DFAM Sequencer defect?

Mother-32, DFAM, Subharmonicon, Grandmother, Matriarch
Post Reply
User avatar
Marxon
Posts: 2
Joined: Fri Feb 10, 2023 12:35 pm

DFAM Sequencer defect?

Post by Marxon » Fri Feb 10, 2023 12:59 pm

Hi all,

seems like my DFAM´s sequencer is somehow faulty. :cry:
After hitting Run/Stop it keeps playing the first step only and repeats it.
Also the Advanced button does not make the sequence to go further.
Same with using a external signal on the Adv/Clock input.
Any suggestions or do i have to send it for repair?

Thanks for any advice
Marxon

EDIT
In meanwhile I disassembled the DFAM to investigate the problem.
Maybe my electronic knowledge is enough to fix it.

User avatar
Marxon
Posts: 2
Joined: Fri Feb 10, 2023 12:35 pm

Re: DFAM Sequencer defect?

Post by Marxon » Tue Feb 14, 2023 11:53 am

I have made some progress with my troubleshooting but couldn’t fix it yet.
Here is what I figured out:
The eight sequencer leds are controlled by an 8 channel 74HC4051D multiplexer and two 8 channel DG408 multiplexer switches are used to route the 2x8 potentiometers.
First I checked the control inputs of all three multiplexeres while the sequencer was running and as might be expected: 0V. 😕
But what’s the reason?
As it turned out, the multiplexers are controlled by an 74HCT393.
It is a dual 4-stage binary ripple counter.
Supply voltage, clock signal, reset pin, everything seemed to be OK
but no reaction from the 74HCT393. So this should be problem!
But hen I realized on my oscilloscope, the clock signal HIGH level
was only about 2V! I quickly desoldered the clock input pin from
the board, connected it to a signal generator: Voila!
The sequencer is stepping forward. Now I need to figure out what causes the voltage drop :|
Measuring the DFAMs trigger output shows instead a correct 5V level signal.
The source of 74HCT393’s clock signal is small 6 pin ic (maybe sot-363)
labeled with „TK“. The smd code reference gives my over 40 entries! :cry:
This will take some time for indentification.
I will keep you updated…

Best regards
Marxon

synthpeter
Posts: 28
Joined: Tue Sep 07, 2021 8:41 am

Re: DFAM Sequencer defect?

Post by synthpeter » Wed Feb 15, 2023 2:44 am

I'd start checking the patch bay, and my first suspect would be the tempo patch point.

Post Reply