That I think is correct. The transistor itself is forming a divider with those inbuilt resistors and that is why the voltage falls to 2.8 volts with it fitted.
What you need to do is carefully measure that 4.9v very accurately and see if it tries to change when the player should be in mute or unmute.
For example 4.924 volts when in mute and if (and it is a long shot but worth checking) it goes to say 4.840 when playing (so unmuted) then that result might point to a failed output stage on the chip.
It means the logic within the chip is trying to change the state but can not.
Ok, a very dummy test would be to solder ca 56kohm resistor from mute pin to ground (with Q105 removed or disconnected from iC5) and see if it can drive it:
Where do you get the schematics from? I seem to be unable to find it on the net.
Anyhow, what is the model of IC5?
Anyhow, what is the model of IC5?
So we are still no nearer.
I know you say there is no remote but I can see on the chip a 'remote' input. I'm also looking at images of this player and it seems it is part of a micro system???? that will interconnect with other units.
You might be chasing a non existent fault... I just wonder if it is in mute.
Attachments
The schematics from hifiengine, the service manual of the 300C is shared with 500C model.
According to the manual IC5 is TMP87PM78F
It is a standalone CD player that can be controlled by Teac amplifier (A-H300), some of those amplifiers have a remote controller that when connected using this control link (standard 1 RCA cable) to the 300C CD player can control the CD player.
My CD player does not have remote controller or IR "eye".
Just to clarify, when it's connected to an amplifier and playing there is no sound output.
after removing Q102 and Q103 (D1302 type) transistors there was sound output from the player and it played perfectly but when I switched the CD player off there is a "white noise" (hiss sound) from the speakers.
after removing Q102 and Q103 (D1302 type) transistors there was sound output from the player and it played perfectly but when I switched the CD player off there is a "white noise" (hiss sound) from the speakers.
🙂 you're welcome.
I don't know what to suggest that you try next tbh... lets think... so if its a standalone player that has a standby rather than an on/off switch (and it must be standby because otherwise it would not hiss when off) perhaps we should look at any power detection circuitry in the power supply.
Ultimately it may well be a problem with the system control (IC) but those things are usually the last option. What I would do faced with this is to look at every pin on the system control chip and confirm that what is present (voltage/waveforms etc) is what might be expected. Look for incorrect or missing inputs.
I can't really think of anything else to try at the moment 🙁
I don't know what to suggest that you try next tbh... lets think... so if its a standalone player that has a standby rather than an on/off switch (and it must be standby because otherwise it would not hiss when off) perhaps we should look at any power detection circuitry in the power supply.
Ultimately it may well be a problem with the system control (IC) but those things are usually the last option. What I would do faced with this is to look at every pin on the system control chip and confirm that what is present (voltage/waveforms etc) is what might be expected. Look for incorrect or missing inputs.
I can't really think of anything else to try at the moment 🙁
Why just not ignore the problem and connect the muting circuit to some led that lights up when device is turned ON?
Care to eleborate how it can solve the muting issue?
I don't care about the mute function I just want to get proper sound out of the CD player.
I don't care about the mute function I just want to get proper sound out of the CD player.
You make life really easy - just unsolder the muting transistors and done you are 😉
But then you may get the hiss when not needed so muting may still be necessary.
You have to find something that lights up when the device is powered on and then connect the steering input of the muting circuit (e.g. via dode) to that element.
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If you have an oscilloscope, check the CN6 pin 3 for the unregulated 11V rail.
Bad caps on the power supply may possible causing unstable DC level (this may become just like a pulse signal) which will be eased by D503 6.2V zener on the output board though, but will still cause the MUTE problem.
I got the similar issue, but my case is for CN6 pin 4 is 60mV nearly 0V, but the audio signals still got muted. In your case, pin4 should be either 5V (via R212 pull-up) or near 0V, IF you go 2.8V, which mean there's an issue with Q504/Q106 circuit, and then caused the MUTE problem.
I swapped all the AL caps on the power supply board, for those replaced caps, they are either totally dead with incredible ESR like 5k or so, or with less than 70% of the capacity remained with increased ESR. Replace them all when possible.