Is anyone familiar with the JBL Synthesis pre-amp?

[[email protected]]

I have a surround sound JBL Synthesis pre-smp. It is behaving VERY
erratically. Some MODE functions work and some don't at all. It
doesnt seem to make much difference which inputs are used, some of the
modes either give one channel or no channels however high the volume
is put. Hall 1 used to work fairly consistently but now it doesn't
seem to work at all. Similarly the tuner input (I use S VID1 for
this) used to work on JAZZ but now it usually doesnt work much at all.

The right hand lights light up when you accress an input which is
connected but with most modes, no sound comes out and with some modes,
only one channel works (not always the same channel!)

The only mode which consistendly works is MONO ENHANCE (with a kind of
falsified sound which you cant use with television on any talk mode
which is how I have it connected) and suspiciously when you try to
access one of the channels which isnt working on both channels, the
non-working channel occasionally flashes on at full volume,
indicationg a dry joint somewhere. But even this isnt consistent
between symptoms, indicating that the unit isnt absolutely sure where
any dry joint is.

Has anyone worked on one of these please?

 

[William Sommerwerck]

Try shutting off the unit, disconnecting it from the wall outlet, and
letting it sit, "unmolested", for at least 24 hours. There is a slight
chance this will fix the problem.

 

[[email protected]]

Try shutting off the unit, disconnecting it from the wall outlet, and
letting it sit, "unmolested", for at least 24 hours. There is a slight
chance this will fix the problem.

I have to say, though recently it had become worse, it has done this
ever since I got it a few months ago when it had been siting on a
friend's shelf for some years (though he reported that the last time
he used it, it did work properly so I will try your suggestion)

 

[William Sommerwerck]

Try shutting off the unit, disconnecting it from the wall outlet, and
letting it sit, "unmolested", for at least 24 hours. There is a slight
chance this will fix the problem.

I have to say, though recently it had become worse, it has done this
ever since I got it a few months ago when it had been siting on a
friend's shelf for some years (though he reported that the last time
he used it, it did work properly so I will try your suggestion).

Hmmm...

Does the unit uses a lithium coin cell for backup? Just wondering.

The fact that it worked before it was put into storage, doesn't prove
anything about whether it would work several years later.

 

[[email protected]]

I have to say, though recently it had become worse, it has done this
ever since I got it a few months ago when it had been siting on a
friend's shelf for some years (though he reported that the last time
he used it, it did work properly so I will try your suggestion).

Hmmm...

Does the unit uses a lithium coin cell for backup? Just wondering.

The fact that it worked before it was put into storage, doesn't prove
anything about whether it would work several years later.

No, there is no lithium cell but there ARE some curious white (what
look like) pot controllers by the L and the R of the phono connectors
which dont figure on the manual for this unit. I wonder what they
are? And I wonder if they contain the solution to the problem of the
apparent dry joints? I am sure there is no way of spraying Tuner Wash
into the pots under them if pots they are but I wonder if they have
just become dirty?