Re: motorboating T100 ??

[Dick Stallings <dicks@ncccs.cc.nc.us>]

Kristofer Kjvrling wrote:
> 
> Hi!
> 
> I'm new to this mailing list, and I hope you guys can help me out!
> 
> Me and a friend have troubles with his hammond T100 from 1969.
> I think the T100 is similar to the L100 with exception of the tube amp in the
> L100, of course! If anyone knows more exakt details about this I'd like to
> know more.
> 
> Surfing around searching for hammond related pages I've repeatedly stumbled
> across the term motorboating. I think, but I'm far from sure, that we have a
> related problem.
> 
> Anyway...
> After 20-30 minutes from turn on the hammond starts to give off a "chopping"
> sound. This is very low frequncy, i.e. there is no distinguishable tone as if
> there would be if there was a power supply hum problem etc.
> I estimate the chopping sound to appear roughly 4-5 times a second (very
> roughly), and increasing in volume as time goes by.
> 
> The thing is, that everything I've dug up on motorboating seems to concern the
> vibrato scanner, and I don't think there is such a vibrato in this organ (I'm
> not sure...)
> 
> So what is the deal here??
> Is it a mechanical or electrical problem?
> And if mechanical is it very hard to fix?
> 
> I'm studying electrical engineering so I was sort of hoping for an electrical
> problem since that makes me feel more comfortable :-)
> But to do accurate troubleshooting a schematic is alwasys nice to have
> and I don't have one!
> Are these schematics hard to come by? I read somewhere that you could order
> service manuals but do they include schematics?
> 
> What I could make out though, was that all parts seemed to be original even
> the electrolytic caps, which tend to dry out after 30 years. So could it be as
> easy as a faulty cap? I mean it's not a 100Hz hum tone problem we have, if
> that was the case the caps would be the first to go!
> 
> Furthermore there was an interesting pice of circuit at the bottom left of the
> organ (looking at it form behind). It is a small circuit board next to the
> volume pedal (which is also out of order by the way) with only one wire going
> in to it, and nothing more! I didn't investigate this closely but it seems
> strange with a circuit with only one connection! (maybe it was grounded
> somewhere out of sight, but I don't think so).
> Does anyone know what this little circuit does?
> 
> I bet you think by now: " Man, that new guy writes long letters..."
> 
> So, is there anyone who has had similar problem with a hammond T100 or anyone
> who knows what needs to be done?
> 
> I'm very grateful for any help!
> 
> Regards
> Kristofer Kjörling
Kristofer,
        Jerry Welch at Organ Service Company ,I'm sure, can supply you with the
service manual with schematics for the T100. I ordered the "M" set and
they are an excellent set of reproductions. Very clear printing and
clear schematics. Every detail is as good as the originals I remember
working with years ago.
        Maybe time is playing tricks on me, but I thought the T series was a
scanner organ; however, the problem you describe is not related to a
scanner. The "motorboating" attributed to a scanner only was present in
the sound when keys were pressed down and the vibrato was on. If you are
hearing this while the organ is just on, but not playing, you have a
component problem ......maybe a filter capacitor in the power supply or
a transistor. They can both produce that "putt, putt, putt" sound.
        Your volume control is an optical sensor controlled by a shutter on the
expression pedal. If the tiny lamp is out you either have no volume or
full volume ..... I cannot remember which at the moment! Sometimes lint,
would get in there and interrupt the light transmission and give erratic
volume control.
        The T was Hammond's first spinet organ with a built-in Leslie. It
really helped us to meet the competition. It had the tone wheel
generator, one switch starting, string bass, two speed Leslie, rhythm
unit....why am I saying this?....you have it before you!!!
        Enjoy your Hammond!
        Dick