Yamaha C-60 Woofer Pumping Problem

[avionic]

R276 289mV DC
R275 5mV DC

Thats not even close. Should have been - 28vdc and +28vdc ballpark..

 

[avionic]

Are you grounding your neg test lead to "E" copper bus. And probing with the pos test lead to each end of the two resistors Should have +/- 27-28 volts on either end of each resistor.

 

[kermit_xc]

alright - correction (you are a true scholar and a GENTLEMAN!)

R275 28.91V DC
R276 31.75V DC

 

[avionic]

Now select AC voltage on your meter and measure the AC voltage on the two red wires coming from the transformer each wire should be 23vac.

 

[kermit_xc]

Now select AC voltage on your meter and measure the AC voltage on the two red wires coming from the transformer each wire should be 23vac.

Both read 24.83V AC

 

[avionic]

Go back to DC voltage. I need to know the base and emitter voltages of TR149 and TR150.

 

[avionic]

 

[kermit_xc]

T149 Vbe: 1.246V, Veb: 1.211V
T150 Vbe: 1.306V, Veb: 1.327V

 

[avionic]

T149 Vbe: 1.246V, Veb: 1.211V
T150 Vbe: 1.306V, Veb: 1.327V

No.....

Are you grounding your neg test lead to "E" copper bus. And probing with the pos test lead to each test point

 

[kermit_xc]

No.....

T149 E: 19.21V B: 20.5V
T150 E: 9.78V B: 9.30V

 

[avionic]

T150 E: 9.78V B: 9.30V

Bingo...

 

[avionic]

Do you have +/- 12vdc on pin 1 and pin 5 of IC107 ?

 

[kermit_xc]

Bingo...

I think so the ultimate source of my -B1 readings?

 

[avionic]

Pick up a couple 4.7KΩ 1/4 watt film resistors.

Are you sure you replaced with a 4.7KΩ resistor for R271 ? Yellow/violet/red/gold

 

[kermit_xc]

Do you have +/- 12vdc on pin 1 and pin 5 of IC107 ?

nope
IC107 1: -21.34V; 5: 5.92V

 

[kermit_xc]

Are you sure you replaced with a 4.7KΩ resistor for R271 ? Yellow/violet/red/gold

yessir - bands match and just re-measured - we are talking about the ones right in front of the TR-149/150 - correct ?

 

[avionic]

Looks like zener diode D133 may be shorted so far.

 

[avionic]

yessir - bands match and just re-measured - we are talking about the ones right in front of the TR-149/150 - correct ?

I think so.

 

[avionic]

The chip IC107 may be history as well.

 

[kermit_xc]

Looks like zener diode D133 may be shorted so far.

indeed it is !!! D134 looks good

The chip IC107 may be history as well.

any replacement options or are we talking unobtanium ?