- Removing Large Electrolytics - 11 Updates
- Vintage equipment voltage measurement - 2 Updates
| Cursitor Doom <curd@notformail.com>: Aug 21 11:46PM I have just spent about 40m trying to unsolder an electro on the board of the Tek 466 I'm currently working on. It showed a ESR of 45 ohms so I needed to hook it out of circuit just to be doubly sure it was really that bad. The electros in question are all fairly large ones in the (linear) PSU section. For some reason they've not used separate boards for the various sub-circuits, so the PSU is just one area of a v.large board which also has components for all sorts of other functions. Anyway, The cap in question has 5 connections to the board: 3 equi-spaced ground tabs around the outside that come straight from the case of the cap and the 2 + and - wires close to the centre. Given 5 in total through-hole connections, it's proving very difficult to remove the cap using suction pump and solder braid cos I cannot wiggle it at all. The best solution IMO would be to heat all 5 tabs at the same time whilst pulling the cap's case from the other side until it breaks free. Is there any tool that enables you to do this? I fear the amount of fucking around I'm having to do otherwise will lead to delamination of the PCB traces and an ugly mess. I cannot even slip a junior hacksaw blade between the bottom of the cap and the PCB and cut it free cos it's obscured by other components. :( -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition. |
| "jfeng@my-deja.com" <jfeng@my-deja.com>: Aug 21 05:18PM -0700 Some people use a butane torch to heat the solder joints gently while pulling on the component. Practice this technique before you do it on something you want to save. I have done this for DIP ICs. Since you are pretty sure it is bad, I would clip the leads, destroying the can beforehand if necessary. |
| tabbypurr@gmail.com: Aug 21 05:55PM -0700 > Some people use a butane torch to heat the solder joints gently while pulling on the component. Practice this technique before you do it on something you want to save. I have done this for DIP ICs. > Since you are pretty sure it is bad, I would clip the leads, destroying the can beforehand if necessary. A torch is a recipe for a badly burnt board. I've always been able to move a multi-legged component at least a tiny amount while melting one or more legs, and rock it back & forth, letting the board cool well if paper. The pcb is slightly flexible after all. Paper boards are weak, vulnerable to heat & the copper comes unglued when hot. Maybe you could cut the 3 outer tabs off flush. NT |
| Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net>: Aug 21 09:28PM -0400 On 08/21/2018 07:46 PM, Cursitor Doom wrote: > otherwise will lead to delamination of the PCB traces and an ugly mess. > I cannot even slip a junior hacksaw blade between the bottom of the cap > and the PCB and cut it free cos it's obscured by other components. :( +1 for can-opening it to save wear and tear on the board. If you measure 45 ohms ESR in-circuit, it won't be better by itself. Cheers Phil Hobbs |
| Terry Schwartz <tschw10117@aol.com>: Aug 21 07:53PM -0700 On Tuesday, August 21, 2018 at 6:46:24 PM UTC-5, Cursitor Doom wrote: > protocols, whether for profit or not, is conditional upon a charge of > GBP10.00 per reproduction. Publication in this manner via non-Usenet > protocols constitutes acceptance of this condition. Depending on what else is nearby, a heat gun can be effective. |
| stratus46@yahoo.com: Aug 21 09:54PM -0700 I use a Metcal which is a 40 Watt iron very well controlled but when removing caps from computer motherboards where there are no thermal reliefs to the ground plane, NO soldering iron can unsolder it alone. The pin can't conduct the heat fast enough. I also have a cheap Chinese hot air tool. Set the temp on the air tool slightly below the melt temp so it won't 'blow' any SMD parts (none on the 466) off the board. This becomes a 2 handed operation. While heating with the Metcal, I 'auxiliary' heat the board with the hot air tool for about 20 seconds. This WILL get hot enough to use your Edsyn Soldapullt to clear the hole and not lift any pads or damage the board. Cutting up the cap and then removing the separate pins is OK IF you can destroy it without damaging the board. I've had excellent results with the aux heating technique which is faster than dismembering the part. Torches are WAY too brutal especially in a Tek. G² |
