Yamaha AX 500u schematic, integrated stereo amp

[1ampman]

I found one on HiFi Engines but the voltage numbers can't be read. I have no sound and the speaker relay will not activate. This is a nice small stereo amp....

[MarkusBass]

I have the schematic but also without visible voltages. But in most cases voltages are not needed to fix an amp (especially if you have a schematic). Have you check whether there is a signal before the relay? If the relay failed, all voltages will be correct. So the voltages in the case will not help.

Mark

[Jazz P Bass]

As Mark said, is the signal reaching the relay?
Is there a voltage drop at the relay coil at power on (after delay)?
The relay may be working but the contacts may not be any good.
As to voltages, the ones that you need, to verify the protect circuit, are not marked as such but the circuit relies on the +16 volt supply.
If there is any Vdc on the output transistors, the protect circuit will engage.
So you need to check out the amp.
Find the relay coil pins. There should be 30 some ohms on the coil.
Use your meter (power off, supply drained) & verify that the output transistors are not shorted.
At power on, measure the emitter voltage of the output transistors. It should be zero Vdc.
If all that checks out you may have a protect circuit fault.
The relay should have a dc voltage on the coil at all times.
Q134 base will go high at power on (after C214 delay)
Q134 turns on Q135 (which connects the relay coil to ground, engaging the relay)
Volts dc on the output will trip Q133, turning off Q134.(which turns off the relay)
Happy hunting.

[1ampman]

I found a blown output and blown .22 ohm emitter resistor. Only 2 outputs per channel. It's a Mitsubichi B1163A flat pack. Are there any direct subs?

[J M Fahey]

They are available on EBay.

[Jazz P Bass]

Probably fake.
They have not made that transistor since 1993.

[1ampman]

the amp uses 2sa1301 & 2sc3280.... I have 2sa1302 and 2sc3281 .... Would they work. the power supply +-57v

[MarkusBass]

Amazon.com: 2SB1163 B1163 PNP Transistor Matsushita: Everything Else

Mark

[Jazz P Bass]

the amp uses 2sa1301 & 2sc3280.... I have 2sa1302 and 2sc3281 .... Would they work. the power supply +-57v

The 1302/3281 combo will work fine.
They simply have a higher rating.

[1ampman]

I found a glass diode Jap#1ss133 it has 57v on one side and the othe side is 42v (bad channel) The good channel has 57v on one side and 1.8v on the other. So what could I sub for this switching diode? I have some switching diodes with different numbers.... and thanks to all......

[Jazz P Bass]

I found a glass diode Jap#1ss133 it has 57v on one side and the othe side is 42v (bad channel) The good channel has 57v on one side and 1.8v on the other. So what could I sub for this switching diode? I have some switching diodes with different numbers.... and thanks to all......

What is the schematic designation of the glass diode.
It sounds like you are measuring the base voltage of the output transistors.
If the base is sitting at 42Vdc, something is shorted.
Check the diode with your meter. (lift one leg from the board)
It is probably o/k, but a driver or bias transistor is shorted.

[1ampman]

I replaced the diode with a 4148 and removed the bias transistor (which tested OK). When I fired it up to check voltage the resistor next to the driver burnt up. I'll get the resistor number so we can be sure what it's used for. I'll also pull the driver transistors like you say. Thx for posting the schematic. Hopefully I won't take too much of your time...

[Jazz P Bass]

If you have not done so already, remove any load (ie:speaker) from the output until the amp is proven stable.
Did the glass diode show up as bad when you tested it out of circuit?

[1ampman]

Todays tests. Q127 output shorted, Q123 driver shorted w/burned out RR221, Q119 tests good, Q139 Bias transistor is good, Q125 output tests good, should I pull Q121 or check it for shorts? I'm not sure how far to back.....