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  #16  
Old 03-04-2007, 03:43 PM
peverett peverett is offline
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I only work on equipment that I own, as I do not have time for anything else. However, even with my equipment, I take Andy's and ChuckA's approach on any equipment made prior to 1960. Replace all paper and electrolytic caps!

I once left a paper cap in an TV agc circuit that had all of 4 volts on it. The TV it was in began to overload as if the AGC was not working properly. Guess what-it was that cap. I have also tried "Reforming" electronics as some have recommended only to have to replace them in a short time due to re-appearing power supply filtering hum, etc.

Trying to a few dollars by leaving old paper or electrolytic capacitors in place is not worth the hassle.
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  #17  
Old 03-04-2007, 10:26 PM
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Phil Nelson Phil Nelson is offline
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I will just chime in and agree with those who replace all paper and electrolytic caps.

All it takes is toasting one expensive power transformer (raises his hand -- yes, I did that), or having to haul a "restored" set back onto the workbench a second time (raises hand again).

As Chuck said, once I am done working on a set, I don't want to see it again for a long time. Other parts can and do fail, but not half as often as cruddy old caps that you leave in place.

Phil Nelson
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  #18  
Old 03-05-2007, 09:31 AM
radotvguy radotvguy is offline
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Well , i am no pro at tv restoration . I mostly did radios for the longest time , but i just started getting into old tvs recently becuase it kinda interesting and fun . Anyway , as far as replacing capacitors , well i had a old magnavox that a friend of mine did a complete restoration on and basically , he recapped the whole tv and i must say it works fantastic . Its been going for 8 months now strong , with no problems or issues . It plays just as nice as it was when my parents bought it new in 1966 . So i have to say recapping a old tv seems to be the most practical thing to do . Capacitors are not expensive either . But thats my opinion .
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  #19  
Old 03-05-2007, 03:29 PM
radotvguy radotvguy is offline
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restorations

Well , i must say i am not a expert at restoring old tvs . I actually just started repairing some of my own stuff . Up until a few months back , i mainly just fooled with radios . However , a friend of mine,last year , restored a magnavox color console my folks bought brand new back in 1966 . He recapped the whole set , replaced any bad resisters, tubes etc . And like i said i am not a expert but i use this tv on a regular basis and it never gives me any trouble whatsever , nor does it even seem to need adjusting. It plays like the day it came home from the store when it was new . So i could agree with the guys who say a old set should be recapped.
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  #20  
Old 03-06-2007, 05:38 AM
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jshorva65 jshorva65 is offline
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I strongly prefer to presume paper capacitors to be unreliable and replace them, however, limited bench space and an aversion to leaving open chassis strewn about the house and shop tends to cause me to "button up" some of my own gear and set it aside to focus on items that customers have sent. My own collection has well-hidden protective devices installed and re-formed electrolytics and each unit will be recapped as time and space permit. Electrolytics, however, are sealed units which can be tested reliably and any such units which can be re-formed to within the often-cited maximum leakage specification of 1/5(sqrt(C*V)) microamperes I prefer to leave in place rather than hanging modern electrolytics underneath the chassis when the original cans are working. I am, however, working on the development of an efficient way of re-stuffing the cans with modern capacitors so as to avoid the need for re-engineering sets to make room for modern electrolytics under the chassis. There are multiple considerations in developing this method, among them is providing terminal lugs on the bottom of the re-stuffed capacitor cans which have mechanical strength to allow them to be used as tie points for other components as was often done in the sets' original layouts. The first few cans I have opened by loosening the crimp along the circumference of their bases often suffer damage to the phenolic wafers which supported the terminal lugs during heating to loosen the insides of the units. I'm working on resolving this issue by practicing on a box of "junk" cans that I have saved.

My aversion to leaving sets open was especially strong when a former live-in girlfriend insisted on her four cats being allowed to have the run of the house and not be chastised for or deterred in any way from climbing on anything, including computer, audio, video, or any other electronics in the house. Aside from her refusing to work, contribute toward expenses, or to share household responsibilities as we had agreed, occasional damage to equipment and the impossibility of playing my extensive collection of vinyl without fear of the turntable being disturbed while operating were among the many reasons for my ending that relationship.

As an aside, my ex eventually did ease up on insisting that the cats not be chasised for climbing on electronic items after I told her of a technical support call to a satellite television service that I had heard about. According to the agent who took the call, it began with the customer stating that, until an hour ago, he HAD a satellite receiver and he HAD a cat. It seems the late feline made the fatal choice of "marking" the receiver as part of his territory, hitting the unit's AC power supply and thus electrocuting himself and blowing out the receiver. After I warned her of the risks to the cats' safety by their being allowed to climb on live electrical equipment, she decided that chastising them was better than risking that they might suffer the same fate as that satellite customer's unfortunate pet.

