C70: Fuse Blew

[avionic]

Using the diode check maybe this is easier..

https://audiokarma.org/forums/index.php?threads/testing-transistors.201303/#post-2362176

 

[Gary D Olson]

OK.. that looks bad...
Post # 55 reading ? Emitter and Base ?

OL both ways between emitter and base

 

[avionic]

Maybe we're both getting tired


OL both ways between emitter and base

Me thinks your meter is FU.. Or that transistor is totally "open" ie. bad

 

[avionic]

With the transistor still remove what is the resistance on pin 4 of the bridge rectifier to chassis ground now ?

 

[Gary D Olson]

With the transistor still remove what is the resistance on pin 4 of the bridge rectifier to chassis ground now ?

7.0 (ohm mode, positive lead on pin 4 and negative lead grounded)

 

[avionic]

OK... Pull and test TR539 and TR546 and C590
Do you have a service manual?

 

[Gary D Olson]

Me thinks your meter is FU.. Or that transistor is totally "open" ie. bad

I just retested. In ohm mode, right? I just tested outside pins only. Neg on left pin and pos on right, then in reverse. Still OL on both.

 

[Gary D Olson]

I think so but I'm wiped out and losing what little competency I have. Hell getting old. Am I in over my head?

 

[avionic]

With TR547 out of the circuit. And the large cap out of the circuit the only possible 7Ω path to ground is a shorted TR545 and TR539.

 

[Gary D Olson]

With TR547 out of the circuit. And the large cap out of the circuit the only possible 7Ω path to ground is a shorted TR545 and TR539.

Okay. I'll need to pick that up tomorrow. And what should I do after they're out?

 

[avionic]

Order some parts..


TR539
https://www.bdent.com/2sa999-mitsubishi-audio-transistor.html
TR545
https://www.bdent.com/2sk246bl-toshiba-audio-transistor.html
TR547
https://www.bdent.com/2sd1047-sanyo-audio-power-transistor.html

 

[Gary D Olson]

Okay. Will pick back up tomorrow. Thanks a million for the help. Feels so unnatural to have my C70 fail.

 

[avionic]

C-70 is one of my favorite pre-amplifiers.

 

[Gary D Olson]

okay, TR539 & TR546 out Please ignore my ADD note taking. notesA999 37E oriented with text facing chimney)
c590 OUT notes (small cap between the two big blue caps)

continuity test
TR539 pos on pin 1 and neg on pin 3: .659v
pos on pin 2, neg on 3: .651v
OL all else

TR546 pos on pin 1 and neg on pin 3: .661v

pos on pin 2, neg on 3: .649v
OL all else

C590 seems dead. no readings coming or going.

​

 

[avionic]

TR546 pos on pin 1 and neg on pin 3: .661v

pos on pin 2, neg on 3: .649v
OL all else​

This is not a normal BJT transistor. It is a JFET junction field effect transistor.

C590 seems dead. no readings coming or going.

Use the ohms function or capacitor check function.

 

[Gary D Olson]

I'm obviously in over my head.

I did try the ohms function on the cap and got nada. Should I be use MΩ? Something else?

 

[Gary D Olson]

This is not a normal BJT transistor. It is a JFET junction field effect transistor.

Use the ohms function or capacitor check function.

Definitely in over my head. No idea the difference between JFET and LBJTQ transistors. Apparently I'm just smart enough to know I'm an idiot. Definitely not smart enough to keep my hands out of such a nice piece of gear as this. I did try the ohms function on the cap and got nada. Should I be use MΩ? Something else?

 

[Gary D Olson]

… or put it back together to send out for repair?

 

[avionic]

LBJTQ transistors.

LOL....

 

[Gary D Olson]

For anyone who may view this thread later and wonder why it came to a screeching halt; I pm'd avionic about sending my C70 off to him for rescue. To that end I'm currently looking at possible banks to rob.

Thank you avionic for attempting to guide me through this.