Providing a DIN audio input to a Philips MCD139B Amplifier

[Joaquín Robles]

Hi People,
Some time ago I bought a Philips MCD139B, it's a DVD Micro Theater with 2.1 audio,
For some reason the set top box stopped working so I'd like to use the speakers (left, right and subwoofer) with my PC or TV out,

I've beeing googling and found this **broken link removed** (page 40) where describes the input provided to the amplifier that is embeded in the right speaker.
My guess is I could use this diagram to provide an audio input to the DIN connector in the amplifier, is this possible? What would you recommend? Thanks

**broken link removed**

 

[dr pepper]

Yes its possible, only if I'm right looking at the connector you'll only be able to use the l&r speakers, as the input socket accepts l&r and sub seperately, ie the cross over is in the main unit.
You could connect l&r direct to the input, then link off the l&r inputs with 1 k resistors to the sub input to create a mono channel, while this would work you'd get full range from the sub so sound quality wont be as good as it could, plus you'd get a little less stereo effect from summing l&r with the resistors.

 

[Joaquín Robles]

Yes its possible, only if I'm right looking at the connector you'll only be able to use the l&r speakers, as the input socket accepts l&r and sub seperately, ie the cross over is in the main unit.
You could connect l&r direct to the input, then link off the l&r inputs with 1 k resistors to the sub input to create a mono channel, while this would work you'd get full range from the sub so sound quality wont be as good as it could, plus you'd get a little less stereo effect from summing l&r with the resistors.

Thanks dr pepper, i'm pretty new here, so I understand that it's possible to connect ie an RCA cable as the audio input? If so, why the diagram shows 11 lines when the jack has only 8 pins? In which pins should l&r be connected? Thanks in advance

 

[Joaquín Robles]

UPDATE
I've manage to found which pins are Left and Right and connected a stereo input. Everything's fine except that the right speaker sounds with too much static and left speaker isn't working at all, any hint? Thanks

 

[dr pepper]

Either you have the connections wrong or the unit is in standby, try connecting stby/mute to ground or +5v.

 

[Joaquín Robles]

Either you have the connections wrong or the unit is in standby, try connecting stby/mute to ground or +5v.

Hi dr pepper, thanks for your help, I've tried what you suggested but either with ground or +5V the sound is instantly muted, it seems that way standby or mute are activated.. I've double checked the connections, everything seems fine but still no sound in left speaker (I've tried plugging another speaker in that connection to verify a possible speaker problem but no luck)..

I found this diagram in the Service Manual, maybe it would be helpful,
I don't understand the table in the top right, to wich pins is it refering? Using an OCR translator the chinese part says something like "Voltage comparator status table", any ideas? thanks

**broken link removed**

 

[dr pepper]

Looks like the stby/mute signal goes to a window comparator, if the voltage on this input is <1.8v or >3.2v the comparator output is high, not sure from the schem whether this would mute or unmute the amp, from what you said I think if the stby/mute pin is >1.8 and <3.2 the amp is unmuted.
The mute function would probably affect both speakers, maybe theres a fault within the amp.
You could connect 2 1k resistors in series from +5v to ground, then connect the junction of these to the stby/mute pin, this will feed the pin 2.5v and the amp should be unmuted.

Remember though if one speaker isnt working this sounds more like an amp fault.

 

[Joaquín Robles]

Thanks dr pepper, i'll buy the resistors and give it a try!

 

[cintuliak]

Hi there I have same system Philips MCD-139 and it stop working ...... I change one IO it was totally burn .... but if I check resist betwen +24V and GND it show 5ohm ...... So can somebody tell me what resist should be there please

 

[dr pepper]

Welcome to the forum.

I didnt really get what you mean, however 5 ohms across a 24v rail probably isnt so bad, if anything I'd expect less.

 

[cintuliak]

thank you for welcome

here is first picture the resistor is burn down and capacitor look little bit old ..... so I change resistor and capacitor and IO ..... but after this everything I do just the check so I measure PIN number 8 = +24V and GND pin number 7 and between these tow PIN is 5ohm resist so I dont know that is something more breakdown or it is OK?

 

[dr pepper]

Just my intuition speaking here, further up it mentiones 5v being available at the o/p connector, and you say the power rail is 24v, that resistor could well be part of a voltage regulator or even a voltage dropper from +24v, the 24v rail because of the power supply caps would read 0 ohm short which is normal, if you meter the 5v pin to ground you'd be meauring the resistance of the dropper circuit, by any chance is the resistor 4.7 ohm?
The old resistor is probably still functional, they can look like toast but still work, good sense in changing it though.

If your worried about powering it up it might be worth making a lamp test socket, which is just a mains plug, short length of cable and a mains socket with a 60w bulb in series with the mains, of theres a short in the equipment the bulb lights instead of something going bang, usefull piece of kit if you do this now and again.