[sdiy] Troubleshooting an ARP 2600

[Bill Keys]

FWIW: I recently found the guts to my old ARP Explorer I. So far, replacing 
the 301's has hit the 100% mark: i.e. _every_ 301 was crapped out. I wonder 
if they're just bad chips or whether it's ARP's design....

The hardest part was taking apart the 4034 filter module (what a PITA). 
Also, the 3086's seem to have close to the same rate of failure - (all 4 in 
the filter are kaput, but the vca's 3086 was okay).

Also, since I have about 30 301's, I'm just popping in new ones - but it 
will be nice to know if the LF411's are better...

+_+_Yes, honey, I know there are 25 boxes of electronic junk cluttering up 
the attic. They will, one day, magically be transformed into a modular 
synthesizer cluttering up the attic.... www.mp3.com/OriginalSimulacrum _+_+



>From: Gavin Muir <gmuir at sympatico.ca>
>--
>Hi all,
>
>I'm doing some work on a friend's 2600 that he has loaned me, and I
>just wanted to run a few things by the list to see if anyone could
>give some guidance.
>
>The synth is operating, however there are some circuits which are
>clearly dead. Firstly, the pulse converter on oscillator 3 is cooked
>(ie. no output). My suspicion here is that the op amp in the circuit
>is fried. Now, the service manual lists this as a strange part
>number; is this replaceable with a standard op-amp (I have heard many
>speak of replacing the 301s with LF411s)? If not, any ideas how these
>amps are selected and what may work here?
>
>Second dead circuit is the S&H. I have been digging around the net,
>and have come up with a thread in which Joachim took part where again
>the problem was the op-amps, and the LF411 was a recommended
>replacement. Is this the best part for the job in the 2600? Is it
>worth going through and pre-emptively replacing the 301s with 411s?
>
>Cheers and thanks,
>
>Gavin Muir


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