Fisher CA-9335 amplifier wont turn on
Kim Voss Schrader
I've been trying to fix an amplifier (subj.) which puzzles me. It has a relay
which is activated when the amplifier comes out of standby but this relay never
clicks. If I shortcircuit the switch of the relay (which turn on the supply to
STKs and so on) the relay clicks when the amplifier is turned on and everything
works perfectly.
The 12V standby-voltage apparently never reaches the relay... I've pretty much
given up trying to decipher the circuitboard and was hoping someone had seen
this exact problem before or had a diagram.
I've checked transistors, resistors ... around the relay but haven't found
anything :-(
Any ideas?
--
Kind regards, Kim Voss Schrader
"Fooling around is like screwing around - without dinner ;-)"
Mark D. Zacharias
Fisher's are pretty notorious for amplifier failures, and if that happens
your speaker(s) will be severely damaged.
Mark Z.
"Kim Voss Schrader" <tekni...@tdcadsl.dk> wrote in message
news:3EE14C43...@tdcadsl.dk...
Ray L. Volts
>
> I've been trying to fix an amplifier (subj.) which puzzles me. It has a
relay
> which is activated when the amplifier comes out of standby but this relay
never
> clicks. If I shortcircuit the switch of the relay (which turn on the
supply to
> STKs and so on) the relay clicks when the amplifier is turned on and
everything
> works perfectly.
>
> The 12V standby-voltage apparently never reaches the relay... I've pretty
much
> given up trying to decipher the circuitboard and was hoping someone had
seen
> this exact problem before or had a diagram.
> I've checked transistors, resistors ... around the relay but haven't found
> anything :-(
>
When a relay fails to engage, it's sometimes part of the design -- it's a
safety feature to protect your speakers. These speaker relay circuits are
used to prevent full power from immediately reaching the speakers when you
turn the amp on. This eliminates the "thud" effect, and saves your speakers
the added stress. Shorting across the terminals and defeating this
protection is begging for trouble.
At any rate, you say the trigger voltage "apparently" isn't reaching the
relay. I presume this means you haven't verified it with a meter? If the
trigger voltage truly isn't there, trace all the way back to the 12v source
(transformer terminals). If the source is good, follow it to the relay,
looking for open zeners and/or resistors, etc. along the way. Find the
point where the 12v ends. If the 12v source isn't good, the prob is with
the power supply (open transformer winding, etc.).
Rodney Thomas
>
> I've been trying to fix an amplifier (subj.) which puzzles me. It has a relay
> which is activated when the amplifier comes out of standby but this relay never
> clicks. If I shortcircuit the switch of the relay (which turn on the supply to
> STKs and so on) the relay clicks when the amplifier is turned on and everything
> works perfectly.
>
> The 12V standby-voltage apparently never reaches the relay... I've pretty much
> given up trying to decipher the circuitboard and was hoping someone had seen
> this exact problem before or had a diagram.
> I've checked transistors, resistors ... around the relay but haven't found
> anything :-(
>
> Any ideas?
These amplifiers usually have a protection IC such as a upc1237 or
similar. The relay can be traced back to either that ic or some type
of discrete protection circuitry. These ICs usually have about 3 ways
of disabling the relay. First, it delays the relay at turn on so you
don't get that turn on pop, next they sense the AC input to turn the
relay off sooner so you don't get the turn off pop. Most importantly
they monitor the dc on the outputs and disables the relay if they
sense significant dc which could fry your speakers.
You may have a bad protection IC or associated circuit. A schematic
for the amp or a PDF of the protection ic would probably help you out.
R Thomas
Ricardo Matos Abreu
>
> These amplifiers usually have a protection IC such as a upc1237 or
> similar. The relay can be traced back to either that ic or some type
> of discrete protection circuitry. These ICs usually have about 3 ways
> of disabling the relay. First, it delays the relay at turn on so you
> don't get that turn on pop, next they sense the AC input to turn the
> relay off sooner so you don't get the turn off pop. Most importantly
> they monitor the dc on the outputs and disables the relay if they
> sense significant dc which could fry your speakers.
> You may have a bad protection IC or associated circuit. A schematic
> for the amp or a PDF of the protection ic would probably help you out.
>
> R Thomas
Or else the protection circuit is performing as it should and the problem is
_really_ DC at the outputs!