EICO 950B Repair & Some Notes on Capacitor Testers 

I did the very same death cap mod to a Heathkit SG-8 and am satisfied that it is safe to use now ! Will do the same with my 950B next.

I happen to like a little cutesy b.s. once in a while.

Electrolytics will be marked with a polarity (+ and -). If you put them in backwards, they can fail very abruptly and vent out nasty smelling smoke. Non-electrolytics are non-polarized and can be connected either direction without hurting the capacitor. This is not to be confused with the "outside foil" marking, which denotes the lead that should be connected to the point closest to ground potential for the purpose of noise shielding.

You cannot heal a capacitor. Just change it!

denbydish Check the online owner's manual. I believe it addresses this. May be related to power factor.

For #3- The idea of discharging the capacitor before removing it from the tester is not a bad idea, but if the switch is only a momentary short and you leave the voltage turned up, then you will obviously short the power supply in the unit, never a good thing. If I remember right, the switch used in Heathkit capacitor testers they do not apply voltage until testing and short the cap before and afterwards, so just momentary contact for the testing. I'm thinking that a simple break before make switch would be the best. One position will make the normal connection to test the cap or reform an electrolytic cap, and the other position will disconnect the cap from the tester and discharge the cap without any chance of shorting the power supply. Honestly, most would just use an alligator jumper connected to one side of the cap and after disconnecting the cap from the tester, simply short the cap out. You could solder a resister in series with the alligators clips in the jumper just for this purpose. No mods to the tester.

Figured it out. Also I had to replace the 100k pot as well, the tiny wires inside were a mess and broken.

Anything 2 watt or greater would be fine. The main hing is that it must be wirewound and not carbon type.

Your time is greatly appreciated..

I use an X1/Y2 safety cap.

Tony, sorry about your name misspell above, a type "O" Anyhow, I have a Sencore TF 46 Cricket Tester that I bought off eBay and the seller claims that everything works, but that's not the Case. The Leakage does not work and I cannot perform a calibration on it. Can you do a tear-down repair on one of these? I have a service manual but for some reason it does not comply with the TF46... it shows components that are not in the meter and wrong numbering etc. Can you assist me? Thank You.

I haven't seen a Sencore cricket since the 1980's when I was working for an industrial electronics shop. They are for testing transistors and FET's. I don't have any info for them, but I remember them being pretty good for testing transistors "in circuit". Sorry I don't know much more than that about them.

Thanks anyway. Nice work you are doing... Keep it up.

Sencore LC-53

The precision caps were still like new, so I didn't have to replace them. They don't seem to go bad very often. They should be available from Digikey or one of the other big parts vendors if you need them.

xraytonyb thanks!

The potentiometers that they use in those are wierwound. If they get intermittent, a lot of times you can't fix them with deoxit. The only good solution I found was to replace them. I found suitable replacements at Elliot Electronic Supply in Tucs,AZ (Just do a search for them online). They only cost me around $10 and were rated for 5 watt instead of 2 and 4 that is originally used. After replacing them, it worked perfectly. Elliott was the only place I could find the 100K used in the leakage pot. As for the 10K for the scale, they are available in a lot of places. Just make sure you get wirewound and NOT carbon. Also, if the two electrolytic caps are leaky, they will trow off your readings. Good Luck!

ALL caps were replaced and all pots test good except the 100k voltage pot, I put in a NEW 5 watt from EBAY seller MARVAC+_2001 "NEW 100K Ohm 5 Watt Wire Wound, Long Shaft Potentiometer - Centralab WW104" I bought two of these from him NEW for $5 each.

xraytonyb I can't say thanks enough for finding these 100k 5 watt pots. I blew mine out three weeks ago and could not find one. I gave up looking and then saw your video. Like others I really like this cap checker. So I'm very happy to find a proper fix. thanks again. subbing you for sure!!!

Glad I could help! These are really great things to have on the bench. Hope you get yours up and runnung soon!

Just letting you know its up and running again. I bought trwo, one of the pots was very close to 100k, so I went with that one. I looked up old64goat's link but he doesn't have any right now. thanks again, glad to get it up and running again.

It causes a feedback loop. ESR increases heat and reduces it's ability to function at higher frequencies(leading to ripple), which causes damage to the capacitor, which causes the ESR to rise even more, and so on and so on. Capacitor death spiral. Some are worse than others at this. Aluminum and tantalum caps are pretty terrible. Ceramics are pretty much immune to the problem. They have microphonic issues and capacitance limitations though.

yes it increases heat, its not it self heat , its also caused by Parasitic resistance , and leakage , also some Caps have parasitic Charge , that is also a reason , some Caps are not discharged and eventually recharge by them selves to about 20% of initial charge , all kinds of stuff , you have indirect and direct causes as well , ESR would be direct there .

connect two 22 mfd @ 450 v in series it will give you 11 mfd at 900 v and will work just fine for replacement. i have the same model and that is what i done.

