Date   : Tue, 17 May 2005 16:58:30 +0100
From   : Richard_Talbot-Watkins@...
Subject: Re: Master power-up failure

Richard Gellman wrote:

> If the cassette relay is clicking wildly, either:
>
> a) The MOS ROM is shagged, and executing arbitrary writes to
> &FE20 (I think, its the SERPROC control reg.).
> b) The SERPROC chip itself is shagged, and is entering some
> weird microcode loop.
> c) The circuitry around SERPROC is damaged in some way,
> causing a charge/discharge circuit to flip the relay.

Another thing which might be worth noting is that even *reads* from SERPROC
(&FE10) appear to make the cassette relay randomly flick on and off.
(*MZAP FE00 in Disc Doctor used to demonstrate this quite nicely.)

I don't know if this opens up any further possibilities - I'm not much of a
hardware guy to be honest.

Rich


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