Are you going to go at one of these yourself, or having one done by another tech? Feel free to bounce questions off me either way... haven't done one for months and months but at this point I pretty much have it down pat. They will present with some unusual issues now and then though, so always opportunity to learn more.
I have little to contribute, except the knob thing. I have the 3001 and 3011A. Both need serious help, far beyond my skills. I can't even use them. Both knobs were totally frozen, wouldn't turn at all.The tuning knob doesn't 'spin' anyway.
AK member par excellence JDurbin located the correct battery and can provide them — or at least he used to. Ask him.It's highly unlikely that the same physical style battery will be available
I've located a direct replacement battery: https://www.ebay.co.uk/itm/Varta-1-V150H-2P-Central-Heating-Timer-Battery-V100R/392045818698
I took the tuner apart in order to get at the battery solder terminals and in doing so discovered all of those stiff wire connectors that make connections between PCBs. On examination they showed signs of corrosion (darkening) and worst of all there were traces of a stubborn greasy substance that clearly couldn't have being doing me any favour wrt reliable connections. Presumably this was some kind of electrical grease/lubricant that was applied at the time of manufacture but has long since dried up. I used a fibre glass pen to shine up the pins and applied Servisol Super 10 contact cleaner to the sockets.
I have managed to free up the stiff tuning situation by applying Si lube using a wire 'dropper' to the relevant bearings of pulleys etc. It's still won't spin from one end to the other, but I'm happy with it how it is. The one thing outstanding now is that backlash in the tuning. With the unit apart I can now see what is happening - to an extent. There is slack between the tuner's plastic drive 'disc' and its shaft/gearing. If you move the tuning knob in one direction it picks up and continues to rotate the actual tuner fine, no problems. If you stop and turn it the other way, then there is a backlash of a few degrees before the tuner itself begins to rotate in the opposite direction. Similarly if you wobble the tuning knob the tuner is unresponsive, you have to turn it in one direction for a few degrees for it to pick up, take up the backlash. But I cannot see how to tighten the coupling between the plastic drive disc and the metal shaft that it sits on. Maybe the drive disc is a push fit onto the shaft and the plastic has deformed with time or something causing it to be slack? Dunno. Help.
You’ve found the correct battery. Caveat to replacing that with the same part is that it will inevitably leak again in the future. I replace them too but knowing that it’ll need to be watched and eventually replaced again. I really need to devise a better, remote located replacement battery installation so that any leakage does not damage that tuning system board and so batteries can be replaced without having to dismantle the tuning system boards - that’s a fairly invasive process.
John
On the battery replacement - I used a large low voltage memory cap there instead. I don't have exact details om hand, as it was done many years ago. The cap is a better long term solution (in my opinion) as it should never need replacement (compared to re-chargeable batteries). On testing, I think it held the stations for maybe 1-2 weeks, but again, this is from memory. You are looking for a unit rated at like 0.1 to 1 Farads (not uF).
I think you answered your own question. There's nothing to ponder.John has kindly given me a good run down on how to do it, but given that the tuning action is now very acceptable (do I really need to spin from end to end?) I'm presently pondering on whether to proceed with dismantling the gearbox or leave it as it is, which is perfectly adequate for my needs. A bad mistake could render the whole tuner useless. So, I'm presently pondering my next move..