..and specifically, of the DIP kind. There sure were quite a few of them with this case!
Topic of the day, a Digitech DSP128 multi-effects rack unit that switches into some kind of a digital noise overload mode at random. This occurs sometimes at power-up, sometimes after the unit has been in use for a while. On the latter, the condition can be occasionally triggered by feeding a loud audio signal in to the unit and then switching to a long reverb preset. Power down the unit for a while, and the problem is gone only to return sometime later.
Prior to opening up the unit, I decided to contact Digitech for the schematics / service manual. The “lazy” way of checking what’s inside, sort of :).. They served a very positive surprise; my email request was responded to in a snap, so about half an hour later I had the schematics at my inbox! Plain amazing.. just wish every synth manufacturer would have it like this! On that note, fuckings to Yamaha’s alledged “older than 15 yrs, put it to the landfill” policy. You sure make fixing my CS-15D a total annoyance!
Anyway, with the help of schematics I was able to swiftly familiarize myself with the inner workings of DSP128. All in all, pretty straightforward digital circuitry. Checking inside the unit it turned out all the chips are even socketed, about as service friendly as it gets. Too bad that the sockets quickly turned out to be the “weak link”.
As a brief scoping session didn’t reveal any abnormal signals (f.ex. odd voltage levels), I figured I’ll try reseating the IC chips a few at a time and power on/off in-between. With this, the unit seemed to change its behaviour on about every cycle. During one, it didn’t even power up completely! Indeed, looking more and more of a socket contact problem.. Not that their spring contacts looked dirty, oxidized or bent. But given the random functioning they had to go (just to be able to investigate other problems, if any) and for the replacement, I chose machine tooled sockets.. Not much else to it than warm up the desoldering station and get going!
Despite looking like single wipe sockets on the outside, the original ones were actually dual wipe type (better contact). I just had to cut one open to check for this ;). As far as I know, single wipe sockets are a common cause of failures due to flaky contacts between the chip and its socket (f.ex. in old arcade cabinets), but got to admit that having similar issues with dual wipe type was all news to me.
Eventually, somewhat 5 hours and +700 de/resoldered component feet later, I had the DSP128 assembled and ready for use. Noise gone and the device seemingly as functional as ever, yay \:D/. Longer test session still pending of course, but it looks (and sounds) promising.
If you want to hear what the DSP128 sounds like, check out this page @ Sealed’s Deep Synthesis Site.