Hi everyone,

I've got a couple questions I'm hoping to get some answers to. Here goes.

1. When replacing Electrolytic’s, specifically the can type what is the common method? In the past I have cut all wires or component leads at the terminals(disconnecting the old lytics completely, but leaving the can in place), connected the lytics to the proper lead/wire and then connected the ground leads together and soldered to the closest ground bus.

I have seen where the local repair shop has just replaced one lytic in a can by soldering the new lytic directly to the can terminal and then grounding the lead to the chassis. Without disconnecting anything from the original terminal.

So my question is which is the best way? I would think it would be best to remove the original lytic from the circuit altogether, but I'm definitely no expert on the subject.

2. What is the proper way to test a capacitor with a multimeter?

Thanks in advance for any help.

Disconnecting the original capacitor is definitely recommended. If the
original part has any leakage, leaving it in the circuit will ensure that
some heat is wasted through that leakage process. Eventually,
the original part could blow out and cause a lot of trouble.

There is not much you can do to test a capacitor with a multimeter.
You can connect it to the ohmmeter leads, and you would expect
a momentary low resistance reading, followed by a transition to infinity.
Any finite resistance measured under steady-state conditions would
indicate trouble. However, since the test voltage applied by a multimeter
is very low, you can get an infinite resistance reading even though the
capacitor would leak under actual operating conditions.

Some multimeter have a capacitance measuring function that is reliable
at least on non-electrolytic capacitors of moderately large capacitance.

An old fashioned capacitor tester in proper working condition is probably
the best thing to have when doing tube work. Good luck, all comments
welcome.

Always remove the old electrolytic from the circuit. As a quick repair, putting the new electrolytic in parallel with the old one _will_ work most of the time. But it's not a good idea. The only reason it can work, is that generally, as electrolytics age, they lose capacity. Paralleling the new cap to the old adds the capacity of a new cap with that of the old. But then there is still an old, dried up electrolytic in the circuit. It will continue to lose capacity, and can eventually fail shorted, or partially shorted - acting like a resistor. You're just asking for problems doing this. Disconnect the old cans. Wire new replacements under the chassis. Also, when possible, avoid replacing only one section of a can - yeah, the others may still be good, but for how much longer? One failed already. Also, it is possible (although unlikely) for a really bad cap to develop leakage between sections.

To test old paper capacitors using a multimeter, do the following. Note, that this only applies to the old wax/paper or molded paper capacitors (like the black stripey ones, or "MicaMold" paper caps) :

Disconnect the cap completely from the circuit.
Switch the meter to the resistance scale, and hold the probes, one in each hand.
Balance the old capacitor across the two probes.
Hold the probes over a garbage can.
Move the probes apart until the capacitor falls.
If it makes a <clunk!> noise as it hits the garbage can, or any variation thereof, it's bad.

<grin>

But seriously, a multimeter won't be of a whole lot of help, because you really need to test the capacitor under working voltage. Even newer meters with cap checking functions only supply a tiny voltage/current, and bad caps won't always show leakage this way. You need something like an old style HeathKit Cap Checker that can supply full working voltage to the capacitor under test.

-Ian

Thanks guys, that was just the info I was looking for.

http://www.audiokarma.org/forums/attachment.php?attachmentid=21058&d=1153513191

My Heathkit Condenser Checker, circa 1949. Has never let me down. Costs a few dollars max on ePay or hamfest or junk shop. Had to re-cap mine first of course. Works great afterwards.

Tests caps at operating voltage and current. Just don't forget it, grabbing the test probes like you're used to doing with a multimeter will numb your whole arm (or worse). Don't ask me how I know that.

Multimeter trick will probably tell you if the cap is completely shorted or completely open, but that's about it. You can identify a bad cap that way but you can't guarantee a good one.

When multi-can electrolytics fail, not only do they leak or go open per section, but very often they short between each section too. Catastrophic results. Always take them out of circuit.

The reason I was asking about checking caps is that I would like to do some diagnostics before doing a total re-cap. I'm in the infant stages of learning repair and would like to be able to pin point a problem area.

Example, I'm working on a 1948 Admiral Tripple Thrill that has Verticle shrink, all tubes test good. I think the problem is in a cap. But I'm not sure which one.

My plan is to do a total re-cap anyway but would like to expand my diagnostic worth. Although it seems to be that if you have to disconnect a cap from the circuit inorder to check it you might as well replace it.

