Hello - I am wanting to replace the 4 larger can electrolytic capacitors in the power supply section of my NAD 2100 stereo amplifier which is about 30 years old. Two of these large electrolytic caps are the 4 pin type consisting of a terminal for the positive, a terminal for the minus, and 2 terminals for mechanical support. I found 2 possible replacements on Digi -Key and the spec sheets for both of these caps have the following cautions from the manufacturers:
"Use the blank terminals for mechanical support only. The blank terminals must not be connected to a solder trace on the PC board, but be electrically isolated from the negative or positive terminal."
"Use dummy terminals for mechanical support only. Make no electrical connection because they resistively connect through the electrolyte to the negative terminal."
My dilemma is that when I look at the underside of the circuit board I can clearly see that these support pins of both of these capacitors are soldered onto traces that lead back to the negative terminal of the capacitors and clearly this is in complete contradiction to what the manufacturers are saying.
Can I safely install these 4 pin capacitors in the same way as the original ones are soldered in?
Also, the second caution statement seems to contradict itself, because it says that the dummy terminals resistively connect through the electrolyte to the negative terminal. I am not sure what "resistively connect" means, but I assume that there would be continuity between the dummy terminals and the negative terminal?
Could have the NAD designers overlooked what the capacitor manufacturers are warning against, or possibly that the way the capacitors were made 30 years ago allowed for the support pins to be soldered to traces that went to the negative pin? Or, could it be that the capacitor manufacturers are just "over warning" against a potential degradation that can happen over time and / or just trying to prevent lawsuits?
The amplifier is working well and sounds good, but I am reading that old electrolytic capacitors should be replaced. I am wanting to replace these power supply capacitors to prolong the lifetime of this amplifier and to prevent potential damage that could occur if these capacitors could blow up or get shorted. These capacitors seem to be very slightly rounded (convex) at the top but there are no signs of leakage.
Also, would it be reasonable to just replace these 4 large power supply capacitors and leave the other 30 very small electrolytic caps alone, or should I definitely replace all electrolytic's which would be very tedious?
Any suggestions or input would be very much appreciated and thank you for your time.
"Use the blank terminals for mechanical support only. The blank terminals must not be connected to a solder trace on the PC board, but be electrically isolated from the negative or positive terminal."
"Use dummy terminals for mechanical support only. Make no electrical connection because they resistively connect through the electrolyte to the negative terminal."
My dilemma is that when I look at the underside of the circuit board I can clearly see that these support pins of both of these capacitors are soldered onto traces that lead back to the negative terminal of the capacitors and clearly this is in complete contradiction to what the manufacturers are saying.
Can I safely install these 4 pin capacitors in the same way as the original ones are soldered in?
Also, the second caution statement seems to contradict itself, because it says that the dummy terminals resistively connect through the electrolyte to the negative terminal. I am not sure what "resistively connect" means, but I assume that there would be continuity between the dummy terminals and the negative terminal?
Could have the NAD designers overlooked what the capacitor manufacturers are warning against, or possibly that the way the capacitors were made 30 years ago allowed for the support pins to be soldered to traces that went to the negative pin? Or, could it be that the capacitor manufacturers are just "over warning" against a potential degradation that can happen over time and / or just trying to prevent lawsuits?
The amplifier is working well and sounds good, but I am reading that old electrolytic capacitors should be replaced. I am wanting to replace these power supply capacitors to prolong the lifetime of this amplifier and to prevent potential damage that could occur if these capacitors could blow up or get shorted. These capacitors seem to be very slightly rounded (convex) at the top but there are no signs of leakage.
Also, would it be reasonable to just replace these 4 large power supply capacitors and leave the other 30 very small electrolytic caps alone, or should I definitely replace all electrolytic's which would be very tedious?
Any suggestions or input would be very much appreciated and thank you for your time.
I would suggest first off to think very carefully first... these forums have plenty of tales of woe regarding recaps that have gone wrong. I'm just saying 🙂
The 30 small electrolytics would probably be the ones to replace to be perfectly honest, much more so than the large reservoir caps.
When replacing small caps always note the polarity value and voltage rating of the actual part you remove, do not rely on board markings, circuit diagrams and values from parts lists. Replace like for like with what is fitted... old manuals can have errors and boards can have caps marked with incorrect polarity. It happens.
The large caps you will have to figure out yourself. If a modern part says do not connect mechanical supports electrically to the circuit then you have to take that at face value. As long as you can fit the replacements securely then there is no reason not to use 2 pin types. Drilling a board to accommodate a different pin spacing is easy provided the pins still lie within the copper print they are supposed to connect to.
