Accent trouble HH/Ride/Crash

Discuss use it and firmware update

Accent trouble HH/Ride/Crash

Postby oer23 » Jul 19th, '18, 10:25

Hello everybody.
I have a problem with accent on the Hat (Hit is ok), the Ride and the Crash, it's always on, the led stays lit at maximum on the step.
The sound of Ride and Crash is very dirty with a strong distortion.
So if someone have an idea, he is welcome.
Thanks.
oer23
 
Posts: 16
Joined: Feb 24th, '16, 20:37

Re: Accent trouble HH/Ride/Crash

Postby domanton » Feb 24th, '21, 21:39

Hmm that's a weird problem. Do you know anything about the history of this particular machine? Did it work before and suddenly was damaged like it is now or did the failure appear gradually, e.g. first HH, then Ride etc..?

When it comes up to problems like this where the failure is only on the digital instruments but all of them, you would search for a circuit part which is shared by all these instruments. Unfortunately the digital instruments are quite well separated here. All of them have their dedicated oscillator for clocking the ROM-output, their dedicated DA-converter which is simple R2R-resistor ladder, dedicated envelopes and so on. But it's possible that opamps or logic gate ICs might be shared by the instruments, because one IC often contains several logic gates like NANDs or Flip Flops. Unfortunately there's only IC58 (4520, part of the address counter for the ROM) which is shared by Crash and Ride.
But Crash and Ride share the DA-converter for Accent (volume). Generally if the Accend DA-converter fails, the instrument will most likely produce no sound, because Accent will be 0V.

A failure of the CPU is rather unlikely because it just creates the trigger and accent data for the instruments and for the CPU it doesn't matter if there is an analog or digital voice being played.


Do you have any electronics experience and lab equipment like oscilloscope?
The general procedure for your type of errors would be:

1. Check oscillators of HH, Crash, Ride if they output approx 60kHz square wave (which is then divided by 2 by the followed clock Divider which gives you approx 30kHz sample rate)
2. Check if Trig and Accent (which is actually always present and setting the volume as mentioned above, it just has different values between 0-5V) are present at all instruments.
3. Check if ROMs are outputting data when triggered.
4. Check envelopes signals driving the VCA after triggering. Note that HiHat and Crash/Ride use different envelope concepts. Hihat uses a normal analog envelope (two different time constants for Open and Closed HH). Crash and Ride use an additional DA-converter for creating the envelope. So the envelope of the sample itself is used as an envelope to drive the VCA. This is used because these instruments can be tuned, thus making the envelope automatically shorter or longer depending on the tune-setting. THis ensures that the whole sample is being played and not being cut off by a constant envelope. Quite cool concept.
domanton
 
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Joined: Feb 24th, '21, 21:32


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