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 Post subject: JVC 1250 8 track player issue
PostPosted: Jan Tue 30, 2018 4:42 am 
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Location: Warner Robins, GA
I have a JVC 1280 8 track player/recorder that is restored which I hadn't used in a few months.

Tonight I went to play a tape and I noticed when the CONTINUOUS PLAY - REPEAT - AUTO EJECT switch is in CONTINUOUS PLAY or AUTO EJECT sometimes I get a noise in the audio which is more like a combination of a hiss and higher frequency buzz, but I can wiggle the tape cartridge and the noise goes away for awhile.

Tried two good tapes so I know it isn't a tape.

Any idea what the issue could be or is it just due to non-use




Also I think the contacts that operate the track change directly control the solenoid. Is there a way to possibly have the contacts control a transistor or other thing that then controls the solenoid in order to reduce the current the foil strip on the tape has to pass? Figure that would prolong the life of the strip.


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 Post subject: Re: JVC 1250 8 track player issue
PostPosted: Jan Tue 30, 2018 5:53 pm 
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Location: Gold Country, (Stanislaus National Forest) California 95235
Is your head demagnetized and is the cable shielding good?

Sometimes those old 8-track decks can get broken shielding where the head would pick up noises from the switch or the solenoid it's controlling.

Also check the solenoid and switch itself and maybe spray the Blue Shower tuner cleaner in there or whatever they call it anymore.

And then take a wand-demagnetizer and go in and demagnetize the heads and see if that helps any.

_________________
2 kinds of men/tape. Low Noise/Wide Range.
LN=kind. WR=abrasive. Engineers=same thing.


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 Post subject: Re: JVC 1250 8 track player issue
PostPosted: Jan Tue 30, 2018 6:29 pm 
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I'll try that, but doesn't explain why the noise is only present in two positions of the switch unless the contacts that control the track change are loose and are moving around with the tape.

I always like the Japanese audio stuff like this as most of the better quality stuff was a step above most everything else consumer grade.

The motor itself is quite beefy with a heavier rotor and a heavier capstan pulley than what a lot of 8 track players with an AC motor have.


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 Post subject: Re: JVC 1250 8 track player issue
PostPosted: Jan Tue 30, 2018 11:04 pm 
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Joined: Feb Sat 12, 2011 2:29 pm
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Location: Fayette County, Pa
I had something similar on an 8 track a while back. It turned out the issue was the sensing contacts. Two factors contributed to it Dirt on the contacts and the polarity of the DC voltage. What was happening was the contact nearest the head was the one with the supply voltage present instead of ground which was the first contact. When the tape went past it, the graphite lubricant on the tape would pick up this DC and although a high resistance would carry this voltage through the coating coming to ground on the next metal item, which was the head itself. This resulted in a hiss / buzzing / frying sound at times. A good cleaning helped for a while, but when dirt built up again the problem returned. I resolved it by simply reversing the leads to the sensing contacts which put the grounded side nearest the head and resulted in that one bleeding off any leakage through the graphite before it got to the head..

And yes, you can switch using a transistor instead of passing this current directly through the sense foil. Some 8 tracks actually use this method on their better quality models.


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 Post subject: Re: JVC 1250 8 track player issue
PostPosted: Jan Wed 31, 2018 2:20 am 
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Sounds exactly like my problem.

Will have to refer to the schematic to see how the switching is done to the track change solenoid. If not through a transistor I will add a transistor and put a reverse biased diode across the solenoid if one isn't already present.


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 Post subject: Re: JVC 1250 8 track player issue
PostPosted: Mar Sun 04, 2018 10:58 pm 
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I've noticed another issue.

Seems the speed is slightly too fast.

Far as I know I have the proper belt and the 60Hz motor pulley, but the rubber mounts for the motor are long gone, although I used some washers as spacers to temporarily fix the issue.

Could that be causing the speed problem?

Also I still have yet to tackle the noise issue.

