No power or no leds - VU Meter showing -5 with no signal

[perfectsnd]

Powered up the console and one of my channels had no leds or wasn't passing any power. I had no routing light, no solo or cut control of any switch response. I replaced both of the 2 amp fuses, but it still continued to have no leds and the VU meter on the channel was showing -5.  I check the pico fuses again and they seemed to be fine.

Any hints on where I should start troubleshooting?

[horizonsound]

I'd be looking at the logic card.

Anthony.

[perfectsnd]

What would I be looking for?   A blown resistor or a bad I/C chip?

-Joe

[horizonsound]

It seems you have lost your +11v logic rail - either at the source, or the logic card.
Nearly all LEDs are driven off the logic card including the VU status LEDs - excepting the routing cards and Dyn/Eq switches.

Do your routing LEDs work up top? If so, then the problem is most likely the logic card. Swap the card for a known good one to confirm, and check the voltages and 10ohm fusing resistors on the suspect card.

If you routing LEDs do not work, then there is an issue with the +11v feed.

Grab a mulitmeter and follow the incoming +11v. You find it fairly quickly.

Anthony.

[perfectsnd]

I have +11v coming in to the D13 diode on the main board, but on the other side of that diode is have 0v.  Also, and I assume this has to do with a bad diode, I don't have 18v on the other side of the 2 amp fuse, but the fuse is not blown.

What is the part number for the diode?  Does anyone where to get that in the states?

Thanks.

[amillar]

Hi @perfectsnd, did you find your problem?

[Dave Dicson]

I had a similar problem on one VU meter were the VU meter was reading (not in VCA mode) and no audio. In my case, I don't remember which one, but I was missing 18 volts on the meter card. The problem was on the upper channel board was not being sent to the meter card.   

[perfectsnd]

Andy,

I have not found the problem. I ordered some diodes and pico fuses from Digikey, but they haven't arrived yet. I know I am not getting 11v passed the diode on the module.

Any suggestions?

[horizonsound]

Hey Joe,

To make sure you don't have a short on the E12 (or E294) logic board, have you tried pulling it, or switching it out?
+11v runs through a few other things on the module as well. LEDs, routing switches.
I've seen some strange things in the past, where an LED was shorted to the front panel causing the +11v to burn out, along with the 270ohm dil resistor on the logic card, and R3 10ohm on the main module.

Check the resistance across the module edge connector for +18 to +11.

Anthony.

[amillar]

I have +11v coming in to the D13 diode on the main board, but on the other side of that diode is have 0v.  Also, and I assume this has to do with a bad diode, I don't have 18v on the other side of the 2 amp fuse, but the fuse is not blown.

I'm confused by this, are you saying you have +18v on one side of the fuse but not on the other? That sounds like a blown fuse? If you don't have +18V then you won't have 11V on the "channel" side of D13. The current flow is from the +18V, through the logic circuitry, through D13, and back out to the +11V (it is a bit strange / confusing!). It isn't really 11V at all, it's a 7V supply hanging off the +18V.

If the +18V isn't there then as you say, everything on the +18V and +11V rails will be at 0V.

I don't think it's a problem with D13, it sounds like a problem with the fuse, or maybe the fuse solder joints or cracked tracks around the fuse.

I've attached the circuit diagram of the 611 fusing and diodes to help with this thread.

Thanks,

Andy

[perfectsnd]

I put a new fuse in and still no power on the 11 volt rail. It looks like this module has had the fuse replaced many times and maybe the circuit board is having a problem, but when I test continuity down the board from the fuse, it tests fine, that is why I am suspecting the D13 diode.

[amillar]

Are you getting +18V now? That's the important question!