Help Assessing Fostex R8 Heads! (Need your two cents)

Steenamaroo said:
I don't know a huge amount about these machines, but I know methodology always pays.
I'd follow JP's whole post, line by line. ;)
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Ok SO - It's seeming like track 4 doesn't play back anything (whether the 4th track on the head recorded it or otherwise).
So we're left with the possibility of either a bad channel card or a fault in the connection to the head? What does it mean if the head is open circut? Could this be possible even if every other channel records perfectly?
 
sammcdougallIV said:
Ok SO - It's seeming like track 4 doesn't play back anything (whether the 4th track on the head recorded it or otherwise).
So we're left with the possibility of either a bad channel card or a fault in the connection to the head? What does it mean if the head is open circut? Could this be possible even if every other channel records perfectly?
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Let's just double-check. Am I right in thinking that you recorded on all 8 tracks, flipped the tape over, and when you played it back, track 5 was playing back (in reverse) something that had just been recorded by track 4?

If so, that means that the head and the connection to it is fine.
Remember that the R8 is a 2-head deck. One of those two heads is an eraser, which means that the audio head is doing double-duty for both recording and playing back. Hence if that track on the head can either record OR play back, it means the head is perfectly fine (in which case that the problem most likely lies in the channel card somewhere).

To answer your question about the head going open-circuit, that's the worst-case scenario. An 8-track record head like this consists of 8 coils, one for each track. If something utterly catastrophic happens, it is possible for the coil to melt on one or more tracks, which destroys the head element for that track. Ultimately an electrical circuit is a closed loop which electricity flows through. If a component fails such that electricity can no longer flow across it, it is said to be open-circuit because it's no longer a closed loop.
 
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jpmorris said:
Let's just double-check. Am I right in thinking that you recorded on all 8 tracks, flipped the tape over, and when you played it back, track 5 was playing back (in reverse) something that had just been recorded by track 4?

If so, that means that the head and the connection to it is fine.
Remember that the R8 is a 2-head deck. One of those two heads is an eraser, which means that the audio head is doing double-duty for both recording and playing back. Hence if that track on the head can either record OR play back, it means the head is perfectly fine (in which case that the problem most likely lies in the channel card somewhere).

To answer your question about the head going open-circuit, that's the worst-case scenario. An 8-track record head like this consists of 8 coils, one for each track. If something utterly catastrophic happens, it is possible for the coil to melt on one or more tracks, which destroys the head element for that track. Ultimately an electrical circuit is a closed loop which electricity flows through. If a component fails such that electricity can no longer flow across it, it is said to be open-circuit because it's no longer a closed loop.
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No - it's actually the worse scenario - track 4 neither records nor plays back anything. No audio will be recorded or reproduced on track 4 no matter what's on the tape.
I'm hoping the problem is to do with the channel card. How best can I access them on the R8? like - how is the best way to remove one without damaging them? doesn't seem like you can pull them from the front.
 
jpmorris said:
But what did track 5 do?
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Nothing. When the tape is flipped and track 5 is playing what track 4 ought to have recorded, it doesn't play anything. So when I record on track 4 + 5 and the tape is not reversed, track 5 will play back the recorded signal and track 4 will not.
when the tape is flipped, neither 4 nor 5 will play back the signal.
 
sammcdougallIV said:
Nothing. When the tape is flipped and track 5 is playing what track 4 ought to have recorded, it doesn't play anything. So when I record on track 4 + 5 and the tape is not reversed, track 5 will play back the recorded signal and track 4 will not.
when the tape is flipped, neither 4 nor 5 will play back the signal.
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Okay, thanks for confirming that. What I would do next if it were me, is get a multimeter and do some continuity tests. I'm a little nervous about the idea of putting a meter directly over the head given that it's the most vital and expensive part of the entire machine, but it might be worth checking continuity on the cable connecting the head to the PCB.

Did you ever try swapping audio cards? I'm not sure whether the head is connected via a bus or point-to-point wiring to the audio card on these machines, I'd have to find a schematic. If it's point-to-point, swapping the channel card won't help because the head would still be attached to the same channel card...
 
One thing I did figure out for sure: the channel card for track 4 WAS bad - but that didn't seem to be the root cause of the issue.
When I swapped channel 3's good card with channel 4's, 4 didn't work at all and 3 recorded with a weak, distorted sound. Changed them back and took out 4's card completely. Back to 7 tracks
 
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