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Reel To Reel All discussions pertaining to reel to reel decks. These include general usage, recording, playback, and service questions. For subjects related to tape itself, see the Open Reel subforum under this one. Obscure service subjects that don't quite fit go in the Help and Do It Yourself subforum.

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  #1  
Old 03-19-2017, 05:19 PM
DrewMeyer DrewMeyer is offline
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Fostex A8 no input signal on only 1 Channel

I just picked up a Fostex A8 deck with accompanying 450 mixer on Craigslist. It's my first foray into R2R after using a cassette portastudio for a couple years. I've been going through it to learn how everything works and come across the first issue so far. I figured out how to use the buss lines to run signal from the mixer onto the tape and have successfully recorded onto all the channels except 1. No signal will show up on the channel 3 VU meter and no signal will record to that track. The weird thing is these decks share the same input for tracks 1-4 and 5-8 so there's just a switch to swap between track 3 and 7. Track 3 does nothing but track 7 works just fine. Has anyone encountered something like this before and no how to troubleshoot this? Thanks!

Last edited by DrewMeyer; 03-19-2017 at 05:23 PM.
  #2  
Old 03-19-2017, 06:39 PM
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Levelanything Levelanything is offline
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Wink

Hi Drew,

I bought an A8 last winter and had the same problem, except mine had a dead track at 5 instead of 3. I have read different things like, "make sure the play/rec head is totally clean," to "it's most likely an internal issue that you'll need to bring in to get repaired." I cleaned my tape path and could never figure out what was wrong with that track. Mine isn't totally dead, but noisy and intermittent. One of my VU meters was dead for another track, but it still played fine.

These are obviously old machines now and unfortunately Fostex didn't have the best build quality and as time goes on (especially after they sit in attics and basements for 15 years.) If you haven't already, really clean the head and make sure there's nothing getting in the way there. These narrow track width machines can lose signal over stuff being on the head that you can't even see so...

If all else fails you'll have a 7-track recorder. It's still 3 more than your Portastudio
  #3  
Old 03-19-2017, 06:51 PM
DrewMeyer DrewMeyer is offline
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Haha that's basically what I figured, I know these Fostex aren't known for their reliability. I gave the heads a real good clean and still can't get any signal, even when I crank the gain so I'm guessing the signal is getting lost somewhere along the way. Like you said though, I've still got 3 more tracks than before haha!
  #4  
Old 03-19-2017, 08:13 PM
vintagepc vintagepc is offline
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It might not be too hard to find the cause with an oscilloscope and a service manual... you can already narrow down that the problem is after the bank switching of tracks, and likely before the head...
  #5  
Old 03-20-2017, 03:35 AM
DrewMeyer DrewMeyer is offline
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I wish I had an oscilloscope, I would probably attempt some sort of repair if I did.

On another note, I've noticed the unit gets pretty hot after it's on for an hour or so. I understand some heat makes sense but this seems a bit much. After an hour or so the transformer feels burning hot. I also notice a smell like when you burn components with a soldering iron but it's not super strong. The unit hasn't been powered on for probably a couple years until now. If this is normal is there a certain range of time I should keep my usage to in order to prevent overheating and damage?
  #6  
Old 03-20-2017, 05:19 AM
vintagepc vintagepc is offline
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Definitely not normal, that's a sign there's something wrong with the deck.

Unfortunately this sounds like the sort of thing that needs trained eyes to work on it before something does give up the ghost and cause more damage... not the kind of issue you can pick away at and learn as you go... since you don't know the seriousness of the problem and how long you have before it's too late
  #7  
Old 03-20-2017, 02:42 PM
DrewMeyer DrewMeyer is offline
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Ok I just saw your message but I've been running it for the past couple hours and now I don't notice any heat or smell but I'll still keep my eye on it. In any case it has a new funny symptom. It was recording perfectly fine before (except channel 3) and actually sounded really good. All of a sudden it now records a high-pitched whine overtop every track. Even with no input signal it still records this sound. It isn't consistent and fades in and out between tracks and varies in pitch. I tried unplugging everything else in the room to isolate the power in case it was an issue with that but no luck. Anybody have any experience with that?
  #8  
Old 03-20-2017, 03:26 PM
vintagepc vintagepc is offline
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That sounds like oscillator or bias frequency creeping into the playback signal. Given the previous comments, could be any number of causes, either related to, or not, the heat/smell reported earlier.

I'll re-iterate my previous comment that it's probably time to have someone skilled look at this deck before anything else goes up in smoke. Given the problems it's exhibited (and now developing new ones)... it's beyond "but it runs okay except for..." territory (which is often already thin ice) and into "you really shouldn't run that anymore until we know exactly what the problem is" territory.

Based on this thread, I'm guessing you don't have a huge amount of electronics experience - without which this isn't something I'd recommend you take on yourself, unless someone here as explicit experience with this problem and can provide specific guidance for you.
  #9  
Old 03-20-2017, 03:54 PM
DrewMeyer DrewMeyer is offline
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Yea that makes sense and is about what I figured. I have some small electronics experience and can solder but I've never worked on something like this before. I was considering doing a recap in the power supply since I've read those caps can go bad and damage the transformer but from what you're saying it sounds like it could be a number of things causing issues and I should just take it in
  #10  
Old 03-20-2017, 05:17 PM
vintagepc vintagepc is offline
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Yes - sadly if this had remained a dead channel only issue we probably would have been able to troubleshoot it with you... just the other symptoms that have me concerned for the set's (and possibly your) well-being.

