[sdiy] Jupiter 8 not booting

Tristan tu at alphalink.com.au
Tue Feb 2 06:06:48 CET 2021


Hi Adam,

That looks like quite a few stages for a reset circuit. It is possible TR2 could have gone bad. 

Also, what else is connected to the reset line to the right? Something else could also be holding the line 
low.

/Tristan

On Tue, Feb 2nd, 2021 at 3:03 PM, "Adam Inglis (synthDIY)" <synthdiy at adambaby.com> wrote:

> 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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