dbx 20/20 display issue

[Matt Mincer]

Hey folks,

I have this EQ a guy brought me to fix. The 250 and 2khz displays don't respond even when I inject those frequencies directly into the input. He's also saying the pink noise generator isn't working but I haven't gotten that far yet. All of the chips are plugins so I've been able to do some swapping. But so far that's hasn't helped. Does anyone know a fix for the problem?

Thx
Matt

 

[painttoad]

look at the crystal(s)

i remember reading about legs corroding away on these and similar adc/bsr units.

 

[NJ_Antonio]

The related 3.3uF/50V capacitor may be bad...

 

[TomInKY]

Just curios if the OP ever got the thing working, because I'm eyeballing one of these now.

 

[tadawson]

(Not the OP . . . .)

Looking at the schematic, looks like the display is an X-Y matrix. If other freqs work, then it would appear that the issue is either a column drive fault on the display side, or a failt on the filter board, not letting signal it (It also appears to be multiplexed.) Rows should be OK, since other freqs work and they share the same row drive circuitry.

The schematic is out there free, if you don't have it already. A little time with a scope/dvm should tell you pretty quickly if you have column drive.