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2465B Replace Aluminum Electrolytics with Tantalum
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See this photo album /g/TekScopes/album?id=66462 for my recent repairs on a 2465B. This 2465B had modest corrosion on the A5 board from leaking aluminum electrolytic capacitors. On this board the pads for C2222 and C2520 were partially eaten away and R2013 itself had failed completely (R2013 pads were OK). A few cycles of applying flux, hot air heating, then wash with PCB cleaner and the board was ready for repair. But I wanted a repair that did not suffer the same fate as the OEM assembly.
Todays aluminum electrolytic capacitors have more robust seals than the ones Tek had available in the 1990's. Also, hand soldering the capacitors to the board avoids severely heating the capacitor seals as happens with wave soldering systems. Still, electrolytic capacitors always eventually fail and often leak electrolyte onto the PCB. Tantalum electrolytics do not have this failure mode, at least not often, because they are made different. So I resolved to replace the four aluminum electrolytic capacitors with SMD tantalum electrolytic capacitors. I understand that Tektronix did something like that with certain 2465B scopes manufactured in Guernsey, UK (see here /g/TekScopes/photo/12841/0?p=Name,,,20,1,0,0 ). So I elongated one pad of each mounting for C2011, C2113, C2331, and C2965. This was simple to do. Each of these capacitors have a through hole or trace on one pad that can be cleaned and a copper foil strip can be soldered to elongate that pad by 1 to 2 mm (I was neat, not precise). This allowed me to hand solder 2917 package size SMD capacitors. I chose 4:1 or better voltage derating and an ESR of less than 1 Ohm in each case. The result is working very well. I will try to report back in 30 years on how the reliability turned out. |
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Lets see that would make me 107 Years Young.
Sounds like you did a good job.?Leon Robinson ?? K5JLR Political Correctness is a Political Disease. From: machineguy59 via Groups.Io <machineguy59@...> To: [email protected] Sent: Saturday, August 11, 2018 3:28 PM Subject: [TekScopes] 2465B Replace Aluminum Electrolytics with Tantalum See this photo album /g/TekScopes/album?id=66462 for my recent repairs on a 2465B.? This 2465B had modest corrosion on the A5 board from leaking aluminum electrolytic capacitors.? On this board the pads for C2222 and C2520 were partially eaten away and R2013 itself had failed completely (R2013 pads were OK).? A few cycles of applying flux, hot air heating, then wash with PCB cleaner and the board was ready for repair.? But I wanted a repair that did not suffer the same fate as the OEM assembly. Todays aluminum electrolytic capacitors have more robust seals than the ones Tek had available in the 1990's.? Also, hand soldering the capacitors to the board avoids severely heating the capacitor seals as happens with wave soldering systems.? Still, electrolytic capacitors always eventually fail and often leak electrolyte onto the PCB.? Tantalum electrolytics do not have this failure mode, at least not often, because they are made different.? So I resolved to replace the four aluminum electrolytic capacitors with SMD tantalum electrolytic capacitors.? I understand that Tektronix did something like that with certain 2465B scopes manufactured in Guernsey, UK (see here /g/TekScopes/photo/12841/0?p=Name,,,20,1,0,0 ). So I elongated one pad of each mounting for C2011, C2113, C2331, and C2965.? This was simple to do.? Each of these capacitors have a through hole or trace on one pad that can be cleaned and a copper foil strip can be soldered to elongate that pad by 1 to 2 mm (I was neat, not precise).? This allowed me to hand solder 2917 package size SMD capacitors.? I chose 4:1 or better voltage derating and an ESR of less than 1 Ohm in each case.? The result is working very well.? I will try to report back in 30 years on how the reliability turned out. |
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And me 108 years.? That is if my electrolyics don't leak out.
