Philips CD 204, dead headphone amp ?

enryfox

Member
2019-02-06 8:08 pm
I recently acquired a Philips Cd 204 I'm in the process of restoring to full working conditions. So far I have fixed the tray (gear and belt broken), replaced all caps in the PSU (actually old Nichicon's were perfectly fine), replaced all low quality Philips caps in all boards but the CDM-1.

I have one last problem to fix, the headphone amplifier: if I connect it to the other boards, RCA output is distorted and headphone output is severely distorted; if I unplug it, RCA output is perfectly fine.

Schematic is attached, it is a simple 1x buffer feeded directly by the RCA output; I checked the cable and it is fine, voltages are fine, caps are new and resistors are not shorted. Only remaining option is a faulty op-amp: it is actually a NJM4560 not a NJM4556, but anyway it appears to be a pretty standard headphone amplifier of those days. Is it a common failure ? Do you have any suggestion for a modern replacement ?

I do not plan to use it (fixed volume is useless) but anyway I would like to fix it.


Thanks
 

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enryfox

Member
2019-02-06 8:08 pm
Unfortunately, the cables are too short and I cannot measures voltages with everything connected. I did test voltages on the other side of the cable: +/- 12 V is ok, signal inputs are at 0 V versus ground (pin 3 and 5). I also tested the cable and it is ok; I cannot test any further.
One hint I have is that when the headphone is plugged into the socket, I can hear a click and that suggest me the output is not at 0 V. 90% is faulty op-amp.
 

enryfox

Member
2019-02-06 8:08 pm
What I'm worried about is the output load handling capabilities: the original NJM4560 is rated for 400 ohm load, while most of similar op-amp's are rated for higher load. The ideal replacement is the BA4580, but I cannot find it in DIP 8 package. The NE5532 is available (and indeed used on the CD204 for the output filter/buffer) and I have also found the LM4562.
 

enryfox

Member
2019-02-06 8:08 pm
The new op-amp arrived but that did not fix the problems.

Even with the new op-amp there are still 8V on the headphone output; while trying to measure voltages, one wire in the cable connecting the headphone amp to the main audio board detached from the plug so the cable has to crimped back ...

I'm giving up, it is really just a race with myself, there is no point in fixing the headphone output, with fixed volume is plain useless.
I have removed the cable and the CD player works beautifully, albeit with one dead headphone socket in the front :)
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
It has to be an easy fix and more to the point I would want to know why connecting this board causes the other issues you mention.

I'm not even going to second guess anything like this but would suggest you check that the board is really plugging in to where it is supposed to and not some other unused connector somewhere. Maybe someone has unsoldered the leads to the board and reconnected them in the wrong positions.

Ultimately there is nothing really on that board and so it is an easy fix... and fun to track down :)
 

enryfox

Member
2019-02-06 8:08 pm
That is exactly my point, it is such a simple board it should not be difficult to find what is wrong.
I actually had checked the cable unplugged and it measured ok, but the moment I was trying to check it plugged-in it started breaking. Now I have to crimp it back before doing any further test.

The sockets look fine to me there is no evidence of any miscabling or foul play. But I guess it has to do with the power supplies as yesterday while I was trying to stick the multimeter probes on the boards and the cable was pulled, the CD started acting strangely, opening the tray un-commanded and showing weird number on the display.

And another aspect is that the moment the headphone works, I will surely disconnect it and leave it off as I do not use it and it is connected directly to the RCA outputs.