Sharp GF9090 Resto

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Hallsy

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OK, so I bought my first (well, maybe not my first, as I had a few back in the 90's - but this is my first proper 80's model!) boom box recently, a Sharp GF9090, I had been looking around at various models and really liked the Sharp GF 9x9x series - saw one going on ebay that looked decent in the pics and was described as in good working order & condition - made a bid, it was mine!

I was quite excited about it, the seller was a bit slow to send which didn't help, but then last week it finally arrived. I opened the box, initially hit with that old musty smoke smell that electronic items take on after being in a smokers house for years on end - but then I started looking closer and it all felt like a bit of an anti climax - the good working box I was expecting was not quite so.

It looked OK (well, not too bad) from afar...



But up close it struck me as something that had been used on a building site!









Some corrosion inside from leaking batteries. The inner batter terminal is very corroded, I'll see if I can revive it, but may have to fit a new one.







Generally though, the internals 'looked' OK



I decided that even though I was disappointed, it was all fixable, so I may as well just plug it in and see what it sounded like. After a bit of fiddling with the power lead I had it switched on! Radio worked OK, switches & sliders scratchy and the tape player was chewing up tapes!!

After a quick clean up of the sliders though, the radio was at least usable. So I cracked on with what I was doing in the garden and left it playing. Over the hours it seemed to improve, initally the RH meter didn't really work, but after a while it started to come to life!

The sound was not quite right though, one channel was weaker than the other. You could see it on the VU meter and also by switching the balance over. It wasn't just that it was quieter, it sounded really flat. On the good channel the bass & treble sliders make a noticable difference as expected, but on the weak channel the bass has no effect and the treble only a small change. I swapped the speakers over, and fault stayed with the amp channel.

I have now stripped her down and have started looking for any failed components. I had a quick look on Saturday, checked the caps & resisitors around the pre & output amp stages but couldn't find anything obvious. Of course, it could be a signal problem at the tuner stage - hopefully tonight I will get more time to take a look.

I've got an HND in Electronics Engineering, but I'm very rusty as for just over 10 years now I have been working with machine tool/CNC/automation control systems and rarely have to get involved at an electronics level.

Any suggestions welcome :)
 

Hallsy

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Apr 1, 2014
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Yesterday morning I had a quick look at the tape deck. After all, this will help me to fault find the channel problem if I can get another source working!

The chewed up tape was a result of what seems to be the usual Sharp problem, a gooey/missing capstan drive rubber.

So I cleaned up the relevant parts with IPA and used a small piece of pneumatic pipework that I had in the shed. It seems to drive OK now by hand, but I have yet to try it under it's own power.

Sharp GF9090 by Hallsy01, on Flickr

Sharp GF9090 by Hallsy01, on Flickr

Sharp GF9090 by Hallsy01, on Flickr

Sharp GF9090 by Hallsy01, on Flickr

One of the heads looked a bit mucky, I gave it a clean up, but possible it will need replacing as it looks a little corroded

Sharp GF9090 by Hallsy01, on Flickr

Sharp GF9090 by Hallsy01, on Flickr

The rest of the unit seems OK, all other functions seem to engage and work OK, the belts don't look particuarly perished, although they are not very tight.

How tight should these belts be? I am used to tensioning machine tool drive belts, etc - but can appreciate that these cassette decks contain a lot of plastic components and not so many bearings, etc so maybe the belts just need to be tight enough to drive with excess tension?

I gave the unit a blow out as it was full of years of dust & fluff, so when I get to work later (rest of the bits are in my bench) I will hook it up and see if it plays OK!

I must apologise for the phone pics in these posts, it was all I had to hand when working on it!!
 

Northerner

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Apr 16, 2012
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Sounds like you're getting there. I see what you mean about looking a bit rough close up, it's had a hard life. But all collections need at least one working but a bit rough box for the garden or when DIYing etc so you don't have to worry about it getting damaged :-)

The belts need to be tight enough to grip but not so tight that it binds or pulls the pulley too hard to the side and slows it down. How tight often depends on the deck and what the belt is doing. I use good old trial and error but the main drive belts on GF's don't need to be that tight in my experience.
 

