Tascam 52 DB Reel to Reel - Rifa X Capacitor Issue

[canidoit]

I don't seem to have much luck buying Reel to Reel Machines, always something wrong with them.

I bought this Tascam 52 DB Reel to Reel which had not been used for several years but when it was last used, it was working.

The issues are:
I am not getting proper levels on the right channel. Sometimes after switching the unit on and off, the levels would act normal, but then the levels on the right channel would drop again.

I also noticed a burning type smell, so I opened it up.

There is a capacitor that seems to have blown causing the smoky smell. It is a 0.047uF capacitor which is soldered between the wires from the power button switch(which turns the unit on and off), as drawn in the picture.

Why would a capacitor be there, is it to reduce noise or hum?


Even though the capacitor is blown, everything functions except for the level issues mentioned. Transport works, motors work, etc.

Can I use any capacitor here as long as it is 0.047uF?

If the machine still runs, do you think if I don't fix this blown capacitor, it is actually damaging something along the line somewhere?

Thank you.

 

[canidoit]

After some googling about caps, I think this might be a DC blocking capacitor since it is on the power switch? The only reason I can think of as to why the machine is still working after this capacitor blew up, as its only for preventing hum. Anyone know if I'm right?

Do I need to stick to this Metal Paper cap, or can I get away with a different type of cap cause this Rifa cap is expensive.

I read that I can choose a higher voltage than 250v (ie 300v), but I should stick to 0.047uF and the same type (Metal paper) cap? Anyone have any recommendations on what is cheap, easy to get and will do the job replacing this blown out cap? I have some Poly and Orange caps, not sure if it would do the job?

Thanks.

 

[NoisyIndividual]

That is an "X Cap".

It is usually placed across the mains to provide protection in the case of over voltage etc.
When it fails, it is specifically designed to fail short, so that anything downstream, including humans, is protected.
You need to Google this.

 

[radardoug]

After some googling about caps, I think this might be a DC blocking capacitor since it is on the power switch? The only reason I can think of as to why the machine is still working after this capacitor blew up, as its only for preventing hum. Anyone know if I'm right?

Do I need to stick to this Metal Paper cap, or can I get away with a different type of cap cause this Rifa cap is expensive.

I read that I can choose a higher voltage than 250v (ie 300v), but I should stick to 0.047uF and the same type (Metal paper) cap? Anyone have any recommendations on what is cheap, easy to get and will do the job replacing this blown out cap? I have some Poly and Orange caps, not sure if it would do the job?

Thanks.

YOU MUST USE THE SAME CAP THERE! That is mains rated, and has mains on it.

 

[canidoit]

Thanks All!

OK, I will stick with the original voltage @radardoug.

I managed to find this in the Service Manual. Z1 is a capacitor?

Its different though, 0.0047/250V instead of 0.047uF on the actual blown cap. It seems to be uF as they use uF in other parts of the manual.
Would using 0.047uF instead of 0.0047uF be an issue? I mean its the original cap that's been there for decades, so I guess not.

How important is the climate category 40/085/21, most of the current caps are different?

I delved further into choosing a replacement cap and some state online I can replace the Metalised Paper capacitor with Metalised Poly Capacitor which is cheaper and easier to get but some say, that the paper cap will add microphonics to the unit, that may contribute to the sound? Is this true, or old wives tail?

The Rifa specs seems to be this one, but not sure what the MR30 is for in the part number name?

Part #PME265MC547MR30 - Capacitor Film​

PAPER CAPACITOR, PAPER, 20% +TOL, 20% -TOL, 0.047UF, THROUGH HOLE MOUNT, it does not state whether it is 250VAC.

Would it be fine if I use a cap that has 10% tolerance instead of 20%?

 

[canidoit]

Also, am I correct in my interpretation of the schematics, that I can install the capacitor any direction?

@NoisyIndividual, googled it and conclude that this is a suppression capacitor, prevents over voltage? Thanks.

 

[radardoug]

It just stops the switch sparking. Also, if you are in NZ or Aus, it should be higher voltage, at least 400VAC.

 

[canidoit]

It just stops the switch sparking. Also, if you are in NZ or Aus, it should be higher voltage, at least 400VAC.

@radardoug, we use 240 volts AC here in Australia, so it would defeat your instructions that it must be the-same cap.

Can I replace this with a Metal Polyester Cap? A cheaper cap that I can buy locally like this one;
MCAP.1-250 .1MF 250V AC NM CAPACITOR
MAINS SUPPRESSION CAP
https://www.radioparts.com.au/produ...-suppression-cap?SearchID=2979766&SearchPos=6
Also, I can only find X2 Metal Paper caps, will this do?

@NoisyIndividual, do you know if this is an X1 or X2 cap, I can't seem to find information on what the original cap was? Thanks.

 

[NoisyIndividual]

Actually I'm not sure now. It looks like the Rifa X caps you find everywhere that often seem to blow up, but X Caps are usually marked X somewhere on it, and I can't see that marking in the photo.

