Oakley VCO

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welhamc
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Oakley VCO

Post by welhamc » Mon Jun 05, 2017 4:40 pm

Earlier today I left my modular switched on by accident when I went out and came back to find that weirdly, the tri and sine outputs on my Oakley VCO are now not functioning properly. I've been using this module for around 3 months with no problems so quite stumped as to whats causing the problems. I've left the modular on for extended periods of time as well, so really not sure!

I've checked all my wiring, tested the continuity of the wires themselves, and checked the power connection but no luck. No bridged connections either. My guess is that because it happened seemingly randomly it could be due to a dodgy component (?)

Looking at the schematic, my guess is that there could be something wrong with either U4, U5 or U6, or Q4 or Q5, are there any specific areas in the circuit I can check to help diagnose this problem?

Weirdly I've just noticed that the pulse output also seems dodgy and there is no output in centred mode except at one specific pulse width setting...

Anyway, gonna properly have a look at this tomorrow but if anyone could offer any advice on where to start I'd greatly appreciate it!

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Synthbuilder
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Post by Synthbuilder » Tue Jun 06, 2017 2:54 am

I think the sawtooth to triangle generator is not working properly.

A single component just dying like that is quite rare when a device is young - unless it has been damaged by heat or static discharge during the building process. The most likely cause then is a cold solder joint - which is where the molten solder hasn't wetted both sides of the joint sufficiently. Usually just applying some more solder to the affected joint will fix this and it's pretty easy to do if you know the area in which to look. This is where an audio probe or an oscilloscope comes in very handy. Flexing the board gently can also reveal a cold joint problem.

I think the fault lies somewhere around Q5 and U6. The SHP-T trimmer may be worth looking at too.

Tony

welhamc
Common Wiggler
Posts: 78
Joined: Mon Oct 12, 2015 9:21 pm

Post by welhamc » Tue Jun 06, 2017 9:18 am

Thanks tony, I think i've found the solder joint responsible, seems to be working again now!

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