Vintage Simmons Drums (UK) Users Group

> Hi all
>
> I received my SDS9 from eBay with 3 sheared off knobs. Looking through
> the archives, this seems to be a common problem, although I don't see a
> definitive replacement part for the pots or the knobs. I'm missing
> Volume, Lo Tom Volume, and Auto Speed. While I wait for parts, if anyone
> sees something wrong with what I am ordering, please let me know!

> I'd love to keep it looking original, but even if I could find the right
> knobs, I can't find a pot with the same shaft. Perhaps someone on the
> list has a lead on these? I've seen an old message that an Ed Rose might
> know - is he still on the list?

> I've never worked on this stuff before, but I have worked on some 80's
> arcade game boards, so I'm not surprised to see battery replacement as a
> big priority

> Electrolytic capacitor replacement? I see some mixed opinions. It can do
> wonders in a CRT monitor, but I don't have enough electronics knowledge
> to know which ones are most likely to cause problems. Maybe in the power
> supply? I hate to mess with something that is already working, but
> perhaps I'll replace any that I have equivalents on hand for.

> That brings me to the next question - schematics. I was hoping to find a
> repository of schematics and/or service manuals - it appears there was
> such a thing, but it was stopped due to abuse. If anyone would be so
> kind to email me a schematic (SDS1 would also be much appreciated), I
> can assure you it will not be sold or redistributed.

Replacement pots "can" be found from some suppliers. Original potentiometers use a thin and somewhat flimsy shaft size. They used to be available in plastic or metal (better choice) but are pretty hard to come buy nowadays as are the matching knobs. There are plenty of "parts brokers" out in the world who seem to do a good job hunting down many old components. Do a search on the net and send out a few emails, you never know your luck.

I agree with Jesper on the battery replacement, if possible go for a replaceable lithium arrangement BUT YOU MUST modify the original circuit to remove the charging capability or you will blow the lithium battery up!! The mod is simple and requires you put a "blocking" diode in series with the battery positive. This will allow power from the battery to feed the SRAM but will block voltage from being applied to the battery.

As to capacitor replacement, yes a contentious issue. Certainly I always replace any caps relating to the PSU side of things. These cop the greatest hammering and depending on the quality, will no longer be within original specs. As to the rest of the circuitry, everyone seems to have there own views ( a bit like climate change..lol). It is true to say it is pretty pointless to simply replace ALL capacitors just because they are old. It is akin to putting a new engine in an old car when really a simple tuneup would suffice.

You need to replace those that are affecting the performance of the device. IF you get to a point where that may be 60 to 70% of the originals caps, then sure it wont hurt to go all the way, but don't do it simply because you can.

Simmons schematics, the old chestnut. The originals floating about are generally poor. They tend to be "cobbled" together, old early revisions, missing bits, user modified, manual merchant stamped and simply incorrect documents of garbage (well that's my view anyway) There are some good copies around but you will need to go to the source of those to get them. Some group members have gone to the time and effort to manually trace and redraw schematics of some simmons gear and these docs are good. If you are looking for good SDS7 service info, next time you go to the crapper, don't flush the paper, use that to do your fault analysis. What you will see on the crap paper is far better than what you will see reading the available SDS7 service manual.

If you Google for "Omeg 4mm" you should get enough hits to point you in the right direction for replacement pots.

My view on capacitors - replace electrolytics wherever they are, PSU or not.  There aren't many in Simmons kit other than the PSU so they're worth replacing.  And if you're working on an SDX power supply, replace all the type X / mains capacitors (or be prepared for them to let out a huge amount of horrible smelling smoke one day).

Schematics - I agree with the previous post, some of them are good, some awful - even the simplest early product schematics have lots of errors, but they're a starting point.  There is a readable SDS7 schematic out there if you look hard enough...  For the products where schematics are just not available (which fortunately appears to be the minority), spend the time making your own and you'll really find out how it works !