Replacing electrolytic caps in a DC power supply - selecting the right ripple current

[tomcat101]

My turntable has developed ripple-like noise that is probably related to the DC power supply, or the motor control section, and likely caused by failure of one or more of the 30 year old electrolytic caps. (Found a post elsewhere that someone repaired their same model with Nichicon caps but no specifics.) I have sourced some caps at Digikey and was told to go with the caps with the lowest ripple current since this powers a high torque DC motor, but now I find this may not be right having read about heating problems etc. All I have are the uF, voltage and size of the caps that need replacing. They range from 470uF 40 volts (primary filters after rectifier - nearest test point is 15 volts) down to a 3uF 63 volt. Right now only replacing the polarized caps with aluminum electrolytics. The power input to the whole turntable is only 13 watts @ 120 AC, and the test points on DC board at various locations range from 10 volts at the motor, to 15 volts at the speed controls. All this suggests that maximum power in the circuit is maybe 10 watts, for a maximum current anywhere at 0.7 amps. Anybody have any clues about what caps I should use regarding ripple currents (RCs), etc specs.??!! I am currently looking at RCs of 370mA for the largest filtering caps and 17.4 mA for the smallest. Without some help, this is a Hail Mary on fixing a beautiful German built Thorens TD126 MKIII that is otherwise near mint and works flawlessly except for this blasted ripple noise when playing records. The strobe says the rpm is right on the money at 33, 45 and 78 rpm. The noise is low level but deadly, and being transmitted by the belt to the platter from the high torque DC motor, which is supposed to be getting about 10 volts according to the schematic. The source is certain because when you turn off the power to the turntable while playing a record, the music slows down, and the noise is gone. Any help on selecting the right caps would be greatly appreciated.

[budm]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

What is the ACV of secondary side winding Voltage of the transformer?
Good clear pictures?

[tomcat101]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

Sorry budm, no idea. The available schematic is very minimal on that aspect, showing almost exclusively the DC portion.

[paulstef]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

I don't understand why you would choose "lowest ripple current"?

In general the higher the ripple current carrying capability of the cap, the better, at least in SMPS. Decreases voltage transients/ripple in the circuit, keeps their temperature low and increases their lifespan.

I'm pretty sure just to get rid of the noise (I assume mains frequency hum?) almost any cap will improve your situation. I would choose any cap with the right uFs/voltage, lowest ESR, highest ripple current and longest specified operating hours I could find.

[tomcat101]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

Paulstef, I did not choose lowest ripple current (RC), Digikey reps did - they had a pow-wow regarding the details on DC PS I have provided above, and got it wrong I think. Before ordering, I wasn't sure and read up some more about overheating caps with wrong RC, and slow recharging rates if RC was too high, etc. Got confused and don't want to wreck the PCB and/or endlessly replacing caps. I believe the noise is caused by a failed electrolytic cap that is not sufficiently filtering the 4-diode rectifier at closest input (470 uf/40V), or down stream to the motor control section, or a failed diode in bridge. Latter is less likely of course. Your advice is in line with what I have been reading about the highest ripple current, so that gives me a lot more confidence. Mucho thanks. Will return to Digikeys vast cap selector grid and re-input uf/V values and see what I find. Do you suggest a specific manufacturer, or will Nichicon suffice.

[stj]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

high ripple, high temperature is what you need.
ESR is not so important on low frequency circuits.

something like panasonic NHG

got any foto's ?

[stj]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

I wasn't sure and read up some more about overheating caps with wrong RC, and slow recharging rates if RC was too high, etc. Got confused and don't want to wreck the PCB and/or endlessly replacing caps.

the charge/discharge rate is limited by the ESR, lower ESR = higher charge/discharge rate.
that's why you need low ESR on high frequency psu's
if the original caps are rated at 85' temperature then they are not low ESR.

[budm]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

ESR.
http://www.vintageshifi.com/repertoire-pdf/Thorens.php

[tomcat101]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

STJ, your response is in line with paulstef. This is really limiting my options - goody. Sorry for my lack of electronics. I am a Biochemist and like most of you guys, cannot "see" what I am doing most of the time. With electrons, it is orders of magnitude below the molecular level, and fast! At least you can see the circuit. Have attached a link to schematic. Hope it comes through.

http://www.hifi-manuals.com/Thorens/...-Mk3/downloads

[stj]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

downloads wont work for me,
can you download the schematic & service manual and then attache them here.

