More tape machine woes: crosstalk in sync only

[RoadrunnerOZ]

The ground lines run straight across each row of cards - not sure where the line to the sync head runs though but easy enough to trace as I’d imagine that there would be a feed straight to the head connector socket you can trace back with a meter and a magnifying glass

 

[RoadrunnerOZ]

With all the cards removed of course

 

[RoadrunnerOZ]

Are the cards numbered - you want to be sure to put them back in the same slots

 

[EmilFrid]

Yes they're numbered and I will put them back in correct order after looking at the board

 

[juanito2008]

I don't really understand what this would show. I already know I'm way out of spec when it comes to crosstalk. Also none of the adjacent tracks are in record. It sounded like you thought both were?

Sorry, i thought the tracks were in record.
But if they are not in record, you don't send anything to the sync head.
It means the sync head can hardly be involved.

Do you have to solder to change the head ?

 

[RoadrunnerOZ]

This occurs when one track is in record, the adjacent tracks are in sync playback mode playing back previously recorded tracks which must come off the record head so the audio lines up - if you listened back off the playback head and recorded the new recording would be out of sync. The meters will show incoming signal if in record and playback signal off tape for non record-armed tracks so the sync (record) head is in circuit for both functions, what’s being seen is audio leakage from the record armed track to the adjacent tracks in sync playback mode.

 

[radardoug]

So can the OP clarify, the leakage only occurs when the adjacent track is in record? Normal sync playback is fine?

 

[EmilFrid]

It is like this: channel one and three are in sync playback, channel two in record and receiving signal

 

[juanito2008]

If i understand well, you have a prerecorded signal on Channel 1 and 3 and on channel 2 in record we see the crosstalk.
Am i right ?
It's confusing because the red light are on channel 1 and 3

 

[EmilFrid]

No, I haven't prerecorded anything, as I wrote before I don't even have to have tape threaded for this to happen. The red lights are peak lights, not recording indicators

 

[juanito2008]

So the level you read in sync playback (channel 1 and 3) has more level than the signal you send on channel 2 ?
really weird!
When you say that you don't even need to have a tape threaded, are you only in rec ready in channel 2 or
do you manage that the multitrack believe there is a tape and you can press record ?

 

[Brian Roth]

No, I haven't prerecorded anything, as I wrote before I don't even have to have tape threaded for this to happen. The red lights are peak lights, not recording indicators

Whoa! Something odd here....

Disconnect line inputs 1 and 3 on rear of the recorder.

Bri

 

[RoadrunnerOZ]

The line input sockets shunt to ground with no jack inserted - anyhow the line input is switched out when in sync playback so you could have a full signal coming in the line in and nothing should show on the meters. All these connections come back to the same board as we have been discussing.
You should be able to leave an input loom connected and no matter how much crosstalk in the loom you should not see anything on the adjacent track meters unless they are record armed and there’s enough leakage to register (or if playing a tape). P222 of the manual diagram 9-105 Connector Board - the repro and rec/bias cards are all also mounted on this board.

 

[radardoug]

The OP needs to clarify. Is channel 2 in record? Not just record armed. If you have crosstalk while not in record, its nothing to do with bias leakage.

 

[RoadrunnerOZ]

The signal on 1 & 3 meters disappears when input signal to track 2 is off

 

[Brian Roth]

OK, I wasn't clear in my "logic". Emil said "I don't even have to have tape threaded for this to happen."

If the machine is not printing a signal to track 2, there should be no signal going to the record head. Relay K1 on the record card will be routing the "hot" side of the record winding to the sync input of the repro card and thus the record winding is disconnected from the record driving amp. Hence, no way for audio on track 2 to leak into 1/3 via the record head.

Although....maybe Emil figured out a way to "fool" the machine into going into record mode with no tape???? Ie, the spooling motors madly spinning in opposite directions and the pinch roller engaged/capstan turning....

Dang....thought I had an "aha!" moment. Still pondering.....

Bri

 

[radardoug]

The signal on 1 & 3 meters disappears when input signal to track 2 is off

Yes, but in or out of record?

 

[Brian Roth]

The signal on 1 & 3 meters disappears when input signal to track 2 is off

Right....that should eliminate bias leakage. I was trying to figure out what other "sneak paths" could be in play here. And it seems it would have to be global in nature from what I've been reading.

Hence my (probably bogus...) idea to start stripping down the I/O wiring connected to the machine.

Bri

 

[RoadrunnerOZ]

When the track is armed it’s the same as being in sync playback mode - until you punch in the head’s not connected to any signal, it should be (if tape were running) playing back what’s on tape like the other tracks - the meters are just monitoring input from the armed track - this should cease (if my tape machine logic is correct here) when play is pressed and they should show what’s coming off tape at the sync head until record is pressed.

 

[Brian Roth]

It was Emil's post #70 that raised my evebrows. Of course, "no tape threaded" isn't totally clear as I mentioned in my post #76. We're just guessing at this point without some clarification.....

Bri