Fixing some issues in Toft Atb24

[darkus]

I recently bought a used Toft Atb24, serial number 000536.

Anyways the console has some issues and I am installing the meterbridge soon so I might as well fix the issues, but I would need some help as Im not familiar with this console. So the issues are:

1. The -20dB led on channel 5 is lit all the time even if nothing is plugged in or sent to any of the inputs jacks (xlr, mon, or line in) even if input gain and channel fader are all the way down.

2. Channel 11 leaks to LR mix regardless of the fader or the position of the LR switch. The channel works like it should with all other busses and pan,solo and mute work also.

3. Channel 3 has a similar issue than channel 11 but the fader has slight effect on the volume. (around 3dB) Signal leaks to LR even if the LR switch is up.

4. Mic input 20 is dead.

The previous owner had swapped channels 11 and 12 and the problem with the channel 11 didnt get fixed, so we know its not the channel card that has the issue. He also recapped some channels which he said were moved to the end of the channel count (23&24).

If you have any ideas what might be wrong, and what should I take a look at, then please, help is needed!
Im thinking if I should replace the pushbuttons on channel 3&11, does anyone know what switch fits to this console?

 

[pvision]

I'd pull channel 11 and put a meter across the contacts of the LR routing switch to see if it switches on & off OK.

If it's bad or intermittent you could try cleaning it with some IPA followed by switch cleaner. For IPA I use a syringe with a large, blunt hypodermic needle

Nick Froome

 

[darkus]

If I need to replace the switches does anyone know what switches will fit?

 

[pucho812]

mic input is dead?
Does the channel pass signal on line?

If it does then there is not much in between the mic and preamp chip(that 1510 or INA217 depending on manufacturing year) that can go wrong.  Essentially before the mic line switch  you have phantom and I will have to check my schematics but I believe the phase is in there too.... If both mic and line are dead, then you have a dead chip which can easily be replaced as it is on sockets...

the led always lighting check for faulty IC chips nd or shorted capacitors.

The leaky channels, hmmmm I'll have to think about that one... 

FWIW the schematic is very similar to an 80B minus things like transformers on the input. Essentially after the preamp stage on the ATB you have an 80B with a lit of ribbon connections going on.  They are fairly easy to work on but a hassle to get apart.

 

[darkus]

Hi,

The channel with dead mic input is passing signal with line input, works as should. Havent measured if the mic input gives out phantom power.

I have a bunch of replacement chips from the previous owner, so I might as well swap same IC's

 

[Andy Peters]

I have a bunch of replacement chips from the previous owner, so I might as well swap same IC's

Do that after you've determined that the ICs in question are actually bad.

 

[pucho812]

Hi,

The channel with dead mic input is passing signal with line input, works as should. Havent measured if the mic input gives out phantom power.

I have a bunch of replacement chips from the previous owner, so I might as well swap same IC's

If the line input is working and the mic input not working then it's not IC1, the preamp chip.  the mic and line go into the same path into the chip after mic/line switch so  that tells me the chip is fine.  there is very little between the chip and the mic input. 
I will look over my notes at home but I would confirm phantom, which can be easily done by checking the channel with a dynamic mic. If the dynamic works and a condenser does not, then there is an issue with phantom power. 

 

[darkus]

If the line input is working and the mic input not working then it's not IC1, the preamp chip.  the mic and line go into the same path into the chip after mic/line switch so  that tells me the chip is fine.  there is very little between the chip and the mic input. 
I will look over my notes at home but I would confirm phantom, which can be easily done by checking the channel with a dynamic mic. If the dynamic works and a condenser does not, then there is an issue with phantom power.

Neither dynamics nor condensers work with the xlr in.

 

[pucho812]

If condenser  mics were not working  but dynamics were, then I would suspect phantom but since both types do not work, there is not much going on.  sorry I got sidetracked las night. Check and confirm that the xlr jack is not broken. Do continuity to and from the jack to the PCB. There is no real protection has to how the xlr mounts and it could be as simple as a broken solder joints.  I will have the rest to check up later,  sorry I got sidetracked last night.

 

[pucho812]

o.k..

it goes like the mic signal comes in and  goes in series through c4/c5 which are 47uF/63V eletrolytic caps.  c4 on the + side of the signal and c5 on the - side of the signal.  Prior to the caps you have the 6,8Kresistors for phantom. After the capacitors the signal  parallels  pass R1on the + side and R7 on th - side which are 47K resistors to ground.  after that they run into the mic line switch and then the phase switch. If the line is working as you said...  then check caps c4 and c5. or resistors r1 and  r7.  You can also check the mic line switch.
cheers.

 

[darkus]

Hi,

thank you so much Sir! I will report back later how it all went!

 

[abbey road d enfer]

2. Channel 11 leaks to LR mix regardless of the fader or the position of the LR switch. The channel works like it should with all other busses and pan,solo and mute work also.

3. Channel 3 has a similar issue than channel 11 but the fader has slight effect on the volume. (around 3dB) Signal leaks to LR even if the LR switch is up.

I would check for shorted line from the direct output or the insert send.
Sometimes inserting the wrong type of jack in the sockets can twist the blades and short them.