I have a question in regards to replacing electrolytic caps, is it better to replace with low ESR caps or are they more a use case replacement where there is a specific reason for using them over normal caps ?

I have some board repairs coming up and a few will be on GPUs and the whole ESR no ESR can be a bit confusing.

I mostly ask because right now here in Australia I can get normal caps for days but ESR caps have a more limited range available at suppliers.

TrashPanda wrote on 2023-03-08, 02:40:

I have a question in regards to replacing electrolytic caps, is it better to replace with low ESR caps or are they more a use case replacement where there is a specific reason for using them over normal caps ?

I have some board repairs coming up and a few will be on GPUs and the whole ESR no ESR can be a bit confusing.

I mostly ask because right now here in Australia I can get normal caps for days but ESR caps have a more limited range available at suppliers.

In most cases you can replace General Purpose (GP) caps with Low ESR without issues, although it has been reported that using caps with extremely low ESR (such as polymers) can lead to problems in certain scenarios such as power supplies, so you probably want to avoid those unless the design calls for ultra-low ESR specifically. Using a low ESR cap to replace a GP won't give you any noticeable advantages in most cases, it's just a matter of choosing what suits you best between endurance, size and price.

The reverse however is not true. If the manufacturer used a low ESR cap you should replace it with one of the same type, using a GP in this case may seem to work at first but you will likely encounter instabilities and severely reduced lifetime as the cap will probably be stressed beyond its possibilities, having to handle large amounts of ripple. So unless you really know what the circuit is doing do not replace low ESR with GP.

What I usually do is I try to find the datasheet of the caps I want to replace and then look for suitable replacements from reputable manufacturers. This site is extremely helpful for finding datasheets, even for chinese garbage brands:
http://www.paullinebarger.net/DS/

Also, all caps rated 85C can be considered general purpose. I suggest replacing those with 105C rated caps in all cases, you'll get better endurance, especially if they are in a hot/cramped space.

TheMobRules wrote on 2023-03-08, 03:17:

In most cases you can replace General Purpose (GP) caps with Low ESR without issues, although it has been reported that using ca […]
Show full quote

TrashPanda wrote on 2023-03-08, 02:40:

I have a question in regards to replacing electrolytic caps, is it better to replace with low ESR caps or are they more a use case replacement where there is a specific reason for using them over normal caps ?

I have some board repairs coming up and a few will be on GPUs and the whole ESR no ESR can be a bit confusing.

I mostly ask because right now here in Australia I can get normal caps for days but ESR caps have a more limited range available at suppliers.

In most cases you can replace General Purpose (GP) caps with Low ESR without issues, although it has been reported that using caps with extremely low ESR (such as polymers) can lead to problems in certain scenarios such as power supplies, so you probably want to avoid those unless the design calls for ultra-low ESR specifically. Using a low ESR cap to replace a GP won't give you any noticeable advantages in most cases, it's just a matter of choosing what suits you best between endurance, size and price.

The reverse however is not true. If the manufacturer used a low ESR cap you should replace it with one of the same type, using a GP in this case may seem to work at first but you will likely encounter instabilities and severely reduced lifetime as the cap will probably be stressed beyond its possibilities, having to handle large amounts of ripple. So unless you really know what the circuit is doing do not replace low ESR with GP.

What I usually do is I try to find the datasheet of the caps I want to replace and then look for suitable replacements from reputable manufacturers. This site is extremely helpful for finding datasheets, even for chinese garbage brands:
http://www.paullinebarger.net/DS/

Also, all caps rated 85C can be considered general purpose. I suggest replacing those with 105C rated caps in all cases, you'll get better endurance, especially if they are in a hot/cramped space.

Cheers for the explanation, so now what defines Ultra Low ESR vs Low ESR, For instance the caps I'm looking at replacing some GP ones with have a ESR rating of 39mOhm @ 100kHz other are 200+mOhm @ 120Khz and then a few I think might be miss-labled drop the Khz and are rated instead in Hz.

