[sdiy] Broken Siel Opera 6, any ideas?

[Mattias Rickardsson]

It seems to be the RESET circuitry (to CPU pin 14) that keeps barking.
The astable schmitttrigger (IC37, pin 10-11) fires repeatedly and
restarts the CPU, and I suspect that the EN6 enable signal from the
Port Decoder IC8 would normally prevent this from happening.

Does this "ring" (wag) a "bell" (watchdog)?

Another problem: it's way past midnight and time for bed. :-)

/mr


2008/8/27 klosmon <klosmon at sbcglobal.net>:
> The Opera 6 (a.k.a. DK600) is a notoriously problematic machine -- I've
> attempted repair of 5 battery-damaged CPU boards, with only two successes
> (as opposed to 40 out of 42 successes for PolySix battery-damaged boards).
> Part of the problem is the circuit board design -- it's close to impossible
> to unsolder & replace any components without affecting the ridiculously weak
> traces that pass between the component pads (and I'm saying this as someone
> with 25 years experience in soldering/desoldering).  Also, this synth has a
> large number of ribbon cables, whose contacts can oxidize over the years &
> cause faulty connection, resulting in poor (or no) performance.
>
> Successful repair of these units involves a detailed familiarity with the
> schematics, a scope, excellent soldering technique,
> much time, and a quantity of luck.  Not for the faint of heart.
>
> The CPU, 2031s (and the power supply) usually run very hot -- these synths
> can also double as room heaters, during the winter months.
>
> ~GMM
>
> Mattias Rickardsson wrote:
>>
>> Hi,
>>
>> I have a faulty Siel Opera 6 opened here, and I've removed the leaked
>> battery and replaced the CD40106 (IC16) that was more or less destroyed by
>> it.
>>
>> Before this, I could see that the voice LEDs indicated that keypresses
>> were assigned to voices in a correct manner, but the panel
>> controls/indicators behaved strangely or not at all.
>>
>> Now, no voices get assigned when pressing keys. The panel
>> controls/indicators are still strange.
>>
>> When I look on different CPU pins on the oscilloscope, many of them seem
>> to "blink" in the sense that they are 0 V for a while and then quickly
>> changing between 0 and 5 V for a while, and so on. This "blinking" occurs
>> with approx 2 Hz. I can see similarly timed things going on in the
>> multiplexing address lines, they are turned on and off at 2 Hz. The panel
>> indicators can show similar blinks when buttons are pressed. The DAC doesn't
>> seem to change its output value.
>>
>> I wouldn't really expect this to happen, unless the CPU has entered some
>> quite useless state waiting for something else to happen... has anybody had
>> a similar experience here?
>>
>> What more... the CPU runs quite hot, the SSM2031 VCOs run EXTREMELY hot.
>> Power seems to be OK everywhere, I havent found any broken PCB lines or
>> other components eaten by the battery acid. The synth has been lying under
>> my bed for a couple of years, can it be the ghosts perhaps?
>>
>> Any advice? :-)
>>
>>
>> /mr
>>
>>
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