Help replacing Rifa capacitors in old Luxor turntable - Page 1
Forum section: electronics / beginners

author: tohtorizorro
author_rank: Contributor
timestamp: November 01, 2024, 12:12:21 pm
content: Hi!I'm restoring an old Luxor combo stereo unit and spotted two Rifa capacitors on the record player that need replacement. I couldn’t find any safety capacitors with matching values in my own part bins so I'd like to better understand the function of the caps in order to ultimately know if other capacitance values could be used.To my understanding the capacitor in parallel with the on/off switch is used to suppress inrush current but have no idea how a fitting value should be determined and the other one between red & blue wires is a total mystery. My knowledge of AC motors is quite limited but I'd really like to get an idea how the motor and speed switching work. See attachments for photos and circuit diagram.PS. What does the symbol with a horizontal line and a dashed one below it mean in the context of capacitor voltage rating? The larger cap has the marking after "630V", see the attached photos.Thanks in advance!

author: Haenk
author_rank: Super Contributor
timestamp: November 01, 2024, 02:17:38 pm
content: (Y/X recommendation removed), PME261 across motor might be better

author: themadhippy
author_rank: Super Contributor
timestamp: November 01, 2024, 02:47:58 pm
content: QuoteDC ,so 630v dc

author: wraper
author_rank: Unknown
timestamp: November 01, 2024, 03:00:09 pm
content: Use ceramic Y2 or Y1 safety capacitors instead of 4700pF, or one rated for 1000V or more, can use polypropylene capacitor too. 630V DC polypropylene for 68n replacement.

author: tohtorizorro
author_rank: Contributor
timestamp: November 01, 2024, 09:07:42 pm
content: Thanks all!I've spent too much time with this thing already and would just like to get rid of it ASAP but can't leave those caps in place. Wouldn't want to pay 20€ shipping costs for a pair of caps but the lowest capacitance X/Y caps I've got are 100nF. Maybe two of them in series could replace the 68nF ?

author: srb1954
author_rank: Super Contributor
timestamp: November 02, 2024, 01:45:56 am
content: Quote from: tohtorizorro on November 01, 2024, 09:07:42 pmUse 3 x 100nF capacitors instead.Parallel a pair of 100nF caps and place in series with another 100nF cap. That would give a total of 66.7nF, which should be close enough to the specified 68nF to have negligible effect on the turntable operation.

author: tohtorizorro
author_rank: Contributor
timestamp: November 02, 2024, 12:46:40 pm
content: Quote from: srb1954 on November 02, 2024, 01:45:56 amThis will work since there is a lot of room inside the chassis.How about the 4.7nF cap across the on/off switch? I'm guessing it could be there to smooth out sharp edges if the switch is closed when the AC wave is at its peak. OTOH it could also suck up the inductive kick back from the motor. Unfortunately I don't know how to evaluate suitable capacitance in either case. Too much capacitance will decrease impedance and start "bypassing" the switch at some point but how much is too much?The 100n caps are out of the question since it would take 20 to reach the ballparkCome to think of it, I'm sure I have junk laying around where I can salvage those blue disc shaped Y caps with fitting values.

author: CaptDon
author_rank: Super Contributor
timestamp: November 02, 2024, 01:16:41 pm
content: The capacitor across the switch is to eliminate contact arcing as the switch is opened. It doesn't do anything other than cause a spark at the contacts if the switch is closed when the capacitor is at full charge voltage. By eliminating the arcing as the switch is opened it eliminates the EMI that could get amplified and damage the sensitive tweeters in the stereo system if the system is being played at high volume levels. Speaking of the loud 'pop' that has huge amounts of high frequency energy, often heard on turntables after the last record is done playing and the turntable shuts itself off.

author: tggzzz
author_rank: Super Contributor
timestamp: November 02, 2024, 01:24:29 pm
content: If you have a charged 4n7 capacitor and you close a switch across that capacitor, what do you think the current flow will be?RIFA is a brand, not a type co capacitor.SomeRIFA capacitors have an integral resistor, which would limit current flows.I suggest you look carefully at theprecisetypesof RIFA capacitor (e.g. PME2616) and find a datasheet to determine its characteristics. Then you will be in a position to select a replacement.For starters, I suggest these key characteristics: AC voltage, X*/Y*, integral resistor or not. The precise capacitance value is less likely to be critical.

author: tohtorizorro
author_rank: Contributor
timestamp: November 03, 2024, 02:24:43 am
content: Quote from: tggzzz on November 02, 2024, 01:24:29 pmYes, I've come across a few failed ones and these also both had cracks in the outer shell. Nice to know about the possible internal resistors.QuoteI thought the circuit and application were simple enough that something could've been suggested but you're right of course. Here's what I found about the original caps vs what I replaced them with:RIFA PME271Y(across the switch)class: Y2capacitance: 4.7nF nominal , 5.9 measuredrated voltage: 250 VACoperating temperature: −40°C ... +100°C"Highest possible safety regarding active and passive flammability"REPLACEMENT(x3 in parallel)class: Y2capacitance: 5.5nF measuredrated voltage (at least): 250VAC& 400VDCRIFA PME2616(across the motor)class: no safety classcapacitance: 68nF nominal, 82nF measuredrated voltage: 630VDC, 300VACoperating temperature: −40°C to +70°C inREPLACEMENT(x2 in series)class: X2capacitance: 74nF measuredrated voltage: 2x250VAC...what do you think?