Another eBay purchase and one I nearly gave up on. This Panasonic RQ-SX20 was described as "untested", which usually guarantees it's well and truly broken.
There were plenty of problems the seller could have described, even if they didn't have a tape or a battery to test it. Corrosion on the battery contacts (not unusual), a Dolby NR switch that had visibly broken away from the circuit board and two screws missing from the case. Of course the belts needed replacing too.
I set about re-soldering the switch to the circuit board, and replaced the belts, but no luck - it just made whirring and clicking noises and still wouldn't play a tape properly.
It turns out it was because of a common problem with these units - a broken clutch retaining ring.
I bought a replacement ring from FixYourAudio.com, reasonably priced and well made (from brass), but it wouldn't stay in place. It seemed like the hole in the center was slightly too big, even though it matched the original ring perfectly. At this point I had decided to throw in the towel.
But... an RQ-SX10 came up for sale on eBay and I got it for about £12 (the SX20 had cost me about the same). I thought I'd have another go and see if the new retaining ring would fit this one. The two players are basically the same - just some extra components on the board of the SX20 to allow it to use an external remote control.
The SX10 also needed new belts, also had a split retaining ring and the new, brass ring also didn't fit this one. So potentially another waste of money.
This is the view with the front panel off. The clutch retaining ring is the black plastic ring in the middle of the board. You can just see the spring it holds in place behind it.
To get to the belts, you have to desolder the board: the 7 solder joints above the motor, top right; the joint next to the bottom left corner of the battery compartment; the two larger joints right of the headphone jack, and the 3 connections above the jack, top left. There's also 5 screws to undo.
(note that you can access the speed potentiometer from the front of the board without desoldering - its just under the motor).
Desoldering is made very easy by using a desoldering iron (available for less than £10 on eBay - well worth it). You're far less likely to overheat pads and make a mess with one.
You can see above where the two belts go (the smaller belt of the two goes around the motor). To get to the motor's belt pulley you need to prise off the grey washer (which doesn't seem to do anything) and lift off the magnetic disc. The magnet is remarkably strong and I found the best way was to slide as much of a flat plastic tool under it as possible then lift.
The clutch is the large black cog in the center, which is pushed down against the white disc you can see in the photo below with a spring. The spring is held in compression by the clutch retaining ring.
This is the white disc and its 'slipmat' which allows the black cog to slip against it at a torque predetermined by the spring. The large black cog, then the spring, then the clutch retaining ring sit on top of this white disc.
The clutch retaining ring is not held in place by the little transparent washer you can see here. That's just for keeping the white disc in place on the metal shaft. The clutch retaining ring should be a friction fit to the shaft of the white disc. Obviously if it is cracked it no longer grips it. I suspect the white shaft gets worn too, which is why the brass clutch ring would not hold.
My retaining ring was split, as you can see above. I sanded within the split slightly with fine sandpaper so that when closed back up, the center hole would be a fraction smaller and would grip the shaft it sits on.
I stitched it together with a quick dab from a fine tipped soldering iron then applied epoxy resin (I actually ended up putting resin all the way around the top of the ring, just in case being out of balance caused any issues).
And with everything back together, it works! Whether the repaired retaining ring will hold up over time, who knows.
A few things to watch for: when you put the front case back on, you need to line the switches up with the tabs sticking out of the circuit board, and line the plastic switches on the case up with this.
The plastic screw threads for the circuit board were split - avoid over tightening the screws.
And when replacing the circuit board, make sure the FWD/REV switch is line up with the mechanism beneath.
So was it worth the effort and money (cost me a total of £37.67 to get one working player)? Probably not. It sounds alright - a bit of audible flutter, and the mechanism is quite noisy, but cassette players don't get much smaller than this and I don't think many look this good.
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