SAE Two amplifier model A-14...no audio output. Help?
 

My electronics tech is having trouble fixing an SAE Two amplifier
model A-14. It has no audio output. If he shorts across a relay the
audio works fine. He has a good service manual but can't track down
what the problem is. Does anyone know what the problem may be
specifically? It was repaired for the same problem by another tech and
the repair didn't last long. I do know that 4 ohm speakers are a no-
no. He's testing with headphones. Sure would appreciate some help
here. Please eMail me at .
Harvey

SAE Two amplifier model A-14...no audio output. Help?
 

On 3ÔÂ27ÈÕ, ÉÏÎç4ʱ01·Ö, rockinnomo wrote:
My electronics tech is having trouble fixing an SAE Two amplifier
model A-14. It has no audio output. If he shorts across a relay the
audio works fine. He has a good service manual but can't track down
what the problem is. Does anyone know what the problem may be
specifically? It was repaired for the same problem by another tech and
the repair didn't last long. I do know that 4 ohm speakers are a no-
no. He's testing with headphones. Sure would appreciate some help
here. Please eMail me at .
Harvey



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SAE Two amplifier model A-14...no audio output. Help?
 

"greenpjs" wrote in message
...
On Wed, 26 Mar 2008 13:01:29 -0700 (PDT), rockinnomo
wrote:

My electronics tech is having trouble fixing an SAE Two amplifier
model A-14. It has no audio output. If he shorts across a relay the
audio works fine. He has a good service manual but can't track down
what the problem is. Does anyone know what the problem may be
specifically? It was repaired for the same problem by another tech and
the repair didn't last long. I do know that 4 ohm speakers are a no-
no. He's testing with headphones. Sure would appreciate some help
here. Please eMail me at .
Harvey

I had one of those years ago that did the exact same thing. The first
time, it was the relay itself. The contacts were corroded. I
replaced the relay which fixed the problem for a few months. Then
whatever drives the relay went out. I ended up just bypassing the
relay with intentional solder bridges and using it like that for
another few years. The only thing the relay does is avoid a minor
"thump" on power-up so it isn't really needed if the amp is operating
normally otherwise. ...Pat

I'm sorry, but that is absolutely *not* the most important reason for the
relay. Whilst there is a delay in activating it to avoid the switch on thump
that would otherwise ensue as a result of the output stage supply rails
stabilzing, its much more important function is to disconnect the speakers
from the output stages in the event of a fault developing which causes there
to be a DC offset at the midpoint. If this is allowed to find its way to the
output terminals, the result will likely be a destroyed speaker cabinet.

So, whilst bridging the (non active) relay will cure a lack of output,
assuming that it is not failing to close because its control circuit *is*
actually detecting a fault, you will have lost any future insurance against
speaker damage, if an output fault should occur ...

Arfa

SAE Two amplifier model A-14...no audio output. Help?
 

rockinnomo wrote:
My electronics tech is having trouble fixing an SAE Two amplifier
model A-14. It has no audio output. If he shorts across a relay the
audio works fine. He has a good service manual but can't track down
what the problem is. Does anyone know what the problem may be
specifically? It was repaired for the same problem by another tech and
the repair didn't last long. I do know that 4 ohm speakers are a no-
no. He's testing with headphones. Sure would appreciate some help
here. Please eMail me at .
Harvey

Hello Harvey,

While I don't know this amp in specific, see if it uses the TA7317
protection IC. It's a great IC and was used by many manufacturers.
I've seen the electrolytic capacitors around the IC cause problems, as
well has high value (150K or 220K as I recall) resistors go off value.
The IC itself rarely fails.

I would not suggest bypassing the relay.

Regards,
Tim Schwartz
Bristol Electronics