Jake Wells thanks, that’s what I ended up doing. I also swapped out the .01uf 400v caps with 103Ks and now it works great. Still might swap out P3 pot for voltage.

I have a heathkit C-3 version of this, which is almost identical (and has an 8uf cap) ...check DigiKey/Mouser, or worst case scenario you might have to venture into high end/crossover caps. Luckily enough 8uf is a fairly common value in vintage guitar amps ....actually there's 'Sprague Atom' 8uf/450V axial's at PartsConnexion ;)

Justradio.com. you cant go wrong!

I went to Just Radios website. Bought two 16uF 350V caps and put them in parallel . That gave me the 8uF at 700 Volts.

The unit uses a power transformer, which provides isolation from mains. Additionally, this isn't the type of test equipment that you connect "in-circuit" or to other test equipment. That said, if you wanted to install a grounded power cord, it wouldn't hurt anything.

The cap bleeds off very quickly. Regardless, all viewers should read and follow the disclaimer at the beginning of this video!

This really is a great video. I'm still watching it and I am going to change my cord to a polarized cord too. What is the purpose of not going to a 3 wire cord? Is it to keep the chassis ground isolated from the earth ground for safety?

Good question. The answer is really not what you would think. The main reason I didn't put a 3 prong plug was because it wouldn't fit through the opening on the back of the case! I didn't want to cut anything because this unit is almost new. In reality, it doesn't need a three prong. The power transformer provides isolation from the line. It does benefit from the polarized plug, just because of the line filter capacitor. If you don't have a polarized plug, you could possibly plug it in so that the hot side of the line is on the capacitor end. The small amount of current that gets through the capacitor would then be connected to the chassis. Touching the chassis and something grounded at the same time could possibly cause a mild shock through that capacitor. If the cap shorts out (unlikely because I'm using an X/Y safety cap), you could get a bad shock. That's why I use the polarized plug! (Long-winded answer!!!)

Okay, I finished the video and I have to say this truly is the most educational video I've seen on electronics and I watch a lot of them. I happen to be at the stage of wanting much better testing measuring abilities on caps because I work mostly on tube amps. So good timing for me. Great job and I look forward to watching your other ones.

solidstate90 ESR is acronym for "Equivalent Series Resistance." It is as if a resistor was in series with a perfect capacitor. It is not leakage. Probably best to understand passive devices can be thought of as perfect resistances, inductance, or capacitances. In actuality the geometrical, mechanical, chemical make-up impart them with other electrical characteristics. This is why the electrolytic capacitor seems out of circuit at the high frequencies. It's physical construction causes this. That's why there is a small paper or disc capacitor in parallel with the electrolytics in many devices. On filtering the line frequency ripple and transients in that frequency range. The other filtering at much higher RF frequencies.

Leakage would be like a resistance in parallel with the capacitor.

They're not polarized. The schematic and build manual is available here - elektrotanya.com/eico_950b_construction_manual.djvu/download.html

Hi Tony, Thanks for the Link... I have a couple question if you don't mind me asking. 1. I change all the caps and I am getting 368 Volts across C9. Is that normal? it blew the 250 volt cap I installed because the volts were too high. 2. My Eye tube is not lighting bright, I check the resistor and it reads 1 meg. Is it that the eye has gone bad and where can I get one to buy? 3. I think my rheostat 100K pot is bad. Can I use a normal 100K pot for a replacement? I would really like your help as you have some experience on this product. Thank you.

I'm not Tony but I'll answer, just tryin to help. 1. 368V across C9 is pretty high, should be around ~200V. I just rebuilt my Eico and it's reading 196V across C9. Check the resistor R8 - make sure it's 68k. 2. They sell eye tubes all over Ebay, maybe other places as well. Boosting the voltage to the eye tube will make it brighter also. Many people have done this to make an old eye tube brighter, the eye tube can easily handle 700-800V, but it might shorten it's life. 3.No, you need a wirewound linear 100k 5 watt pot. I found mine from here for $12 - www.elliottelectronicsupply.com/5-watt-wire-wound-potentiometer.html - it's the only place I've been able to find them.

Thanks Dacke, this helps a lot. The 68K is reading 76 K so I will change it and retest. Thanks again for the info.

Strange, I knew it would drift a bit but that's not off by much. Something else may be going on. Could be a issue with the eye tube. Check R10 also

@Nawlins EICO is Electronics Instrument COmpany from New York city. They made electronic test equipment in kits to be built by the user

@Nawlins didn’t ELCO make boats in the 40s?