Resistor behavior

laatsch55 said:
Why are they prone to failure Joe??
Click to expand...

If I remember right......

#1 failure mode is high leakage or shorting.
#2 High ESR.
#3 Open or low cap value.

I kinda remember failures caused by ripple or noise riding on a DC voltage which basically exceeded the voltage rating of the cap. The caps would physically blow apart in some conditions.

Robert
 
Why are they prone to failure? Often its from heat cycling, even when its within its perscribed operating temp. range.
 
Went through those bassids like candy, notorious for shorting out and crowbar-ing power supplies in the old nav test station.

Replace it with what you have... can't hurt.
 
Used them for supply Pi filters, because they can handle reverse voltages better than electrolytics and for little else.
 
They are unreliable because they are unreliable. This is the primary bulk filter for that oscillator. If you replace it with an aluminum, use a very low ESR type or you will see that oscillator noise elsewhere in your deck. Not a general purpose aluminum type
 
Needed some shrink tube so drove "into town" to get some. I should know better than to do that mid morning on a Saturday. An hour and a half round trip turned into 4.

Before I left I did some reading about tantalum capacitors and it would appear a new-ish generation of ceramics (monolithic) have replaced or can replace them. i got some of those (10uF 50V) and some tantalum's again plus some 100V and 160V 10uF electrolytics. During my morning "research" I read that ESR gets lower in electrolytic's as voltage gets higher.

I am strongly inclined to use the monolithic ceramic - non polarized though it is. Do you guys concur?
 
62vauxhall said:
Needed some shrink tube so drove "into town" to get some. I should know better than to do that mid morning on a Saturday. An hour and a half round trip turned into 4.

Before I left I did some reading about tantalum capacitors and it would appear a new-ish generation of ceramics (monolithic) have replaced or can replace them. i got some of those (10uF 50V) and some tantalum's again plus some 100V and 160V 10uF electrolytics. During my morning "research" I read that ESR gets lower in electrolytic's as voltage gets higher.

I am strongly inclined to use the monolithic ceramic - non polarized though it is. Do you guys concur?
Click to expand...

Yes
 
Well, encouragement so far. Put in that ceramic monolithic and resistor R27 stayed cool to the touch so thanks to one and all.

Still blows me away that I looked for a C29 on the board so many times and overlooked it each and every one. Preconception, assumption, whatever - it never occurred to me that 25V 10uF could mean anything but an electrolytic.

With any luck, I will be able to solder all those wires back onto the board without incident. But the fun part will be looking for the fasteners I removed three years ago and when found, remembering how it went back together.

Regarding that earlier photo I inserted of the tantalum saying it was green but looked black, turned out it was neither. It was actually blue - once.

IMG_3435.jpg

Damn camera - won't properly shoot Macro anymore. Time to start looking for another $20 Craigslist Special.
 
62vauxhall said:
Well, encouragement so far. Put in that ceramic monolithic and resistor R27 stayed cool to the touch so thanks to one and all.

Still blows me away that I looked for a C29 on the board so many times and overlooked it each and every one. Preconception, assumption, whatever - it never occurred to me that 25V 10uF could mean anything but an electrolytic.

With any luck, I will be able to solder all those wires back onto the board without incident. But the fun part will be looking for the fasteners I removed three years ago and when found, remembering how it went back together.

Regarding that earlier photo I inserted of the tantalum saying it was green but looked black, turned out it was neither. It was actually blue - once.

View attachment 30269

Damn camera - won't properly shoot Macro anymore. Time to start looking for another $20 Craigslist Special.
Click to expand...

is that the only dingleberry in the deck? If there are more, you might as well get them replaced while you are in there. 24V on a 25V cap is never a good design idea from a reliability perspective.
 
Gepetto said:
is that the only dingleberry in the deck? If there are more, you might as well get them replaced while you are in there. 24V on a 25V cap is never a good design idea from a reliability perspective.
Click to expand...

Well, that high was short lived but good point.

No more on this particular board but reviewing the parts list, there are some scattered around elsewhere.

*2 on what's called Amplifier A board - 16V 10uF
*2 on what's called Amplifier B board - 35V 0.15uF
*2 each on Dolby B Encode & Decode sections 16V 10uF.

So far, I've been able to identify Amp A & B and they don't look too terribly hard to dislodge. Maybe with them out of the way, the Dolby board(S) will become evident.

So back to the parts store on Monday and the tribulations continue.
 
I did not know there was such a thing as a brick & mortar electronic parts store these days.
 
Bradrock said:
I did not know there was such a thing as a brick & mortar electronic parts store these days.
Click to expand...

Yes, scarce indeed.

When I started frequenting them, there were four I used to hit. One went all gung-ho with metal detectors and prospecting so now a waste of my time. Another went heavy into A/V hardware, 3D printers, kits, etc. but never have what I want and the poor few semi-conductors they sell is limited to NTE.

The longest standing one was in business since 1971/72 but shut down for good a few months ago. A lot of people got speaker foams there and I bought lots of belts, bulbs and long obsolete things they still had on hand. They also had thousands of tubes and a couple of good ol' drugstore tube testers for customers to use. A grandfather started the business and his son and grand-sons were the staff. Then he died and not long after, his son. The grand kids and their mom decided to shut it down for their own reasons.

The fourth is one that opened in the late 1970's. Until fairly recently I never bought a lot there, preferring instead the one that recently closed. But within the last two years, they expanded, moved to a nicer, larger store and have gotten a hell of a lot busier. Although it is a Chinese family who runs it and consequently sell mostly stuff sourced in Asia, I've never had any complaints about what I've bought there - no counterfeits that I've heard of. I don't think they'd risk their reputation. There's a really good selection of parts, chemicals, hardware, supplies etc. and I've even had special orders made for a few transistors. When I need stuff I go there first but if I come away dry or mostly dry, I use the online usual's.

I will miss those bulbs, belts and foams though.
 
You must log in or register to reply here.
Back
Top