Alpine mdr-m500 turns on but there is no sound

[Perry Babin]

Do the voltages on the 494 change significantly if you set the supply to 12v, 13v and 14v?

No need to post all of the voltages. This is simply to see if the amp is sensitive to the input voltage.

 

[Mjimenez]

No change is the same

 

[Mjimenez]

only that of pin 12 increased from 12v to 12.7 there is almost no current consumption

 

[Perry Babin]

The following may defeat part of the protection circuit so be careful.

Solder a bridge between the collector and emitter of Q615. Does the amp power up normally?

If so, does it produce clean audio?

Clamp all FETs to prevent them from overheating if there is a problem.

 

[Mjimenez]

now the 12v of the pins 8 and 11 arrive but there is still no pulse in the 9 and 1p

 

[Perry Babin]

Are the components in this amp epoxied to the board?

I'd like you to remove R636(?), 820 ohm but I don't want you to destroy it.

 

[Mjimenez]

I just measured the q616 and in the input pin enter 4.5v when placing the remote and in a second they go something else is pulling it to 0v

 

[Mjimenez]

Oky no problem

 

[Mjimenez]

ready and remove it

 

[Mjimenez]

Wow you are a genius on to !!! now I guess something bad there

 

[Mjimenez]

Turno on

 

[Perry Babin]

Does the amp produce clean audio?

 

[Mjimenez]

I do not have audio, there is only rail voltage +28 and -28 in some cases in 2 banks there are only 25v

 

[Perry Babin]

Are you sure that you're looking at the terminals of the output transistors that are connected to the rails?

There is only one transformer and one set of rectifiers so all rail voltages should be identical.

Do you see any DC across the speaker terminals of any channel?

 

[Mjimenez]

I'm sure

 

[Mjimenez]

There is no DC in the terminal

 

[Perry Babin]

How can you have different rail voltages if all are directly connected to the same rails?

 

[Mjimenez]

Apparently they are the ones that come out of the tda7571

 

[Perry Babin]

In general, if the term 'rail voltage' is used, it's referring to the main rails that are produces to supply power to the output transistors.

For other supplies, if the term 'rail' is used it's specific as in ±15v rails or 5v rail.

 

[Mjimenez]

Oky good what I see are those of 25v now it remains to check the operational amplifiers, see if it comes to you audio