Ok cool
More tape machine woes: crosstalk in sync only
- Thread starter EmilFrid
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Edit: never mind, with cards fitted there is continuity
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Record head ground on pin L of the record bias card is supposed to be tied to pins 6, 7, 8, F, H, J which are supposed to be connected to 0V - pin 19 of the power supply connection on the connector board - the 30V ground - one of the three 0V black cables connected to this board
What about the Line In grounds?
All connections right back to the power supply at the power supply?
Maybe reflow all solder joins for incoming cabling, reinstall the board, reinstall all the cards and check for crosstalk - then if no change try removing card pairs (rec/bias and repro) one channel at a time and see if the problem persists and drops out with one pair out of circuit - bit tricky doing adjacents with a card pair missing but you get one adjacent at that location and you may find the problem is residing on a particular card or location with a card installed. If it does you can then eliminate if it’s the rec/bias or the repro card or if the location by swapping in cards from another channel.
I've now reflowed the solder joints in question, as well as swapped cards back and forth but with the same crosstalk across the board as before. I also checked the line outputs of adjacent cards and it shows the same clean sine wave that I sent to the track in record mode. If I remove the head, the crosstalk disappears, like before. I also, without high hopes, tried tying the head's GND directly to the GND trace on the connector board with no success. At this point I have zero clue what's going on.
At 10 khz the wave is even louder on the adjacent tracks than on the one in record mode, but sensitivity drops A LOT to an ok crosstalk at 1 khz.
Edit: also, the further away I get from the channel in record mode, the smaller the crosstalk
At 10 khz the wave is even louder on the adjacent tracks than on the one in record mode, but sensitivity drops A LOT to an ok crosstalk at 1 khz.
Edit: also, the further away I get from the channel in record mode, the smaller the crosstalk
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Pulled cards one by one?
Do you have an oscilloscope you can check the dc rails and grounds with?
juanito2008
Member
- Joined
- Feb 25, 2017
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- 16
It's difficult to answer you.
You ask someone to answer a weird problem. Either in your problem description or your crosstalk problem.
If i sum up.
First your problem description :
-You have a perfectly working machine.
-You change the heads.
-The heads has connectors. So you don't solder, resolder anything.
-You have your crosstalk problem.
-You put back the original heads.
-The problem remains
There is no explainations for that. Even if you bend a pin or whatever. As your crosstalk problem is on all tracks.
You probably forgot to tell us something.
Second, your crosstalk problem :
-Your crosstalk level is higher than the signal you record on a well aligned machine.
How can it be ?
Do you think there is a possibility you invert the recording and playback heads ?
I doubt you could aligned the machine anyway.
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The connectors have all the same number of pins so that is possible - but the machine still would see three sets of heads with 16 mag coils and whether repro and rec heads were swapped or not it shouldn’t do what it does. The crosstalk - falling away as you move further down or up - indicates some failed ground or radiated/conducted signal in the connector board which also contains all the cards. It’s actually quite a simple setup if you look at the service manual schematics.
Unless a logic chip has failed which does the switching??
Ok so I didn't fall asleep yet.
@juanito2008 I'd say this is difficult to answer because it is a difficult issue, and I feel like I cannot really grasp it fully. I didn't mix up the heads as they've got different connectors – repro is female and sync is male. Also the heads are in a spot physically where this mix-up would be impossible unless you're a not-very-gifted individual. And yes, it was easy to do the regular alignment, at least to begin with, because most of the routine is done off the repro head. It wasn't until I went into sync that I noticed this issue. I don't know what that last bit is about, if it's a dig at my ability to align a machine or just an unfortunate way of expression.
And yeah, how can this excessive crosstalk be? I'm thinking hard about that one and I've tried a few things this far without any luck. Will follow @Brian Roth and @RoadrunnerOZ advice and pull out the scope. It seems like we're suspecting a grounding issue somewhere and that is what I will focus on for a while.
@RoadrunnerOZ logic is a fair guess and I've looked into that myself, but cannot find any way for that to be the cause.
Ok time to try to sleep
@juanito2008 I'd say this is difficult to answer because it is a difficult issue, and I feel like I cannot really grasp it fully. I didn't mix up the heads as they've got different connectors – repro is female and sync is male. Also the heads are in a spot physically where this mix-up would be impossible unless you're a not-very-gifted individual. And yes, it was easy to do the regular alignment, at least to begin with, because most of the routine is done off the repro head. It wasn't until I went into sync that I noticed this issue. I don't know what that last bit is about, if it's a dig at my ability to align a machine or just an unfortunate way of expression.
And yeah, how can this excessive crosstalk be? I'm thinking hard about that one and I've tried a few things this far without any luck. Will follow @Brian Roth and @RoadrunnerOZ advice and pull out the scope. It seems like we're suspecting a grounding issue somewhere and that is what I will focus on for a while.
@RoadrunnerOZ logic is a fair guess and I've looked into that myself, but cannot find any way for that to be the cause.
Ok time to try to sleep
juanito2008
Member
- Joined
- Feb 25, 2017
- Messages
- 16
I agree with you. But how he brakes a ground plane or whatever if he only swapped two connectors ?
He should have done something else in the machine. Recapping, wiring...
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