962 questions

System 55 • System 35 • Model 15
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962 questions

Post by Omega56 » Fri Aug 03, 2018 3:17 pm

Hi everyone,

maybe someone can help me understanding how a special part of the 962 is working. I have cloned the 962 and everything seems to work well. The only thing I do not understand is the connection of the jack socket in J8 (third socket of the signal inputs) In the service manual I see, that if this socket is not plugged in, only Stage 1 and 2 should be active and the last stage is skipped.

I tried to understand the logic behind and perhaps someone can agree in principal what I found out...

Lets start at the beginning when I power up the modul. In almost all cases stage 1 is active, lamp L1 is on and stage 1 is active. What happens now with the 3 flipflops and the rest of the logic.

The non inverting output of the first Flip-flop shows a high signal (about 1V), via R17 and Q5 L1 is on. The SET input of the second Flip-Flop is also high. The inverting output is low, Q6 blocks, L2 is not shining. The inverted output of the second FlipFlop is high. Now, independant if the socket of the third Signal Input jack is plugged in or not, the output (Pin5) of MC717p is low, so the SET input of the third Flip-flop is low. The non inverted output of the third flip-flop is low, Q7 blocks, L3 is not shining. Pin1 of MC717p is high, the output (Pin3) is then low. Pin 9 is also low and so Pin8 is high. The output (Pin14) is low and leads to the SET input of the first Flip-flop

So, everything is good, stage 1 is active, stage 2 and stage 3 are inactive.

Now I press either the button S2 to get Stage 2 active or via Shift in I generate a clock impuls which pushes the information of the SET inputs to the non inverting Outputs of the 3 flip-flops.

What's going on now?

The inverting output of the first Flip-flop goes low (at the end of the first round a low signal was set at the SET input, see above), Q5 blocks and L1 goes out. Now the inverting output of the second flip-flop gets high, Q6 is conductive and L2 gets on. At the inverted Output is now a low signal. Now the switch contact of the socket J3 becomes important.
When I understand it right, in this case the switch contact should have no contact to anything. R24 is connected to 3,6V (I checked that by studing pictures of the PCB, because in the Service manual there is no information). So via R24 there is a high signal at Pin 7 of MC717p and therefor a low signal at the SET Input of the third flip-flop. The non inverting output of this flip-flop is low, Q7 blocks, L3 is not on. Via R24 und R25 Q5 gets conductive and at Pin2 of MC717p is a low signal. Now Pin3 (output) gets high, Pin 8 on low and Pin14 goes high and also the SET Input of the first flip-flop.

So, at the end, stage 2 is active, stage 1 and 3 are inactive.

Now the same procedure, Either via Button or via clock impuls, the SET inputs of the 3 flip flops will be pushed to the noninverted outputs.

What's going on now?

The high signal on the SET Input of flip-flop 1 will be pushed to the non inverted output und will therefor turn on Stage 1 again. Q5 will be conductive and L1 is on. So, stage 3 was skipped and only stage 1 and 2 were active

And now to the scenario, where the a jack will be inserted into the 3rd socket of the Signal Inputs. When I am right, now the switch contact of this socket should be on ground.

Now we're going back to the point where stage 2 is active. At the inverted output of the second flip-flop is a low signal and therefor also at Pin6 of MC717p. Since the switch contact is now on ground, Pin7 of MC717p is also low and as a consequence the output (Pin5) shows a high signal and this is connected to the SET input of the third flip-flop. With a new clock impulse the output of this flip-flops will be high, Q7 will become conductive, L3 is on and stage 3 is now active. Since the inverted output is high Pin9 of MC717p is also high and at the end Pin14 gets high and finally the SET Input of the first flip-flop gets high. After the next clock signal, the content of the SET Input will be pushed to the non inverted Output and Stage 1 will be active. So we had all 3 stages active, one after the other.

Did I get everything correct so far or did I make somewhere a mistake?

Now the the final question: How can I achieve, that a switch contact of a socket will be on ground when a jack will be inserted an does have no contact to anything when the jack will not be inserted? Is this doable with a mono socket or a stereo socket? And if yes, how....

Thanks a lot for your patience and maybe someone does have answers to my questions.


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Re: 962 questions

Post by ummagumma » Sat Aug 25, 2018 12:45 pm

you may get better info at muffwiggler, they tend to DIY a lot there

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