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

[Travis Thatcher]

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?

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?

On Wed, Oct 1, 2014 at 1:06 PM, Steve Lenham <steve at bendentech.co.uk> wrote:
> On 26/09/2014 17:43, Travis Thatcher wrote:
>
>> Trying to troubleshoot why step 8 of an Arp 2500 1027 Clocked
>> Sequential Controller does not produce any voltage on any of the 3
>> outputs, nor does the gate out work. I'm wondering if anyone knows
>> what chip/circuit the TD1-10 is and also what PL-#s are?
>>
>> http://www.guitarfool.com/ARP2500/images/1027_sch.jpg
>
>
> Are we right to assume that the other stages work OK?
>
> Does the stage 8 panel lamp light up at the appropriate time?
>
> If so, I would start looking round the lower PNP transistor in the
> associated driver section ("TD-8").
>
> If not, it seems likely that you either have a bad divider Z7 or a broken
> joint/trace between Z7 pin 8 and the TD-8 section.
>
> Should be easy enough to follow the signals through even with a DVM - as
> long as you can access the circuitry when it's live. The signals from Z7 to
> TD-x go low when active and are pulled up to +15 otherwise.
>
> HTH,
>
> Steve L.
> Benden Sound Technology
>
>
>
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