[sdiy] Bizzare Solina Problem

[Michael Ruberto]

I am repairing a friends Arp Solina with many issues. So far I managed to 
fix everything but the bass section which generates the cello and contrabass 
presets. These don't sound at all. While going over the circuit I find a 
blob of solder connecting pins 5 and 6 on the top 709 (refer to .jpg schemo 
below). Naturally this becomes my first suspect and I remove it with my 
solder sucker. Problem is I get no sound at all now, even from the other 
voices which are generated on a different PCB. Even weirder, is that the 
bass PCB does not connect to the other voice PCBs and has it's own key 
bus...

After a thorough signal tracing I find that all note tones are working and 
the combined audio from them  can be found on pin 5 of the bottom 709 when 
keys are pressed. However, that's where the signal ends. There is no output 
from the bottom 709.

Looking back at the top 709 I find that the 470 ohm 1 watt resistor at it's 
output is too hot to touch. The output also remains constant at ground level 
when keys are pressed. Since it isn't producing a trigger the audio is not 
passing through the crude VCA-like circuit of the bottom 709.

So my next step is to try replacing the top 709 and I have the part on 
order. What's still bugging me though is the solder bridge. When I short 
pins 5 & 6 on the top 709 all the other voices come back and this is very 
bizzare and puzzling to me. Anybody have ideas on this?


http://www.somnium7.com/samples/solina-bass_02.jpg
http://www.somnium7.com/samples/07.pdf

M. A. Ruberto

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