One of the cats hacked up a hairball on my workbench at one point. Fortunately, there was nothing sitting open on the bench at the time and no paperwork sitting out to possibly be destroyed. The carelessness of other family members and a sibling who once fired 6 or more shots from an air rifle into the laminated safety glass on a nice '68 Zenith B/W portable's 12" CRT taught me to not leave equipment out in the open. My "kid" brother and a friend of his were trying to see if they could get that CRT to implode while I was out on a date with one of a series of girlfriends during my teen years. Of course, beating the crap out of him for it wasn't an option. A few years later, when he asked me to "cover" for him while he cheated on a girlfriend of his, I got even by making sure he got caught. lol The "other woman" dumped him, and the "steady" girlfriend kept him on a short leash for a while. Didn't really do anything to get him caught other than a crummy job of discouraging the "steady" from showing up at the house while the other girl was there. Got even for that shot-up picture tube.
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  #21  
Old 03-06-2007, 09:50 AM
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Pete Deksnis Pete Deksnis is offline
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both sides...

Quote:
Originally Posted by jshorva65
Electrolytics, however, are sealed units which can be tested reliably and any such units which can be re-formed to within the often-cited maximum leakage specification of 1/5(sqrt(C*V)) microamperes I prefer to leave in place rather than hanging modern electrolytics underneath the chassis when the original cans are working.
I agree and get a warm fuzzy when the original electrolytics are doing their thing in a power supply (I tend to replace those used elsewhere), but the first time I grabbed a hot metal can tended to temper my opinion.

However, in my current operational CT-100 both the 200 uF, 250V doubler circuit electrolytics are still doing a fine job after 53 years . All the rest are new and hidden away, at least hidden away under the chassis. It's my compromise.
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  #22  
Old 03-06-2007, 12:52 PM
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jshorva65 jshorva65 is offline
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It's a shame that A.G. Tannenbaum doesn't have that massive list of NOS twist-lock and other electrolytics posted anymore. They were a great resource and the format of that list made it a fantastic reference tool. They even gladly exchanged any that I couldn't get to re-form to that 1/5(sqrt(C*V)) specification on all sections, and there was only ONE of the many I had bought from them that I ever needed to exchange. I almost went through a week of mourning over their site having done away with that list. Talk about an amazing Mallory/Sprague/CDE/WE cross-reference, that site was great and right on the Web. It was a huge disappointment to click the link in the Vendors subcategory of my Favorites and get a "Not Found" error.
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  #23  
Old 03-06-2007, 10:04 PM
peverett peverett is offline
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As stated before, I have had very poor experience with "reformed" capacitors lasting. They had low hum just after re-forming, but it soon returned. For this reason (and to prevent expensive power transformers from being damaged), I always replace these.

I do leave the originals in place for cosmetic reasons in some cases. Disconnected, of course.
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  #24  
Old 03-06-2007, 11:42 PM
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jshorva65 jshorva65 is offline
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In a well-designed circuit, only about 2/3 to 3/4 of rated working voltage is actually applied across any electrolytic capacitor. With re-forming to the stated maximum leakage specification, actual operating DC leakage current will be far below maximum permissible. I have had excellent results, even with equipment which is kept in the less than ideal environment of my basement workshop. Variations in temperature and humidity are the main reason my 547 requires maintenance every 3 years and why I perform maintenance at 2 year intervals.

I provide additional overload protection to prevent marginal performance from becoming catastrophic chain-reactions, and I've seen far more cases where catastrophic failures resulted from well-meaning attempts to re-engineer component layouts to make components which did not meet one or more of the original selection criteria of the original part fit than from any other cause. As stated, though, I am working toward a solution to the shortcomings of restuffing cans. I have, however, had very good results with properly tested and re-formed original and/or NOS units. Being bitten by an unexpectedly "live" can often results in accidental damage to internal components due to involuntary recoil from the shock. This is yet another reason why I minimize re-engineering. I suppose a reasonable compromise when re-engineering would be to wrap all exposed cans with a single thickness of PVC tape to minimize shock hazard from a "floating" can.

