite, N: infinite
2. With switch on the same readings create the exact same results. Is this the issue?
Notes: no connection to the power cable and mains outlet for this test. A fresh fuse was installed and intact.
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Those readings are correct, as you're measuring with reference to ground.
What you want to measure, with the unit unplugged, is between L and N: OL with switch off, & around 10 ohms with the switch on.
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Oh, cool. Thanks Chris!
9.4 ohms when switch is on. Infinite with switch off.
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Then you are good on the primary side of the transformer. The problem must exist on the secondary side.
I don't know if it has been mentioned, but backward caps can blow the fuse.
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I've checked a lot of the caps, but I can't promise that I've checked all of them. One of the biggest issues with this build is the fact that many items were installed with incorrect alignment so there's a strong chance that there's a cap causing the grief. I'll check and report back.
In the meantime, what should I measure next?
So far I've checked the Schottky rectifiers and all are reading as though they're undamaged and I've confirmed that they're correctly oriented. I have tested for shorts to earth along the various power lines (6.3V heater power and main power), but not sure if I should be looking for something other than a short to earth.
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Confirmed that all caps and diodes are correctly oriented.
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Try a slow blow fuse if you have or can get one. Same amp rating as the stock fuse.
Ken
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Is the stock fuse with the S.E.X. fast or slow acting? I have the fuse that's in my personal S.E.X. but I thought they were fast fuses that are provided.
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Yes, try a slow-blow fuse. Found this thread which suggests the same:
http://bottlehead.com/smf/index.php/topic,974.msg7176.html#msg7176 (http://bottlehead.com/smf/index.php/topic,974.msg7176.html#msg7176)
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Next step is the third paragraph in my previous post.
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OK. Tested with a slow blow fuse with no joy, but it allowed me to here an electronic sound which seemed to come from the tube socket nearest the HP jack.
There was a lot of excess solder on the socket pins prior to my efforts to suck away as much as possible and I noticed that the tube doesn't seat properly in that socket (it sits about 1-2mm off the chassis plate). I'm wondering now if there's some arcing or something going on in the socket. Would that cause excess current flow?
The good news is the tube is still fine (especially because I'm testing with my own tubes because he didn't have his handy), but I can't see any visual clues of where the problem lies and I'm not exactly sure what I should be testing for.
Paul, I just re-read your post and realised you are suggesting powering up without the tubes installed. I'll try that when I get back home after a short errand and get back to you.
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No tubes. Blown fuse.
This time I used a quick blow fuse so I couldn't hear any noises, but with no tubes installed there is still a very definite problem. There is a visible layer of flux on the ceramic between A1 and A8, but no solder and 280k ohms so I don't think that's the issue.
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Great! Now we know it's not the tubes or the primary circuit, so it must be one of the power supplies.
It is not that uncommon for a bit of solder to wick down into a tube socket pin, blocking the tube from fully entering, so your approach of sucking as much of the excess out as possible is a good one. Pay special attention to pins 7 and 8; they are the heater and if they are shorted together that will indeed blow the fuse. Also, since it's happened a few times, make sure the sockets are correctly oriented with the notch at the center towards the power transformer. A few people have mounted them 180 degrees rotated by accident!
That said, if you don't see the problem there I'd test the high voltage first, just because it's easiest:
There is a single wire at power transformer terminal 6. Disconnect it temporarily; this will disable the high voltage power supply. If it still blow fuses then the problem is in the filament power supply or wiring. If not then we'll look into the HV supply.
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Thanks Paul.
I disconnected the black wire from transformer terminal 6 (it connects to terminal strip contact #1 at the other end). Still blowing fuses so the issue is obviously in the heater circuit.
I've fully rebuilt the C1-5 terminal strip since the amp started blowing fuses so I'm confident the fault isn't on these contacts, but could be a faulty diode or could be at the other end of one of the connections coming from C1-5.
I'm guessing I should disconnect the heater wire next to isolate C1-5 from the tubes?
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Disconnected heater wire from C1 & C2. Still no joy.
I'm going to do another visual inspection for shorts. I have tested the diodes in situ, but not sure if I need to remove them for accurate testing. I'll await your guidance with my sincere thanks.
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Sorry for the multiple posts - I'm trying to cover as much as possible to minimise delays due to our time zone differences.
I decided to remove and test the capacitor from C1-2 in case it was blown during initial attempts to power up, but it tests the same as a new one using the diode function on my meter (i.e. counter climbs gradually to about 1500 before reading infinite)
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Wow - you've done some good guessing!
If I am reading your posts right, it is now down to the heater winding on the transformer and the recifiers/resistor/capacitor.
