[sdiy] Prophet 600 diagnostic eprom?

mail mail at m4moti.com
Sun Jun 19 23:59:11 CEST 2016


Eric,

I spent a lot of time working with GliGli in the early days helping to 
test the upgrade and reviewing the code.  Here are some things to try:

Put the GliGli Teensy back in and pull the two RAMs and the EPROM -- 
they are not required and removes them from the equation as mentioned 
elsewhere in this thread.

GliGli does not necessarily come up with the banner -- but it should be 
working.

Next, follow the SCI P600 service manual 
(http://www.synfo.nl/servicemanuals/Sequential/SEQUENTIAL_PROPHET-600_SERVICE_MANUAL.pdf) 
and connect a scope to the output of the DAC.  You should see the trace 
pattern as on p 2.12.  If you do not, you have a problem before the 
DAC.  If you do see an nice stair, pattern, then the problem in on the 
analogue board.  Play some notes and you will recognise the traces 
moving per the EGs or LFO -- poetry in motion...

Now put the original Z80, EPROM and 2 memory chips back in.  Do you see 
a similar pattern?  If not, your CPU or memory is bad.

Next, check U414 which drives the current from the DAC to the MUXs.  
This chip and the DAC are bottle next through which all the control 
voltages flow.  It that looks good, then it is time to start "decoding" 
which MUX (the 4051s) are bad.  Sometimes, they appear fine but they can 
be sloppy and cause the unit to fail.   It might be good to compare 
voltages between different channels for say, the filter cuttoff and see 
if they are good.  So, for example, if you have no output from a set of 
parameters, trace those control voltages back to see if you find the 
4051 that MIGHT be causing the issue.

Little by little you should be able zero in on the problem areas and 
might come down to a couple of 4051s.

I have not mentioned the front panel but you can disconnect that and 
then test again.

Good luck and let me know if I have been unclear.

Bulghur

On 6/19/16 13:13, Florian Anwander wrote:
> Hello Eric,
>
> can you disconnect the voiceboard from the CPU board? It should work 
> alone until the tuning procedure.
>
> If it does not come up, then you may try replacing the RAMs. But this 
> is a shot in the mist. I think of the RAM because a broken gate would 
> make the CPU stop always at the same point.
>
> Florian
>
> On 19.06.16 21:31 , Eric Frampton wrote:
>> Hi Florian -
>>
>> The banner doesn’t even come up. It sticks on some random segments 
>> (and sometimes is just blank), and that’s it.
>>
>> e
>>
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