I've worked on sets where a recoil from a shock had snapped tuning slugs and/or toppled and destroyed IF transformers. The all-time worst case of "permanent display piece" I have ever seen was, unfortunately, a very rare early color chassis whose owner had re-engineered one too many stages in the process of recapping (flyback toasted, IF transformers wrecked, severe instability in the few circuits that hadn't cooked). Failure to do a basic preliminary inspection is another catastrophe waiting to happen, as another unfortunate customer's listening test on a just-acquired vintage stereo receiver ended with a small fire under the power transformer, preventable had he merely checked to make sure that the fuseholder on the rear panel had not been bypassed before powering up. That unit was eventually restored to working order, but not without a costly transformer transplant.

Not at all advocating the careless handling of "unobtainium" here, merely pointing out that selection criteria other than just capacitance, working voltage, and leakage current are involved and there are potential trade-offs involved in re-engineering which require some careful consideration. Your mileage may vary.
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  #25  
Old 03-07-2007, 11:39 AM
andy andy is offline
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---

Last edited by andy; 12-07-2021 at 02:14 PM.
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  #26  
Old 03-08-2007, 07:20 AM
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jshorva65 jshorva65 is offline
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Testing ESR without an expensive ESR meter ...

Regarding ESR testing, the actual test is accomplished by applying a low amplitude AC signal across the capacitor under test and measuring amplitude across the capacitor. Expensive ESR testers use a sinewave signal, but squarewave will also work. Here is a link to a DIY test adaptor for checking ESR with a scope or a DMM with an AC 200mV or 300mV range available. http://octopus.freeyellow.com/99.html. The circuit is simple and powered by an ordinary 9V battery. The author begins with a simplified version based on a hex inverter I.C. and does an excellent job of explaining the operating principle and the limitations of the simplified version before going on to provide a schematic, parts list, description, and operating instructions for the improved final version. By using a dual trace scope and applying the direct output to the other input, direct comparison of the two waveforms on the scope screen is possible. Paper capacitors should be replaced ASAP when restoring a vintage set to working order, but electrolytics with sufficiently low ESR, low leakage, and capacitance within factory-specified tolerance may be left in place once properly tested and re-formed and will thus minimize the need for re-engineering and the potential danger of replacing a superior part which has survived 50 or more years with a modern part whose reliability may be questionable due to cheap construction.

I will be constructing one of these for evaluation and will post my findings here.

Doesn't the fact that the vast majority of these sets that have been spared from ending up in landfills can be brought back to life once they find their way into the hands of those such as ourselves who care enough about preserving them to make the effort factor into the reason why we love them so much? Restoration would not be possible at all had the vast majority of these sets not been so well-enginnered and well-constructed in the first place.

"Time Capsules" were one of those 70s phenomena that I seem to remember, where items from the era were stored away to be reopened decades later. I challenge someone with the means to do so to arrange for a suitable restored and known-working vintage set, metered Variac, sealed bag of new "Orange Drop" caps, restored B&K TV Analyst, modern cheapie TV, DVD player, test pattern DVD, service literature and instructions to be sealed away to be reopened in perhaps 50 years just to see which set still works.
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  #27  
Old 03-08-2007, 07:11 PM
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Chad Hauris Chad Hauris is offline
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I don't think the ESR meter we have was too expensive...it's nice to have a factory made pre-calibrated unit. It has really proved useful especially in solid state equipment.
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  #28  
Old 03-28-2007, 05:18 PM
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Chimes Chimes is offline
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I don't understand the reluctance to replace old electrolytics. Reforming is a gamble at best. New electrolytics don't cost much, certainly much less than a new power transformer. As the old cap would say, "replace me now or replace me later (and maybe along with some other component I took out)". If you can't stand the look of new caps under the chassis, then re-stuff the cans.
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  #29  
Old 03-28-2007, 08:26 PM
peverett peverett is offline
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I do not understand the reluctance either. I am just now working on a 1967 Motorola B&W TV, a hybrid set. I replaced a resistor in the AGC section and the set began working. However, I noticed after one hour of playing time, the horizontal would begin shrinking. I checked and the low voltage supply was falling. Then I noticed the filter cap was ever so slightly warm.

Replaced filters-problem fixed. Another example of what these old electrolytics will do if not replaced. Other caps are mylar, etc. These are still in the set.
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  #30  
Old 03-29-2007, 07:57 AM
radotvguy radotvguy is offline
mike g
 
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b & k analyst

I just purchashed one of those B&K analyst units . I am kinda new to tv repairs however i must say its a really nice piece of equipment and it has a lot of functions. Mine its pretty much all original with all test leads and original manuel . Its appears to have all original electrolytic caps still inside . Should i change them ???? I cant wait to learn how to use this . I have seen these unit but never had one before .
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