[sdiy] Jupiter 8 not booting

p. hendricks ph at comcast.net
Tue Feb 2 06:25:07 CET 2021


not very helpful as it was over 10 years ago. But the eproms, were loose 
on mine, similar issue , opened it and someone had added a business card 
adding pressure to them-- lower right. added more pressure on those 
contacts and was fine, well, sold it.


On 2/1/21 9:06 PM, Tristan wrote:
> 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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