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

Steve Lenham steve at bendentech.co.uk
Wed Oct 1 19:06:29 CEST 2014


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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