burnt capacitors on faderboard

[ilmenator]

Well I exchanged the AD8803 on a fader board that had two stuck faders, but without any change: the same two faders are still stuck when the console is powered on.
However, when I move the fader board to another position (say from 1-8 to 9-16), then different faders are stuck. That tells me that the problem is not related to the fader board itself, but it must be coming from the brain board!? Cross-testing confirms that: putting in a different fader board, the same two faders are stuck.

[Jondav1120]

Hi Ilmenator,

Did you check the +/-16v supply on the fader board, or just off load at the power supply?

Regards

John

[ilmenator]

Hi John,

I checked the 16V across the rail caps on the brain board and I get the exact same values as when measuring without a load at the power supply.

I have also exchanged the brain boards between the two consoles, but strangely enough that doesn't seem to make a difference for how the fader boards behave. I'm a little lost now, I have to confess...

Thanks, ilmenator

[Jondav1120]

Hi Ilmenator,

Are the faders stuck as soon as the power switch is turned on? Or, do they stick once the CPU has booted up fully?

John

[ilmenator]

Hi John,

the faders are stuck only after the CPU has booted fully and the initial fader motion has been executed by the CPU. Before that, there is no mechanical difference between the stuck ones and the loose ones.

The PCB area around the Darlington transistors (Q2, Q3, Q4, Q5 driving the fader motors) is getting hot - I cannot determine which of those / if all are getting hot, as the faders are in the way. But I guess that is not unusual, as the fader motor is driven continuously against -infinity.

ilmenator

[Jondav1120]

Hi Ilmenator,

WHat happens if you operate the "Fader motors off" button on the console? Do the faders unstick?

Regards

John

[ilmenator]

Hi John,

that does not have any positive effect - the corresponding LED will go on and off when operating the "Fader motors off" button, but the faders are stuck anyways. However, after toggeling the button sometimes more than the two faders are stuck. Also, there is an audible "release" noise coming from the faders when operating the button.

One more observation (on this PC/PSU I can switch on the console's power supply and the PC's power supply separately): as soon as the CPU is powered down, the fader motors are released and the faders can be moved freely again.

In the meantime I have also replaced the rail capacitors on the brain board as described in http://www.sonido-7.com/d8b/photos/large/RCIdentifier.jpg, but that has not changed anything (and the desoldered caps measured ok).

ilmenator

[Jondav1120]

Hi Ilmenator,

This is very puzzling...
1. The fader motors are free until the CPU boots up. This means that it can't be one of the fader drive transistors failed (it would lock the fader immediately in that case)
2. The fault does not transfer with the board. The connection between the Brain board and the Fader boards is a serial data link, so it's unlikely to be anything on the brain board. If the fader board was sending faulty data to the brain board the fault would still transfer with the board.
It is almost as if the brain board is actively telling the fader motors to drive past their lowest position.
Have you tried a fader callibration?

Regards

John

[ilmenator]

Hi John,

no fader calibration yet, as I am still stuck with a broken 9-faders-board. However, I could transplant the fader board from the other console... I will try that next. Thanks!

ilmenator

[ilmenator]

Hi John,

quick update: fader calibration has actually freed up the faders!

So far I have only reconnected one block of 8 faders, but this is looking good - thanks a lot for your input!

I'll post more once I have confirmed the other faderboards are working, too.

Thanks, ilmenator