Capacitor ESR - Page 1
Forum section: electronics / projects

author: alank2
author_rank: Super Contributor
timestamp: November 13, 2020, 05:23:16 pm
content: I'm using a peak atlas ESR+ to measure the two large capacitors in a Commodore 1541 disk drive:7380uf 0.10ohm esr 6800u 25v4630uf 0.08ohm esr 4700u 16vAccording to the chart in the peak book, for this size/voltage cap, the ESR values are double (4700) or triple (6800) what is in the table.Is this anything to be concerned about? I am thinking of recapping some parts of the computer and was checking the drive to see if I should do it too. It does work though is squeaky - I need to find out how to lubricate it.

author: Miyuki
author_rank: Frequent Contributor
timestamp: November 13, 2020, 05:30:26 pm
content: Do they have any type or serial number?

author: alank2
author_rank: Super Contributor
timestamp: November 13, 2020, 06:56:58 pm
content: They are marked SU and they are blue. Mid 1980's for their age I'll bet.

author: bob91343
author_rank: Super Contributor
timestamp: November 13, 2020, 07:17:41 pm
content: Unless it's causing a problem, I wouldn't worry about it.

author: Vovk_Z
author_rank: Super Contributor
timestamp: November 13, 2020, 11:35:37 pm
content: Can you check your ESR meter with a really good one low-ESR cap?As for me, 0.10 and 0.08 R is a bit higher than it has to be for such large caps. But it depends on actual place characteristics too: if it is hot there, or if it is high-frequency or low-frequency, if it is easy to recap, etc.

author: Shock
author_rank: Super Contributor
timestamp: November 14, 2020, 02:52:06 am
content: If it's a keeper and was mine I'd give it a full service especially if there is leakage starting to show around those mains filter caps at either end.I'd probably clean the sockets, backup the rom, replace the thermal grease on the regulators, replace the electrolytic and tantalum capacitors, clean and lubricate the drive, clean the heads, calibrate it then stick it back on the shelf hahah.If you don't have a lot of experience you want to avoid messing around but if you have a few dollars to get decent caps and time to bond with it without doing damage I don't see the problem.

author: mariush
author_rank: Super Contributor
timestamp: November 14, 2020, 03:03:55 am
content: Quote from: alank2 on November 13, 2020, 05:23:16 pmThe chart in the peak manual is based on what typical MODERN series of capacitors are rated for.You have capacitors from the 80s or 90s or whenever that unit was manufactured. Back then they didn't have quite as good formulations for electrolytes which results in higher ESR compared to equivalent capacitors from modern series.You should desolder at least one lead of the capacitor to make sure that capacitor is not in parallel with other capacitors or resistors, which would affect the measurement - yes, you can measure in circuit, but the fineprint is "provided you know how to measure and be aware results won't be correct when other components are in parallel with the capacitor.If you do decide to recap, consider using older series of capacitors which now would not be considered to have very low ESR. I'm thinking series like Panasonic FC or Nichicon PW - as a food for thought, Nichicon PW 6800uF 25v has 0.014 ohm esr, and same for Panasonic FC 5600uF 25v, highest 25v rated in the series.Also, is there even a switching power supply powering the device, or is there a classic linear transformer power supply?If it's a classic linear transformer providing power, then the ESR of a capacitor is really not a big concern, it doesn't have to be very low.

author: Shock
author_rank: Super Contributor
timestamp: November 14, 2020, 06:37:39 am
content: Pretty sure they are all linear there is a large transformer under the PCB. Some models have an additional electrolytic or two. My concern would be damage from physical leakage or a shorted tantalum taking out a regulator.

author: kripton2035
author_rank: Super Contributor
timestamp: November 14, 2020, 07:12:37 am
content: +1 with Shock

author: Vovk_Z
author_rank: Super Contributor
timestamp: November 14, 2020, 10:28:08 am
content: Are they of an axial type? Then it is ok if they have a bit larger ESR.