Author Topic: Tough Problem To Locate Need Help  (Read 15206 times)

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Offline jitter

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Re: Tough Problem To Locate Need Help
« Reply #75 on: April 29, 2016, 05:34:29 pm »
I edited my previous post.

Thanks for the explanation! I downloaded the service manual, and will follow the circuit. Does that cap filter the step down voltage from the 5 volt supply?

I take it you mean C457. I would consider its function more to be like a buffer of the 2.7 V and to keep the output of IC410 stable.
Most voltage regulators require some capacitance with a certain amount of ESR to stay stable. Ageing caps will slowly drift outside those specs.

IC402 likely draws current from the 2.7 V in a pulse like fashion which could have caused instability in the 2.7 V once the cap wore beyond a certain limit.
« Last Edit: April 30, 2016, 09:20:18 am by jitter »
 

Offline tony3d

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Re: Tough Problem To Locate Need Help
« Reply #76 on: April 29, 2016, 05:42:04 pm »
I edited my previous post.

Thanks for the explanation! I downloaded the service manual, and will follow the circuit. Does that cap filter the step down voltage from the 5 volt supply?

I take it you mean C457. I would consider it's function more to be like a buffer of the 2.7 V and to keep the output of IC410 stable.
Most voltage regulators require some capacitance with a certain amount of ESR to stay stable. Ageing caps will slowly drift outside those specs.

IC402 likely draws current from the 2.7 V in a pulse like fashion which could have caused instability in the 2.7 V once the cap wore beyond a certain limit.

Yes, the 457 is the one I replaced. I see what you mean. Makes sense!
 

Offline tony3d

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Re: Tough Problem To Locate Need Help
« Reply #77 on: April 29, 2016, 05:44:34 pm »
It's been playing for hours now with no problems! Someday, I may muster up enough nerve to actually replace the cap with a proper surface mount cap, but first I need to buy a few things LOL! If I were to do that, I would probably just replace all the caps. A year ago I replaced both drawer belts.
« Last Edit: April 29, 2016, 05:48:13 pm by tony3d »
 

Offline jitter

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Re: Tough Problem To Locate Need Help
« Reply #78 on: April 29, 2016, 05:52:24 pm »
Makes me want to buy tweezers!

The quick and dirty (very dirty) thing I often do at work if I'm lazy is heat one pad and pin of the cap, wait till all solder under that pin has melted and then tilt the cap up as far as it will go without applying much force. Then repeat the other pin the same way. Often it works first go, sometimes I need to go back to the first pin if a solder bridge was drawn.

Now this is not a recommended method, but in a pinch, it should work. Just make sure you don't tilt the cap before the solder on the pad has completely melted (it extends under the cap), you don't want to lift the pad too.

I don't think I would recommend keeping the original cap in place as it may leak electrolyte and corrode the traces on the pcb.

It's been playing for hours now with no problems! Someday, I may muster up enough nerve to actually replace the cap with a proper surface mount cap, but first I need to buy a few things LOL! If I were to do that, I would probably just replace all the caps. A year ago I replaced both drawer belts.

Yes, it seems likely that eventually other caps will go too, but for now: enjoy the music!
« Last Edit: April 29, 2016, 05:56:32 pm by jitter »
 

Offline tony3d

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Re: Tough Problem To Locate Need Help
« Reply #79 on: April 29, 2016, 06:58:14 pm »
Makes me want to buy tweezers!

The quick and dirty (very dirty) thing I often do at work if I'm lazy is heat one pad and pin of the cap, wait till all solder under that pin has melted and then tilt the cap up as far as it will go without applying much force. Then repeat the other pin the same way. Often it works first go, sometimes I need to go back to the first pin if a solder bridge was drawn.

Now this is not a recommended method, but in a pinch, it should work. Just make sure you don't tilt the cap before the solder on the pad has completely melted (it extends under the cap), you don't want to lift the pad too.

I don't think I would recommend keeping the original cap in place as it may leak electrolyte and corrode the traces on the pcb.

It's been playing for hours now with no problems! Someday, I may muster up enough nerve to actually replace the cap with a proper surface mount cap, but first I need to buy a few things LOL! If I were to do that, I would probably just replace all the caps. A year ago I replaced both drawer belts.

Yes, it seems likely that eventually other caps will go too, but for now: enjoy the music!

Yes, Eventually I will replace it with the proper surface mount cap! I am going to buy tweezers first though. Should have them anyway. I looked for any signs of leaking around the caps, and didn't notice anything.
 

Offline Brumby

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Re: Tough Problem To Locate Need Help
« Reply #80 on: April 30, 2016, 03:45:55 am »
Whether you fit an SMD capacitor of just keep the one you have used won't really matter - but removing the faulty one is a good idea.
 

Offline tony3d

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Re: Tough Problem To Locate Need Help
« Reply #81 on: April 30, 2016, 10:45:59 am »
I can buy tweezers for my AOYUE Solder Station for $31.00! I may order those next week. Then it should be a pretty simple desolder event LOL! So once I remove the old one just use braid to soak up all the old solder off the pads, then coat them with new solder, and solder in my new cap correct?
 

Offline jitter

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Re: Tough Problem To Locate Need Help
« Reply #82 on: April 30, 2016, 10:55:17 am »
No, you need to hold the cap in place and apply the iron while adding solder.
What you describe is done all too often, but since (most of the) flux has already gone, you don't get as good a join.
 

Offline tony3d

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Re: Tough Problem To Locate Need Help
« Reply #83 on: April 30, 2016, 11:13:03 am »
No, you need to hold the cap in place and apply the iron while adding solder.
What you describe is done all too often, but since (most of the) flux has already gone, you don't get as good a join.

