Vintage Pioneer SA-520 amplifier faulty display and aux-in

[Wirko]

Evetything seems fine so far ... you shoud be getting the same 19.6 V on the zener diode. Its wires look as if they were oxidized though, so it may be hard to make proper contact with multimeter probes.
Next step would be to solder the Q23 back into the circuit, then power the amplifier on and measure the voltages at all three terminals of the transistor relative to ground. We'll soon see if it's good or bad.

 

[Robee]

Evetything seems fine so far ... you shoud be getting the same 19.6 V on the zener diode. Its wires look as if they were oxidized though, so it may be hard to make proper contact with multimeter probes.
Next step would be to solder the Q23 back into the circuit, then power the amplifier on and measure the voltages at all three terminals of the transistor relative to ground. We'll soon see if it's good or bad.

Ok, waiting for the replacement Q23, Wirko. I don't feel like doing the soldering with already cut leads because I'm not that used.

In the meantime I'll try to clean the zener leads and measure it again.

I will get back to you as soon as the q23 arrives. Thank you again

I tested the diode voltage again but in DC: it has the proper voltage! My bad

 

[Wirko]

You can solder the transistor to the bottom (copper side) of the PCB if its leads are too short. It's tricky and dirty, not something I'd usually recommend. Also, do you happen to have any other transistors on stock? Almost any of the NPN type, and powerful enough (= large enough) would do.
There's one more thing you can do for the sake of diagnosis: look into the VFD in total darkness. You may see a faint glow of heating wires (red horizontal lines) or display segments (blue/white). Each would indicate that a specific part of the electronics is working.
As for the multimeters, I have two other models from the same series. Very good for what you pay.

 

[Jacky_BEL]

Is there a way to visually inspect the VFD for damage , cracks? Maybe it has lost it vacuum and then it won't work anymore.

 

[Robee]

You can solder the transistor to the bottom (copper side) of the PCB if its leads are too short. It's tricky and dirty, not something I'd usually recommend. Also, do you happen to have any other transistors on stock? Almost any of the NPN type, and powerful enough (= large enough) would do.
There's one more thing you can do for the sake of diagnosis: look into the VFD in total darkness. You may see a faint glow of heating wires (red horizontal lines) or display segments (blue/white). Each would indicate that a specific part of the electronics is working.
As for the multimeters, I have two other models from the same series. Very good for what you pay.

I'm glad to know I bought a good multimeter. I wanted a cheap one since I'm not a pro but I even wanted something not too bad. I checked on web forums and read a guy saying it was good. I bought it from China.
I'll check if I can give soldering a try... And I'll check the darkness trick

Is there a way to visually inspect the VFD for damage , cracks? Maybe it has lost it vacuum and then it won't work anymore.

Didn't think that. I will check this out too.

Thanks guys!

 

[Robee]

Thank you very very much. I fixed it resoldering the old transistor. However I would haven't never found the problem without your help because the transistor was just the one you said.
I will never thank you enough. Should you happen to be in Italy, Sardinia, let me know and I'll tell you where I am. I owe you some drinks!

Video

 

[Wirko]

Thank you very very much. I fixed it resoldering the old transistor. However I would haven't never found the problem without your help because the transistor was just the one you said.
I will never thank you enough. Should you happen to be in Italy, Sardinia, let me know and I'll tell you where I am. I owe you some drinks!

View attachment 237583

Video

That's great! I'm glad to be able to help repair old electronics. So, the only thing that failed were the solder joints of the transistor, which probably had been knocked too hard?
Tracking down the point of failure is sometimes hard in old stuff, wires and PCB tracks break, every switch and resistor and capacitor can break down but still look like new, etc. And of course the solder, cracked because of old age and mechanical stress, which results in unreliable electrical contact (cold joints).

 

[Robee]

That's great! I'm glad to be able to help repair old electronics. So, the only thing that failed were the solder joints of the transistor, which probably had been knocked too hard?
Tracking down the point of failure is sometimes hard in old stuff, wires and PCB tracks break, every switch and resistor and capacitor can break down but still look like new, etc. And of course the solder, cracked because of old age and mechanical stress, which results in unreliable electrical contact (cold joints).

Yeah! It was the joints. Actually I'm not sure whether they desoldered because of my little delicate cleaning some years ago or because they reached too high temperature. Anyway i didn't do a visual check up then i found it only when i was pointed to the Q23 by you and the others.
Thanks again Wirko