Date   : Tue, 17 May 2005 12:09:29 +0100
From   : Richard Gellman <splodge@...>
Subject: Re: Master power-up failure

Hi,

I was just about to go into a lengthy discussion about the clicks made 
by the flyback transformer and the high-voltage capacitors, then you 
went and gave output voltages :P

Does the sound chip make any noise (however random)? If not, then the 
MOS is starting up and silencing the sound chip (it starts up in "noisy" 
configuration).

Can you confirm its the cassette relay clicking? An ohmeter across the 
topmost two pins of the cassette connector will confirm this.

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.

All of this of course, may or may not have any relevenace to the machine 
not responding. I'd check the circuit board for damage/interference, 
notably around the MOS ROM (top right corner, in its own socket).

-- Richard

Richard Hobbis wrote:

> If it's any help I just tested the voltages at all 4 points on the 
> motherboard and they came up 5.03V, 4.9V, -5.02V, 5.02V
> And I assume it's the cassette motor relay kicking in.
>
> Cheers
> Richard
>
>
> Richard Hobbis wrote:
>
>> Hi all,
>>
>> Hopefully you can help diagnose a problem that I have with a Master 128.
>>
>> It was working fine earlier this evening, although it did appear to 
>> take a second or so longer to turn on and give me the welcoming Beep. 
>> I played XOR and Repton for a bit then turned it off and went for 
>> dinner.
>>
>> Now, turning it on again nothing happens except for what sounds like 
>> a relay clicking on then off again after about a second or two. The 
>> click comes from the right rear corner underneath the Econet part of 
>> the circuit board. I can feel the vibration of it clicking in & out 
>> through the case.
>> Is there a relay in that area? I really have no idea and can only 
>> guess - but some of you guys sound like electronics gurus so someone 
>> must know! ;8D
>>
>> It's my favourite Master - built-in 3.5" drive and DFS1770 - please 
>> help!
>>
>> Cheers
>> Richard
>>
>>
>
>
>