Now that the radio works, where the h@ll did this sine wave come from?

[Ken]

Top radio board woks fine it seems, but I now have a 20Vpp sine wave fricken everywhere. Sometimes it's attenuated, but still there, even when the main power switch is turned off. By everywhere I mean including ground. It seems to be the strongest at the power supply, with the full 20v seen at Fuse 502 down by the bridge in the power supply. It goes almost all the way away when the power cord is pulled.
My next step will be this afternoon when I have some time to sit down and swap in known-good functional parts like the amplifier board & power supply to see it's affect. I can't do this with the tuner board & main cassette board because they have had parts removed for the ongoing repair.

I'm just hoping that this is a normal modulation I'm seeing or something like that. I haven't looked at the manual yet but I think it's 19khz or something. Like I said, later today. The radiator in the truck has a leak that needs to be fixed and the wife wants a hi-def antenna up on the garage for the Seahawks game. Thanks ahead of time for a chime-in if somebody's seen this before.

 

[Ken]

Whew, that was an adventure!

Well, it looks like this sine wave is here to stay, at least temporarily. I thought swapping out the damaged middle board would affect the signal, but no. Then swapped out the amp board for the other one and it's still there. I'll check the bridge & the power supply tomorrow night. A symptom of this problem could be that the radio tuning meter always reads between 2 & 3 (even when the deck is on) and as a battery check it pegs to the right.

Byproduct of swapping out the broken middle board, the deck now works (yay!) Had to re-swap a whole bunch of parts, like both lever-actuated switches along with their associated 30 pin sets of contacts (play & record,) both meters, and 4 of the variable resistors.

Still a long way to go, but I'm starting to see the light at the end of the tunnel. Double yay!

 

[jimmyjimmy19702010]

Keep going, I'm super impressed with your dedication!!

James....

 

[skippy1969]

Man you are determined! Way to go, pretty soon you'll have it all sorted out.


Sent from my iPhone using Tapatalk

 

[Ken]

Boy howdy, I just got a chance to see some of other peoples repair work that's ongoing. I've been buried in my own so far I've not been able to keep up with all the cool shiat other people are working on, specifically Joe and Trippy. Way to go, it's looking really sweet on your projects. I guess it's that time of year.

Thanks for all the kind words, guys. I actually put this off for 4 years, but NOW is the time. Santa's bringing me a fully-functioning Tele for Christmas this year.