940 Cassette Deck (CR-905) anyone know anything?

[alight]

Hi there!

My cassette deck on my Wentworth isn’t working swimmingly. Got a lot of noise on the left side when changing volume and the deck itself, when you put a cassette in does very little (although I think the motors are turning)

Anyway- I’ve got the thing out of the car which was painful in itself but wondering if anyone has any resources / manuals / useful photos for the CR905 deck and specifically how to replace the belts as that’ll be my first port of call if I can work out how to do it!

[mister grimsdale]

Regarding the cassette deck, there's only one drive belt, easily accessible once the deck is out, but all the ones I've seen have been in good condition. I've had the cassette deck fail in a couple of these, and in both of them it was down to the small gear in the photo losing some teeth. That gear seems to be much more fragile than its neighbours and once removed it continued to shed teeth just through being handled. I did investigate having a replacement 3D printed a while back, but the thing is so small that the resolution wasn't up to the job. That was for FDM printing, but things seem to have moved on a bit and I've just sent off an enquiry to see if I can get an SLA-printed gear. We'll see.

[alight]

Originally Posted by mister grimsdale

Regarding the cassette deck, there's only one drive belt, easily accessible once the deck is out, but all the ones I've seen have been in good condition. I've had the cassette deck fail in a couple of these, and in both of them it was down to the small gear in the photo losing some teeth. That gear seems to be much more fragile than its neighbours and once removed it continued to shed teeth just through being handled. I did investigate having a replacement 3D printed a while back, but the thing is so small that the resolution wasn't up to the job. That was for FDM printing, but things seem to have moved on a bit and I've just sent off an enquiry to see if I can get an SLA-printed gear. We'll see.

I managed to open mine up and found out it was the same gear that’s failed on mine - would be interested to see if you get a lead on the 3D printing route!

[mister grimsdale]

Well the guy reckons he can do it, and at a sensible price, so it'll be down to the accuracy or otherwise of my CAD model. Measuring the gear accurately was quite tricky, especially as both bits of it have odd numbers of teeth, so I might need to tweak the CAD and go round again, but should have something to try in a few days, with luck. I'll report back on progress.

[alight]

Originally Posted by mister grimsdale

Well the guy reckons he can do it, and at a sensible price, so it'll be down to the accuracy or otherwise of my CAD model. Measuring the gear accurately was quite tricky, especially as both bits of it have odd numbers of teeth, so I might need to tweak the CAD and go round again, but should have something to try in a few days, with luck. I'll report back on progress.

Brilliant news. I would offer my gear to help with the cad drawing however it very much complete fell apart the moment I touched it so it’s not much good for anything 😂

[mister grimsdale]

Unfortunately, the guy has has now done a test print and he said that even on a 4K SLA printer, that gear is just too small. I may try and get it done on an 8K printer, but for now I've ordered some casting silicone and I'll try and make a mould. I've got one deck that still has the gear intact, and I'll cast from that, with fingers crossed that it doesn't disintegrate in the process!

Some will say that it's not worth the effort when I could buy a modern replacement. They'd be right, of course, but it's very satisfying getting the old stuff working again.

[loki_the_glt]

Originally Posted by mister grimsdale

Some will say that it's not worth the effort when I could buy a modern replacement. They'd be right, of course, but it's very satisfying getting the old stuff working again.

Not only that, but new in-car cassette-players don't seem to exist, and transferring to CD/USB devices take forever!

[mister grimsdale]

Well, after further unproductive discussions with another 3D-printing guy, and some time-wasting with RTV silicone that refused to cure, there's progress. I cast a silicone mould from my last intact example of the failing gear wheel. I was a bit nervous about this, wondering if the silicone would pull its teeth out, but it survived and gave me a very satisfactory result.
Used the silicone mould to cast a polyurethane replica. The first attempt had a lot of bubbles in the mix and produced a gear with missing teeth, but the second attempt worked well. I made a little vacuum degassing chamber from a glass jar and was able to pump it down to about 60mm Hg with one of those cheap hand-operated vacuum pumps that are sold for brake bleeding.

