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TAS465 A1 PCB - why is C437 bi-polar


Jon
 

Hi all,

Does anyone know why C437 fitted to the TAS465 A1 pcb is bi-polar ? It's the bulk cap for the -5.2VC supply . Other caps on this board are Nichicon VX and provide the bulk caps for the +8.6VA , -8.6VB , +5.2VB and -5.2VB supplies. Looking at the service manual C437 is shown as polar on the schematic but the parts list shows it as 10VAC. I don't understand why the rationale for fitting a bi-polar cap here. Does anyone have any knowledge of this ?

Thanks,

Jon


Siggi
 

On Wed, Oct 7, 2020 at 8:01 AM Jon <jonathan_harrison@hotmail.com> wrote:

Does anyone know why C437 fitted to the TAS465 A1 pcb is bi-polar ? It's
the bulk cap for the -5.2VC supply . Other caps on this board are Nichicon
VX and provide the bulk caps for the +8.6VA , -8.6VB , +5.2VB and -5.2VB
supplies. Looking at the service manual C437 is shown as polar on the
schematic but the parts list shows it as 10VAC. I don't understand why the
rationale for fitting a bi-polar cap here. Does anyone have any knowledge
of this ?
Hey Jon,

That's pretty curious. Note that this decouples -5.2C, which is a somewhat
isolated sub-supply drawn from the -5.2A. It looks like this supply is only
used by U403/U404, which are the transistor arrays responsible for
switching the attenuator relays. Maybe the inductive spike from those
relays is the reason a bipolar capacitor was chosen there?

Siggi


Jon
 

Hi Siggi,

Thanks for your reply. I guess if there aren't any diodes on the relays that's certainly possible.

Jon