Archive of the former Yahoo!Groups mailing list: Vintage Simmons Drums (UK) Users Group

My comment on the state of schematics was intended to be a bit "tongue in cheek" so to speak.
You are right about there is a "reasonable" copy floating around - it is a bout 10meg in size, BUT
it is still pretty hard to follow if you have little knowledge or experience in electronics. Who ever
drew up the SDS7 diagram used a lot of "schematic shorthand" and for the uninitiated it will confuse
the hell out of them. If you look closely, you will also notice a number of "floating" circuit connections
that simply go no where. Again unless you refer back to IC data sheets and have an understanding as
to what is intended, you will certainly come up against a wall of grief.

As to capacitor replacement, it doesn't matter what the area of interest (electronics) it is always a contentious issue with many arguments for and against. After years (many decades) of experience
in this industry I have come to my own conclusions on this topic.

1) PSU's "cop a hammering" and bad filtering will always impart noise on the DC supply lines so I
give these a fair bit of attention when servicing. If the device is over 10 yrs old I will usually replace
all PSU caps. That being said, I have seen a hell of a lot of service mount stuff that is quite recent that
are showing failing electrolytics. I can't explain exactly why but I have my suspicions it has something
to do with 2 factors - a) poor quality components and b) highly compact placement with little thought
gone into factors of component heating. Simply put, the caps are being cooked off by heat generated by
surrounding components. Electrolytics vent off and dry out overtime. Like old Nicad batteries they tend
to "electrically form" after a while and fall out of spec, the quality of the component tends to determine
the nature of this issue but is no guarantee against failure.

2) Tantalums are like "penny crackers", they all go bang. Replace them.

3) ceramic types are generaly low tolerance specs and over time quite stable. Unless one is identified
as bad, don't worry about them.

4) Mylar and other "modern" type caps - see 3 above.