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Post by yakkmeister on Apr 13, 2012 0:31:39 GMT -5
Hey guys,
Been working on my Dano and I have discovered that the stacked pots on it are reading faulty, just like the last ones did.
I figure the problem lies in the user and not in the machine.
As much as it annoys me to have to wait several weeks for parts to arrive from the USA for this guitar, I now need to buy new pots - again. What I would like to do, this time, is avoid all the irritation and make sure I don't stuff it up again.
What are the most likely ways that I could have soldered wrong and how can I make sure whatever it was I did to the pot doesn't happen again?
NB: I stripped apart one of the old pots and there was no obvious damage.
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Post by sumgai on Apr 13, 2012 2:34:47 GMT -5
ym, Most soldering damage is a result of an underpowered iron - too low a heat! You need beaucoup power to get the heat to the point of contact as quickly as possible. In this way, the solder melts soonest, and you can remove the iron all the sooner. The less time the point of contact receives heat, the less time there is for that heat to build up and start traveling to places where it's not wanted. By no means is this an authoriation to break out the flame-thrower! Probably 95% of the time a simple 40 watt unit will be just about right. You might want more power for the back of a pot, or way more power (a Weller 100 watter!) for soldering ground wires to an amplifier chassis made of solid steel, but otherwise, stick to what the Pro's use - something along the lines of 40 watts or so. Bournes pots are not known for being low quality, but even so, the old maxim goes "Always test your new-bought items before installing them. For a pot, check it with a meter first!" This can save a lot of headache/hassle down the road, just ask almost any member here. HTH sumgai
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Post by roadtonever on Apr 13, 2012 5:21:17 GMT -5
Obviously its difficult to say who/what's to blame. Sumgais advice is spot on but another thing for your consideration is using an Amphenol ground lug washer
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Post by yakkmeister on Apr 13, 2012 21:43:39 GMT -5
Sumgai:
I am using a variable power unit set to 450 degrees C and I had pre-tested the pots and they worked fine.
Perhaps I am just holding it on too long on the back?
Roadtonever:
Yeah, that could mean less soldering to the backs of pots, I guess - I'll see what's around here...
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Post by sumgai on Apr 14, 2012 3:52:20 GMT -5
ym, That works out to 842 degrees, in my native units. I'd say that should be warm enough to do the job quickly, so now we're down to two things - time: you're applying heat longer than necessary; or else your solder itself is of poor quality (which would pretty much require you to apply heat longer). I know, I know, solder is solder, and it lasts practically forever, but even so, there are 'better' quality solders out there. My preferred brand is Kester, but like cars and guitars, everybody has their personal favorite. I don't know what's available down there, you might check with John, ozboomer or gumbo, they could probably give you a leg up.... Other than those two things, I'm fresh outta ideas..... sumgai p
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Post by yakkmeister on Apr 14, 2012 5:48:12 GMT -5
Sumgai:
There is pretty much only dicksmith and jaycar brand stuff here (that I know of). These are the only pots I have had a problem with - CTS pots on my Canora were (and still are) fine, gotoh pots on Epicifica are still perfect and the soldering job I did on a squier active 5-string bass is still going strong - same iron and same solder... I think these pots may be too flimsy and I need to be super-extra careful not to over-heat them ...
Thanks for the help - it simply *must* be the heating time.
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Post by gumbo on Apr 14, 2012 6:30:25 GMT -5
..other than 'tinning' both surfaces first..the back of the pot AND the and of the wire... ...fresh out of ideas too... ...except that (as people have said) pots DO vary, and therefore their ability to withstand however many megatrons of heat will also vary.. if tinning the back of the pot is the difficult thing to do, perhaps it's in the type of flux (I use paste flux in a syringe..which you can buy from JayCar or Altronics for not a lot of AUD) and / or the level of cleanliness of the pot body itself before attempting the soldering exercise in the first place... Probably doesn't, but HTH...
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Post by newey on Apr 14, 2012 7:34:55 GMT -5
Since the obvious explanations all seem to have been addressed, it's likely time to go back to the beginning and re-examine the problem.
While pots can certainly be fried by excess heat, it's pretty tough to do so, and it doesn't sound like yakky has been overly ham-handed.
