entropy continued?

This is where we talk about testing, measuring and repairing things. Sometimes we have to repair the equipment we use to test, measure and repair other things. It's an endless cycle of fixing the broken things we need to fix other broken things.
billshurv
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Re: entropy continued?

Post by billshurv » Mon Apr 22, 2019 6:00 pm

Well Finally got some time to test out my infinity subwoofer that had been malingering for 2 decades. And it doesn't. There is sound, but at very low level. Bit of basic fault finding and oddly the output does not change if the output relay is activated or not. If the relay is open there is a 10k resistor in series with the woofer coil. OK that would do it. It would be way too much good luck for the obvious electromechanical component to have gummed up in the open position.

But the bad luck is that, even if it was, this was not a unit designed for servicing. No plate amp on the back to unscrew. You have to cut wires to remove the baseplate, then unsolder more to get the amp module out. Fergit about easy probing with a scope whilst runnning! What were they thinking*?

At this point the temptation to take the speaker out, shine a torch in to look for the relay and give it a good tap before cycling it a few dozen times is high!

*The service manual is an oddly specific combination of specific instructions for dealing with known faults and arm wavy faff that suggests bar those you give up and throw it in the skip :).

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mediatechnology
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Re: entropy continued?

Post by mediatechnology » Mon Apr 22, 2019 8:46 pm

We are coming off of a waning gibbous moon.
My hunch is good thump on the relay may work.
https://ka-electronics.com

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billshurv
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Re: entropy continued?

Post by billshurv » Tue Apr 23, 2019 3:50 am

What does intrigue me with this design is that there is a single relay there that serves for operate/mute functions as well as cut out for various fault conditions. It leaves power to all the active stages on, including the velocity feedback. When you mute the signal is still being delivered and amplified and the velocity feedback will be applying as much adjustment as it can in vain. Clearly the amount of correction in servostatik is small (which thinking about it makes perfect sense, just never thought about it.

But given current regs the idea of a standby switch that leaves all power on is amusing :)

billshurv
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Re: entropy continued?

Post by billshurv » Fri May 17, 2019 4:56 pm

wife is away for weekend so time to try and get this sub woofing. drive unit out no problem but then realised that the sub is on its side so the main board is at the top. Stick camera in and take a pic. Locate what looks to be a relay and reach in. Yup, feels like a relay too. Hit it then powered up. Nothing. power down, hit it harder and try again. This time after about 20 seconds the drive unit starts vibrating across the floor. So it was the relay. Just going to try again....


...yup. That of course is my good luck with the obvious thing being the fault for the weekend :). Now where are all the allen bolts to re-assemble...

billshurv
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Re: entropy continued?

Post by billshurv » Fri May 17, 2019 5:19 pm

Hmm well that shakes the room. Need to run a frequency sweep and get the levels adjusted as its a tad high at the moment :). Job for tomorrow.

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