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On ?Saturday?, ?August? ?11?, ?2018? ?09?:?07?:?45? ?PM? ?CDT, Leon Robinson <leon-robinson@...> wrote:
Lets see that would make me 107 Years Young. Sounds like you did a good job.?Leon Robinson ?? K5JLR Political Correctness is a Political Disease. ? ? ? From: machineguy59 via Groups.Io <machineguy59@...> To: [email protected] Sent: Saturday, August 11, 2018 3:28 PM Subject: [TekScopes] 2465B Replace Aluminum Electrolytics with Tantalum ? See this photo album /g/TekScopes/album?id=66462 for my recent repairs on a 2465B.? This 2465B had modest corrosion on the A5 board from leaking aluminum electrolytic capacitors.? On this board the pads for C2222 and C2520 were partially eaten away and R2013 itself had failed completely (R2013 pads were OK).? A few cycles of applying flux, hot air heating, then wash with PCB cleaner and the board was ready for repair.? But I wanted a repair that did not suffer the same fate as the OEM assembly. Todays aluminum electrolytic capacitors have more robust seals than the ones Tek had available in the 1990's.? Also, hand soldering the capacitors to the board avoids severely heating the capacitor seals as happens with wave soldering systems.? Still, electrolytic capacitors always eventually fail and often leak electrolyte onto the PCB.? Tantalum electrolytics do not have this failure mode, at least not often, because they are made different.? So I resolved to replace the four aluminum electrolytic capacitors with SMD tantalum electrolytic capacitors.? I understand that Tektronix did something like that with certain 2465B scopes manufactured in Guernsey, UK (see here /g/TekScopes/photo/12841/0?p=Name,,,20,1,0,0 ). So I elongated one pad of each mounting for C2011, C2113, C2331, and C2965.? This was simple to do.? Each of these capacitors have a through hole or trace on one pad that can be cleaned and a copper foil strip can be soldered to elongate that pad by 1 to 2 mm (I was neat, not precise).? This allowed me to hand solder 2917 package size SMD capacitors.? I chose 4:1 or better voltage derating and an ESR of less than 1 Ohm in each case.? The result is working very well.? I will try to report back in 30 years on how the reliability turned out. |
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On 8/11/2018 4:28 PM, machineguy59 via Groups.Io wrote:
See this photo album /g/TekScopes/album?id=66462 for my recent repairs on a 2465B. This 2465B had modest corrosion on the A5 board from leaking aluminum electrolytic capacitors. On this board the pads for C2222 and C2520 were partially eaten away and R2013 itself had failed completely (R2013 pads were OK). A few cycles of applying flux, hot air heating, then wash with PCB cleaner and the board was ready for repair. But I wanted a repair that did not suffer the same fate as the OEM assembly.That 30 years might not be so far off. Has anyone on this list ever seen one of these solid Ecaps ever "wear" out? I often replace aluminum electrolytics with the solid SMD parts. I have yet to see one of these fail in service. -Bert |
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So you replaced parts who's current main failure mode is less capacitance with a part who's known normal failure modes are burns up in flames taking out the PCB or short circuit taking out the parts before? And we won't even touch on the questionable ethics of Tantalum. I have NEVER seen a quality electrolytic made after the mid 1990s leak unless it was over temperatured or over voltaged. I'm pretty sure that is a bygone problem.
Doesn't seem like a smart move to me. A modern LOW ESR 5k hour 105C electrolytic should be far Superior to Tantalum with the ESR going 2-4 octaves higher with a safer part. You could possibly use a X7R or X5R MLCC for even lower ESR that goes 10 octaves longer and reliability but some of those older circuits are not ceramic stable and X7R/X5R are micro-phonic, where other options are not. |
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I don't share your disdain for tantalum electrolytic capacitors.? Their dramatic failure modes to happen when they are operated near their rated voltage.? For this reason, I de-rate their voltage application by more than 4:1.? That seems pretty safe by most accounts.? Also, I chose capacitors with an ESR equivalent or less than the aluminum capacitors they replaced (smaller ones were available at higher ESR).? I know nothing of the "ethics" of tantalum capacitors or their vendors. ?
