Dead ADR S04 Parametric EQ

[user 40373]

I've been trying to get one of my S04 Parametric EQ's to pass signal with much luck. It has stacked boards, top board has the line amp section and the bottom board is the EQ, and the bottom board is working fine (swapped with a working unit) so I believe the top board has to have the issue. I've swapped op-amps with no luck, so I'm guessing it's somewhere in line amp. If I boost all the EQ's to the max I can faintly here the effect. Can someone a bit more skilled at reading schematic help me pinpoint some areas to look at. All electrolytic have been replaced, so I'm wondering if it could be a transistor.

 

[Brian Roth]

Do the + and - 18 VDC rails measure with the correct voltages?

Bri

 

[user 40373]

Do the + and - 18 VDC rails measure with the correct voltages?

Bri

Yes they are right on the money

 

[Script]

I'd start by checking for mechanical connectivity : from input via all switches and pots to output.

 

[pucho812]

I would trace signal with an o-scope

 

[user 40373]

I'd start by checking for mechanical connectivity : from input via all switches and pots to output.

I replaced all the switches, I own a lot of Scamp modules and they are often to cause of failure, but I still have issues. I don’t have a scope so I’ve just be using a meter to beep out connectivity.

 

[abbey road d enfer]

I agree with pucho, you need to trace the signal. i know it's a pita in the Scamp modules, because of the layered construction, but it's the only way to find where the issue is.
If you don't have a scope, you may just use a sniffer. You can make one using a small amp and speaker; you must use a 0.1uF capacitor and a 10k resistor in series to make the probe.
You start with the input stage and continue through the different stages until you lose signal.

 

[musika]

Another fault that I find that is common to these modules is that the Molex connector on the board's edge needs to be reflowed or replaced due to the mechanics of the rack pins when inserting. It's one of the first things I look at on a Scamp module.

 

[user 40373]

Another fault that I find that is common to these modules is that the Molex connector on the board's edge needs to be reflowed or replaced due to the mechanics of the rack pins when inserting. It's one of the first things I look at on a Scamp module.

That’s a good thought. I’ll try reflowing. By chance do you happen to know the part number for the molex connectors? I was also wondering that the part was for the pins on the racks the modules insert into, I need to order a few to use all the functions on panner modules

 

[musika]

I had trouble trying to find the exact Molex part for the 9 pin that is soldered to the rack. I have a parts backplane, so I have been successful at pulling used parts from that.

 

[user 40373]

I had trouble trying to find the exact Molex part for the 9 pin that is soldered to the rack. I have a parts backplane, so I have been successful at pulling used parts from that.

You’re a genius, that worked! Saw a cracked solder joint on one of the legs going to the bottom board and now it’s working.