BoomboxLover48

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Good job!

I hope you lubricated the capstan with white high temp Lithium grease. It works better than light machine oil and prolongs life of the bush bearing assembly!

A 5.0 mm to 8.0 mm stretch/elongation is okay for the main flat belts to hold it without slipping.
 

Hallsy

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Apr 1, 2014
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Thanks for the comments chaps :)

It will be a bit of work, but I don't mind. I like a project!!

Boomboxlover48 - thanks for the suggestion, I have added a small amount of grease to the capstan shaft/bushes - I've also set the flywheel freeplay to 0.1mm. I have read suggestions from other tape deck manuals of between 0.005 & 0.2mm freeplay, so aimed for somewhere close to the middle!
 

Beosystem10

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Hallsy said:
Thanks for the comments chaps :)

It will be a bit of work, but I don't mind. I like a project!!

Boomboxlover48 - thanks for the suggestion, I have added a small amount of grease to the capstan shaft/bushes - I've also set the flywheel freeplay to 0.1mm. I have read suggestions from other tape deck manuals of between 0.005 & 0.2mm freeplay, so aimed for somewhere close to the middle!
The bushes are Oillite bushes if you must lubricate those, then the way to do that would be to marinate them overnight in oil - light oil of some sort, even non-Dexron ATF such as Shell Donax is fine - and refit to the carrier once they've dripped a little. Oillite bushes absorb the oil and release it gradually throughout the life of the bush. Now I accept that many such things have probably served several times as long as their makers expected the devices to which they were fitted to last but all grease will do is clog the pores in the surface of the bushes and prevent their releasing any oil that's still in there. Think of them as metallic sponges. Grease is for the parts that slide against other parts, such as all of those bits of random steelwork that connect the control buttons to various bits of mechanism.
You'll be fine with that amount of play at the flywheel, it shouldn't get hot enough to close up even by a micron, I think that mine's running rather more and it's still OK. For now. :blush:

As for the way the thing looks, that's not too bad, it's all fixable and my eBay one arrived looking worse than that, but given how easy these are to strip down and put back together afterwards, it's also quite simple to bathe them and give them a splash of paint.

Mine is still very far from perfect aesthetically, below is a picture I took after I'd given it a good clean but before I attended to the scratches:



It looks a whole lot better than that now, it's just a matter of finding the time to keep it that way. Yours will be grand soon enough! :thumbsup:
 

BoomboxLover48

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Marinating doesn’t work when you take out an old bearing with wear debris in nanometer size plugging the 15- 20% pores in it. :nonono:

In many cases after lots of use will always smear the pores to close it. So practically pores are sealed to begin with.

They need to be thoroughly cleaned and vacuum impregnated with light oil or type of oil recommended. :yes:

Vacuum impregnation with oil! This is practically impossible for users like us to do. ;-)

Trust me lithium light grease I used for it and most of my decks ran for over 25 years with no issues.

My late radio engineer from Philips was the first person to teach me and also our BB and electronics Expert Norm reminded me about this white Li grease to use on Oilite (bronze alloy) bushes for better longevity.
 

Hallsy

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Apr 1, 2014
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Thanks for the tips on the oilite bushes :)

I can see that both suggestions are valid, but would perhaps agree with boomboxlover48, if the bushes have any wear at all, the pores will possibly be blocked. I have used a smear of grease - hopefully all will be well!

Other than that there's not too much to see here at the moment, been busy working away in the garden this long weekend, but I did manage to find a little bit of time to carry on with my 9090.

I was getting fed up with the musty 80's electronics/ashtray smell, so decided to fully strip the box down and give it a quick bath.

There was a fair bit of DNA floating around!

20140417_113924 by Hallsy01, on Flickr

20140417_093451 by Hallsy01, on Flickr

20140417_162009 by Hallsy01, on Flickr

Quite a familiar site to most of you I'm sure - the other half wasn't too sure though!

20140417_093904 by Hallsy01, on Flickr

The battery terminals cleaned up fairly well, although the end of one of them snapped off so I soldered a little bit of copper on to make up the difference..