So (as the studio rats say), "Let's take it from the top . . ":
Please tell us what the "faulty reading" was and how it was measured. Did you double-check the settings on your meter and then recheck the reading? Were the pots entirely "wired in" when you got the reading, or only partially so?
And:
What did you check and how did you check it?
Lastly, this is one of those supposedly-obvious things, but one that catches people out occasionally when reading pots which are wired into a circuit:
You can test a volume pot once it is wired into a circuit, and you will see a change in resistance as you move the knob. Not so with a tone control, since a regular multimeter uses a DC battery and the cap blocks the current.
So, was it the half of the pot that you had wired as a tone which gave you the "faulty reading"?
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Post by yakkmeister on Apr 14, 2012 22:00:35 GMT -5
Newey:
I measured the pots as soon as I unpacked them by measuring between wiper and both ends then between both ends. There was the correct resistance for all 4 pots (2x 2 stacked).
When the guitar was mostly assembled (no strings) I tested the volume and tone controls by gently tapping with a screwdriver. This showed that neither volume nor tone controls were functional.
I tested the volume pots in circuit and found that there was some change in resistance but not much. The pots were then removed and tested again - the volume pots, with treble bleed removed, worked on one side (wiper and right hand lug) but not the other. The tone pot was measured in the same way as when it was unpacked - between wiper and lugs then between both ends. The reading, this time, was open-circuit in all positions.
I stripped down both the original and the replacement pots. The wafer read that the resistance material was functional but there was no continuity between the faulty lug and the material strip. The tone pots had no continuity between the strip and either lug. Everything else was perfect, clean, unburned and no signs of overheating - the original pots didn't even have dust in them.
The crazy part is, I don't see a way for the heat from the back of the pot to transfer into the lugs in order to burn out that connection without scorching the bejeezus out of the wafer.
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Post by sumgai on Apr 14, 2012 22:55:46 GMT -5
ym,
I do believe that you've gotten a bad batch of pots - from Bourne, no less! Time to have a chat with your supplier as to warranty, etc. You're correct, if there's no obvious (to the eye) damage, then there should be no problem - heat damage would be very visible, no doubt about it.
If all else fails, I hope you bought these with a charge card of some sort. You do have the power to get the seller's full attention if/when you utter the magic words "How about I just tell my card company that I didn't get what I ordered, and ask for a refund?", or words to that effect. Obviously this is a last resort, and not to be abused, but it is a valid tool in your arsenal of potential solutions.
HTH
sumgai
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Post by yakkmeister on Apr 15, 2012 5:32:24 GMT -5
Bad batch? Bugger ...
I'll email the supplier and ask what they can do - I have dropped about $1,000 on parts with them so far. $24 pots should be a little more robust.
Thanks - I'll still be trying to solder quicker, as a matter of course.
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Post by roadtonever on Apr 15, 2012 7:23:40 GMT -5
Are those pots the type that have really thin metal cases(made by Alpha I believe)? If so I've had those die on me after only one cycle of soldering and re-soldering. Some more ideas for you: Solder to the side of the pot rather to the back of it. Try flux. If the original pots keep failing on you consider placing the pot with CTS dual-concentric (Allparts EP-4585-000), the values wont match so you'll need to open them up and replace the wafers from donor CTS pots, only takes 10 mins with needle nose pliers. HTH
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Post by yakkmeister on Apr 16, 2012 7:49:59 GMT -5
It would seem to me that the pots are not particularly thin and they seem to be of identical construction as the original (only the tone and volume sections are inverted). The original pots had withstood several cycles of my ham-fisted soldering in the past, only to die recently with my latest attempt. The failure, interestingly enough, is the same for both new and old pots.
I will try soldering to the sides...
I am going to do that star-ground thing to prevent as much soldering as possible to the pots and I have purchased a flux pen to get all fluxxed up in that job.
I was going to go so far as to get some soldering paste but it was prohibitively expensive. So, too, is the getting cts pots and modding them. If, however, this next lot dies, I will do just that.
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Post by sumgai on Apr 16, 2012 13:00:02 GMT -5
ym,
I just realized.... Before you start a discussion with your supplier, look around the web at other forums and such, and see if others are having the same kinds of problems. If you can assert that you're not the only one with an issue, your chances of satisfaction should go way up.
Good luck!
sumgai
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