The most common area to have problems on most any old tv will be the verticle circuit. Everything has to function just right to have a full and correct raster. You can be certain you have a bad cap right now. If you just want to play around, and not do the wholesale recap just yet, find the vertical circuit and seek out the caps, then replace them one by one until the problem goes away. The first old set I brought back to life was a '50 Philco and I had little in the way of experience, plus no schematic. So, I turned the chassis over, noted the location of the vert. osc, then followed wired from the vert. hold and lin controls, and looked at what was there. I found a number of caps. With each replacement I saw the picture improve. This is one way to learn as you do it.

Lots of shops have done the "leave in circuit" shortcut. Maybe some of them don't know better. Best, I think, to install a terminal strip near the base of the can and then just transfer everything over.

Like has been said:

1. Disconnect the old cap and leave it physically attached to the chassis. Leaving the old cap in circuit is just asking for trouble sooner or later. I still run into a few modern TV's where the "technician" just bridged an electrolytic cap across the underside of the PC board, leaving the old cap in place.

2. Always replace all sections of multi-section caps even if the other sections are good. I found this out the hard way on a 19" GE solid state B&W and a 19" solid state Sylvania color TV. Both times, the set worked for about a week and then another section of the can went bye-bye. Even though it means more work, I now always change the entire cap.

3. I'll agree that those old style cap testers from 50 years ago are the best way to actually test a cap at rated working voltage. Well, the BEST test for a cap is a new cap.

4. I'm now to the point where I change all paper caps and the cardboard tube electrolytics. I'll sometimes let the can caps slide, depending on how new the equipment is and if the old cap runs warm or not.

Lots of shops have done the "leave in circuit" shortcut. Maybe some of them don't know better. Best, I think, to install a terminal strip near the base of the can and then just transfer everything over.

Another possibility is to gut out the old cap, and hide the new caps inside it. AFAIK, the electroytic chemicals are not super poisionous or cargogenic, but avoid eating the stuff anyway.

If you want to practice diagnostics, please replace all of the electrolytic capacitors first.

In a 1948 TV, there is zero chance that the electrolytics will be safe and reliable for long-term use, even if they seem to sort-of work at the moment.

If you burn up an "unobtainium" power transformer when an electrolytic goes out, you will be very, very sorry (been there, done that).

Once the electrolytics have been replaced, you can replace the paper caps one at a time, powering the TV back up after each replacement and noting any changes. Hey, now the picture is not so jittery. Now the vertical or horizontal control locks in better. It's easier to adjust the picture size to fill the screen. And so on.

In some projects, I have taken notes during the process, and marked each replacement on the schematic with a highlighter or pencil.

There are a number of vintage TV service books that will be helpful. I have a handful of them -- Mandl's Television Servicing from 1952, various Coyne books, etc. They explain a lot of theory, since they were written for radio servicemen who were learning about that new-fangled TV thing, people who learned radio while serving in WWII, and so on. Look on eBay for such books -- they're usually cheap.

Whether to install new electrolytics under the chassis or "restuff" the old cans with new caps is often a matter of taste, although some times the available space forces you to restuff the old can. This article has more info on that topic:

http://www.antiqueradio.org/RCA630TSTelevision.htm

Have fun!

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

When I "did" my RCA CTC-4 last year, I removed all electrolytics from the circuits, leaving the original cans on top of the chassis for the sake of appearance. I did not re-stuff them. The next steward of the TV can do so if he/she chooses. All other caps, paper and 'lytic, were removed from the chassis and replaced with new caps. Likewise the VT-71 J in the collection.
I also, years ago, left an old cap connected when a new one was soldered in. There was a fuse in the line that saved the power xfmr when the original cap shorted.

When possible, I leave the cans disconnected and hide the replacements. Sometimes, this is not possible. I have restuffed some cans due to lack of space. In some cases, I had to eliminate the can completely because the replacements wold not fit inside. On one set I did, I cut the can off and reused the terminal lugs, hiding the new ones underneath.

Some portables are a lot easier. In most cases, I left the cans in place and hid the new lytics in convenient places. Eliminating selenium rectifiers can help too. Hope this helps.

Eliminating selenium rectifiers can help too

Ok, great information so far, thanks to everyone for the advice.

This brings me to the next question and that is, How do you replace a Selenium Rectifier? How do you choose the proper diode and how is the new diode wired?

The only info the Sams Photofact give me is Current rating .32MA

Can I replace all Selenium Rectifiers with the 1N4007? Is it that simple?