| Cursitor Doom <curd@notformail.com>: Aug 22 10:12AM On Tue, 21 Aug 2018 21:28:10 -0400, Phil Hobbs wrote: > +1 for can-opening it to save wear and tear on the board. If you > measure 45 ohms ESR in-circuit, it won't be better by itself. Well, it's hardly surprising for an electro of this age. Clearly the original component from a scope with a s/n indicating it was manufactured 44 years ago! What was more surprising was that only 2 out of 6 electros in the PSU section showed abnormal readings (the remaining faulty one has gone leaky). -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition. |
| tabbypurr@gmail.com: Aug 22 04:03AM -0700 On Wednesday, 22 August 2018 11:12:10 UTC+1, Cursitor Doom wrote: > 44 years ago! What was more surprising was that only 2 out of 6 electros > in the PSU section showed abnormal readings (the remaining faulty one has > gone leaky). Sounds about par for the course. Go back further to paper caps and it'd be a surprise to find any still working properly. And yes, micamold were paper caps. NT |
| ggherold@gmail.com: Aug 22 06:29AM -0700 On Tuesday, August 21, 2018 at 9:28:19 PM UTC-4, Phil Hobbs wrote: > measure 45 ohms ESR in-circuit, it won't be better by itself. > Cheers > Phil Hobbs Right I'd hack up the component and pull pin by pin. I do use a hot air rework station on some rotary switches... it's faster than all that hacking. George H. |
| Cursitor Doom <curd@notformail.com>: Aug 22 03:03PM On Tue, 21 Aug 2018 21:54:12 -0700, stratus46 wrote: > I use a Metcal which is a 40 Watt iron very well controlled but when > removing caps from computer motherboards where there are no thermal > reliefs to the ground plane, NO soldering iron can unsolder it alone. You're not kidding. My largest iron is 40W/80W switchable. 40W won't touch it and I'm not risking 80W! The biggest problem seems to be the cap case - a long 1" dia aluminium tube with 3 tags at the bottom going straight to PCB grounds. It's acting like a very effective heat sink. Going to have to trash the caps from above.:( -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition. |
| John-Del <ohger1s@gmail.com>: Aug 22 09:33AM -0700 On Tuesday, August 21, 2018 at 7:46:24 PM UTC-4, Cursitor Doom wrote: > otherwise will lead to delamination of the PCB traces and an ugly mess. > I cannot even slip a junior hacksaw blade between the bottom of the cap > and the PCB and cut it free cos it's obscured by other components. :( You need to preheat the board. BTW, rocking a component while desoldering is a recipe for disaster if the board in question is a multi-layer. An internal foil can be separated from the plated-through hole if physical assertion is used. If you can't remove the board to put it in a pre-heater, aim a hair dryer at it for about 10-15 minutes (a real heat gun can blister it). When the board is good and hot, it will have far less propensity to sink off heat from your soldering iron tip. |
| "Ron D." <ron.dozier@gmail.com>: Aug 21 07:35PM -0700 When calibrating tube testers it really matters. Otherwise a parallel resistace should work. Many DMM's have a 10 M input Z. A "Typical" scope might have a 1 M shunted by 22 pf or so. When you add a x10 probe the input Z should be 10 ohms resistive. Many DVM' had say a 50 uA movement with some sort of resistance (meter movement+series), Ohms/V is the reciprocal of current. So, your actually measuring a current through a fixed resistance with a scale in volts.` |
| stratus46@yahoo.com: Aug 22 02:00AM -0700 Most DVMs I've worked with are 11 Meg regardless of voltage settings. This is not 'stupendous'. A 50 KΩ/Volt meter on a 1000 setting will be 50 Meg but is only 250K on a 5 Volt setting. I've been using DVMs for service for nearly 40 years and have not run into any faulty readings because of an 11 meg load with one exception. In a Sony BVP30 broadcast camera they use a 200 Volt power supply for the electrostatic deflection. The 11 meg load was way too LOW to get valid readings We had to get a high voltage probe which is over a giga ohm to get useful readings. G² |
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