I'm not sure how long I expect the cast gear to last -- since I've started this I've found a supply of 'toughened' casting urethane that may be better, but the ordinary stuff seems as sturdy as the original. It's currently undergoing a bit of an endurance test on the bench and has played through a couple of cassettes so far, including properly reversing direction at each end.

Oh, and got a new MOT, so quite pleased overall.



Alight, I'll be making a few more of these in case they turn out to be short-lived, and because I've got 250g of casting resin left, so if you would like one (no warranty!), ping me an address and I'll send you one -- assuming you haven't discarded your deck in disgust already. You obviously managed to get the thing apart to get the old gear out, but just for the record, here's what I had to do:

Remove the drive belt.
Remove the spring (1) from the cam follower thing.
Remove the two screws (2) that hold the plate carrying the white gear wheel and move the plate aside. It's attached to the motor by wires, but the motor can be removed (two screws) and the whole assembly put aside if you prefer.

Inside the cassette compartment there's a clear plastic sheet that sits over all the drive gears, that locates on two posts and is held on by plastic retainers. Pop these retainers off and remove the plastic sheet.

At the back of the cassette compartment remove the retainer that holds the slotted arm onto a boss on the change gear. (8 in the second photo; I'd already removed the retaining washer when I took this.) Be gentle. I managed to ping the metal boss off the plastic pip on the gear, and getting it back on was a faff as the top of the pip is peened outwards to retain it. Disengage the slotted arm from the boss.

Undo the screw (3) that holds the subchassis with all the cassette reel drive gearing on it.
Ease the subchassis out of the deck, disengaging the two metal tabs at the back end and freeing the plastic tab from the spring (4). As you withdraw the subchassis, the almost completely hidden spring (5) will come out and get lost.

The small gear next to the culprit needs to be removed, and then the failed gear. Both are held on by small split plastic washers. These break fairly easily, but I replaced the one I broke with a small circlip.

On reassembly the main difficulty is getting all the bits aligned when replacing the subchassis with all the reel drive gears on it. I started by fitting the change gear spring (5) back onto its tab; the centre loop fits onto the tab nearest the edge of the chassis and the long 'L'-shaped end engages with another tab further forward, under the replacement gear. I was able then to hold it in place with a finger inserted through the front of the cassette compartment whilst lining up the other end to sit between the black gear and the white gear that sits below it. Line up the slider (6) on the subchassis with the arm on the main chassis. Just out of sight in the photo are two small metal tabs (7) that need to be eased outwards against spring pressure to allow the subchassis to settle into place. Engage the slotted arm inside with the boss on its gear. Once everything is lined up and the gears are in mesh it's possible to engage the fixing screw hole with its post without the need for any significant pressure and refit the screw. Refit the retainer for the slotted arm, replace the clear plastic sheet and its retainers.

Refit the motor, the small subchassis and the drive belt, mount it all back in the radio and you're good to go. Mine took a couple of manual reverses to get all the cams and gears in the right places before it would auto-reverse, but after that seems to do all the things it's supposed to do and (touch wood) hasn't eaten a tape so far.

[alight]

Originally Posted by mister grimsdale

Well, after further unproductive discussions with another 3D-printing guy, and some time-wasting with RTV silicone that refused to cure, there's progress. I cast a silicone mould from my last intact example of the failing gear wheel. I was a bit nervous about this, wondering if the silicone would pull its teeth out, but it survived and gave me a very satisfactory result.
Used the silicone mould to cast a polyurethane replica. The first attempt had a lot of bubbles in the mix and produced a gear with missing teeth, but the second attempt worked well. I made a little vacuum degassing chamber from a glass jar and was able to pump it down to about 60mm Hg with one of those cheap hand-operated vacuum pumps that are sold for brake bleeding.

