[sdiy] Re: P5

[klosmon]

Sounds like it needs re-trimming;  the service manual details what to check 
on the CPU board (power supply, master oscillator offsets, etc) and how to 
trim it, if necessary.

This could be a result of component ageing, or possibly an indictation of 
component fault -- unless it's something drastic, you should still be able 
to trim the instrument to tune where you want it.

~G


At 03:15 AM 7/11/2005, you wrote:
>Hi Harry,
>
>Thanks for the reply.
>
> > My (long gone) P5 tuned with the pot at 12:00 high.
>
>Ah, thought so. It didn't seem to make much sense if this wasn't so.
>
> > I'd check the voltage of the wiper with the pot centered.
>
>Done that. And gone further into the auto-tune circuit too. There's a
>switching circuit that locks out the tune pot and the pitch bender when
>in auto-tune. But the voltage of this circuit does not waver with the
>pots centralised when the switches are closed again after the auto-tune
>has finished its run. There's something else common to all VCOs causing
>them to be offset when not in the tune routine. For now, it has me
>stumped.
>
>One possibility is something that JH mentioned on the AH list many years
>ago about the S/H timing. This is different in the auto-tune routine as
>it is in normal operation. It could be that I have excessive droop [!!]
>somewhere in there. But on all VCOs... mmm, very odd.
>
>I'm sure I'll get there. Need to get the humming transformer fixed first
>though.
>
>Tony