Studer A80 Capacitors replacement

I have rescued this Studer A80 from an old recording studio.
Someone replaced the big capacitors. The fastening is difficult, they are longer than the original ones and do not have screw to fix.
I am considering replacing again.
In the service manuals, I don't see all of these condensers ....
I await expert advice ...

AudioIngenia said:

I have rescued this Studer A80 from an old recording studio.
Someone replaced the big capacitors. The fastening is difficult, they are longer than the original ones and do not have screw to fix.
I am considering replacing again.

Click to expand...

The screw situation is easy to solve, you can solder directly to the capts and also have some capacitor brackets to secure them in place, but you have to know the values and find them in the schematic.
These caps have to be in the schematic

Epcos/TDK makes stud mount capacitors that fit.  There is a guy on eBay who sells kits.

Hello

AudioIngenia said:

In the service manuals, I don't see all of these condensers ....

Click to expand...

In the service manual you have a "survey of groups" (section 7/5 for A80 Vu)
window "power transistor and phase shift capacitor" GR4 (group 4) you have all capacitor mounted to chassis, EL1 to 14
Also section 8/4 "survey of motor supply" you'll see all the capacitors, across the motors at right side, as all value in a table just below
You can also go to section 8/13 for example, "contactor" schemo, you'll see the capacitor across the motor "outside" the schemo, with value and notes to look at sec 8/4 and GR4. As any pcb schemo that point to power transistor or capacitor that are mounted to chassis.

Best
Zam

I think I have identified all the capacitors.
Maybe select the Kemet brand

Completed work. Isolated electrolytic with Silentblock  ;D

AudioIngenia said:

Completed work. Isolated electrolytic with Silentblock  ;D

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Why?!

What is silent block?

The chassis (including screw) of electrolytic capacitor is connected to negative value. Therefore it is strictly necessary to isolate from the aluminum structure of the Studer A80. For this I have used rubber anti-vibration isolators (silentblock)

Hello

AudioIngenia said:

The chassis (including screw) of electrolytic capacitor is connected to negative value. Therefore it is strictly necessary to isolate from the aluminum structure of the Studer A80. For this I have used rubber anti-vibration isolators (silentblock)

Click to expand...

Usually big chassis screw mounting capacitor come with rubber washer and M8 plastic nuts.
Best
Zam

AudioIngenia said:

The chassis (including screw) of electrolytic capacitor is connected to negative value. Therefore it is strictly necessary to isolate from the aluminum structure of the Studer A80.

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Are you sure? So an A80 has a negative supply rail?

I've never seen Studer gear from that era to have a negative rail. What is it used for? What PCB name in the schem?

squarewave said:

Are you sure? So an A80 has a negative supply rail?

I've never seen Studer gear from that era to have a negative rail. What is it used for? What PCB name in the schem?

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A80 audio path run on +/-12V
x89 series desk run on -22V, so you'll have issue if you hook PSU caps neg leg (screw) to chassis, big screw mount PSU caps are mounted on fiberglass assembly in the PSU module.

Best
Zam

zamproject said:

A80 audio path run on +/-12V

Click to expand...

If those caps are C3, C4 connected to the POWER SUPPLY UNIT 1.081.320 board, that's not where +-12 is derived. The +-12 for audio stuff comes from the STABILIZER PCB / AUDIO 1.080.964 which uses two 16VAC windings.

But I'm not familiar with the A80 so I could easily be wr-wr-wrong. This is just what I see from looking at the schem.

squarewave said:

If those caps are C3, C4 connected to the POWER SUPPLY UNIT 1.081.320 board, that's not where +-12 is derived. The +-12 for audio stuff comes from the STABILIZER PCB / AUDIO 1.080.964 which uses two 16VAC windings.

But I'm not familiar with the A80 so I could easily be wr-wr-wrong. This is just what I see from looking at the schem.

Click to expand...

I just give example to say that there is negative rail (relative to chassis/ground) in A80 as other Studer product of this era.
Not for the contradiction, just to say what's true

You'r probably right about the specific caps we talk here, still I'm not sure it's a good idea to make electrical conduction from can to chassis for those screw mount capacitor, as you then will have two path to ground.
That's why capacitor like this usually come with isolation mount part, and I'm surprise the OP don't have them fitted with
Saying that, silent block will work too  ;D

Best
Zam

As long as there's no current between the can and chassis, it doesn't matter. It would be very simple to test. Just put alligator clips on your DMM, clip one to the chassis, the other to a 10K resistor, set the DMM to measure mA and then touch the other end of the resistor to the negative of the cap. If you don't see any current (a few 10's of uA is fine), then it would be perfectly fine to just mount those caps directly to the chassis. But again, I'm not really familiar with the A80 at all so carry on ...