I'm not sure how long I expect the cast gear to last -- since I've started this I've found a supply of 'toughened' casting urethane that may be better, but the ordinary stuff seems as sturdy as the original. It's currently undergoing a bit of an endurance test on the bench and has played through a couple of cassettes so far, including properly reversing direction at each end.

Oh, and got a new MOT, so quite pleased overall.



Alight, I'll be making a few more of these in case they turn out to be short-lived, and because I've got 250g of casting resin left, so if you would like one (no warranty!), ping me an address and I'll send you one -- assuming you haven't discarded your deck in disgust already. You obviously managed to get the thing apart to get the old gear out, but just for the record, here's what I had to do:

Remove the drive belt.
Remove the spring (1) from the cam follower thing.
Remove the two screws (2) that hold the plate carrying the white gear wheel and move the plate aside. It's attached to the motor by wires, but the motor can be removed (two screws) and the whole assembly put aside if you prefer.

Inside the cassette compartment there's a clear plastic sheet that sits over all the drive gears, that locates on two posts and is held on by plastic retainers. Pop these retainers off and remove the plastic sheet.

At the back of the cassette compartment remove the retainer that holds the slotted arm onto a boss on the change gear. (8 in the second photo; I'd already removed the retaining washer when I took this.) Be gentle. I managed to ping the metal boss off the plastic pip on the gear, and getting it back on was a faff as the top of the pip is peened outwards to retain it. Disengage the slotted arm from the boss.

Undo the screw (3) that holds the subchassis with all the cassette reel drive gearing on it.
Ease the subchassis out of the deck, disengaging the two metal tabs at the back end and freeing the plastic tab from the spring (4). As you withdraw the subchassis, the almost completely hidden spring (5) will come out and get lost.

The small gear next to the culprit needs to be removed, and then the failed gear. Both are held on by small split plastic washers. These break fairly easily, but I replaced the one I broke with a small circlip.

On reassembly the main difficulty is getting all the bits aligned when replacing the subchassis with all the reel drive gears on it. I started by fitting the change gear spring (5) back onto its tab; the centre loop fits onto the tab nearest the edge of the chassis and the long 'L'-shaped end engages with another tab further forward, under the replacement gear. I was able then to hold it in place with a finger inserted through the front of the cassette compartment whilst lining up the other end to sit between the black gear and the white gear that sits below it. Line up the slider (6) on the subchassis with the arm on the main chassis. Just out of sight in the photo are two small metal tabs (7) that need to be eased outwards against spring pressure to allow the subchassis to settle into place. Engage the slotted arm inside with the boss on its gear. Once everything is lined up and the gears are in mesh it's possible to engage the fixing screw hole with its post without the need for any significant pressure and refit the screw. Refit the retainer for the slotted arm, replace the clear plastic sheet and its retainers.

Refit the motor, the small subchassis and the drive belt, mount it all back in the radio and you're good to go. Mine took a couple of manual reverses to get all the cams and gears in the right places before it would auto-reverse, but after that seems to do all the things it's supposed to do and (touch wood) hasn't eaten a tape so far.

I’m not sure how you’ve managed to do this but it’s bloody impressive!

I can’t send you a Dm as I haven’t got enough posts - but if you pop me one more than happy to receive a gear and pay for any postage and definitely contribute to a pint or two for your hard work!

[mister grimsdale]

There's a postscript to this. I'd been using a cassette adapter (Sony CPA-9, but they all appear to work much the same way), so that my daughter could play music from her phone through the cassette player. This has gears inside it and a small wheel that looks as though it should be driven off the capstan when the drive is in the required direction. In the 'wrong' direction it retracts and simulates end-of-tape, forcing an auto-reverse. Mine seems to have lost a rubber O-ring off said wheel (the most recent iteration of the device appears to have a little loop of tape in there instead) and, as became apparent whilst I was bench testing the repair, was forcing auto-reverse continuously. That puts extra strain on the chain of small gears and undoubtedly hastened the failure. A new 5mmx2mm O-ring seems to have cured that, but I'll be keeping a close eye on it from now on.