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Sharp GF9090 - Muddy Sound


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#1 Atomtan

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Posted 16 December 2016 - 11:14 AM

I have been restoring a GF-9090 for some time, which I thought I had fully sorted but the sound from the tape deck seems distorted and what I can only describe as 'muddy'.  The radio sounds perfect, and is so different from the tape playback.

 

So far, I have changed all belts and the idler tyre.  I have also cleaned lubed the box mechanism, as well as deoxit the sliders and cleaned the head, capstan and record bar.

 

I was not keen on the box when first found it in terrible, but totally complete state.  However, the longer I look at it, and the more I work on it, I am getting more and more attached to it and would love to see it fully working.

 

Having searched around this and other forums, I am getting the feeling it could be a capacitor / board issue but don't really want to embark on a cap changing mission unless one of you with more knowledge than me can suggest I need to go this way.



#2 MyOhMy

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Posted 16 December 2016 - 11:24 AM

The first thing I would do is clean & demagnetise the tape head, this is a simple & quick operation.  Look for another source of the problem only if this doesn't fix the problem.  If you don't possess a Demagnetiser (Demagnetizer) Cassette, you could probably find one on fleaBay, expect to pay £10.00-£25.00 for a fair deal in these times of shortages.)



#3 caution

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Posted 16 December 2016 - 12:12 PM

Have you tried adjusting the alignment screw on the tape head? This will create muddy sound quickly if it's even a bit off.



#4 Atomtan

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Posted 21 December 2016 - 12:59 PM

I shall go with the demagnetiser and cleaner first, then follow some of the YouTube videos about head alignment but am a little nervous as it looks like it could be difficult to get right.

Thanks for the advice and I will report back with progress....

#5 T-STER

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Posted 21 December 2016 - 06:48 PM

Hey Atom, I had the same issue with the same box as you many yeras ago when i started off. I got the box all working but the tape sounded pretty rough and I just couldn't figure it. In the end my list of what i thought i had done i hadn't done properly so i set about doing it all again:

 

1. Clean the record bar, really well. Get some Deoxit in there, blow it out with compressed air and repeat with another batch of Deoxit F5.

2. Get some isopropyl alcohol on a cotton bud and really clean the head, i bet more gunk comes off. While there check the head for wear, how does it look?

3. Demagnetize the head, use a tape if you have one.

4. While the box is apart (it's easier) adjust the tape head azimuth. It's quite simple with the screw next to the head. Put a tape in and play it, one you know very well and adjust the head accordingly until the sounds improves.



#6 Atomtan

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Posted 29 December 2016 - 12:16 PM

The head had a lot of residue on it which took forever to clean off.

I will get a close up photo of the head next time I have time to meddle with it.

Despite not being 100%, it sits with pride in my living room and I continue to find its appeal as a box grows on me.

Will re-do the list you suggested. Is it the screw to the left or right of the head as you look down on it?

#7 baddboybill

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Posted 29 December 2016 - 12:26 PM

The head had a lot of residue on it which took forever to clean off.

I will get a close up photo of the head next time I have time to meddle with it.

Despite not being 100%, it sits with pride in my living room and I continue to find its appeal as a box grows on me.

Will re-do the list you suggested. Is it the screw to the left or right of the head as you look down on it?


You will see the tiny hole for tiny philips head screwdriver. Unit has to be in play mode and playing in order to adjust it to best sound. It's best to demagnetize screwdriver ;-)

#8 hopey

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Posted 12 January 2017 - 11:46 PM

Sounds like the pinch roller, you can test by pressing play (without a tape) and try to stop the roller with your fingertip it should take a bit of pressure to stop it turning. If it stops with minimal pressure there's your problem.Good Luck.



#9 Atomtan

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Posted 16 January 2017 - 05:54 PM

Found a few minutes to test the pinch roller tonight, and absolutely as predicted, the pinch roller can be stopped with the minimum of pressure, yet on other boxes, it's very difficult to even slow it. This is not a problem I have seen before so I had better start researching.

Thank you for the help so far.

