Channel 3 Not Working on the Sherbourn

[Youthman]

This morning, I was going to do some A/B testing between the LaScala Trio and the RF-83 / RC-64 and discovered channel 3 on the sherbourn amp is not working.

Front light does not light up for that channel. I unhooked the input and the speaker cable to both channel 1 and channel 2 and the front light for those channels is on so that tells me it's something inside the amp. I'm really hoping just for a blown fuse.

I had previously taken the lid off the amp when I first got it. Any guidance as to where the fuse might be?

Looking at the back of the amp, I just noticed the "LDS Speaker Detector". I'll switch that to see if it gives me any warning light.

Unique to Sherbourn is our LDS, (Load Detection System) that allows the amp to sample the signal before powering up and will detect if the “load” is within safe parameters.

[TasDom]

No mention of fuses that I can see.

From the manual:

72100a.pdf

Check and make sure that the LDS switch is set to
the full clockwise direction (position 7). Connect
the two power cords and turn on the amplifier’s
power switch on the front panel. The front panel
blue light will illuminate and the LDS LED (on
the rear panel) will show the status of the speaker
connection at the speaker output terminal of speaker
number 7. If the LED is green, it indicates a good
speaker connection has been made and a correct
speaker impedance has been used. Orange indicates
an open circuit or a speaker of higher impedance
is used. Red indicates either a short circuit connection
or a speaker impedance that is too low for
the amplifier.
Sequentially test each speaker connection by winding
the switch in a counterclockwise direction from
7 through to 1 observing the LED color for each of
the 7 positions. If a red or orange color is detected,
check and rewire the connection of that channel
until the LED turns green.
Note – For the model 5/5210A, channels 3 and 4
are not installed and you will see orange when
rotating the LDS Switch to positions 3 and 4.
You must never turn the LDS switch to the OFF
position whenever an LDS LED is RED during the
above checking. This could connect a dead short
to the amplifier which may cause damage.
Activating the 7/2100A and
5/5210A
After checking through every speaker connection
with the LDS switch and having confirmed that all
LDS LEDs are green, then remove the tiny locking
screw between the OFF and 1 position. Turn
the switch to the OFF position which will fully activate
the 7/2100A or 5/5210A. The power-onstandby
control is then handed over to either the
external 12V DC Trigger, or the Music Trigger, or
the always power ON position (but controlled by
the front panel power switch) depending upon how
the trigger mode setting is made. Make sure to reinstall
the locking screw so that the LDS switch
cannot be turned because to do so will immediately
disable the power on setting of the switch.
Power Cords
In order to obviate the need to install a special 20/
30 amp circuit (that will be required if seven 4 ohm
speakers are used) your 7/2100A or 5/210A has
been equipped with two power cords. Please note
that the rear “Master” AC receptacle must be connected
to the AC power first in order to allow power
to enter the “Slave” receptacle of the amplifier. The
amplifier will not power up if only the rear “Slave”
receptacle is connected to AC power.

Edited May 14, 2014 by Tasdom

[Youthman]

Appreciate the PDF Tasdom. I briefly looked online with my phone before work but didn't locate the manual .

I'll do some testing tonight after work.

[dtel]

No mention of fuses that I can see.

Where would they even put it ?

Could it be the Sherbourn is not getting a center signal ?

[CECAA850]

I guess it could be a first but I don't recall seeing an amp without a fuse of some sort. What are the black knobs on the rear of the unit in the corners?

[CECAA850]

Aren't the mono blocks interchangeable?

[Youthman]

The amp is back up and running. I removed the 12v trigger from the back, turned it on and all amps powered up. Plugged the 12v back in and all is back to normal. Very strange. It might go out again but for now, it's working perfectly. Thx everyone.

[Frzninvt]

When I first got mine channel 6 was intermittent. I took it apart and reflowed the solder on the inputs to the amp board and have not had a problem since. It was a bit of a pain to get the amp back together but totally doable. I also had issues with the single banana jacks not making good contact. I switched to the ones that are one solid piece with two pins and that helped as well.

[Holden1]

On 5/14/2014 at 12:23 PM, CECAA850 said:

I guess it could be a first but I don't recall seeing an amp without a fuse of some sort. What are the black knobs on the rear of the unit in the corners?

Those "knobs" are feet to stand the unit upright on the floor when installing so as not to damage the connectors on the back - they extend just over an inch or so and are rubberized like a standoff.  The Sherbourn 16/800 for example is about 60 lbs and you have to first wrestle alligators to be in good enough shape to rack on of these old units.