Power supply recap isn't as critical in these newer sets as the older 60s/70s era ones. The A-8 has good quality (Nichicon, Nippon, or Panasonic, if memory serves) modern electrolytics, whereas older sets have a lot of paper & oil based capacitors which are far more problematic susceptible to failure in "interesting" (read: explosive/damaging) ways.

Quick commentary on recapping:

A recap isn't a "fix" for problems, it's a preemptive step folks will tend to do *after* a set is working properly. If it works first, you have a baseline for its condition and any new problems can be traced to something you touched.

If it's not working... you don't know whether any further issues are a result of a mistake in your work, or a preexisting problem you just didn't see yet. Always have a good baseline before you make changes, or it's easy to make things worse.

I won't turn this into a debate as to whether or not to recap sets, but generally you'll find two main camps -

1. Recap to prevent problems with aging capacitors that have (on paper) reached the end of their life, and possible more expensive future failures.

2. Leave it as is and only replace anything known to be bad. (i.e., don't recap)

Generally there's a lot of info that goes into the choice... age of the set, condition it's in, construction type/quality, performance, usage (sat in storage/moderate/hard life...) etc. etc etc... Pros and cons to each side, with the end result being a personal preference.

We can discuss if you're interested in the things that add weight to each side of the decision if you like, but I don't want to derail your thread too far.
  #11  
Old 03-20-2017, 06:08 PM
DrewMeyer DrewMeyer is offline
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That makes sense, thanks for the info. You mentioned bias frequency leaking into the signal, could you explain this a bit more? Is this caused by improper adjustments on the bias or is it a faulty component?
  #12  
Old 03-20-2017, 07:01 PM
DrewMeyer DrewMeyer is offline
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One more thing I forgot to ask about. If I play the unit with no tape the left hub spins clockwise and the counter counts down. Is it supposed to do that?
  #13  
Old 03-20-2017, 07:59 PM
vintagepc vintagepc is offline
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Since it started happening suddenly, most likely a failed component rather than bad adjustments.

The recording and erase circuitry has two high frequency signals, one used to drive the erase head and blank the tape, the other used to "bias" the audio signal for recording so it plays back properly and doesn't sound like crap (That's a deep read if you're interested in the theory, someone here can probably provide a reference in their sleep...)

What is probably happening is a component has failed and is either allowing those to leak into the playback circuit, via another path, or the filter isn't matching the generated frequency any more and not filtering it out properly.

The fact it varies with time is probably a sign of it drifting in and out of phase/frequency either with itself or with the filter that's intended to remove it.

I'm glossing over a lot of the details because there are other places that could explain these bits far better than I ever could, but hope that's got you enough info to start looking in the right direction for more info. \

And yes, that's normal, the deck will spin each reel at low torque in order to provide the correct take-up and supply reel tensions on the tape. The right hub should also spin counterclockwise, unless the "EDIT" switch is set wrong (or possibly the take-up arm is in the wrong position, I can't recall if this deck has servo tension control or not). They spin fast because there's no load on the motor.

Last edited by vintagepc; 03-20-2017 at 08:03 PM.
  #14  
Old 03-20-2017, 08:34 PM
DrewMeyer DrewMeyer is offline
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Quote:
Since it started happening suddenly, most likely a failed component rather than bad adjustments.

The recording and erase circuitry has two high frequency signals, one used to drive the erase head and blank the tape, the other used to "bias" the audio signal for recording so it plays back properly and doesn't sound like crap (That's a deep read if you're interested in the theory, someone here can probably provide a reference in their sleep...)

What is probably happening is a component has failed and is either allowing those to leak into the playback circuit, via another path, or the filter isn't matching the generated frequency any more and not filtering it out properly.

The fact it varies with time is probably a sign of it drifting in and out of phase/frequency either with itself or with the filter that's intended to remove it.

I'm glossing over a lot of the details because there are other places that could explain these bits far better than I ever could, but hope that's got you enough info to start looking in the right direction for more info. \
That makes a lot of sense, thanks for all the info! This definitely seems above my skill and knowledge so I'll take it to a tech and see what they can do. Thanks again for your help, I would have probably just run this thing until it blew up without your warnings!

Quote:
And yes, that's normal, the deck will spin each reel at low torque in order to provide the correct take-up and supply reel tensions on the tape. The right hub should also spin counterclockwise, unless the "EDIT" switch is set wrong (or possibly the take-up arm is in the wrong position, I can't recall if this deck has servo tension control or not). They spin fast because there's no load on the motor.
That's exactly what I figured, I just wanted to be sure some fault in the circuit wasn't turning it the wrong way. Thanks again!
  #15  
Old 03-21-2017, 05:50 AM
vintagepc vintagepc is offline
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Glad to help.

If you post your approximate location here, folks can recommend some "good' techs in your area. There are a number of unscrupulous ones out there that charge several hundreds or thousands of dollars and don't actually fix/do anything, or make a hack job of it.

Unfortunately I can't point to any specific usernames of reputable folks from here, as I don't know any of them here that work on Fostex units.
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