ESR meter trap

>"It does not test for high leakage, being wrongly marked in the factory or installed backwards. "

I heard of lytics marked wrong. The shop that got them said they all blew up. Turs out when they paid a bit more attention the negative lead was longer than the positive lead.

I remember a very long time ago in a small Sony TV the rectifiers were marked backwards, and so was the board ! That was a fun one.

 

On Monday, 5 February 2018 10:57:40 UTC, jurb...@gmail.com wrote:

"It does not test for high leakage, being wrongly marked in the factory or installed backwards. "

I heard of lytics marked wrong. The shop that got them said they all blew up. Turs out when they paid a bit more attention the negative lead was longer than the positive lead.

I remember a very long time ago in a small Sony TV the rectifiers were marked backwards, and so was the board ! That was a fun one.

I once found a stuffing error I'd made many years before. A 16v lytic was in backwards on a 21v rail - had never caused any problem though.


NT

 

[Chuck]

On Sun, 4 Feb 2018 13:32:17 -0800 (PST), John-Del <ohger1s@gmail.com>
wrote:

On Sunday, February 4, 2018 at 2:29:53 PM UTC-5, Chuck wrote:
On Thu, 1 Feb 2018 00:00:24 -0800 (PST), Phil Allison
pallison49@gmail.com> wrote:


Hi,

few here would disagree that using an ESR meter is the fastest and surest way to find bad electros. If the meter reading is several times or more higher than normal, that electro must go.

This week, I saw a Fender tube amp with pretty obvious filter electro trouble that almost caught me trusting my (Bob Parker) ESR meter too much.

Under a steel cover were five, "IC" brand 22uF, 500V axial electros - from the symptoms I figured ones immediately following the rectifiers diodes must be bad. The ESR meter agreed, giving open ( >100ohms) ESR readings for two and good readings for the remaining three.

While extracting the bad pair from the PCB, I realised they were wired in parallel. The electros looked in good condition so my suspicions raised, I peeled back the case with nippers to loosen rubber bung and take peek inside.

Turned out there was NO metallic connection between the positive lead and the rest of the capacitor. The bung and lead stub simply fell off. I opened the other three and found two more in the same condition while the last was perfectly OK with all its connections in place.

The electros concerned are exactly like the ones in this pic:

http://www5.austlii.edu.au/au/legis/qld/consol_act/cc189994/s268.html

The ESR meter was fooled by the fact (except for one) the caps had NOT gone high ESR, but had suffered severe corrosion of the plus leads where they entered the cap roll.

I have to agree with the author of the linked page, Illinois Capacitors have produced a bad batch and full replacement is the only smart option.




.... Phil




Grass Valley fiber cards had +15 -15 V power supplies where the 220uf
axial caps checked good for ESR with the Bob Parker meter in circuit
but were faulty.


How did they check out of circuit with the Parker meter?

Bad.
Earlier in this thread I described a 33uf electro reading less than an ohm in circuit, and 350 ohms out of the circuit. The culprit was a surface mount 1uf film cap with an ESR of <1 ohm right if you can believe that across the 33uf fooling the ESR meter.

---
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus