The Workbench

Re: Beocenter 8000 CD stopped working

yachadm — Thu, 20 Jan 2011 14:39:47 GMT

These are Vishay BC NFR25 Fusible, non-flammable resistors.

Do not replace them with any other type.

In the Philips CDM2 Service Manual, they are listed as safety components, not to be substituted with anything else.

I have stock of these on hand.

Metal Film are not wise replacements here anyway, even if the originals were not the NFR type.

In power circuits, Carbon-type resistors still handle heat much better than metal-film. As technology develops, this may change, but right now, this is the case.

Metal-film are excellent for audio circuits, though.

See this article:

http://www.condoraudio.com/wp-content/uploads/Reviews/How-to-Choose-Replacement-Capacitors-and-Resistors.pdf

Of course, the high-current here is obvious - the fusible resistors burned. The BC560 (PNP) series would not last long under normal conditions. They are excellent transistors in signal applications, though - very quiet!

Menahem

Re: Beocenter 8000 CD stopped working

Agent00soul — Sat, 01 Jan 2011 17:39:43 GMT

Marcus:
If the fifth band is purple that means that the tolerance for the resistor is +-0.1%.

WOW, you're right. I wonder why they used them and if the low tolerance is neccessary.

Even more strange are the three resistors below the burnt ones that seem to have TWO gold bands. That's not covered by my resistor colour code guide. Are they really gold?

Well, I suppose if the purple bands really mean something else, the burnt ones would be 10 ohms 5% and the three below them would be 1 ohm 5%.

Re: Beocenter 8000 CD stopped working

Marcus — Sat, 01 Jan 2011 16:51:23 GMT

If the fifth band is purple that means that the tolerance for the resistor is +-0.1%.

Re: Beocenter 8000 CD stopped working

Agent00soul — Sat, 01 Jan 2011 15:02:14 GMT

Die_Bogener:

The cheapest coal resistor is good enough... 5% 0,25W.

What type are the original resistors, by the way? They have five bands: brown-black-black-gold-purple.

I have never seen a resistor with a purple band for tolerance. Does in mean 0.7%? It can hardly be 7%, as it has four bands for resistance value, whereas 5% carbon film resistors have only three bands. I would guess they are some kind if metal film resistors, as they look very similar to 1% metal film resistors and have the same number of bands.

Re: Beocenter 8000 CD stopped working

Die_Bogener — Sat, 01 Jan 2011 12:16:19 GMT

The cheapest coal resistor is good enough... 5% 0,25W.

Use the Fairchild BC328...

Vishay BC Components was PHILIPS some years ago, ähm, they bought it ... ;)

Re: Beocenter 8000 CD stopped working

Marcus — Sat, 01 Jan 2011 12:04:26 GMT

So I have had a look around and tried to find all the things I need:

Resistors Which one of these would be best suited?

Transistors: BC328 and BC338

Capacitator: 47uF

Re: Beocenter 8000 CD stopped working

Agent00soul — Fri, 31 Dec 2010 12:33:17 GMT

OK, I suppose this is one of the exceptions then. Elfa has the BC368, which might work (NPN, Ic-max 1 A). A suitable PNP transistor could be the BC640, which Elfa also stocks.

Re: Beocenter 8000 CD stopped working

Die_Bogener — Fri, 31 Dec 2010 10:09:28 GMT

The BC550 will have a very hard time, to replace with his 100mA maximum current a 800mA type BC328/338...

And it has a reason, why B&O used this type of coal resistors. 0.6W metallfilm with its high capacity for overload will cause also a hard time for the stressed components... the resistors are fuses and for limiting the current during overload. If you use a 10W type, it will never blow, just the motor or the power supply will burn ...

Re: Beocenter 8000 CD stopped working

Agent00soul — Fri, 31 Dec 2010 09:59:02 GMT

I replace basically any small signal transistor with BC550C/BC560C. As long as it looks the same, it will usually work. There are exeptions of course, but they are few. You need to make sure it's a NPN or PNP transistor of course. FETs are another thing.

For resistors I always use 0,6 W metal film. That way I only need to stock one type and can buy 100 at a time, which makes the cost acceptable.

Re: Beocenter 8000 CD stopped working

tournedos — Fri, 31 Dec 2010 06:06:48 GMT

Any regular 10 ohm resistors will do, metal film 0.3W for example. Don't up the power rating much though, or they won't act as fuses as they were designed to anymore.

There's plenty of discussion on that C2103 on the forum, most recently here. The easiest way out is to get a ready assembled kit of all caps worth replacing on this board from member Dillen, then you'll get types that are known to work.

If you get stuck with the transistors, I can drop a pair in the mail for you. I always buy a larger batch of cheap components like this even if I need only one at that time.

Re: Beocenter 8000 CD stopped working

Marcus — Thu, 30 Dec 2010 19:05:51 GMT

Hmm.. Checked Elfa and they dont stock bc338-25 or bc 328-25 transistors, as far as resistors go what kind of resistor should I get, Does it matter if I get carbon, metalfilm or metaloxide resistors? Should there be any specific effect handeling spec? There is also a couple of different variants on capacitators, apart from it being a philips and blue, do you by any chance know what detailed specs it should have? I really want to get this right the first time and have my beloved stereo back to playing my CD's.

Re: Beocenter 8000 CD stopped working

Agent00soul — Thu, 30 Dec 2010 14:46:31 GMT

Those 10 ohm resistors definitely look fried. Time for a trip to Elfa...

Re: Beocenter 8000 CD stopped working

tournedos — Thu, 30 Dec 2010 11:07:03 GMT

That's a detailed enough picture

Near the two wires to the spindle motor, you see the two driver transistors (6124 and 6125). Above and below them are the two 10 ohm safety resistors. They obviously have been hot, the lower one seems to have even bubbled a bit, perhaps enough to create smoke. Measure them, and you should also test the two transistors. Might be easiest to just replace all four components.

If the transistors need to be replaced, make sure to get the higher gain (-25) versions instead of basic BC328 and BC338. There must be reason why those were used originally.

Re: Beocenter 8000 CD stopped working

Die_Bogener — Thu, 30 Dec 2010 11:01:57 GMT

Replace transistor 6124 and 6125 and the two burnt resistors direct next to them. That's all.

And replace 2103 by a 47uF 16V axial type. Either original Philips or the newer type "BC" components. It must be a blue cap, nothing else. This cap is picky.

Re: Beocenter 8000 CD stopped working

Marcus — Thu, 30 Dec 2010 11:00:56 GMT

I've uploaded a picture in the first post. From what I can tell none of the components look burnt. Going to make some measurements after our daughter has fallen asleep. Which of the components are most likley to be faulty?