Sorry, the cap value should have read 100nf-63v, or .1uf-63v, NOT .1nf it is early here...LOL!
--- In Simmons_Drums@yahoogroups.com, "simmonssds7fan" <ptmetcalf@...> wrote:
>
> I replaced all the polyfilm caps that were rated at .1nf-63v on the board as I was told that these were "worn out and at the end of their useful life". I was also told that it was the ones in the mux/demux circuits that would be faulty specifically, that those are "usually the problem". It was my decision to replace all of them on the board of this value since I figured, if the mux/demux ones are worn out and they are all the same age, then it made sense to replace them all.
> I'm in the USA and the power transformer is wired up to run at 115V.
> The erpom chip I used for the 3.0 OS is of the same type as the original. It is an Intel 27128a chip. I bought a bought a bunch of NOS ones a while ago for extra sound proms for my sds7 and tested them all a while ago, and yes I did use a prom eraser to make sure it was good to go. Also, I do have a good prommer and know how to use it. I'm sure it's not in the OS EPROM since the unit does the same thing with the 3.0 as the 4.0 OS that was installed in it when I first got the machine.
>
> I will try the "lick test" next......we'll see what happens next I guess...
>
> --- In Simmons_Drums@yahoogroups.com, "philmurr" <philmurr@> wrote:
> >
> > I'm from the "replace electrolytics caps" school. Especially the power supply section. I can't remember for sure, but think there are only half a dozen electrolytics on the board, and none of them doing anything "critical".
> >
> > It's not unusual for an SDS9 to run hot (underneath) as that's where the PSU board is connected. Where in the world are you, and what is your mains voltage, as the transformer is multi-tapped and the unit will run quite happily on a higher tap, unless you're in the UK in which case you've got no choice :(.
> >
> > With the box running and doing the random triggering, lick your finger and touch the top of all chips, see if any dry out quickly, an indication of them running hot.
> >
> > Are you sure the ROM chip you replaced is fast enough (and is the RAM original for the same reason?)
> >
> > Can you also check the +5V at various points on the board (esp. furthest away from where the power connector is). On one of mine I connected a 100uF or similar near the CPU chip just to help the power supply out and it stopped it doing odd things.
> >
> > From memory, and I haven't checked the service manual recently, I recall there is a "full-on" test mode that you can put the unit into, can anyone else confirm ?
> >
> > Phil.
> >
> > --- In Simmons_Drums@yahoogroups.com, "simmonssds7fan" <ptmetcalf@> wrote:
> > >
> > > Alright then.....let me run the issue by you then and see what you think it is.
> > >
> > > When you power it up, it initializes normally. Then the low tom circuit trigger led comes on and sound is faintly generated, sounds like a constant "doom-doom-doom", then it slowly stops. After the low tom stops any one of the other toms or snare will trigger randomly at full volume until they are all triggering at the same time, generating a buzz/white noise. The bass channel never does this, only the snare/rim, and the toms. The unit gets rather warm when it does this. If you shut it off and let it sit until it gets back to room temperature, it goes back to near normal and the cycle repeats. I have changed the OS chip to the 3.0 version, it did have the 4.0 version, but it only slightly helped.
> > >
> > > Any ideas which mux/demux chip I should start with? I'm thinking the low tom, but I don't understand if it starts with that one and it goes off, how it could influence the others to randomly trigger like that. Wouldn't that mean they all have issues?
> > >
> > > --- In Simmons_Drums@yahoogroups.com, "gordonjcp" <gordon@> wrote:
> > > >
> > > >
> > > > > If the mux/demux caps are worn out and ALL the caps are the same age on the board, wouldn't it make sense to change them all? They are cheap enough.
> > > >
> > > > They don't wear out. They rarely fail. When they do, they cause very, very distinctive faults.
> > > >
> > > > It's worth noting that just about the only capacitors I have ever seen fail have been electrolytics used in cheap crappy switched-mode power supplies (which you don't have here) and disc ceramics used at high voltage or in RF amps. In synthesizers I've changed maybe a dozen genuinely faulty capacitors in 20-odd years.
> > > >
> > > > Capacitors don't fail, and they don't wear out.
> > > >
> > > > > As I stated previously, that didn't change the issue I'm having with it, so now it has to be the mux/demux ICs, as stated earlier in this thread by Michael himself on the issue with this machine that this member is having.
> > > >
> > > > Of course it didn't, and now you've got to do what you should have done to begin with - diagnose the fault! The 405x family multiplexers do fail, with either an output getting "stuck" usually to one supply rail or the other, or the inputs just not switching at all. Get an oscilloscope, track down the fault, and replace just the part that has failed.
> > > >
> > > > > If I've replaced all the caps with the proper values and it does the exact same thing it did before, how then could I have created more problems? Can you please explain that theory?
> > > >
> > > > How good is your soldering? Are you sure you read all those capacitors correctly? Are you sure you didn't damage the fragile through-hole plating on the boards? Are you sure you didn't zap something with static?
> > > >
> > > > I won't touch ∗anything∗ that's been "re-capped". I often see synths that have been "re-capped" by some Expert Synth Doctor that then never quite works right again, and then they're just too much bother to put right.
> > > >
> > > > Don't muck about. Track the fault down and fix ∗just that fault∗.
> > > >
> > > > --
> > > > Gordonjcp MM0YEQ
> > > >
> > >
> >
>