> From: sndgroom@...
>
> Unfortunately I replaced the ADC0804, but nothing changed,
> there must be something else too.
> If I understood correctly
>
> http://www.rhodeschroma.com/?id=polarisserviceadjustmentscheckout
> on the "What To Do If You Lose Your Memory" after a total
> reset ant tune all, I should have a scratch sound,
> instead my polaris s totally silent

Is the new 0804 running cool? If so, there was still something wrong with the old one, and it needed to be replaced. You should also look at pins 2, 3, and 5 to see if there's any activity. You should see regular active-low strobe pulses on START ADC, you should see EOC going low a short time later, and then see a strobe pulse on RD ADC. The strobes are down in the microsecond range, but EOC stays low until the data is read, or maybe until the ADC is started again. If you don't see any activity, the CPU may be unable to communicate with the ADC, in which case you'd have to work backward to see if Z28 is generating those strobes, and if Z29 can read EOC.

As to the tuning failure, Tune All will disable all the channels if the CPU is unable to control the synthesizer channels, or unable to measure what they are doing. There are lots of things involved in that:

1) The computer needs to be able to control the DAC voltage.

2) It needs to be able to control the sample-and-hold circuits, to deliver the appropriate DAC voltages to the synth channels.

3) It needs to be able to control the latches that set the analog switches in the synth channels, including the one that diverts the output of a channel into the ALT OUT line during tuning.

4) The output board needs to convert the ALT OUT into the SYNTH ZCD line going back to the main board.

5) The CPU needs to be able to select a subdivision of the SYNTH ZCD frequency, and route it into the timer input so that it can measure its period.

There's a lot of circuitry in there. However, by forcing the channels back on after the tuning fails, or bettery yet, forcing one easily accessible channel back on, you can play on that channel, and see if you have reasonable control over it. Can you get the oscillator to play over a wide range of frequencies? If you crank the filter resonance, does it oscillate? Can you hear any sound from the channel through the audio output? Does it respond to sliders or levers?

--

Ciao, Paul D. DeRocco
Paul mailto:pderocco@...