Yamaha yst-sw012 subwoofer no worky

[nosaj]

I'm working on a yamaha subwoofer the 15v -+ rails were blown replaced the zeners and got the power supply back up. Still no signal so i want to trace through the circuit.
So given front end of this amp has a LPF and HPF what frequency should I be using? i see the frequency response is 28hz to 200 hz . So I'm guessing a 100 hz is a good target.

Looking at the input sensitivity it says 50 mv (50hz 50 watts, 5 ohm) Does this mean input a 50hz signal will yield 50 watts into a 5 ohm load?

Thanks,
nosaj

[g1]

100Hz should be good, and 50mV seems to be what it needs to give full power at 50Hz (50W into 5 ohms).

[Jon Snell]

R45 & 46 usually fail if the wrong mains voltage is selected but can fail for other reasons as well.
Have you 0v on pin 10 of IC1?
50W into 5R means what it says.

[nosaj]

R45 & 46 usually fail if the wrong mains voltage is selected but can fail for other reasons as well.
Have you 0v on pin 10 of IC1?
50W into 5R means what it says.

R146 was burnt as well as the zeners.
And yes there is voltage at pin1 about 3.45vDC so i guess a new module is in order.

nosaj

[nosaj]

New module
Pin1 3.8vdc schematic shows .2
Pin2 .01 .2
Pin3 0 0
Pin4 -31.8 -34.9
Pin5 14.3 14.5
Pin6 4.95 1.1
Pin 7 -2.85 -1.1
Pin8 -32 -35.2
Pin9 32 35.1
Pin10 3.96 0

Pins1, 6, 7, 10 stickout to me but not sure where to go on it.

nosaj

[The Dude]

By "new module" I presume you are talking about the output IC? Pin 10 is the output and has substantial DC voltage. I would be looking for where that's coming from.

[g1]

You had that voltage at pin1 with the old and new power IC. It can only be coming from IC6. Why?

[nosaj]

I'll followup with IC6 voltages tomorrow.
Thanks,
Jason

[nosaj]

Ok IC6
Pin1 -14.87
pin2 -14.85
Pin3 0
Pin4 -15
Pin5 -14.86
Pin6 1.9
pin7 3.9
Pin8 14.85


Further descrepancies include IC6 listed as upc4570 9pin sip. The service manual corresponds. But in trying to figure out why I am missing pin9. The sip reads as njm4580 an 8 pin sip. Its looks like the A portion of the sip is bad to me.
nosaj

[Jon Snell]

Pin 8 has to be the same as pin 7 they are connected together! Are you reading the correct orientation?

[nosaj]

Pin 8 has to be the same as pin 7 they are connected together! Are you reading the correct orientation?

Well I do know IC 6 is not a 4570 Its a 4580 8 pin sip. I will double check the model and look for any pcb identifications and report back.
nosaj

[g1]

njm4580 pinout is different than upc4570. There is probably a different version of schematic.
Or if it is a failed repair attempt, someone may have installed the wrong part.

[nosaj]

Nope not a failed repair. The silk screen on the PCB shows 1 and 8 on each end. IT is a yst-sw012. Only service manual i can find is the one I linked.
i do have some njm4558s on hand to test with.
nosaj

[g1]

So it seems the board is a different version using the 4580. Your pins 1&2 (where measured voltages are same) correspond to pins 7 & 8 on schematic.
Datasheet attached.

With pin3 at good 0V, pin1 should also be 0V (supplies at pins 4 & 8 are good)

[Jon Snell]

Well I do know IC 6 is not a 4570 Its a 4580 8 pin sip. I will double check the model and look for any pcb identifications and report back.
nosaj

YST-SW012 schematic attached.
Quoting the correct model number and any suffix would have helped, my crystal ball seems a little foggy!
Yes, the first part ot the 4580L appears to be faulty.