Philips CD960 Query

[Gravissima 64]

I have a query about my Philips CD960, which I bought new back in 1988!

The player works perfectly as it always has, but yesterday I noticed that it smelt rather hot, and was giving off a phenol like smell which I would associate with a hot circuit board. The heat sink on the back of the machine also felt warmer than I remember.

Anyhow, I took the top off this morning, and Hoovered out the dust which had accumulated. Nothing is obviously burnt.

Having cleaned it out I have set it running with the top off, on a table (well away from my Quad valve amps, which obviously don't help)! It is running perfectly, but the smell persists, and the small copper heat sink on the power transistor at the very back of the main circuit board feels rather too hot for comfort at about 90° C. The adjacent copper heat sink is much cooler. The heat sink on the back of the machine also feels cooler today

I can only seem to find a service manual in Dutch, and my Dutch is very limited, so I don't know which circuit this power transistor is regulating.

Does anyone have any experience of similar problems on these machines. And is there anywhere that I can obtain a manual in English? I realise that Philips is a Dutch company, but I cannot believe that these players were only ever serviced by Dutchmen!

Any help would be very welcome.

Regards,

Gravissima

[Gravissima 64]

I should add that since posting the above, I have checked the voltages at thee two power regulators (with copper heat sinks) using a Fluke 87 DMM, and these seem slightly at odds with what I would expect.

The unregulated voltage on the negative rail (the hot regulator) is 19.6 to 19.7 volts, whilst the positive rail is 20.6 to 20.7 volts. This would suggest to me that the negative rail might have a higher load.

The regulated output from both regulators is 13.7 volts (both + and -). The circuit diagram I have (in the Dutch manual) suggests that both rails should be 12.0 volts.

Gravissima

[amc184]

I have checked the voltages at thee two power regulators (with copper heat sinks)

Actually, these aren't monolithic regulators, they are transistors, each part of a discrete regulator. They provide power to the DACs, output stage and headphone stage. They should be outputting +/- 14V, so your measurements of +/- 13.7V seem okay.

If you have an oscilloscope I would have a look at the output of these discrete regulators. They might be oscillating, or maybe the ripple into or out of them is excessive.

I would say if there is a fault I would look at the regulator itself, as I can't really see anything downstream of it breaking and consuming more current, at least not without some more dramatic symptoms.

[Gravissima 64]

Thanks AMC. That makes sense. Checking with a 'scope also sounds like a good idea, so I will do that later today to see if there is anything unusual going on.

Your suggestion about HF oscillation may also be relevant; as I note that the heat sink involved does not get excessively hot until a CD is played, but once it is hot it stays that way, even when the player has been idle for an hour or two.

The only fault I have had previously was a large electrolytic which went open circuit without warning, (about ten years ago). Maybe a smaller decoupling capacitor has done the same thing.

Thanks again.

Gravissima.

[Mooly]

Agree with AMC re the scope check and I too can't really see anything drawing enough current to cause this.

Silly question... is your mains voltage OK... not too high... and is the player if adjustable set to the correct voltage, 240 (as was then) and not 220v.

A couple of volts extra dropped across a reg increase temperatures more than might be imagined sometimes.

Are you sure that it is really at 90 degrees C. That is too hot and would I think contravene what is allowable for a surface that can be touched.

[Gravissima 64]

Thanks Mooly.

Our mains voltage is currently between 243 and 245 volts. This is sligtly higher than the nominal 240 volts specified for the machine, but it has never caused a problem before.

I switched the player on an hour ago, and just checked the copper heatsink temperature (negative supply rail) with an infra red thermometer. It was 61 °C.

The copper heatsink on the positive supply rail was 40 °C.

(Note: These are small internal heatsinks mounted on the main PCB, and are not usually accessible. The large heatsink on the back of the machine is only moderately warm.)

I have loaded a CD and will check again in an hour. By that time I will have a chance to get the 'scope out and have a closer look at what is going on.

However, it does concern me that the negative supply rail shows all the symptoms of having a much greater load than the positive supply rail. I would have expected them to be more or less equal.

I think I have located a service manual in English from the USA, which should provide some useful information. Just waiting for the e-mail to tell me where it is!

Nigel.

[Lautar]

remove headphone amp if not used

eng circut this RapidShare: 1-CLICK Web hosting - Easy Filehosting

[Bill Fuss]

IMHO, if you like the player it's time to recap it anyway. It could very well be the caps starting to fail.

[Mooly]

I wouldn't be concerned at unequal current draw on the rails... it's not like it's feeding just balanced circuitry.

I suspect it's probably all OK tbh, but see what the sope shows.