The contact that is grounded is the one closest to the head and it is grounded through the bracket that the contacts mount to which is attached to the chassis.

I also did use a PNP transistor to switch the solenoid which seems to work quite well.


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 Post subject: Re: JVC 1250 8 track player issue
PostPosted: Mar Mon 05, 2018 3:30 pm 
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Location: Fayette County, Pa
Alignment of the pulley is a factor. If the belt does not ride at the center of the pulley it will run slightly fast since the center of the pulley is raised slightly to center the belt. So you will need to replace the rubber mounts to hold the motor at the proper height.

BTW, I don't have a schematic of that deck but I assume it uses an AC motor. The following applies only to those with DC motors. Those that have a DC motor also have an adjustment inside on the motor governor that allows for speed adjustment. These are notorious for getting out of whack since the contacts wear over time. Speed becomes erratic or wrong when they fail.


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 Post subject: Re: JVC 1250 8 track player issue
PostPosted: Mar Mon 05, 2018 4:27 pm 
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Yes it uses an AC motor, but it also uses a round belt not the typical flat belt most 8 track decks used.

The recommended belt I first got was slightly too small so I sent it back and got one slightly larger.


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 Post subject: Re: JVC 1250 8 track player issue
PostPosted: Mar Tue 06, 2018 5:08 am 
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Location: Gold Country, (Stanislaus National Forest) California 95235
Tube Radio wrote:
The recommended belt I first got was slightly too small so I sent it back and got one slightly larger.
Those - like their mid-60's one-motor-wonder portable reel to reel decks also uses the Superflex (white) neoprene belts (or sometimes absorbothane if it has to be slightly sticky to grab onto other plastic parts) neither of which are made anymore - vs the normal-flex black belts that's all over everywhere.

So you have to watch out that the next size larger belt of the normal flex variety doesn't lose grip and give you all kinds of wow and flutter that wasn't there to begin with.

The only way I've been able to deal with that in most cases (but not all) is to use the larger size normal-flex variety - get - or have machined - a slightly bigger drive sleeve for the motor - and then find the motor speed adjustment and stop it down just a tiny bit.

Of course for a lot of decks that don't HAVE a varispeed - on the motor or otherwise - then sometimes you have to tweak the drive crt a little bit (maybe you get lucky and there's a little bitty resistor in there you can clip and replace w a potentiometer/rheostat to get your varispeed back) and then go on from there.

_________________
2 kinds of men/tape. Low Noise/Wide Range.
LN=kind. WR=abrasive. Engineers=same thing.


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 Post subject: Re: JVC 1250 8 track player issue
PostPosted: Mar Tue 06, 2018 5:22 am 
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Best I can remember I think it had a round black belt on it, but it was stretched some and wouldn't grip right. This one grips pretty good and there's no wow or flutter that I can detect with my ears.


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 Post subject: Re: JVC 1250 8 track player issue
PostPosted: Mar Tue 06, 2018 3:34 pm 
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Joined: Feb Sat 12, 2011 2:29 pm
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Location: Fayette County, Pa
Tube Radio wrote:
Yes it uses an AC motor, but it also uses a round belt not the typical flat belt most 8 track decks used.

The recommended belt I first got was slightly too small so I sent it back and got one slightly larger.



That would also be an issue I neglected to mention in my previous post.. With round belts the size of the belt is important, and you also have the diameter of the belt itself to consider. Too large a belt diameter will not properly seat in the groove on the pulley and usually causes the machine to run too fast. Too small and it will not have sufficient grip to maintain speed and will cause wow or flutter.


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 Post subject: Re: JVC 1250 8 track player issue
PostPosted: Mar Tue 06, 2018 4:47 pm 
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The belt itself looks like it sits properly in the groove.

Could not using the rubber grommets on the motor mount cause a speed issue?

Ultimately I think I will need to find an 8 track player I know is at the right speed and record a test tone and see what frequency it is at on this player.

Or find an 8 track test tape.


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