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On the other hand, I know that SMD aluminum electrolytic capacitors are known to leak electrolyte onto the PCB.? Newer ones may not do it so often, but they do it.? When they do, they nearly always destroy portions of the board.? Tantalum electrolytic capacitors do not leak.? I considered ceramic capacitors but their capacitance values are voltage sensitive and that dictates significant voltage derating for them too. On ?Sunday?, ?August? ?12?, ?2018? ?02?:?20?:?50? ?PM? ?CDT, Hawker <rick@...> wrote:
So you replaced parts who's current main failure mode is less capacitance with a part who's known normal failure modes are burns up in flames taking out the PCB or short circuit taking out the parts before? And we won't even touch on the questionable ethics of Tantalum. I have NEVER seen a quality electrolytic made after the mid 1990s leak unless it was over temperatured or over voltaged. I'm pretty sure that is a bygone problem. Doesn't seem like a smart move to me.? A modern LOW ESR 5k hour 105C electrolytic should be far Superior to Tantalum with the ESR going 2-4 octaves higher with a safer part.? You could possibly use a X7R or X5R MLCC for even lower ESR that goes 10 octaves longer and reliability but some of those older circuits are not ceramic stable and X7R/X5R are micro-phonic, where other options are not. |
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On Sun, Aug 12, 2018 at 12:42 PM, machineguy59 via Groups.Io <
machineguy59@...> wrote: I don't share your disdain for tantalum electrolytic capacitors. TheirI have been using Kemet T494 series SMD -55 C to +125 C Low ESR Tantalum for a very long time in aviation products and have not had issues. They claim to use "conflict free Tantalum". I have also used high quality electrolytics with higher diameter to length ratios if I needed really big capacitance. Regards, Mark |
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On Sun, Aug 12, 2018, 17:58 Mark Goldberg <marklgoldberg@...>
Huh. Who knew tantalums could be emotionally conflicted. Mark |
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tom jobe
Hi Mark,
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That is an interesting point you make about using aluminum electrolytics with a higher diameter to length ratio. A recent capacitor discussion on Tekscopes included links to capacitor data sheets about the brand and series being discussed, and in one of the data sheets I saw that even within the same series of capacitor the ratings went up with larger diameters. Wish I could remember the exact brand and series of capacitor so I could find that same data sheet again. tom jobe... On 8/12/2018 2:58 PM, Mark Goldberg wrote:
On Sun, Aug 12, 2018 at 12:42 PM, machineguy59 via Groups.Io < |
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tom jobe
Look at the data sheet for the Nichicon HE series capacitors, in the 'endurance' section it says that the capacitor's life doubles (in hours) when you go up from 6.3 mm to 12.5 mm diameter.
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This fits right in with what you are saying about skinny capacitors. tom jobe... On 8/12/2018 3:43 PM, Mark Goldberg wrote:
On Sun, Aug 12, 2018 at 3:23 PM, tom jobe <tomjobe@...> wrote:Hi Mark,I have been told that skinny electrolytics dry out faster. |
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Oh but they are!
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I've met several who were so conflicted that they thought they were resistors. Adrian On 8/12/2018 11:17 PM, Mark Wendt wrote:
Huh. Who knew tantalums could be emotionally conflicted. |
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LOL!? LGBTQRC?? ;-)
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Mark On 08/13/2018 04:44 AM, Adrian wrote:
Oh but they are! |
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Tantalums are really good when used properly.
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1) ESR / ripple current rating MUST not be exceeded, creates internal self heating that will lead to internal shorts. 2) Use them for high frequency, low voltage switching regulators. 3) De-rate working voltage by 50% as a minimum. 4( Not much available at 35VDC and up MLCCs are a very reliable alternative to small tantalums On Mon, Aug 13, 2018 at 4:38 AM, Mark Wendt <wendt.mark@...> wrote:
LOL! LGBTQRC? ;-) |
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