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Author Topic: Otari 5050 8-track Issues: Noise, Static  (Read 4732 times)

Offline slorinczi

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Otari 5050 8-track Issues: Noise, Static
« on: August 22, 2009, 10:18:09 PM »
Hi Folks,

I own an early-model (two "suitcases") Otari 5050 1/2" 8-track. My understanding is that the machine was used regularly as recently as 10 - 15 years ago, but has been pretty much dormant since then. I cleaned and de-magged, and aligned and calibrated it for +6 (I understand Otari recommends +4). All in all, the machine set up very easily and needed very little adjustment.

However, after tracking a couple of songs, I'm noticing a disturbing static. It's audible on some tracks while monitoring in "source" (some worse than others) and worst of all, it's occasionally making its way to tape.

Seems like there's two issues: The random static during monitoring, and then a harsh kind of clipping distortion (definitely dependent on the source material) during playback.

I've ruled out my mics, cables, and pres. I've thoroughly sprayed out all the pots and card slots. I'm going to realign the deck to make sure I didn't majorly goof. Aside from that, any suggestions? I really can't tell if the caps on the cards are original; some people on other forums have suggested that the popping noises / static may be due to bad transistors on the rec / repro cards, but honestly I wouldn't even know how to test them. (Just checking voltages on all three legs?)

Anyway, I'm pulling out what's left of my hair and I'm open to any suggestions or advice!

Thanks,
Seth


Offline ironbut

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Re: Otari 5050 8-track Issues: Noise, Static
« Reply #1 on: August 23, 2009, 12:29:59 AM »
Hi Seth, welcome to the forum.

When you said that you "sprayed out" the pots and card slots, did you use any contact cleaner on them? That's one of the first things to do with a machine that's been in storage. Even when it's covered or boxed, dust gets in and the lack of use will let it gum things up. I use a combination of spray cleaners like DeOxit D5 on pots and switches and MG Chemicals "Super Contact Cleaner (you can find both at electronics and well stocked computer stores). The Mg chemicals cleaner is really nasty stuff and you just wipe contacts (like edge connectors) with a lightly dampened q tip then reinsert whatever it is that you cleaned.
I think there's a pretty good chance that what's happening is that one of the many multi-pin connectors or card slots connectors is oxidized and not making a proper contact. The best thing to do is go board by board and pull each connector and reconnect it (with the power off!) then check and see if it's solved the problem. If you go board by board rather than just doing all of them at once, you'll be able to localize the problem in case it happens again.
Be careful pulling and reinserting any connectors or boards since some circuit board material can get brittle after decades. Take your time and if you have a service manual, look at that section and try and make sense of what's going on in there. Even if it doesn't make much sense to you right now, if you do this each time you get inside of your machine, you'll start to understand little by little.
Another thing to check is whatever it is that electrically connects the two sections together. That would tend to be a weak spot.
steve koto
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Offline Tim

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Re: Otari 5050 8-track Issues: Noise, Static
« Reply #2 on: August 24, 2009, 01:49:42 AM »
If it's a somewhat continuous static, then a noisy transistor or IC could be the problem.  Even caps and resistors can get noisy, but it's less likely.  You'll need a schematic diagram, an oscilloscope, an audio oscillator and a test probe. It helps to first inject an oscillator tone (1kHz) into the input. Starting with the line input, check the outputs of each transistor and IC to see where the static shows up.   You will see the static riding on the waveform when you get to the defect part's output.  You can also use a good channel as a reference to see what a good waveform should look like.

If this sounds like something you may not want to get into, then the deck may need to go to the nearest repair shop.

Tim
Tim Leinbaugh
Service Technician
with RTR specialty.

Offline slorinczi

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Re: Otari 5050 8-track Issues: Noise, Static
« Reply #3 on: August 28, 2009, 02:52:12 PM »
Gentlemen:

Thanks much! In brief, yes I sprayed out the pots and card slots with DeOxit, but I did not clean the electrical connections between the modules. When I first hooked the deck up, I noticed right off the bat that the pins were all somewhat oxidized, but didn't take the time to clean them. I will now do so!

Also, a tech friend suggested carefully cleaning and spraying the hi / lo output switches mounted on the repro cards. He has to do it continually on a deck he services.

Finally, thanks I will hook up the scope (I only use it for alignment currently). I'm fairly new to solid-state repair, but if I follow the manual I'm sure I won't blow too much up....

Again, many thanks!

-Seth