Help on HP 82901 drive

I've just checked my unit for you. I get 1MHz on pin 24 of the FDC chip (as expected) and about 250kHz on pin 26 (read clock). There is twice this frequency (500kHz) on pin 11 of the LM361. More interestingly I've checked the supplies to the LM361. I get +12V on pin 1 (+ve supply), +5V on pin 14 (output stage +ve supply) _and_ -9.5V on pin 6. So there is a -ve supply (I'd half-suspected there was, knowing that other HP drive units which use a load of transsitors + an LM361 as the VCO/PLL also have a -ve supply). I've not yet discovered where it comes from, it must be generated on the controller board (my guess is that those 2 metal-can transsitors at the front left corner have somethign to do with it). Can you check the supplies on your unit. If the -ve supply is missing it could explain a lot. -tony