[budm]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

Service manual, not in English.

[mariushm]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

You won't need super special capacitors with very low esr or high ripple for this circuit. In fact, such high end electrolytics and polymers may affect the sound quality but in practice with regular ears and speakers.

Look for something good and cheap, 105c rated, 1-2000h, maybe series like Panasonic FC, FK, NHG even or Nichicon HD, HE, PW , united chemicon lxy, kze , Rubycon PX , ZL , ZLH ... these are common series of capacitors you can find at distributors like Digikey, Mouser, Farnell, TME.eu etc

Keep in mind that you can buy capacitors rated for higher voltages when you replace your existing ones, so for example a 470uF 40v could be replaced with a 470uF 63v.

[tomcat101]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

mariushm, cheap is not in my vocabulary when it comes to my music. Costly is the only thing that comes to mind. But I do not want to pay a fortune for repairs that I may be able to do myself. I have a lot of experience changing out parts from various lab instruments, but these are canibal activities that are obvious repairs.

I don't mind spending the dough, but all of the caps I have looked at so far are less the $1 each. I would gladly spend 10x this amount per cap to fix it, but I don't see this as possible since none of the options are that costly from anybody. Thanks for your input.

Anybody have an idea on my "problem" cap. I have to go with a 3.3 uF cap as the 3.0 is not available in limited quantities. The rule of +/- 20% variance should not be a problem with this cap I assume?, but hate making assumptions. Digikey rep told me this should not be an issue, but am beginning to question some of their notions, with good reason (see all of the above). Depends on rep of course. Someone at Newark told me it "has to be 3.0uF".......

This instrument looks like it just came out of a time machine after 30 years. Suspect it sat in the box after minimal use and has not seen a stray electron in all that time. Probably fragged some caps on first power up!

[stj]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

no, your right.
3.3 or 3.0 makes little difference.
the original is probablty atleast 25% less than that now anyway.

[tomcat101]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

thanks stj for that 3 uF correction. Love your facebook notion.

Also thanks to budm for posting the direct link to the schematics. My 85 year-old uncle almost lost his bowels when he saw that schematic. He could not believe that a "record player" had so much complexity in it. He is very old school. I had to tell him it is not a crank-up Victrola, but a true transcription turntable. But then he prefers to work on lawn mowers.......

[mariushm]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

tomcat, I meant cheap as in cheap compared to capacitor series designed for switching power supplies, series with very low esr, very long lifetime and so on. The series of capacitors I mentioned are not low quality, and the brands I mentioned are all premium ones, good quality and reliable.

Otherwise, there are plenty of other brands that have a less than stellar reputation like Samwha for example, that I could have suggested.

Another thing.. lots of audiophiles swear by some particular series of capacitors, Panasonic FC in particular. They think the specific type of electrolyte in such capacitor (which is different, not same chemical formula as the electrolyte in Panasonic FM or FR for example - fm and fr are low esr series) makes the sound more pleasing to the ear.

Personally, I don't think human ears are that trained and I don't think majority of people have such quality speakers and such good rooms to notice differences between capacitors.

But if you're into that, you should look into audio-grade series of capacitors like Nichicon FW, KA, KZ ... Digikey usually stocks some combinations of these.

Your circuit doesn't have lots of parts that heat up a lot, unlike the case of computer power supplies where capacitors are sitting very close to heatsinks. So, having a lifetime of 6000 to 9000 hours at 105c is really not something that would matter to your circuit, even a capacitor rated for 2000 hours @ 105c would last decades in your system.

[stj]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

Love your facebook notion..

too bad you didnt see me venting my opinion on "hashtags" the other day then!

[tomcat101]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

thanks for the clarification mariushm. I have always been a big fan of Panasonic, so I will certainly take your advice on those in my next search. I do know that the audio version is not critical in this applciation as the caps are not in the audio stream, but if they are "audio" grade, they are probably better than "general" anyway.

stj, I would be happy to have a deja vu all over again on hashtags here if you like. The market is sure hammering the hashtags out of them recently......

[stj]

Re: Replacing electrolytic caps in a DC power supply - selecting the right ripple cur

https://www.badcaps.net/forum/showpo...postcount=1143