#10 Atomtan

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Posted 09 February 2017 - 03:06 AM

Finally found a couple of hours last night to try out all the ideas from above.

 

I purchased a head demagnitiser which may have helped a little, but the sound was still muddy.

 

I ordered a new pinch roller from a guy in Germany (I took a chance on the 9191 roller being the same, and purchased that one).  I then dis-assembled this part of the unit following the excellent video on YouTube.  I felt the head adjustment was the last thing I would do if all else failed.

 

As my pinch roller could easily be stopped in playback by a finger, I decided to bend its tension spring, just a little to see if that would help also.

 

When I compared the new roller I had acquired, it looked a little different (the internal spindle was bigger), and I suspect the diameter was a touch smaller, but I fitted it as the surface of the old roller was really 'shiney' and in my opinion, the rubber did not feel right.  After re-assembly i noticed the pinch roller could no longer be stopped by my finger in playback which seemed to support Hopeys comments above.

 

I decided to chance it, dropped in a cassette before re-assembly and hit play............and....Total success,  To hear what had been troubled, muddy sound be transformed led to a huge smile.

 

Thank you all for your comments, and to Hopey for what was the final solution.

 

Only problem now, a box I purchased for £10 covered in cack has worked its way into my heart.  Its no big performer, but its sound seems quite rich to me.  I went looking for other old cassettes to play in it, so guess I need to find a space for it...



#11 T-STER

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Posted 09 February 2017 - 12:28 PM

Glad its all fixed mate, and you know what the GF9090 is a cracking box i think. It's one of my earliest boxes and it has a great look, it's not too big, good rich sound with loads of knobs and buttons and it rocks.



#12 Fatdog

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Posted 10 February 2017 - 03:27 PM

These kinds of posts bring a smile to my face.  :-)   I love it when an old boombox is happy again.



#13 Atomtan

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Posted 15 February 2017 - 09:15 AM

Thought I should end the thread with some finishing photos.

 

Here is the completed unit once fixed and fully cleaned.

 

I have attached two further photos showing:

 

- The parts I have replaced. Interestingly, on my unit the idlers tyre came out almost intact, but it was obviously deteriorated enough to be one of the problems.  The original still sat nicely on a WD40 straw and had not started to turn to goo, but it was very misshapen.

 

- One shows the original pinch roller that came from the unit.  I am pretty sure the unit has not been apart before, and so all of the internals would have been originals.

 

- One photo shows the new pinch roller in place (at the moment of final success), which i think shows the replacement roller I purchased has a much bigger spindle (and smaller tyre), but despite it being a fraction smaller, it works perfectly.  I think the photo also shows the retaining spring which adds pressure to the pinch roller.

 

In the end, great advice on here and S2G, taking my time and working through the components turned a junker into something I am really proud to own.  The exercise taught me to not give up, as there can be a number of interrelated issues that you need to sort, before success comes.

 

 

Attached Files



#14 Ghettoboom767

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Posted 19 February 2017 - 01:17 PM

Great job,I have one if these to.😎

#15 Quanghoster

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Posted 16 February 2018 - 04:47 PM

Just started taking mine apart - it only arrived on Wednesday...lol.  I had one of these in the early eighties and couldn't resist getting on I saw on Ebay.  This thread caught my eye because I have one remaining problem.  The playback is great with a tape that came with the unit.  However, the left channel is low volume.  Originally the left vu meter was low aswell but I found that fiddling with the ALC switch cleaned it's contacts and now the vu meters on record are the same.  However, playing back the recording shows the left channel low, both on output and vu meter.  The funny thing is my old one I seem to remember was the same so I thought I'd ask if anyone had come across the same issue of have I bought my old one back? lol



#16 hagarthefish

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Posted 05 March 2018 - 08:18 AM

Great job and great information. I'm about to start work on my first boombox, so the info rocks!



#17 Reli

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Posted 05 March 2018 - 04:14 PM

I don't know if anyone else mentioned it, but a pencil eraser can be used to clean the tape head, if alcohol alone isn't enough. But you have to be gentle with it.