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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 28th Dec 2021, 2:35 pm   #1
stiggyd
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Default Sony HMK-70 tape deck issues

I've just picked up a second Sony HMK-70 music centre to replace my old one as mine had an electrical issue I couldn't diagnose.
This new one is in great condition, was sold as not working but all it took to get the turntable back up and running was soldering a wire that had come loose from a tonearm switch and some general fettling to get the auto-return etc working.

Anyway, the other issue is with the tape deck. Play, fast-forward and rewind are pretty weak and stop/don't start.

I've replaced the spindle belts and I'm working up the courage to replace flywheel belt (this will take a bit of work since its completely unaccessible from the top so I need to either remove the tape deck or completely disassemble)

The one thing I'm confused about is the idler wheel.
In my old HMK the flywheel contacted the idler wheel during fast forward and rewind by hitting the rubber "belt" or whatever you'd call it on the idler. My new deck however contacts the nylon of the idler.

It looks like the rubber "belts" are in the correct places on both decks, as in they are in their respective grooves. The idler wheels between both machines appear to be completely different though even though the music centre is the same model and the tape decks look identical as far as I can see.

I've attached images of both so you can hopefully see what I mean:

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Old 28th Dec 2021, 2:37 pm   #2
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Default Re: Sony HMK-70 tape deck issues

Just had a thought: Is the new deck's idler upside down?!
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Old 28th Dec 2021, 2:45 pm   #3
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Default Re: Sony HMK-70 tape deck issues

Sorry for the post spam but I think the new one is in the correct orientation, the old one is upside down.

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Old 28th Dec 2021, 9:20 pm   #4
DMcMahon
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Default Re: Sony HMK-70 tape deck issues

Yes agree the new one appears to match the Service manual drawing.

Does the old one (with the idler apparently upside down) mechanically work OK ?

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Old 28th Dec 2021, 10:23 pm   #5
stiggyd
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Default Re: Sony HMK-70 tape deck issues

The old one also had the same issues with the fast forward and rewind not starting/giving up as well, I'm going to assume this is mostly due to the belt that I'm working up the courage to replace. Both of them seem to play fine though. Just quite inexperienced with cassete decks and assumed that its weird for the metal flywheel to be driving the idler directly on the nylon. Unfortunately its difficult to see in the service manual how they are meant to interact due to the blown up diagrams
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Old 28th Dec 2021, 10:39 pm   #6
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Default Re: Sony HMK-70 tape deck issues

The new one looks wrong with the idler upside down. The circlips also look totally incorrect I suspect someone has tried to dismantle the deck and didn't note how it was built up and reassembled wrong.
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Old 29th Dec 2021, 12:48 am   #7
stiggyd
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Default Re: Sony HMK-70 tape deck issues

Well I think I might be dumb.

Looking at the rest of the page of the service manual, its clear that all of the components are displayed from the other side (upside down). So yes, the new deck's idler was indeed upside down.
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I have now returned it to the correct orientation and things have very slightly improved.
It just seems that the flywheel is quite easily stopped when giving a slight bit of resistance to the spindles, so I'll have to develop the courage to change that belt!

Thanks for all your help!
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Old 29th Dec 2021, 1:12 pm   #8
murphyv310
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Default Re: Sony HMK-70 tape deck issues

The main belt is very common even many years ago. It's much easier with the deck fully removed.
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Old 29th Dec 2021, 2:24 pm   #9
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Default Re: Sony HMK-70 tape deck issues

The main capstan belt is the most likely cause of the problems. They cause all sorts of strange symptoms when they get tired.
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Old 29th Dec 2021, 5:53 pm   #10
stiggyd
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Default Re: Sony HMK-70 tape deck issues

Well I spent a few hours taking out the tape deck and taking it apart. It was a very complicated operation to get to the main belt including a stripped-screw-drill-out disaster along the way!

Anyway I replaced the main belt and some other belts I found lurking in there.
The good news is that fast forward and rewind are pretty strong now.

My new problem is that the audio is pretty warbly, maybe the dirty old tapes I used to test it out aren't very free flowing or the belt I used was not the ideal one. But I'll investigate that another time.

Either way, I'm happy it at least works now. I'm probably never going to even use the tape machine which makes me wonder why I went through all of this in the first place!

Anyway, thanks for your help.
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