The 30 small electrolytics would probably be the ones to replace to be perfectly honest, much more so than the large reservoir caps.
When replacing small caps always note the polarity value and voltage rating of the actual part you remove, do not rely on board markings, circuit diagrams and values from parts lists. Replace like for like with what is fitted... old manuals can have errors and boards can have caps marked with incorrect polarity. It happens.
The large caps you will have to figure out yourself. If a modern part says do not connect mechanical supports electrically to the circuit then you have to take that at face value. As long as you can fit the replacements securely then there is no reason not to use 2 pin types. Drilling a board to accommodate a different pin spacing is easy provided the pins still lie within the copper print they are supposed to connect to.
Its unlikely the original caps are the same manufacturer let alone capacitor series, so the warnings that apply to the modern caps aren't likely to be issues with the original caps. I'd take the warning seriously.
Why not use 2 pin caps and deal with the mechanical integrity in a different way? Like cable ties and silicone or glue.
For the large caps, do you think that I could just cut off the 2 mechanical support pins (and thus not solder them in) and use a bit of hot glue to support the cap if necessary? This way I could still easily utilize the 22.5 mm board spacing for the plus and minus pins. (I did not find any 2 pin cap types with that spacing.)
Many thanks for your reply and good advice.
Many thanks for your reply and good advice.
I'll echo Mooly's comment. When an amplifier or receiver is 'recapped', it is quite common for the electrolytic caps in the signal path to be replaced but the power decoupling caps (*particularly* the reservoir caps) to be left as is.
Have you tried to gain any insight into what the original caps are and maybe find out more about their pin designation?
The original cap is Elna 10,000uF 80V 85 deg C
4 pin radial can 22.5mm spacing between pos and neg pins
35mm diameter 65mm height
Other markings CE69W(P) Black
Amplifier NAD 2100
Thank you for checking this.
4 pin radial can 22.5mm spacing between pos and neg pins
35mm diameter 65mm height
Other markings CE69W(P) Black
Amplifier NAD 2100
Thank you for checking this.
Just finished repairing an 1999 vintage amp and all capacitors apart from the big ones on the power supply where well inside tolerance, example a 47uf with 46uf after 20 is a good one for me.
Personally, I'd retain the mechanical support of the two dummy pins and just CUT the traces that connect them to the negative terminals. Just my 2¢.
Mundorf Capacitor 10000uF 80Vdc MLytic® AG MLGO
The Mundorf has 10mm pin pitch. If traces permit, you could drill two new holes for each.
Otherwise, you could buy some standard snap-ins, add leads to them, and jack them up above the pcb with washers.
The Mundorf has 10mm pin pitch. If traces permit, you could drill two new holes for each.
Otherwise, you could buy some standard snap-ins, add leads to them, and jack them up above the pcb with washers.
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I’m guessing but I imagine the capacitor’s two mechanical mounting pins are attached to the can itself. The can is full of electrolyte liquid which is a conductor and surrounds both positive and negative plates (which are rolled into a spiral). The positive plate has an oxide layer which is an insulator. So the mounting pins conduct to the negative plate through the electrolyte.
Provided the mounting pins are at the same voltage as the negative pin, there will be no current flow through the electrolyte. The confusing thing is that the data sheet says not to connect the mounting pins to either of the other pins, not just the positive pin. Maybe not what they really meant?
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I wouldn't do so, not the same way.
It was two options noted here, modify board to insulate support pins, or snip support pins completely. I have done the latter for one of my projects about 10 years ago with older Nichicon caps with 2 extra support pins. Those support pins are needed to lower possibility of failure when you ship assembled devices and it needs to withstand all the vibrations and possible rough handling during it. Support pins were introduced to avoid additional operation of gluing big caps to the pcb on the assembly lines.
Personally I would snip support pins (again).
If you feel safer with additional support just glue caps to the pcb. Two small blobs of neutral silicon caulking (SiliconeII) works very well (I prefer black). Hot melt glue work also comparably well and you can get glue sticks in black.
The Kemet BHC ALP20 and ALP22 series datasheets do not have the warning you mention about the unconnected pins. Be careful when changing from ALP20 to ALP22 series as although the pinouts are the same, some ALP20 values went from 40mm diameter to 35mm diameter, which also means changing from 5 to 4 pins.
Many thanks to all who replied and I appreciate you sharing your knowledge and the help you provided. Many good suggestions were made and it is now clear to me that if I do replace these filter capacitors that I should heed the manufacturers warnings (even though they may have been worded somewhat ambiguously) and simply not connect the the support pins. I would probably snip them off and use a bit of glue to help keep these parts in place. Thanks.