[log2Participant]

I determined the fader motors were driven with 5volts. I put a oscope on the 5v supply and changed layers with all the faders set to move from top to bottom. I saw that the 5v supply stayed solid at 5v. I just kept tracing the 5v power path until I found the point where the supply would sag on a heavy fader move. I did this from the bottom of the board as the faders cover up most of top side of the board. After I found the sag I flipped the board and found the tiny green PTC fuses. I ohm metered the fuses they were all bettween 2-5 ohms. They should be .2-.3 ohms. They are surface mount so it really takes two soldering irons to heat up both sides and pull off the compents like chop sticks. Its helpfull to have solder flux to solder the new part on, but not necessary if you have flux core solder. Also keep in mind if you over heat the pars soldering them on they will “trip” and take a few minutes to cool off and return to low ohms. And too much heat could damage them.

[log2Participant]

Opps. looks like pics were too large.

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[log2Participant]

So, I finally had some time to look at the qu-32 again. Turns out the problem was some PTC fuses on the fader boards. Each board has four fuses and they where all damaged. My guess is the dirty faders cuased more current to be pulled through the fuses, combined with hot air temp cuased the fuses to fail. PTC fuses don’t open like a regular fuse they go to a higher resistance. With only one or two faders moving in any bank it could reach position. If three faders needed to move per bank the high resistance of the fuses made the motors move to slow. After cleaning the faders and installing new PTC’s the console works great again.

[log2Participant]

Keith, Thanks for the detailed reply.

Glad to hear you went to the “side mounted pots on the SQ” I’ll be placing an order for a SQ5 right away.

Regarding my QU; I did have the board looked at by a authorized AH service center. The tech checked the 12v power to the boards and it was ok. He diagnosed it as dirty pots. Before spending the $900 for repair I decided to have a look myself. I was not convinced it was just dirty pots due to the problem happening only on odd faders of the first bank, and even faders on the second bank. Also, “zeroing” each fader when in “fader flip” worked fine on all faders.

I put the board on the bench yesterday. Here is what I have figured out so far- Any change of page or a “fader flip” works if less than 4 faders need to move in any bank of 8 faders (1-8, 9-15, 16-23, 24-32). I looks like each bank of 8 is globally current limited. This is confirmed by measuring the fader motor voltage. When asked to move 4 or more faders (in that bank of 8) the voltage drops from 5V to aprox 1.5V.

I am not sure if this is a friction problem, or the current limit is triggering at too low a threshold? Curious it only affects the odd faders on the first 16 and the even on the last 16. I have ruled out noise on the pots with a scope. Its for sure a motor current issue.

Not sure what my next step will be, as I don’t have a schematic and the 5V circuitry is hidden under the fader pots.

Any further help would be appreciated.

[log2Participant]

Thanks for the reply’s. I did find out the individual faders are not cross-compatible between the QU and SQ.

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