Dorrough Electronics was a pioneer in multiband broadcast processing. This is a model 610, the digitally controlled sucessor to the original 310. These are mostly in collector’s hands now, although a few undoubtedly remain in service.
Dating to the 1980’s, it had several operational issues to address and a few poorly done repairs to undo. Starting with that midband 0dB LED that is not correct for the unit. Far too bright.
These units came with a Dorrough loudness meter built in the front panel. Still prized by audio engineers, they are available for sale new.
Here is a look at the main chassis with the front panel removed. From the left- Low, Mid, High processing boards. Power supply, Limiter board, Output amplifier board.
The power supply needed to be completely redone with new capacitors and voltage regulators.
Another common problem, found here, are failed Tantalum capacitors. Plenty were found in this unit. They are usually easy to spot as they’ll have a hole blown in the side, or be completely destroyed.
Each of the three audio processing boards has a tantalum cap on each of the 3 power supply rails. All had failed.
Also failed- the output chokes on the line amplifier.
Every adjustment pot was replaced. Fortunately still available new.
And every switch.
The unit was then aligned and shipped back to the customer.