So I don't know, despite me claiming I did, in haste.

 

[radardoug]

Here you go.
https://nz.rs-online.com/web/p/rc-network-capacitors/0209213?gb=s

 

[canidoit]

@radardoug Thanks for the link!

If I were to use Metallised Polypropylene 47nF, Volt Rating: 275/250VACCapacitance Tolerance: +/-10% std +/-5%Operating Temperature: -40°C to 85°CValue
https://www.jaycar.com.au/47nf-250v...os=3&queryId=f949105ef5f333466f5bb26ea85b513b
It has a tollerance of 10%, do you think that would be OK?

I mean, the worst that can happen is that it should just suppress the sparks earlier than if I were to use 20% tolerance? Is this way of thinking correct?

 

[canidoit]

I have decided to buy the Suntan TS08S Metallized Polypropylene Film Capacitor - X2, 275VAC, 0.001-2.2uF, 10%std, 40/110/56. This is sold as 47nF at Jaycar even though the specs does not really state it is.

https://www.suntan.com.hk/pdf/Plastic-Film-Capacitors/TS08S-275VAC.pdf
From my understanding in my research so far, for X2 purpose across the line in equipment, Metallized Poly is better than Metallized Paper as it is less prone to blowing up like the Rifa. For its purpose - the uF requirements are flexible(can be close enough to what is required) and is not strict on tolerance 10% or 20%, but the voltage is more strict where it cannot be lower than the actual power source, ie. must not be less than 240volts Australian for my application. This is listed under 250VAC even though it is written as 275VAC, but some online suggest, the 250VAC are of lower quality and the go to now a days are 275VAC or 310VAC for X2 capacitors.

Feel free to correct me if I am wrong but I am only going off what I have found which is a mashup of online information which I may have misinterpreted. Correct me, the sooner the better, as I am about to solder in this bad boy!

@radardoug, I decided to get the Suntan as Rifa seems to get alot of flack for blowing up and also the price is cheaper and availability is quicker, no wait time, I have it now.

Thanks all for their replies!

 

[Admiral-dk]

Some of these old style Rifa Caps had an inbuild resistor in series with the capacitor and where meant only for applications like this (across a switch) ...!
Replacing them with a normal Cap is often rather bad - both for the Cap and for the Switch ....

Per

 

[canidoit]

Some of these old style Rifa Caps had an inbuild resistor in series with the capacitor and where meant only for applications like this (across a switch) ...!
Replacing them with a normal Cap is often rather bad - both for the Cap and for the Switch ....

Per

I was concerned about that too Per, but this cap is also made for AC power use. So far, I tested it for 6 hours and it seems fine.

 

[murrayatuptown]

If the original Rifa X-Class capacitor had a transparent/translucent amber colored coating, you may eventually find info online about some Rifa metallized paper safety capacitors having either a design change or being discontinued because of failure rate. They were prone to exhibiting fractures in the dip coating. I don't remember an electrical failure mode or modes, but a known issue with a manufacturing process. Discontinuation would make sense instead of good and bad date codes coexisting.

I found it when looking up one that I had a few dozen specimens of. They were NOS dual-primary power transformers with a mains range switch and suppression capacitor on a PCB ass'y soldered to the transformer terminals. They were individually boxed. Every one I opened was fractured.

I could consider the capacitors unused in the sense they did not have operating hours, but arguably they were 'used' via a soldering process, suggesting a problem related to the soldering temperature. I don't know if the failure also occurred on never-installed parts, but there was an acknowledged defect.

Interestingly, metallized paper construction is still used (available in current catalogs) in some safety-rated suppression capacitors.

Despite still meeting various safety ratings, I am surprised metallized paper still has a place in the industry. I suspect specific parts are committed to a product when EMI/EMC performance has been achieved & certified. But that would be in a more complex line filter circuit with X, Y and inductors.

For a private repair of an antique, I would personally also have leaned toward an MKP part of equal or higher safety classification. I don't know of any advantage to metallized paper but it may be still be manufactured because there is still market demand for certain construction.

In this case, I'd agree with the other remark that a higher AC certified safety class voltage rating (400 vac vs. 275 vac) would be a good idea because there is much less 'safety margin' left on a 250-275 V part under high-line 240 V service conditions.

A higher-rated part of same capacitance is probably larger and more costly & might not have been available when the machine was built.

Construction methods of 'safety-rated' AC capacitors are interesting. Corona is one of their main enemies. This is part of why AC ratings of DC-rated capacitors vary so much (usually plotted in a datasheet instead of marked when they are not Class-certified), and why DC voltage test performance data for AC-rated capacitors is so high.

A capacitor across switch contacts is accruing hours in its statistical lifespan when the switch is open (off) and enduring transients when operated from closed to open. When the switch is closed (on), the capacitor is 'protected' by the closed switch contacts.

Capacitor reliability is a fascinating topic to me, aside from all the romance about about what dielectric is preferable for some audio.

Murray