Filtek MK3a: No Low Freq Adjust

[samgraysound]

Hi all,

I'm trying to fix a Filtek MK3a EQ module. The low frequency adjustment has no effect on the signal whatsoever. It passes signal fine and all the other bands are working normally.

The schematics I've been able to find don't seem to match up to what I'm seeing inside the chassis, none of the resistor values seem right, there's a ton of 330ks connected to op amp pins and not single one of the schematics, the caps don't seem to be where the schematic shows them in the circuit either.

Some caps have been replaced but there's still a few original electrylytics on (what I think) is the lo eq section. I'd like to replace them but I don't understand the codes printed on them, and due to the schematics stuff I'm not sure of there value. The codes are: 39, F63, K5, K6

Plus everything is in German.

Have you worked on the internals of these?
Do you have any suggestions on how to proceed?
Do you have any leads or thoughts on the schematics?
Do you recognize the Capacitor codes?

Attached are schematics I have plus a pictures of the caps

 

[samgraysound]

schem 2

 

[samgraysound]

schem 3

 

[samgraysound]

Picture 1

 

[samgraysound]

Photog 2

 

[synthiaks]

Check the inside pics here

https://www.vintagetools.de/Vintage-Modules/Equalizer-Filter/BFE-FILTEK-MK3.html

If this is the same as your module i would guess that the Goldish/silvery caps are not Elektrolyths but some polystyrene or other plastic. I wouldn't change them. The tantal drops should go though. They tend to short when they fail.

 

[samgraysound]

no mine are different:

black face
completely different pcb layout
the toggle switches on mine aren't pcb mount
different transformers

same rotary switches

I will take some more pictures when I get home.

 

[samgraysound]

here's the faceplate:

http://auxsend.net/preampsandeqs/2011/07/11/filtek-mk3-parametric-equalizer/

 

[samgraysound]

Yeah, I have Mk3a and it looks like my schems are Mk3d

 

[Brian Roth]

Last year I worked on some Filtek MK3??? modules (don't recall the exact version).  In two of them, I eventually discovered that some original "through holes" on the circuit board had somehow become disconnected from the top side to the bottom.

Bri

 

[samgraysound]

The module was working until a week or so ago.

The tantalum drops are all just labeled K10, anyone know what that code means?
Anyone have schems for Mk3a?

Sam

 

[skanker]

The module was working until a week or so ago.

The tantalum drops are all just labeled K10, anyone know what that code means?
Anyone have schems for Mk3a?

Sam

Did you manage to find the correct paper work for this module?

Im wanting to identify the large grey and orange ceramic capacitor as seen in the image attached as i damaged one of them when doing a repair but have no idea what value to replace it with

Any info is most welcome

 

[samgraysound]

No I never got papers