RCA CTC40 Audio issue

[freakaftr8]

Anyone ever had the audio go out on one of these puppies. I studied the schematic and it all points to IC301 being the culprit.

I heard of this STK being weak or unreliable. Does anyone happen to know the value of IC301 for the audio output. Also if anyone has one to sell, let me know. Think im going to use this for my daily set. The CTC17 has some more bugs to work out at a later time.

Thanks

[bgadow]

I have a pile of NOS RCA parts but I'd need a part number to look it up. Might get lucky. Got the Sams? That will have the P/N in it. I can dig it out if you don't have the #, probably be too tired to do it tonight, though!

[rca2000]

It is on the somewhat large, stand-up sink-- and it is in a TO-66 case,, near the middle of the chassis. It runs on pretty high voltage--for a transistor--about 150 volts or so--IIRC. I'll have to look in my manual for my 2000 to find out for sure--since the audio output circuit is the same--only that DC volume control BEFORE the audio preamp IC is different. The preamp IC drives the transistor--and it drives the output transformer--and then the speaker.

These HV NPN transistors are known for their tendency to "break down" and not produce any output--or little output or scratchy sound. That is a Class A amp--and it runs HOT--regardless of the volume setting--and so...they sometimes "die' after some time.

Check the collector of that transistor and see if there is apprecible voltage there--I KNOW it is over 100 volts. if NOT...check and see if that emitter resistor is open--and if it is....the transistor has likely taken a dump. Particularly--if the sound just "quit"--that transistor is suspect.

One way or another--we CAN walk you thorough getting that ol' girl "talking " again.

[jeyurkon]

I have some NOS parts too, but like bgadow would need the part number.

John

[freakaftr8]

Hey cool thanks for the help guys. I let you know my findings when I get home tonight.

[freakaftr8]

Well heres what I have. Two section of one large heat sync tith 2 TO-66 style transistors. Off the collector of the suspect one I am getting 155v and the emitter is -.700v or so. THe schematic says about -1.5 off the emitter and 155v off the collector. . Off the other transistors collector I am getting 75v. and -5v off the emitter and the schmetic says -10.5v off that emitter. Does this mean these TO-66 style transistors are ok?

[freakaftr8]

Excuse my stupidity... This chassis came out of a combo unit famed the Royal Dane. The chassis sent 120v to an amplifier that was shared with the stereo. And of course I had a speaker tied into a low level output. So all I needed to do was wire the leads into an amplifier and viola. Sound... Great sound..

Thanks again guys.. Back to the Zenith. lol

[bgadow]

Ha! Felt good to figure that out, didn't it? FWIW, I have the IC, #126871. Back on the shelf she goes...

[freakaftr8]

Lol thanks Bryan