I'm referring to replacing it with a new SMD CAP. If you don't coat the pads first how does the solder get underneath the cap? I figure if I remove the old one, may as well have it look right.
 

Offline jitter

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Re: Tough Problem To Locate Need Help
« Reply #84 on: April 30, 2016, 11:37:47 am »
It would be the same as with the through hole cap, but you get to see less of the action  ;) . The solder will be drawn under the pin by capillary force.

With SMD components, you want them to sit flush against the pcb before you start soldering. This goes especially for muli-legged components such as ICs but it's nice to have a cap sit straight on the board as well. That means removing old solder first.
To make things easier, you start with adding fresh solder to one pad only and then fix the cap on that pin first. Make sure it's aligned properly before you solder the other side.

This vid does it that way (but try to align the cap with fewer attempts  ;) ), what I always do in addition is inspect the first pin and redo it with a bit of fresh solder if it doesn't look nice and shiny.

« Last Edit: April 30, 2016, 11:46:20 am by jitter »
 

Offline tony3d

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Re: Tough Problem To Locate Need Help
« Reply #85 on: April 30, 2016, 12:12:41 pm »
It would be the same as with the through hole cap, but you get to see less of the action  ;) . The solder will be drawn under the pin by capillary force.

With SMD components, you want them to sit flush against the pcb before you start soldering. This goes especially for muli-legged components such as ICs but it's nice to have a cap sit straight on the board as well. That means removing old solder first.
To make things easier, you start with adding fresh solder to one pad only and then fix the cap on that pin first. Make sure it's aligned properly before you solder the other side.

This vid does it that way (but try to align the cap with fewer attempts  ;) ), what I always do in addition is inspect the first pin and redo it with a bit of fresh solder if it doesn't look nice and shiny.



Ok. Thanks for the video! I always apply the heat to  8)the leg, pad first then add solder to through components, but never worked with SMD STUFF BEFORE. With tweezers to remove old components, and these techniques, I'm getting a much better understanding. I may just look for some old circuit board with these type of cylinder SMD caps on it to experiment with first. Would not want to do anything to damage the boards pads at this point.!
 

Offline tony3d

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Re: Tough Problem To Locate Need Help
« Reply #86 on: April 30, 2016, 12:17:20 pm »
Wonder if it would be OK to first coat the board pads, then use a flux pen to coat the caps pads, then solder it in place? Just be less to fiddle with.
« Last Edit: April 30, 2016, 12:21:19 pm by tony3d »
 

Offline jitter

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Re: Tough Problem To Locate Need Help
« Reply #87 on: April 30, 2016, 12:46:07 pm »
It'll work too.
 

Offline tony3d

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Re: Tough Problem To Locate Need Help
« Reply #88 on: April 30, 2016, 12:51:37 pm »
 

Offline tony3d

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Re: Tough Problem To Locate Need Help
« Reply #89 on: April 30, 2016, 03:13:09 pm »
I know that the cap I replaced was 10uf only because I downloaded the service manual, and looked it up. So the middle number is the capacitance, the bottom the voltage limit, what's the top number for, and how go you know if the capacitance is "uf", or "nf" just by looking at the cap. This cap just says 10.
 

Offline jitter

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Re: Tough Problem To Locate Need Help
« Reply #90 on: April 30, 2016, 06:48:24 pm »
Good question.

Usually the appearance of a cap betrays its technology. An electrolytic capacitor, ceramic capacitor, metalized film capacitor, tantalum capacitor (among others) are all looking quite recognizable (google them).

Once you know the type, you know the typical range of values and the unit used. An electrolytic capacitor uses uF (or more correctly µF) as unit, i.e. micro Farads. On a cap with enough room to print on, you will see e.g. 10 µF/16 V. On this SMD cap space is limited and only 10/16V was printed.
Sometimes you can't even find the values without looking up a code in a datasheet. The one in the image below is a 4.7 µF cap, and I believe "J" should be in a table in the datasheet for the max. voltage.



SMD ceramic capacitors have no value printed on them. Through hole ceramic capacitors use the unit pF, pico Farads. Often only a value is printed on it, say "104". It's the same system (as e.g. for resistors) with value and multiplication (power of 10), so 104 means 10 · 104 = 100,000 pF = 100 nF = 0.1 µF. Often a code needs to be looked up to know more, e.g. the max. voltage.
« Last Edit: May 01, 2016, 07:11:01 am by jitter »
 

Offline tony3d

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Re: Tough Problem To Locate Need Help
« Reply #91 on: May 01, 2016, 01:00:14 am »
Good question.

Usually the appearance of a cap betrays its technology. An electrolytic capacitor, ceramic capacitor, metalized film capacitor, tantalum capacitor (among others) are all looking quite recognizable (google them).

Once you know the type, you know the typical range of values and the unit used. An electrolytic capacitor uses uF (or more correctly µF) as unit, i.e. micro Farads. On a cap with enough room to print on, you will see e.g. 10 µF/16 V. On this SMD cap space is limited and only 10/16V was printed.
Sometimes you can't even find the values without looking up a code in a datasheet. The one in the image below is a 4.7 µF cap, and I believe "J" should be in a table in the datasheet for the max. voltage.



SMD ceramic capacitors have no value printed on them. Through hole ceramic capacitors use the unit pF, pico Farads. Often only a value is printed on it, say "104". It's the same system with value and multiplication (power of 10), so 104 means 10 · 104 = 100,000 pF = 100 nF = 0.1 µF. Often a code needs to be looked up to know more, e.g. the max. voltage.

Thanks again for the explanation!
 


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