On Wed, Aug 16, 2017 at 7:12 PM, Chuck Guzis via cctalk <cctalk@classiccmp.org> wrote: > On 08/16/2017 10:40 AM, Tony Duell via cctalk wrote: > >> >> I have just looked at it, and unfortunately it is of no help with this >> question (I assume that if manuals for other versions of the FD235 >> exist, they will be similar). Most of the manual is replacing mechanical >> parts, doing the head alignment, etc. There are schematics of the >> spindle motor and the logic PCB in the manual, but the latter is one >> big ASIC (containing all the digital circuitry, the read channel, etc) >> with a few passives hung off it. There is no theory-of-operation >> of that IC, or block diagrams in the manual, alas. > > Exactly--there have been many versions of the PCB for the 235HF. The > schematic that I have (obtained back in the day via Teac's "FAX on > demand") mostly show a large anonymous ASIC. Same for the 235J (ED > version). This probably also obtains for most other 1.44M drives as > well--though if I looked, I might get lucky. > > AGC and bandpass filtering wouldn't be unexpected, however.
Filtering, sure, and there are a couple of LC filter networks connected to this ASIC. But I am not so sure about AGC. I've looked at the schematics for some 5.25" drives and I can find no AGC circuits. Nor on the Sony 3.5" full-height 600rpm drives. So I would not be at all surprised if there was no AGC on this Teac. -tony
