Mysterious Korg Tape Echo Failure

[neddyboy]

I decided to change the tape loop on my Korg Stage Echo since the signal was getting a bit noisy. The unit worked just fine before this. I put in a new loop that I bought a few years ago -- correct tape etc. I cleaned the heads and demagnetized them while I was in there, got it all back together and...nothing. Signal passes, the reverb part of the effect works, but I get no echo. I thought maybe I put the tape in backwards so I tried flipping it. Nothing. I've tweaked all the controls, tried different loops, made sure the tape path is correct etc. WTF? Did I kill the heads with the demagnetizer? I did it the way I've always done, which I now see is wrong. I turned the demagnetizer on near the heads, stroked the tip on each of the heads, then slowly withdrew the demag to three feet from the heads. I looked up directions and tried again, triggering then moving the demag in from three feet etc. but still nothing. Ack! Any tape head gurus out there?

[Enzo]

Got the old tape? SLip it back on and play. There should be something already recorded on the tape, so if it has a sound on sound setting, see if it will play back the old tape.

Otherwise, I';d want to scope it to see if the bias oscillator is working, and I'd tape on the play head to see if I get a pop out the output.

[neddyboy]

Hey Enzo, thanks for the reply. I've put the old tape back in, but I get nothing. I've tried two new tapes (both sides) and the old one (both sides). This unit has five heads that I assume to be Record, Playback, Playback, Playback, Erase. I'm not savvy enough to do the other stuff you mentioned, and it would be a huge coincidence that the bias oscillator went bad at exactly the same time I installed the new tape. The unit worked great until my "maintenance". Any other suggestions?

[Enzo]

It would be a huge coincidence if you just dropped a tape on it. But if you had to do ANY disassembly, that is exactly when a wire can get knocked off of something or a connector pulled halfway off some pins.


I was not suggesting anything fancy. To make echo, the thing rtecords your sound onto the tape, and plays it back a second later from a different head. That means at any time the tape SHOULD be full of whatever had been played through it. To get no echo, you either have a problem where it cannot play back what it has recorded, or it cannot record onto the tape.. By slapping an old tape into it, hopefully that tape is full of old recorded sound. Many echo machines have a sound on sound setting, which means it will record onto the tape, then you can play that back while playing along with it. In other words, unlike during echo, sound on sound doesn;t erase. So playing the old tape might reveal that the system will play back sound that is already on the tape, meaning the problem is a lack of record. Or it won't make sound, meaning the playback area has the issue.

Have you ever taken a small screwdriver and tapped the end of it onto a pole of your guitar pickup? It makes a pop sound. By doing something similar on the playback heads, you can see if the playback part works. If you get a pop, it is working.

[neddyboy]

Okay, gotcha. So if the old tape doesn't play back you're saying the issue is in the playback, right? The Korg doesn't have any way to turn off the erase head, other than rerouting the tape around the erase head. Regardless, there's nothing on the old loop, or I'm not getting any playback with the old tape loop. I thought maybe I had turned the machine on while I was demagnetizing and had fried something in the circuit. Apparently the demag can damage the circuit that drives the record head, but none of the sources I've seen tell me what component might have been fried. I'm going to try to use my multimeter to see if there's any signal coming into the record head. I'll also do the "pop" test you suggest. Oh, and I didn't disassemble anything, just cleaned the heads and demagged, so no chance to bump anything loose.