I'm sorry to say this because it will be a pain, but you should remove the diodes from one of the transformer terminals, 4 or 5. If I were you I would remove the from both and unbolt the power supply terminal strip. Then see if you can blow the fuse - it is extremely unlikely that the transformer winding is internally shorted, but we need to be sure. At this point, only the transformer primary (which you have already confirmed is correctly connected) is connected. In the unlikely event that the fuse still blows, the transformer is suspect - but that winding is only 0.095 ohms and you probably can't measure the difference between that and a lower resistance.
Assuming you do NOT blow the fuse this time, then the power supply that you pulled off, and probably have in your hand, is somehow shorted or incorrectly wired or has bad components. I can't see enough in the pictures to tell what is going on, and you may find that a bright light, magnifying glass, and a lot of patience is needed even if you have it in your hand. But that's why I suggested removing it all.
Again, if it were in the Bottlehead lab and my job was to fix it, I would just throw is away and build a new one. But you would have to request and wait for the parts, so make your own judgement about how much time to spend puzzling it out.
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Wow there isn't much left now. Just a thought, double check the black jumper wire on terminals C1 to C4 in case its on the wrong terminals.
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Thanks Paul. I'll do that now and maybe rebuild the C1-5 strip yet again. I have all new components (some of which I have used in the current setup depending on the visual state of the old components. I'll use all fresh components this time around.
Mark, thanks for mentioning the jumper because I don't know if there is one!? But I'm not near the amp to check so it might just be my memory - I'll go looking specifically.
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Mark, I might owe you a beer! Just checked and the C1-C4 jumper is missing. I noticed that nothing was connected to the capacitor at C1 when I removed it for testing, but was so focussed on testing it that I forgot to check the manual to see if it was somehow correct.
I'll add the jumper and test as soon as I can. Could that have caused the blown fuses do you think?
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Culprit found. The transformer itself is the issue :(
I'm assuming this means a replacement is required?
I'm attaching photos of the exact configuration when the transformer blew the last fuse (and also made an obvious, but very brief buzzing sound)
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Further to last post. Visual inspection shows no signs of shorting with excess solder, etc. Could this issue have been caused by powering up in the original, faulty configuration? Or could it be caused by excess heat applied to the transformer? There's no signs of heat damage to the plastic at the base of the terminals, but I'm trying to work out what to tell my friend. "It's busted and we don't know why" is always an option, but it'd be nice to let him know some semblance of the cause of his troubles and if he has to buy a new transformer (i.e. if it's not considered a random product fault) it'd help to explain what he did wrong.
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Contact Eileen for a replacement transformer. Tell her that PJ says it was bad from the start.
Looking at your most recent photograph, I see three wires on terminal 5 and one on terminal 4. There should have been two on each. It's a manufacturing error - the first time I've seen this.
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I'm sorry, I don't think we can deduce that from the photos. Looking at the shelf full of PT-7s we have, there is an extra turn of one of the two wires attached to terminal 5, and that could be what we are seeing in the photo. I'm late the party, but has anyone suggested measuring the resistance of the primary and secondaries now that you have them all disconnected from the circuit?
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I don't think so, Doc. Can you tell me from where to where I need to measure?
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Start by making sure all the wires are disconnected from the power transformer. First check for shorts between windings.
For the primary to high voltage secondary measure the resistance from power transformer terminal 1 to terminal 6 - should be infinite.
Primary to heater secondary measure from 1 to 4 - should be infinite
high voltage secondary to heater secondary measure from 6 to 10 - should be infinite
Now check the DCR of each winding. I will give you what I measure, your numbers may be a little different.
Primary (1 to 2) 36.8 ohms
High voltage secondary (6 to 7) 40.8 ohms
The heater secondary will be too low a resistance to measure above 0 ohms with pretty much any regular meter and this is why PJ didn't suggest it for the heater secondary. So - and again I'm not sure if this has already been covered - check very closely what PJ suggested, make sure that you have two wires coming out from under the coil wrapper to each of terminals 4 and 5, not three wires to one of them and one wire to the other. If you could take a photo from directly over the terminals it could help us to help you verify the wire count. I'm not saying it's impossible for the transformer to have been mis-terminated in production. We went through our entire stock this morning from two different production batches and we didn't find any here that were mis-terminated. So we can certainly send a replacement with a high degree of confidence if the one you are working with was miswired.
It is also possible that there could be a short in the IEC socket wires coming from the socket to the transformer. I see a fair amount of melted wire insulation on that build, and it might be worth comparing the build with the assembly manual photos of the power switch and power entry wiring on pages 23 and 24.
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Thanks Doc. I'll do all that and report back.