20140417_205149 by Hallsy01, on Flickr

So then I reassembled the box again to carry on fault finding. It's not super clean yet, just clean enough to work on without getting annoyed!

Sadly my tape deck is still no good, the PVC tubing I used for the capstan drive is slipping, so I've ordered some 2mm id silicone tubing - that should do the trick.

I think I have found the cause of the weak LH channel as well. As I said before, it seemed that the bass slider had no effect, and the treble didn't have a lot either.

Had a probe around on the back of the sliders and one side of the bass slider is open circuit to the wiper, and the treble slider has some high resistance on one side also. I tried cleaning them in situ but it has made no improvement. I will have to remove them and have a proper look. Hopefully once I have the sliders sorted it will bring up the weak channel!
 

Beosystem10

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:thumbsup: Mine eventually came good with Servisol S10 sprayed through the sliders about half a dozen times, so don't despair just yet. ;-)

Tip: If using a bath for this job causes domestic disharmony, try cleaning parts in the dishwasher if you have one. Dishwashers are great for this sort of thing as long as you give the machine a good clean before you next poach a haddock in there.
I'm told that you can even do something called "washing the dishes" in dishwashers. Marvellous inventions!

As for grease, it might not hurt on well worn bushes but grease does have a nasty habit of creeping and the last thing you need where a silicon sleeve is attached to a shiny steel capstan is grease getting in about at the interface there by capillary action.
Vacuum what now?



That way has been working fine for the past 30 odd years. OK, so it requires patience and isn't used in production these days but we can't all have the means by which to impregnate these things under vacuum. ;-) Consider that the pores are greater in area than the extent of any wear since those very same pores see to it that any swarf from the inside of the bush will break up into a dust far smaller in particle size, a bit - according to the tribology specialist from work, who just loves being called at home to discuss these things the night before term starts :lol: - similar to the way in which any foreign bodies smaller than the holes in a mesh will do less harm reintroduced to their original carrier than they would if retained by a proportionately finer mesh, in other words, any swarf that did find its way into the pore structure of that bush would have to be too small to be held there or it wouldn't have separated in the first instance. That tribology guy, bless him, his head looks just like that 1980s Tefal commercial.
 

Hallsy

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Apr 1, 2014
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Well, I've made a bit of progress now.

I replaced the PVC tubing with some silicone tubing on the capstan drive, and now the deck is playing well. The APSS isn't working correctly (looks like part of the solenoid is missing) and the auto stop doesn't work (belt slipping) - so I'll end up re-belting this and trying to work out how the APSS solenoid shuttle should be.

As for the weak left channel, I had traced this to LH side of the bass slider being open circuit. Removed the slider and found that the wiper had broken it's plastic welds and so wasn't making contact. It was also still pretty filthy after spraying Servisol on them.

You can see here that one of the wipers is drooping..

Gf9090 bass slider by Hallsy01, on Flickr

And that the carbon tracks were a bit dirty..

Gf9090 bass slider by Hallsy01, on Flickr

So after a dab of super glue to keep the wiper still and a clean up of the tracks, it looked much better!

Gf9090 bass slider by Hallsy01, on Flickr

Gf9090 bass slider by Hallsy01, on Flickr

Then I quickly reassembled, got home and put in the only tape I had to hand (Bad)....wow, not only does the tape deck work, I now have bass on both channels!

But then, I noticed that now the RH channel sounded a little weak :( In my haste to get the bass slider sorted I had forgot to double check the treble slider. Metered that out and found that the wipers were OK, but the RH carbon track was open circuit. So that was removed and opened up just the same - this time I used a little silver paint to reconnect the carbon film to the pin.

This left both sides of the treble slider pretty close (110k and ~105k iirc), but I found that the carbon tracks on the bass slider were some way out, 110k and 85k.

Now i have it all back together again, it actually felt like the bass was a bit weaker than yesterday (would the fixed treble slider have that effect on the circuit?) - but I could be imagining it. Either way, both channels, although not perfect (RH sounds like it has more mid & volume than the LH), they are a lot closer than they were.

