ESR meter trap

Hi,

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

This week, I saw a Fender tube amp with pretty obvious filter electro troub le 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 mus t be bad. The ESR meter agreed, giving open ( >100ohms) ESR readings for tw o and good readings for the remaining three.

While extracting the bad pair from the PCB, I realised they were wired in p arallel. The electros looked in good condition so my suspicions raised, I p eeled 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 t he 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:

formatting link

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 e ntered the cap roll.

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

.... Phil

Reply to
Phil Allison
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** Ooops - wrong link !!!

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

formatting link

.... Phil

Reply to
Phil Allison

Actually the ESR meter was correct. The effective series resistance was provided by the gap in the wiring.

Reply to
jurb6006

way to find bad electros.

Handy. Yes. Useful. Yes.

Surest? No.

Just replaced a surface mount 33uf/25v on an LG sustain EBR31872801 board w hich had image persistence issues and rash. The board would show improve i n operation with heat added to the board. Because of the amount of sm elec tros on the board, I used my ESR meter with tweezer probes as removal of su rface mount electros for testing is not practical. C49 33uf/25v checked abo ut a half ohm in circuit so I moved on. The rest of the sm electros on the board checked fine as well. After I found the problem with the scope, I tes ted the defective cap for s**ts and giggles and it read good value but >300 ohms ESR out of circuit. Before installing the replacement cap, I took an ESR reading of the empty lands and it read half an ohm. The only other cap parallel to it is C43, a 1uf surface mount film cap with an ESR of ...... . 0.5 ohms.

Reply to
John-Del

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:

formatting link

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

***********************************************

I had a Fender Hotrod Deluxe in a couple of months ago with an identical problem. All 3 of the 22uF caps were leaking and measured bad ESR.

The 47uF were fine.

I figured at the time it must have been a faulty batch of IC capacitors. They weren't THAT old, and ALL of them suffered the same fate.

This amp was motorboating like crazy, but only on the distortion channel.

Gareth.

Reply to
Gareth Magennis

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:

formatting link

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

***********************************************

I had a Fender Hotrod Deluxe in a couple of months ago with an identical problem. All 3 of the 22uF caps were leaking and measured bad ESR.

The 47uF were fine.

I figured at the time it must have been a faulty batch of IC capacitors. They weren't THAT old, and ALL of them suffered the same fate.

This amp was motorboating like crazy, but only on the distortion channel.

Gareth.

********************************

Maybe there is a polarity difference between clean and distortion channels, haven't checked.

Gareth.

Reply to
Gareth Magennis

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** Like this one ?

formatting link

FYI:

My service notes show that the same Fender amp was here in July last year, with no external signs of trouble with any electros.

.... Phil

Reply to
Phil Allison

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** Like this one ?

formatting link

************************************

Identical!

Gareth.

Reply to
Gareth Magennis

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.

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Reply to
Chuck

t way to find bad electros. If the meter reading is several times or more h igher than normal, that electro must go.

ouble that almost caught me trusting my (Bob Parker) ESR meter too much.

om 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.

n 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 ins ide.

d the rest of the capacitor. The bung and lead stub simply fell off. I open ed the other three and found two more in the same condition while the last was perfectly OK with all its connections in place.

one high ESR, but had suffered severe corrosion of the plus leads where the y entered the cap roll.

have produced a bad batch and full replacement is the only smart option.

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

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 mou nt 1uf film cap with an ESR of

Reply to
John-Del

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** How uninformative.

Bob's meter tests ESR, far and away the most common, age related failure mode of electro caps.

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

.... Phil

Reply to
Phil Allison

al caps checked good for ESR with the Bob Parker meter in circuit but were faulty. "

this can happen if there arew good caps in parallel with the one under test . Like the supply itself might have a 220uF, but there could be a bunch of

1 uFs across the vcc/Vdd of a few ICs which will make it read good in circu it.

Same with banks of lytics. i have found that on many powwer supplies you ol y have to bridge one in a bank to test the unit. this is from the TV days w hen we got in a TV that is dead, to put a bunch of caps in the PS oly to fi nd it has screen or Tco problems and is not worth repairing. So I started j ust taking out one and putting one cap in its place, and I didn't even cut the leads, I let it stand up. I had a stash of caps at the bench for this p urpose and saved some money, which of course was part of my job, we weren't wasting a bunch of caps anymore. Once you cut the leads it is alot harder to install on a sometimes overcrowded PC board.

Same thing applies to computer motherboards. just one will get it to work. They use alot of them because of ESR, ESL and ripple current. they might ha ve five of them in there adding up to 10,000 uF, but a single 1,000 will ge t it working temporarily. One time I did that and it turns out the problem corrupted the BIOS and the system did "hang permanently" in the lingo of th e manufacturer.

Everything is so cheap now servicing is all about saving money. People don' t care because you can get a new one so cheap, and they don't care that the quality is even worse. Some do, or are comfortable with their old equipmen t. People who finally learned the whole menu on their TV or whatever, or ha ve older high end stereo equipment. Even then you can't waste money without good reason. Some people want ten buck caps and all thin film resistors i n the audio path, change them all. But they are willing to pay, the average sheeple is not.

And those cap values in uF are not that critical. And contrary to popular b elief it is NOT good to up the voltage rating. the parameter that really ma tter are theesr and ripple current cpacity. You really think am SMPS runnin g at 100 KHz needs 10,000 uF worht of filtering ? Shit, 10 uF will do it if it can handle the ripple current and has low ESR. and the two go hand in h and. higher ESR causes an AC voltage drop which produces heat by actual pow er dissipation in the cap. That destroys it prematurely. they got it timed so it lasts through the warranty, and they hope not much longer. Only a few companies build everything so if you need to buy a new one they benefit an yway.

That is one of the main reasons I do not fix TVs anymore. Actually most new er equipment, f*ck it. Built cheap and specifically hard to service. I got tired of fighting it. And they are winning beause they REALLY control the p arts ow. You can get two TVs the same model and there could be five differe nt variations on the chassis, and almost none of the parts are interchangea ble. And then there is alot of software and firmware that gets corrupted, a nd bad caps can cause that.

Reply to
jurb6006

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.

Reply to
jurb6006

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

Reply to
tabbypurr

Bad.

Reply to
Chuck

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