Yamaha rxv-497 /Power supply problem/

[coojoe_213]

Hi. I have problem with PS on this amp.
The problem is +15 V /my voltage is 11.68/ In service mode i have 48 value, normal value on PS are 54-84.
There is nothing shorted, i change some capacitors /c138, c139 and c145 but the same situation/. Could you where i wrong?

[madan1]

Re: Yamaha rxv-497 /Power supply problem/

Are you getting the right V readings on q123?

B - 14.7V
C - 35.9V
E - 15.3V

[budm]

Re: Yamaha rxv-497 /Power supply problem/

https://www.badcaps.net/forum/attach...2&d=1494612444

That is an error in the diagram for the Voltage reading of NPN Transistor Q121, it is showing Base Voltage of 14.7V and the Emitter of 15.3V that means that Transistor is not BIAS on, you cannot have Emitter Voltage be more positive than the Base Voltage for NPN Transistor and expect it to be on.
The output Voltage on the Emitter Voltage will be about 0.6V less than the Voltage at the Base, so to get 15V output, the Base Voltage will have to be at least 15.6V.
So verify what you have on Q121. It may be bad Zener diode for this linear regulator circuit. The negative 15V supply functions the same way but made for Negative Voltage.

[coojoe_213]

Re: Yamaha rxv-497 /Power supply problem/

At this moment i have 39 V - collector , 10.3V - emitter, 10.3V - base on Q121 /c4495/.
R177 is good (1om).
On cathode D109 -10.3V, anode - 0V?
I thing to change this zener d109. What do u thing?

[budm]

Re: Yamaha rxv-497 /Power supply problem/

At this moment i have 39 V - collector , 10.3V - emitter, 10.3V - base on Q121 /c4495/.
R177 is good (1om).
On cathode D109 -10.3V, anode - 0V?
I thing to change this zener d109. What do u thing?

Check that Q121, the Emitter Voltage is the same as the Base Voltage so it may mean that you have shorted E-B junction of that Transistor.

[coojoe_213]

Re: Yamaha rxv-497 /Power supply problem/

Hi everyone. Problem solved. ZD109. After replace, all is perfect. Thanks all.

[budm]

Re: Yamaha rxv-497 /Power supply problem/

But did you verify that Base and Emitter VDC are no longer showing the same Voltage value? They cannot be the same.

[coojoe_213]

Re: Yamaha rxv-497 /Power supply problem/

I have on Q128 emmiter -14,8V (3.6ma) which is perfect. This negative voltage powered all operate amps in all receiver.

[budm]

Re: Yamaha rxv-497 /Power supply problem/

I am talking about Q121 in post 4. If the E-B junction is shorted then then the transistor is no longer part of the regulation circuit.

[coojoe_213]

Re: Yamaha rxv-497 /Power supply problem/

Hi, on Q121 voltages are the same in service manual, becouse before i buy diode, i change D109/D110 (they are same). At this moment D109 is original, D110 is equivalent diode which i buy. Voltages are 36.2/15.5/14.9