I then adjusted the tape head as it sounded a bit muffled - used the method of adjusting in mono - sounds much better, until I turned the tape around, lol!!

It seems that the cassette door doesn't hold the tape in the same place as it does with door open when adjusting, so I'll have to get it right by trial & error or try adjusting the door.

I'm getting to the point where I'll probably start on the cosmetics soon, but it has certainly whet my appetite for a bigger box. This one doesn't sound bad, but the bass isn't very punchy (but then I am comparing it to separates and half decent AE floor standers, lol!!).

I'm going to add a Line-in mod, I plan to use a switched stereo socket inline with the tuner output and radio/tape switch - hopefully all will go to plan. There is an unused hole on the remote/external mic input panel, so it won't look out of place.

Feel like I'm making a bit of progress now!
 

Fatdog

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Hallsy said:
Quite a familiar site to most of you I'm sure - the other half wasn't too sure though!

20140417_093904 by Hallsy01, on Flickr
Ah, yes, the Full Patron!! That's what we endearingly call a boombox bath. You are doing a fantastic job of bringing this beauty back to life. :-)
 

Northerner

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These sort of threads are invaluable for the next guy doing a resto on one of these...takes time and effort to tell the whole process...good work :-)
 

Hallsy

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Apr 1, 2014
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Thanks mate - glad some people find it helpful - I was worried I might be teaching people to suck eggs, but I like taking photos and documenting stuff anyway - might need to remind myself what I did one day, lol!!

Anyway, with the box starting to work a bit better, I decided to look at adding a line in. I didn't want to have to use the tape circuit so tapped into the tuner output, before the radio/tape switch. Again, I know this kind of thing is old news, but here is where I tapped in with a switched stereo 3.5mm socket...

Sharp gf9090 Line in mod fullsize by Hallsy01, on Flickr

Sharp gf9090 Line in mod fullsize crop1 by Hallsy01, on Flickr

Sharp gf9090 Line in mod fullsize crop2 by Hallsy01, on Flickr

and obviously I connected the line in ground to a convenient ground on the board.

Crappy pics, but here is how it looks inside..

20140501_213113 by Hallsy01, on Flickr

20140501_210644 by Hallsy01, on Flickr


For now it is just left loose whilst I was testing it out. Long term I will mount it at the side panel with the remote & mic inputs, as there is a spare hole here already. So basically, when the socket is empty, the n/c contacts carry the radio signal as normal, when a line in plug is inserted, the external source is routed to the tape/radio switch.

So, after trying it with a lineout cable from my ipod...............it worked!!

But........the input signal is too high, the VU meters were going off the scale, volume past 2 (on the box) was pretty loud and starting to distort.

So I made an L pad attenuator circuit to go between the line in socket, I guessed at around -6dB, and I have tested it tonight, but it's still not enough, so I will try -10dB and see how it sounds. http://amps.zugster.net/articles/attenuation#L-Pad

I guessed that the input impedance of the amplifier circuit would be 47k ohm (typical for a phono input apparently) as the later GF9x9x models that have a phono in go directly into the tape/radio/phono switch, so it stands to reason they should be a similar level. I will measure it to be sure, but I was at work and my boombox was at home!! So for R1 I used 24k and for R2 47k.

This may or may not be the correct way to do it, but it dropped the level by around 5 to 6 dB, but it's not quite enough.

Out of interest, what kind of peak level is ideal? +1dB? 0dB? I have read about amplifiers being tested with +1dB signal, when testing for maximum output wattage and clipping point, but not really sure what I should be aiming for?? Answers on a post card!?

Once I've got the electronics pretty much sorted, I'll be moving on to the cosmetics :) One question I have, how would be best to get the speaker cones white again? Any type of paint I can use that won't effect the sound/performance?

I've also bought another box.........the collection is starting, lol!!
 

Gino73

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Jul 3, 2014
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Hi all ,
excuse me my intrusion, i have a problem with the rubber hose on the capstan of my sharp GF 5858 , could you tell me where i can found it or in alternative the right internal and external diameter measurement for replace it ? Thanks in advance
 
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