I do believe there has been excess heat and excess solder applied at various times during the initial build. I've replaced anything that I can that looks too far gone and have tested the IEC socket for shorts with no issues found.
I'll do all the testing, take notes and report back soon.
Thanks again for your help everyone - I feel like this poor kit was cursed from the outset!
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Start by making sure all the wires are disconnected from the power transformer. First check for shorts between windings.
For the primary to high voltage secondary measure the resistance from power transformer terminal 1 to terminal 6 - should be infinite. Infinite
Primary to heater secondary measure from 1 to 4 - should be infinite Infinite
high voltage secondary to heater secondary measure from 6 to 10 - should be infinite Infinite
Now check the DCR of each winding. I will give you what I measure, your numbers may be a little different.
Primary (1 to 2) 36.8 ohms 9.5 ohms
High voltage secondary (6 to 7) 40.8 ohms 40.9 ohms
The heater secondary will be too low a resistance to measure above 0 ohms with pretty much any regular meter and this is why PJ didn't suggest it for the heater secondary. So - and again I'm not sure if this has already been covered - check very closely what PJ suggested, make sure that you have two wires coming out from under the coil wrapper to each of terminals 4 and 5, not three wires to one of them and one wire to the other. If you could take a photo from directly over the terminals it could help us to help you verify the wire count. I'm not saying it's impossible for the transformer to have been mis-terminated in production. We went through our entire stock this morning from two different production batches and we didn't find any here that were mis-terminated. So we can certainly send a replacement with a high degree of confidence if the one you are working with was miswired.
It is also possible that there could be a short in the IEC socket wires coming from the socket to the transformer. I see a fair amount of melted wire insulation on that build, and it might be worth comparing the build with the assembly manual photos of the power switch and power entry wiring on pages 23 and 24.
The transformer terminals are attached with the following:
T1: 1 thin wire
T2: 1 thin wire
T4: 2 thick wires (I believe - hard to see clearly)
T5: 2 thick wires
T6: 1 thin wire
T7: 1 thin wire
T10: 4 thick wires
The following photos will hopefully show what I am seeing. I've taken them in order from terminal 1 to terminal 10 with a full shot at the end.
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Once again, Doc gets to keep the corner office!
No idea what the problem is at this point. The measureable windings are fine, the unmeasureable one looks fine, the primary wi..
wait a minute. 10 ohm primary? That's a 120v PT-7, not a 240v as shown on the label. Crap, we should have seen that a lot earlier!
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Good job it was blowing fuses or you would scraping capacitor goo off the ceiling :)
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Once again, Doc gets to keep the corner office!
No idea what the problem is at this point. The measureable windings are fine, the unmeasureable one looks fine, the primary wi..
wait a minute. 10 ohm primary? That's a 120v PT-7, not a 240v as shown on the label. Crap, we should have seen that a lot earlier!
Oh, so it's a mis-labelled US power transformer? (Just checking I'm unsderstanding correctly)
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Yup, that is what Paul indicated. Somehow I would expect the 240V transformer primary to be a higher resistance, and impedance.
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Yup, it is Grainger. 120V PT-7 = 10 ohms, 240V = approx 36 ohms.
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IMO, this info should be some sort of sticky note or part of FAQ, so that in the future everyone can easily determine whether a transformer received with the kit is the correct one or not... Just my 2 cents.
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IMO, this info should be some sort of sticky note or part of FAQ, so that in the future everyone can easily determine whether a transformer received with the kit is the correct one or not... Just my 2 cents.
Nice idea.
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OK, now you guys see where I was headed. I have to base these troubleshooting procedures upon what I have found to be the most likely scenario. Here it was that you had a 120V transformer, as that was in my experience far more likely than a miswired one.
What I have found is that it is often more expeditious to start with the user collecting data in a methodical fashion rather than offering three or four guesses as to what may be wrong. I have lead folks down a twisted path and created frustration at times when I have thrown too many possible scenarios into the mix.
Our apologies on the mix-up, and we will send the proper transformer.
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IMO, this info should be some sort of sticky note or part of FAQ, so that in the future everyone can easily determine whether a transformer received with the kit is the correct one or not... Just my 2 cents.
This is less than a 1 in 1000 situation, and as we rewrite manual, we tend to put a section in about measuring AC voltages once the transformer primary is connected.
The number of posts, however, about whether there is something wrong with a 120V PT-7 with a primary that isn't exactly 10 Ohms would come up a lot and provoke unnecessary hysteria.
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and as we rewrite manual, we tend to put a section in about measuring AC voltages once the transformer primary is connected.
brilliant idea :)
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provoke unnecessary hysteria
He may mean that about the staff here.