Technics SA-EX310 dead...no sound, no display

[Francesc V.]

Hi:

I am trying to bring back to live this amplifier. So far I see that main transformer doesn't receive 220V. It doesn't receive voltage because relé is not activated and doesn't close the main AC circuit to the transformer. (It's not activated because Base of transistor is not excited.......base is connected to pin2 that comes from the main PCB)

Between pin 1&3 I am getting 6.3V, which seem correct......is this the "standby" for the PCB?

Pin 2.....the one connected to base is tagged as "relay". So as soon as it gets the right voltage, the relé will receive about 21V dc....... and then all voltages should be present in the PCB. (that's my analysis that maybe is wrong).

What's the part that triggers this pin2?

Is it this part? (don't see it conneceted to the connector, but it says "relay"..)






Regards,
Francesc.

P.S: Service manual attached for reference

[lotas]

Re: Technics SA-EX310 dead...no sound, no display

This relay starts (gives a command) the microcontroller U901 (25 pin).

[R_J]

Re: Technics SA-EX310 dead...no sound, no display

Rely control is by U91, pin 25 (noted by lotas)
Also locate Q902 and check if you have 5.1 volts on emitter and collector. (page26)

[Devil_rider]

Re: Technics SA-EX310 dead...no sound, no display

Do you get voltage on the power button? If yes make a temporary short to try to start the Amp. During my time with Panasonic I saw switches going bad a lot. Also on this unit the fan and the power amps are the weak parts( not related to your present issue though)

[Francesc V.]

Re: Technics SA-EX310 dead...no sound, no display

Hi:

Pin 25 in the microcontroller has 5.1V.
Both Collector and emitter in Q902 have 5.1V
In the power boton PCB, there is also 5V. As soon as you click the power boton it goes to 0 for a second, so I foresee some kind of trigger there.

I will disassemble front panel in the meantime.......to see if I visualise something wrong there.
What do you think about injecting voltage in the Q751 Base to power up everything? (or shortten C-E)

Regards,
Francesc

[lotas]

Re: Technics SA-EX310 dead...no sound, no display

Is there 5v on the Q751 base?

[Francesc V.]

Re: Technics SA-EX310 dead...no sound, no display

Yeap!!! it's fixed...........it had "nothing".
Desassembled front panel. Cleaned PCB and connectors with isopropanol and came back to life.

I will be testing it to see if everything is ok.

Regards,
Francesc.

[Francesc V.]

Re: Technics SA-EX310 dead...no sound, no display

Is there 5v on the Q751 base?

Before cleaning...........base had 0V. Now it has the voltage you mention.

[Devil_rider]

Re: Technics SA-EX310 dead...no sound, no display

Good job!