OBERHEIM SYNTH

Hi
it appears as if the LFO itself is faulty.

Did you try Split Sounds? For Single sounds only the primary LFO circuit is 
active. For Split/Double sounds two separate LFO circuits are effective. If 
the primary LFO is defective on the first programme, you should be able to 
have LFO modulation in the second programme of the Split.
If both LFOs are failing, the problem is probably with the control panel 
itself, or the ROM-program is dying (EPROMs were meant to live 20 year at 
max) .

Cheers
Mondo

Dear Stephan,

so it is appears to be a faulty primary (lower) LFO which is located at the 
lower control board, left side in the middle.

1) If the LFO is not running at all:

Check U11 (LM324) - eventually swap for a minute with e.g.  U70 or U71 
(TL084) and see if LFO is now running. Else check U2 (4053)- swap for a 
minute with e.g U153 of upper LFO.


2) If LFO is running slow, but does not change frequency when twisting pot 
on control panel or changing programs:

Check  U43 (TL084) on lower control board - eventually swap for a minute 
with e.g.  U70 or U71
Then Check U45 (4051)  on lower control board - eventually swap for a minute 
with e.g.  U46 or U50

3) Above all and in any case, always consider to check the Modulation Panel 
(Bender and 3rd LFO) first. THIS is the HEART of the OB-Xa (also OB-X). If 
something is wrong there, nothing will go right with modulation  (LFO, S/H) 
or tuning of the main section  and voice boards.

BTW: Make yourself comfortable with the principal function of each element 
inside the Obie, before making any adjustments or repairs.

Good Luck!!