[sdiy] ARP 2500 schematic question for 1027 Cocked Sequential Controller

[Travis Thatcher]

I replaced the PNPs for those stages, so I'll check the lamps and 10k
resistors next.

The one vco will switch to about 80hz in low mode, in high its
inaudible. The different waveforms do work, as you can hear the
difference when you select them. PWM works fine as well. The second
vco does not seem to be affected by the switch. Going to bring a scope
in tomorrow to see if its just at above-audio rates.

On Wed, Oct 1, 2014 at 5:10 PM, Steve Lenham <steve at bendentech.co.uk> wrote:
> On 01/10/2014 21:58, Travis Thatcher wrote:
>>
>> Fixed the stage 8 issue by replacing a PNP in the typical driver
>> circuit.  The lamps don't light on the first two stages but I can't
>> really test things under power in the ARP. Ordering a few Cinch
>> connectors and some 12v lamps.  Any reason I couldn't replace one of
>> the lamps with an LED+current limiting resistor?
>
>
> No, that should be fine.
>
> If the stage 1 and 2 CVs are working OK then there are only four things that
> could be causing the problem - the upper PNP, the 10K base resistor to that
> transistor (they are carbon comp parts so could go bad), the bulb itself or
> a cracked joint/trace. Not too hard or expensive to replace all three
> components.
>
>> As for the dual VCO, I replaced the summing LM301 and still no dice on
>> either VCO. I'm going to be rolling my own current source module for
>> another VCA that's missing one.  Anyone have and suggestions on
>> further troubleshooting of the VCOs not responding to any type of
>> control input, including the tune pots?
>
>
> What sort of frequency are the VCOs stuck at? High or low?
>
> Cheers,
>
> Steve L.
>
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