Trouble with desk; all solo lights lit on startup

  • Thread starter Thread starter henderwood
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henderwood

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Hi
I know it's an old cheap desk, but when I turn on my Mackie CR1604-VLZ desk, all the solo LEDs light up.
Nothing is working
Any ideas please?
 
I don't know the answer, but you'd be better off posting this in the analog forum. Some folks there could help.
 
I took a look at the service manual. There appears to be OPAmps that control the SOLO leds, either sensing input and flickering or full on when SOLO is selected on a channel. These OPAmps plus the OPAmps in the audio signal chain get powered via a cable harness header/plug Power Distribution P1. It could be as simple as a loose plug on the header. It also could be back in the power supply section that develops the +/- 16vdc, such as one of the voltage regulator chips or something else. Not sure what your skill level is for working on something like this and a few images I found of a 1604 disassembled didn't look too friendly for opening it up to access things. If you can get at the plug P1, perhaps removing it and reseating it may help with some luck, otherwise checking various points with a meter for the 16 vdc supply voltage may be the next step. Below is an image I denoted the plug P1 on the Main board.

1604 solo led ps.webp
 
Thanks so much for your interest.
To answer your question, my willingness to 'give things a go' far exceeds my skill level in this area :)
Preliminary results...
The voltages on P1 are as follows:
7 -31V
6 -16V
4 -31V
3 -16V
1 31V
 
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Your edit switched polarities of your measurements. I was liking the first ones better :) (although those seemed messed up)

Black meter lead in the Neg jack on the meter and to a Ground point in the mixer, right?

There is a P1 on the power supply module which is AC voltage from the transformer. It's the P1 on the Main circuit board is where you should be measuring
 
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It was a late night, but yes, I have my polarities organised now :)
I faffed around with the power supply and somewhere in the mix the voltages on the power strip returned to normal. I partially assembled it for a re-test and the only life is still in the unanimous enthusiasm of the solo LEDs. Still no 'power on' light or other life-form. After a few minutes, a capacitor in the power supply area went off with an impressive plume of smoke. I've purchased a replacement but haven't got to that repair yet.
So it's been some fun so far. I'm not angsting, but enjoying the process. With the capacitor replaced, I guess I'll be looking for the next thing to check.
cheers
 
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