[sdiy] Jupiter 8 not booting

Roman Sowa modular at go2.pl
Tue Feb 2 08:20:54 CET 2021


My wild guess is that something is loading the RESET line too much. Is 
it that voice cards are also reset by this line? If you can disconnect 
anything else from this line and leave only this CPU, you could see if 
anything changes. Then look, possibly with ampmeter, which board is 
causing trouble.

Roman

W dniu 2021-02-02 o 05:03, Adam Inglis (synthDIY) pisze:
> Could I trouble some patient soul to cast their eyes over this circuit 
> and explain what should happen?
> The JP8 CPU reset circuit is in the grey box on the right half of the 
> image.
>
>
>
>
> My jupe has been taking its time booting these last few months, 5 or 
> 10 minutes, and now sometimes is refusing to boot at all. 
> (Occasionally it will boot as usual in a couple of seconds after going 
> through the tune routine, so the fault appears to be intermittent).
> Up on the bench, when failing to boot, I measure the reset pin 26 on 
> the CPU as 1.4 v. When it boots successfully, that voltage takes a 
> second to go from 1.4 up to 4.9 volts.
> So I’m suspecting something in the reset circuit.
>
> When working:
> Transistor 1 measures
> E  = 00 v
> C = 0.14 v
> B = 0.59 v
> Transistor 2 measures
> E = 00v
> C = 4.9 v
> B = 0.14 v
>
> When not working the only change is the collector of TR2 doesn’t come 
> up above 1.4  v
>
> cheers
> Adam
>
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