The picture below shows where I took the measurements (in ohms) - I assume they are the correct positions as I don't have a head pinout.
04-083529 34660 Broken
Red = Erase = 90.8 85.8 87.6
Blue = Track 1? 14.6 13.7 14.3
Green = Track 2? 14.3 13.9 13.8
While looking again in detail I noticed that this has the mandatory mod 2.3(c) to add a 47nF Cap between pins 9&12 of IC1 (circled in yellow) - I added this to 34660 myself which I forgot to mention in my last post. All drives have the mandatory mod 2.3(a) slow start 22uF C7 fitted to reduce the effect that damages the tapes mentioned in a previous post.
Although this is a later serial number I swapped the roller for one with a ratchet tensioner (undoing mod 2.3(e)) from the faulty one as it came with the funny looking one in the inset (34660 has the ratchet...) - in actual fact the shaped roller was upside down to the photo and created a nice indent all around the test cartridge for me... so maybe it was faulty at manufacture or had a bad repair? (It was one I bought from e-bay).
Out of interest when I revert the ratchet roller to my faulty one the motor continues to spin and does not report "MD not present" on CAT but does do so on FORMAT which is why I suspect a fault on the ULA... The unusual roller just adds to its problems... Anybody got some spare rollers they can donate? Or suggest a suitable donor device / source?
By the way I also measured the (still original) resistors on 34660 and they show 153/182ohm so not as high as 5% would allow - and this works fine on a QL...
So apart from this drive being a bit unreliable for some reason it does seem similar to the star performer... (i.e. new caps, all mods etc) just no luck on a QL.