Mitsubishi DA-L70 - NO Sound - Help Please.

[Paulluap]

Hi
I have a DA-L70 stereo unit that I have had for years. I brought it from a secondhand shop. Never had a problem with it. I don't have speakers plugged into it, just use RCA outputs to another amp.

One day I went to show it off and it wouldn't turn on. Found the F901 fuse had blown. Replaced fuse and the system started up again.
I thought fixed, replaced some belts on the tape deck while it was open, all good to go. But I never tested the RCA output until I recently replaced my amp I am using.
That's when I worked out I have no output from the speaker terminals, RCAs or the head phone jack on the DA-L70.
Found drawing and pretty sure the protection relay is not turning on.
I was told to replace the Amp STK4151.

I have installed a new STK4151 amp but the unit is still not working.

The voltages have changed though on pins 1 to 18 as shown in red on the attached. Voltages in black were before I change the amp. Not sure what to look for next.

Any help would be appreciated. A few drawings attached.
Cheers Paul

 

[Nigel Goodwin]

If you're not using the speaker outputs, then you don't need the STK4151 - you could simply remove it.

From your voltage readings the new STK looks to be faulty, those chips are pretty well long obsolete, and any for sale could well be fakes - pin 10 should be zero, and it's not. A minor mistake in fitting it (should as a solder short across two pins) could have instantly killed the chip as well.

Take the chip out, and use it without, just as a preamp (as you do anyway).

 

[Paulluap]

Hi Nigel
Thanks for the fast reply. Brought the amp from Ali-express so probably is a fake. Lol
I will remove it and see if it works.
Cheers Paul

 

[Nigel Goodwin]

Hi Nigel
Thanks for the fast reply. Brought the amp from Ali-express so probably is a fake. Lol
I will remove it and see if it works.
Cheers Paul

Presumably the muting circuit, as well as disconnecting the speakers, also mutes the preamp stages - and the high negative voltage on pin 10 will certainly trigger the muting circuit.

 

[Paulluap]

Mate you are a legend!!!!
Removed the amp and it works perfectly.

Thanks so much Nigel.

For future events, what do you mean by this " A minor mistake in fitting it (should as a solder short across two pins) could have instantly killed the chip as well"

Cheers Paul

 

[Nigel Goodwin]

Mate you are a legend!!!!
Removed the amp and it works perfectly.

Thanks so much Nigel.

For future events, what do you mean by this " A minor mistake in fitting it (should as a solder short across two pins) could have instantly killed the chip as well"

Cheers Paul

If you accidentally shorted out two of the pins when installing it, which isn't hard to do, then the chip could easily be instantly blown when you powered it up.

Incidentally, we keep refering to it as a 'chip', where really it's not - it's a 'module', essentially a ceramic substrate with surface mount components on it.