[sdiy] ARP 2500 schematic question for 1027 Cocked Sequential Controller
steve at bendentech.co.uk
Wed Oct 1 23:10:27 CEST 2014
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?
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