[sdiy] EMS synthi AKS - sequencer info

[RMC]

Hello

I thought that both "S" sequencers had failed. I was wrong - they're working 
fine! Hopefully this info will get archived and be of use to future AKS 
repairers/users.

The reason I thought they didn't work is twofold; firstly, the MF7104 
(MF50052T  or MM5056 also) static shift registers were boiling hot - too hot 
to touch for more than a few seconds. I assumed that they had failed and 
were sitting on the PCB just acting as loads for the LM309K (which, by the 
way, also gets hot enough to metaphorically almost fry an egg on!)

Secondly, there was no pitch CV information getting to the VCOs. I didn't 
get chance to measure the DAC outputs (R-2R ladders, switched by NPNs into a 
741 op-amp) but that was my next step when I found time later this week.

However, I spoke to Robin Wood today and he's pointed out that the vertical 
joystick control that shows an arrow pointing towards "zero" actually has to 
be *switched* beyond zero - click! - into the sequencer position. I didn't 
even know that that happened!

Having tried that, I now find that both sequencers work fine.  However, I 
was still concerned about the very high temperature (I plan to try to 
measure the can temperature). Robin said "they all do that - put out of your 
mind any worries that they've failed. They'll work fine". He was right of 
course!

I plan on trying to find some heatsinks and a way to blow air through the KS 
case to keep things cooler. In the confines of the case I can't see that the 
PMOS shift registers in their TO-100-10 cans would last long, so if I can 
cool them by some neat (unobtrusive) method, it can only be a good thing to 
do. Along with sourcing some replacements, if at all possible.

So there we have it - egg on face but now I have a pair of fully working 
AKSs! Apart from that one pesky envelope shaper - must get round to that . . 
.

Final note - the umbilical lead is shown in the circuit diagram for the KS 
(http://www.hinton-instruments.co.uk/ems/ks.gif) as having some inline 100k 
resistors on pins 1 & 6. Someone helped me out (thanks Magnus) with 
observations on his AKS which didn't have the inline resistors;  so when I 
made up some leads, I went ahead and fitted the 100ks to the back of the KS 
connector, thus making the leads standard pin-pin wired (and you can double 
them up to make them longer).

Cheers

RMC, England