These GP ones are part of powerstages and possibly filtering for SDram so they could actually be ESR caps, ill be sure to look them up in that list you linked.

Date: 3/9/2023
GPU Model: PNY Verto NVIDIA GeForce FX 5700VE 256MB
Problem: Massive artifacting at BIOs
Work Performed: Replaced all capacitors, attempted reflow of main GPU core
Result: No change
Extrapolation: Bad VRAM or VRAM path
Comment: No other obvious damage to the card.

TheMobRules wrote on 2023-03-08, 03:17:

In most cases you can replace General Purpose (GP) caps with Low ESR without issues, although it has been reported that using caps with extremely low ESR (such as polymers) can lead to problems in certain scenarios

What matters is the time constant equal to the product of capacitance and ESR, see attachment.
Small ESR * big capacitance = stability region.
Do not use small polymer capacitor, like 10u*10V.
Use 100 - 560u * 6.3V in same case, and ypu got no problem.
Use big cased General use polymer capacitor from "third line manufacturer" , like SAmwha FB/Capson PS/Lelon
10mm dia, like the Capxon PS 2200u*6.3V.
its ESR is 12mOhm, which is comparable to the same UNITED CHEMI-CON KZE 1500u * 6.3 (23 mOhm) on meny old video/Matherboards

• GPU Model: BFGR6800OC BFG GeForce 6800 128M DDR
  Problem: no video at boot, when used as secondary gpu, yellow exclamation in device manager if windows didn't bluescreen during boot
  Work Performed: set Radeon 7000 as boot video, flash attached 6800un.rom
  Result: boot with video and info
  Extrapolation: bad firmware
  Comment: I assume some previous overclock gone bad
• GPU Model: 128A8N343DX EVGA GeForce 6800 128M DDR
  Problem: no video at boot, when used as secondary gpu yellow exclamation in device manager if windows didn't bluescreen during boot
  Work Performed: set Radeon 7000 as boot video, flash attached 6800un.rom
  Result: boot with video and info
  Extrapolation: bad firmware
  Comment: I assume some previous overclock gone bad
• GPU Model: BFGR68256GTOC BFG GeForce 6800 GT 256M GDDR3
  Problem: no video at boot, when used as secondary gpu yellow exclamation in device manager
  Work Performed: set Radeon 7000 as boot video, flash attached 6800GTun.rom
  Result: boot with video and info, with severe artifacting
  Extrapolation: bad firmware, solder gone bad?
  Comment: I assume some previous overclock gone bad and overheat, causing additional bga failures
• GPU Model: BFGR73512GT BFG GeForce 7300 GT 512M DDR2
  Problem: no video at boot, when used as secondary gpu yellow exclamation in device manager
  Work Performed: set Radeon 7000 as boot video, flash original BFG firmware
  Result: boot with video and info
  Extrapolation: bad firmware
  Comment: I assume some previous overclock gone bad
• GPU Model: GF7600GT nVidia GeForce 7600 GT 512M DDR2
  Problem: no boot, even when just a secondary card
  Work Performed: connect to SOIC8 clip and reflash generic 7600GT firmware
  Result: still no boot, even when just a secondary card
  Extrapolation: hardware failure
  Comment: I assume some previous overclock gone bad, or overvolted the card to complete failure

Date: 2/10/2024
GPU Model: Dynamic Pictures Oxygen 202
Problem: Card was damagedon arrival. One ram chip had a damaged corner and some pins were missing. Damaged capacitors on the back of the pcb.
Work Performed: Pins were repaired and connections were made. I was unable to identify the missing capacitors on the back of the board.
Result: An image is displayed but heavily distorted, making the card unusable.
Extrapolation: The missing capacitors probably play a role for the card not working. No technical information is available for the card.
Comment: I was offered a full refund for the card. But I wanted to repair the card so the (eBay) seller offered a partial refund.