SV: [sdiy] Jupiter 6 troubles

[karl dalen]

You shall have logic levels out from the LS04 otherwhise something
are a bit faulty.800mV from logic is not what you should expect, 
have you checked the supply to the LS04?

KD

--- Jeff Farr <moogah at gmail.com> skrev:

> I've got a JP6 here for who the lights are on, but nobody seems to be
> home.  All the buttons on the panel boards light up but don't respond
> to being pressed.  A quick look through the service manual and I
> believe that there are 3 things to check for:
> - The timer circuit is working properly
> - The main uC (8031) is functioning
> - The PROM is functioning
> 
> Now, I've never scoped the output of a crystal oscillator and the JP6
> uses one peirce oscillator buffered by inverters for the main uC and
> two slave uC's.  You can see the schematic here:
> http://www.asymetrik.org/Jupiter6_PierceOSC.bmp
> 
> Probing around I can see an oscillation of about +-6mV at the right
> frequency for the crystal.  However, it appears biased at about 400mV
> on pins 1, 2, 3, 6 and 8 and about 800mV on pin 10 (output to the main
> uC).  Now, I'll admit I don't know exactly what is inside the uC and
> exactly how the inverters should be operating in this situation but I
> wouldn't want DC present in my clock signal without some blocking
> caps..
> 
> Now.  If it turns out that this circuit is actually working properly,
> but the PROM was dead, is there a way to test that the uC is working?
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