This is pretty typical of Fender schematic/production differences – not too alarming. In addition, the signal pull-down resistor, R304, is shown as 10K but the actual resistor is 20K. The footswitch schematic is not correct – it’s actually backwards on the schematic. The Fender Prosonic schematic (for the combo amp, the head did not have reverb), had several errors in the reverb section. The condition persisted with the reverb turned off with the footswitch. The footswitch was cleaned and checked for continuity to ground. I did notice a faint high-frequency reverb slap on striking damped strings with the reverb control “off”. The Prosonic is a rare and highly sought-after amp – hard to find because the people who have them tend to hang on to them. The amp features cascading gain stages with Master volume and an interesting 3-position rectifier selector for 1: Class A, tube rectifier/cathode biased, 2: Class A/B, tube rectifier/fixed bias, and 3: Class A/B, solid-state rectifier, fixed bias. The Class A setting is very reminiscent of a Vox AC30. It is probably closer in design to a Mesa or Marshall. The Prosonic was a complete departure for Fender. They only made 300 of the red “Lizard Skin” amps, this was #5 / 300. This particular Prosonic was produced in 1995 or early 1996, based on the Serial Number and the transformer codes. The Lake Oswego amps are supposed to have better-quality components than the later models. Later, production was moved to Corona, and those amps are indicated by the prefix “CR”, and were not labeled "Custom Shop".
The “LO” prefix to the serial number indicates that the amp was made at the old Sunn Amp factory in Lake Oswego, OR, and labeled “Fender Custom Shop”. The Prosonic was designed by Bruce Zinky of the Custom Shop, but none of these amps were actually built there, nor were they sold as Custom Shop amps. I had a client bring me his 1995 Fender Prosonic (in red Lizardskin!) with an unusual complaint - that in the studio, with reverb "off", he could still hear a slight reverb slap-back at low volumes.