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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 26th Mar 2017, 1:32 pm   #1
ITAM805
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Default Hitachi cassette puzzle

Hi all

I have an Hitachi SDT-900 music centre back in my life again after 33 years. It was a top end machine in it's day, circa 1980. I was given it around 1984 by a guy who was emigrating, he said there was a problem with it, there was, a winding on the mains tx had burnt out. Anyway, I fixed it, and gave it to my buddy who used it till his death in 2009. It then went to his sister, who kept it under the bed gathering dust until I picked it up yesterday.

Happily the amp section, radio and remote seem to work perfectly, I've yet to try the record deck. However, the cassette doesn't work. I found, not unexpectedly, the capstan belt had disappeared save for the dreaded black gloop, which had completely coated the pulley and seized the motor. The rest of the belts were of course stretched beyond hope, also they are completely the wrong width for the pulleys, so I guess someone has been in there.

The thing is, I'm unsure what capstan belt to get and where it goes in relation to the white plastic pulley (arrowed)? It doesn't touch the flywheel and has no signs of belt contact, but if I fit a wide belt, (the pulley is approx 7-8mm wide) then it is kind of in the way? The yellow arrow is the approximate position of the capstan motor pulley when in place, pic 3 shows the capstan motor in place, L/H side.

Any help would be appreciated, many thanks
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Old 26th Mar 2017, 2:11 pm   #2
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Default Re: Hitachi cassette puzzle

This is testing the old memory. I have repaired loads of these in the day ,are you sure that it is a flat belt drive to the outer of the flywheel and not one from the motor to a small pulley on the flywheel ,you may need to remove the flywheel the gain access to this . Not sure though!Mick.
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Old 26th Mar 2017, 2:21 pm   #3
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Default Re: Hitachi cassette puzzle

Hi Mick, not I'm not sure either ! The remnants of the belt appeared to fill the full width of the pulley so I assumed that was what the replacement should be?

The flywheel just lifts off and there is another 'running' surface under the top of it, but it didn't look like it would line up with the pulley?. It's not easy to see what goes on anyhow as it's covered up in use

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Old 26th Mar 2017, 3:23 pm   #4
paulsherwin
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Default Re: Hitachi cassette puzzle

As you may know, some designs used a narrower belt than the motor pulley. The belt rides on a slightly raised section in the centre.
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Old 26th Mar 2017, 4:04 pm   #5
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Default Re: Hitachi cassette puzzle

Thanks Paul, yes that looks like it's the case, as a full width belt would touch the top of the white pulley. On the face of it, it seems a silly idea to have put it so close to the belt, unless I'm missing something? So I suppose I just have to take pot luck on the belt width then?

Mick, regarding the lower pulley, it doesn't line up with the capstan pulley at all, so the belt must go on the big flywheel rim. The lower one does line up with the plastic pulleys but they had a skinny square section fitted, not connected to the flywheel running surface, which looks all wrong, so I dont know

edit: there appears to be a wear mark on the flywheel which suggests the belt size
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Old 26th Mar 2017, 5:26 pm   #6
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Default Re: Hitachi cassette puzzle

Any reasonable belt should ride the pulley correctly. 4mm is a common size but even 2mm will probably work. Obviously you really need the dimensions from the original parts list but I appreciate that isn't possible. The mark on the flywheel is as good a guide as any, especially if it matches the very faint wear mark on the pulley.
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Old 26th Mar 2017, 5:28 pm   #7
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Default Re: Hitachi cassette puzzle

What is the white pulley between the motor and the brass disc ? it looks like it takes a flat belt and then on to the under side of the flywheel maybe. Mick.
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Old 26th Mar 2017, 9:51 pm   #8
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Default Re: Hitachi cassette puzzle

Mick, the white pulley is one of the R/W and F/F drive, which is driven by the R/H motor. The brass section drops down to engage white pulley underneath. That said, rw/ff only runs for a second or so then turns off, maybe the capstan needs to be turning for these to operate correctly?

As I say, they must be the wrong belts throughout in this as all the pulleys are 7mm wide but have 1mm square section belts fitted

Paul, thanks for the belt info
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Old 4th Apr 2017, 11:33 pm   #9
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Default Re: Hitachi cassette puzzle

Hi all, I finally got round to fitting a new 5mm belt and the machine now plays. However, the take up spool isn't working correctly, it has feeble torque which leads to tape spilling out of the cassette sometimes.

The FF/RW works fine, having lots of torque on the spindles in either direction so the belt, although the wrong width appears usable. Seeing as this belt also operates as the tape tension on the R/H spool in play, how does it works, is it a slipping clutch or is by lower voltage supplied to the motor?

Many thanks
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Old 5th Apr 2017, 7:49 am   #10
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Default Re: Hitachi cassette puzzle

Well done on your progress so far.

It almost certainly works by employing a slipping clutch, though there may be a rubber-tyred idler which isn't meant to slip which is actually slipping, reducing the torque to below what it's meant to be.

Look at the middle photo in post 1. The brass disc (with the purple line overlying it) may be part of a clutch: it may be coupled to the white Nylon pulley underneath by virtue of a felt disc, pressure being supplied by a compression spring. Have a look.

Nick.
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Old 5th Apr 2017, 9:12 am   #11
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Default Re: Hitachi cassette puzzle

what's that idler I spy lurking below (circled). Looks like it could be used for take up. Give it the once-over with fine sandpaper and let us know...
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Old 5th Apr 2017, 10:08 am   #12
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Default Re: Hitachi cassette puzzle

Nick and Ben, many thanks.

Wouldn't you know, the gremlins have been at work over night, the mech is not powering up today, so now I have to trace the fault in the PSU before I can proceed

Nick, the brass disc/white sprocket is pulled down and engages the teeth with the pulley beneath, only in RW/FF mode. In 'play' mode, the disc is forced up and out of the way by a spring, as shown in the pic 1 (p #5). Thanks for the suggestions
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Old 5th Apr 2017, 7:56 pm   #13
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Default Re: Hitachi cassette puzzle

Hi guys. After much wasted time trying to trace a power fault, I discovered a slack fuse holder !

I roughed up the rubber wheel as advised and the tape take up initially improved and music issued forth from the player for the first time since who knows when But after 10 minutes or so it suddenly stopped again So I took the thing apart again and discovered the tension for said rubber wheel is dependant on belt tension, and the 1mm square that I slung in there just isn't tight enough. So another better fitting belt will be the fix I reckon.

Now, can I fix the seized turntable ...
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