Philips NG5151/01 Disc Jockey Auto- Capacitor Questions

[Old Sparky]

I have recently replaced a couple of capacitors (C4 & C6, both 5n6) and R4 (220k) in one of the above, as all were out of tolerance.  The player is now working, but should I, on safety grounds, replace the isolating capacitors (C7, C9, C11, & C12), all of which are 4700pf red ceramic disc types, the first 3 isolate the pickup from chassis, the last is a 'spark suppressor' fitted across the motor on/off switch, with modern class 'X' (or should that be class 'Y') types? N.B. This model was fitted with a 3-core mains lead from new by Philips. This is shown in the circuit diagram.

[Mark Hennessy]

A schematic would be helpful, but personally, I would replace the isolation capacitors.

Class X capacitors are rated to be used between phase and neutral, and are designed not to fail catastrophically (should a spark occur thanks to an imperfection in the dielectric, the heat generated should cause the dielectric to swell up and self-heal). Of course, don't mention "Rifa"

Class Y capacitors are rated to sit between phase and "earth", or neutral and "earth". Of course, for a Class 2 device, "earth" is not Protective Earth, but it would be the chassis of the instrument - which might or not be accessible to the end user, depending on the design. Failure of these can cause electric shock, so they need to fail O/C.

Class Y capacitors tend to be low in value because otherwise they would cause excess leakage. 4n7 is entirely typical.

Just to add to the confusion, sometimes you come across capacitors that are double-rated (class X and Y). Most class X capacitors are X2, but X1 and X3 exist - possibly others. Likewise for Y. The differences are related to the pulse handling ability IIRC.

So, class Y is appropriate for the isolation capacitors.

For the spark suppression capacitor, it has to be rated to handle the AC mains. However, you could argue that worst-case, should the cap will fail short the motor will simply run continuously - perhaps not the end of the world? But honestly, mains-rated caps aren't that much more expensive, so chancing it doesn't really make sense. Alternatively, you could just leave it alone, as it's not a safety-critical part and it's not obviously faulty? Ultimately, it's a bit of a judgement call, but the motor winding will limit the available energy, so I can't think of an obvious safety problem here.

Needless to say, don't risk buying mains-rated caps on eBay! Counterfeit components is a big problem in the industry, and for safety-critical parts, it's worth buying from Farnell/RS. Even those guys occasionally get caught out, but at least you've exercised "due diligence", should the worst happen.

[Old Sparky]

Thanks, Mark. Iwas thinking much along the same lines. Those 4n7 ceramics are well over 50 years old, maybe 55, as they're original fitments, so I'll fit some new class 'Y' ones. If I don't have suitable ones, I'll get them from a reputable source such as CPC , CHS or Maplin, and I certainly won't be using RIFA caps, having replaced those a few times in other equipment over the years!

[Refugee]

Be aware that it is not just RIFA capacitors and NOS are as bad as ones that have been in use.
http://www.forum.radios-tv.co.uk/viewtopic.php?t=2868&p=29262#p29262

[Old Sparky]

Checking that link brings a requirement to register or sign in before access to the 'Radios-TV.co.uk forum is permitted.

[Refugee]

It will do. The thread is in the members section of the forum.
The important bit is the photo of the split capacitors. They are branded WIMA.

[Old Sparky]

I've sourced some Class 'Y' capacitors from an independant components shop in Cheltenham High Street (One of the very few left in business these days), and will fit these in place of the over 55 year old red ceramic disc types. Having fitted an autochange spindle and overarm to the deck I find that it operates, but usually drops a record then switches off. Removing records from the autochange spindle is difficult, as the record keeper is difficult to retract, so it looks as if a clean & relube is called for. Only to be expected in something made in 1960 which hasn't been used for many years, I guess!

[Mark Hennessy]

Bit of a trek, depending on where you are in Oxfordshire. You should have kept going and called in to see me - the kettle is always on

Tell me more about this shop - despite being just up the road, I rarely go to Cheltenham, so hardly know it.

That's because I spent a year working in Tewkesbury when I was a student, and was taking driving lessons at the time. The nearest test centre was Cheltenham. It's a truly horrid place to drive, and yes, I failed. As a result, I have tried my best to erase the entire experience from my memory! I certainly didn't expect to be back in this part of the country some 10 years later, but life is funny like that...

But on the occasions that I have passed through, I note that driving there is a difficult as I remember - even with 20+ years of driving experience. Shudder

[Nick]

... an independant components shop in Cheltenham High Street (One of the very few left in business these days)...

Would that be Harding's Electronics? Not been there for years - didn't know it was still around...

[Old Sparky]

Mark, I don't drive, so, to get to Cheltenham, I take the oncew wekly bus from Chipping Norton on a Saturday, which allows for just under 2.5 hours in the town. Nick, the shop is indeed Hardings, who stock quite a wide range of parts & components, plus equipment of various types, Hardings is typical of the type of shop once found in most larger towns.